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Port of Cape Town SEA – Table Bay Marine Ecology
Strategic Environmental Assessment for the Development of
the Port of Cape Town
Specialist Study on
Marine Ecological Aspects
Prepared For
CSIR on behalf of
The National Ports Authority
Prepared by
Dr R Carter1, Dr N Steffani2 and Ms S Lane3
1
Specialist Consultant in Applied Marine Science, 8 Francolin St, Somerset West, 7130.
email: [email protected].
2.
Pisces Environmental Services (Pty) Ltd. 22 Forest Glade, Tokai 7945.
email: [email protected]
3.
Sue Lane & Associates. Professional Services in Environmental Planning and Management.
5 Muswell Hill Rd, Mowbray 7700.
email: [email protected].
SEA Port of Cape Town
Date of Issue
June 2003
Port of Cape Town SEA – Table Bay Marine Ecology
SUMMARY
The Port of Cape Town is the southernmost commercial port in Africa, at the apex of
one of the world's major shipping routes. The port is situated in Table Bay, which is
an open, log spiral embayment in the southern Benguela Current ecosystem.
Encompassed within the bay is Robben Island and surrounding it is the major
metropolitan area of Cape Town. The major natural factor controlling ecology in the
Table Bay region is coastal upwelling which supplies inorganic nutrients to surface
waters and drives the high biological productivity characteristic of the southern
Benguela Current. The major human influences on Table Bay are land based
sources of pollution, coastal engineering structures and shipping activities and
pollution derived from ships.
The strategic issues focussing this specialist study are derived from an identification
of the rights all interested and affected parties have to a healthy, well functioning
environment, in this case specifically the coastal marine environment. To maintain
ecological function Table Bay requires the retention of as near a natural state as
possible, which coincides with the rights of the people to unpolluted seawater,
abundant sea life and clean inter- and subtidal habitats. Accordingly this assessment
concentrates on Table Bay ecology and risks posed by development and operation of
the Port of Cape Town.
Seven different ecological habitats are recognisable in Table Bay:
 Sandy beaches extending from the Salt River mouth north past Blouberg
 Rocky shores extending south of the harbour past Sea Point, at Blouberg Rocks
and at Robben Island
 Artificial surfaces of the harbour itself plus the shore protection extending towards
Salt River
 Subtidal sand substrata and
 Subtidal rock substrata in the bay itself
 The water body in Table Bay, and
 The water body in the port.
There is a dearth of published ecology and biological distribution data specific to
Table Bay but the available local and regional information indicates that each of the
identified habitats support biological communities characteristic of the region except
for the artificial surfaces associated with the Port of Cape Town. There is no natural
analogue for port breakwaters and harbour walls but species occurring there are
common in the region even though the overall community structure may be different.
Overall the benthic communities in Table Bay are typical for the West Coast, are not
unique to Table Bay and cannot be classified as locally, regionally or internationally
important biodiversity resources. This also applies to the pelagic fish and the marine
mammals occurring in Table Bay, as these are widespread on the South African west
(and south) coast. Further, Table Bay itself does not appear to be critically important
as either a foraging or breeding area for these fauna or as a fishing area.
The resident seabird community is a strong exception to this, especially the endemic
African Penguin and Bank Cormorants. Approximately 36% of the global population
of penguins forage in continental shelf waters adjacent to Table Bay, these birds
coming from the breeding sites at Dassen and Robben Islands and, to a lesser
extent, Boulders beach in False Bay. Robben Island supports the third largest
breeding colony of Bank Cormorants in the world. Both species are considered
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Port of Cape Town SEA – Table Bay Marine Ecology
vulnerable under the IUCN criteria and represent internationally significant
biodiversity resources.
Table Bay receives effluents and contaminants from pipelines, storm water outfalls,
spills and discharges from shipping, ship repair facilities in the Port of Cape Town
and atmospheric deposition. In terms of ecological impacts the most serious of these
is oil pollution from operational and accidental spills from ships and discharges within
the port with chronic and acute effects on seabirds and other organisms in Table Bay
and the port. Table Bay appears to be well flushed especially by winter storms and
waves and there is no evidence of contaminant build up in sediments over time.
There are, however, horizontal concentration gradients in contaminants, with
sediments and biota adjacent to contaminant sources showing higher levels than
more distant sites. There is no evidence of any marked distortion in biological
community structure outside of the harbour area that is attributable to pollution.
Within the harbour area harbour wall communities at the heads of the various basins
are depauperate. This appears to be due to chronic pollution by oil, trace metals and
antifouling compounds (e.g. organotin compounds, Igarol-15) in these locations, the
effects of which diminish towards the entrances of the basins.
Both development of, and normal operations associated with, the Port of Cape Town
pose risks to Table Bay marine ecology. Nine main classes of risks were identified in
these two categories:
Development Risks
 Permanent changes in the distribution of wave energy in Table Bay due to the
extension of seawalls into the bay arising from the expansion of the container
berth and potential extension of the harbour area towards Milnerton.
Consequences of such expansions include changes to beaches (slopes and/or
sand particle size distributions) on the eastern side of Table Bay with related
effects on the intertidal sand beach community.
 Temporary losses of seawall biota during construction or extensions of berths or
breakwaters.
 Removal or alteration of subtidal sand habitat through capital dredging.
 Transient deterioration in water quality through elevations in turbidity at the
dredge and spoil dumps during capital dredging.
Operational risks
 Maintenance dredging carried out episodically throughout the life of the port with
the following potential consequences:
 Dumping of dredge spoil in Table Bay resulting in inundation of benthos
 Remobilisation of contaminants from the dredge spoil with associated acute
effects on biota, and
 Transient increases in turbidity levels.
 Release or transfer of contaminants/pollutants into Table Bay from the port and
its operations.
 Release or transfer of contaminants/pollutants from operational discharges from
shipping or spills from shipping accidents.
 Release or transfers of alien species into Table Bay via ballast water discharges
and/or from discarded biological materials during cleaning of ship hulls
 General disturbances to the larger fauna in Table Bay from shipping.
Evaluations of these risks identified 22 potential impacts on Table Bay ecology or
associated ecological sustainability indicators. Eight of these were considered to be
of medium or high significance as listed below:
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Port of Cape Town SEA – Table Bay Marine Ecology
Risk - Breakwater or outer harbour extensions modifying wave energy and
distribution in Table Bay causing alterations to beach slope and particle size
distributions on the sand beaches extending from Milnerton northwards.
Impact - Potential alteration to or loss of intertidal sand beach biota, particularly
white mussel (Donax) and plough snails (Bullia).
Impact Significance - medium.
 Risk – Disposal of harbour dredge spoil.
Impact – Acute toxicity for biota from remobilised contaminants (e.g. trace metals)
in the spoil.
Impact Significance - medium
 Risk – Release or discharge of trace metals into the port and transfers to Table
Bay.
Impact – Chronic and acute toxicity for Table Bay biological communities.
Impact Significance - medium
 Risk – Release of hydrocarbons from ships directly into Table Bay through small
volume operational discharges.
Impact – Chronic toxicity for all Table Bay biological communities and chronic
oiling of seabirds.
Impact Significance - medium.
 Risk – Accidental large volume oil spills from ships into Table Bay.
Impact – Acute and chronic toxicity for all Table Bay biological communities but
especially acute oiling of penguins, cormorants and other seabirds.
Impact Significance – high
 Risk –Release or discharges of hydrocarbons into the port and transfers to Table
Bay.
Impact – Oiling and acute and chronic toxicity for Table Bay intertidal
communities, kelp beds, harbour wall communities and seabirds
Impact Significance – high
 Risk – Ship's ballast water discharges transferring alien species to Table Bay.
Impact – Modifications to Table Bay biological communities.
Impact Significance - high
 Risk - Discharge or dumping of biological material removed from ship hulls
during maintenance cleaning and/or painting transferring alien species to Table
Bay.
Impact – Modifications to Table Bay biological communities.
Impact Significance – high
All except the risks derived from oil/hydrocarbon discharges and spills can be
mitigated by NPA to the extent that their respective significance ratings are reduced
to 'low'. Because of potential effects on specifically African penguins and Bank
cormorants even chronic oil discharges in the port can have serious consequences
for these seabirds in Table Bay. Large volume spills either within or advected into
Table Bay can have disastrous consequences for the survival of these species. It is
considered that, at best, mitigation can reduce the probabilities of occurrence of spills
but not remove the possibility. Hence the threats remain and potential impacts cannot
be classified as 'low' significance.
The other risks associated with planned port development can be mitigated by NPA
and hence there is no apparent constraint posed to development by Table Bay
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Port of Cape Town SEA – Table Bay Marine Ecology
marine ecology. On the contrary, consolidation of the terminals, rehabilitation and
repair of berths and associated service infrastructure, especially bunker supplies,
offers the opportunity of reducing current levels of operational contaminant and
pollutant discharges to the port.
Three recommendations arise from this assessment:
 Develop and apply appropriate mitigation to each of the risks identified as having
potential impacts rated higher than low significance. This will reduce all but those
associated with oils to the acceptable significance levels.
 Collaborate with and support existing monitoring programmes run by the City of
Cape Town, MCM, MCM and SAMSA and the port itself to ensure that the
identified stressors to marine communities remain below trigger levels (=
precautionary monitoring). Establish baselines for effects monitoring and institute
appropriate effects monitoring programmes. Where necessary commission
appropriate research to clearly identify sources of the various environmental
stressors to facilitate management interventions when required.
 Ensure that all stakeholders and interested and affected party groups are
adequately informed on the environmental performance of the Port of Cape Town
during all development phases and also regularly in terms of operational issues.
This is probably best achieved through a combination of forums and newsletters.
Implementation of these recommendations should result in the following benefits for
NPA in the Port of Cape Town development and operation and improve the
sustainability of future port and port-city planning:
 Reductions in negative environmental effects from current port operations.
 Guidance on screening out inappropriate developments or projects at an early
stage.
 Gaining the co-operation of others with influence or jurisdiction over activities
impacting Table Bay marine ecology (City of Cape Town, SAMSA, MCM, DWAF)
to reduce risks, and.
 Minimise risks that port development and operation may encounter serious
opposition from stakeholders, interested and affected parties and the general
community due to natural or social environmental considerations.
Note that a major strategic issue outside of the terms of reference for this
assessment is that of possible sea level rise and/or increases in the severity and
frequency of storms associated with global warming. Should firm evidence of this
become available NPA should re-assess its development, operational and
contingency plans to deal with the anticipated macroscale changes.
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Glossary and Definitions used
Acute toxicity
Rapid adverse effect (e.g. death) caused by a substance in a
living organism. Can be used to define either the exposure or
the response to an exposure (effect).
ADU
Avian Demography Unit, University of Cape Town.
Allochthonous
Organic material that is developed or derived outside a
particular waterbody
Anthropogenic
Produced or caused by humans
Autochthonous
Organic material that is developed or produced within a
particular waterbody
Benthic
Referring to organisms living in or on the sediments of aquatic
habitats (lakes, rivers, ponds, etc.)
Benthos
The sum total of organisms living in, or on, the sediments of
aquatic habitats
Biodiversity
The variety of life forms, including the plants, animals and
micro-organisms, the genes they contain and the ecosystems
and ecological processes of which they are a part
Biomass
The living weight of a plant or animal population, usually
expressed on a unit area basis
Biota
The sum total of the living organisms of any designated area
Bivalve
A mollusc with a hinged double shell
Chronic toxicity
Chronic Lingering or continuing for a long time; often for
periods from several weeks to years. Can be used to define
either the exposure of an aquatic species or its response to an
exposure (effect).
Chronic exposure
Typically includes a biological response of relatively slow
progress and long continuance, often affecting a life stage.
CMS
Centre for Marine Studies, University of Cape Town
Community
An assemblage of organisms characterised by a distinctive
combination of species occupying a common environment and
interacting with one another
Community composition
All the types of taxa present in a community
Community structure
All the types of taxa present in a community and their
relative abundances
Contaminant
Biological (e.g. bacterial and viral pathogens) and chemical
introductions capable of producing an adverse response
(effect) in a biological system, seriously injuring structure
or function or producing death
Criteria (water quality)
Scientific data evaluated to derive the recommended
quality of water for different uses
Detritus
Unconsolidated sediments composed of both inorganic and
dead and decaying organic material
Ecologically sustainable development
Development that improves the total
quality of life, both now and in the future, in a way that
maintains the ecological processes on which life depends
EIA
Environmental Impact Assessment
Effluent
A complex waste material (e.g. liquid industrial discharge or
sewage) that may be discharged into the environment
Guideline trigger values
These are the concentrations (or loads) of the key
performance indicators measured for the ecosystem, below
which there exists a low risk that adverse biological
(ecological) effects will occur. They indicate a risk of impact if
exceeded and should ‘trigger’ some action, either further
ecosystem specific investigations or implementation of
management/remedial actions.
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Guideline (water quality)
Numerical concentration limit or narrative statement
recommended to support and maintain a designated water use
Habitat
The place where a population (e.g. animal, plant, microorganism) lives and its surroundings, both living and non-living
HWM
High water mark
IMO
International Maritime Organisation
IUCN
International Union for Conservation of Nature and Natural
Resources
Macrophyte
A member of the macroscopic plant life of an area, especially
of a body of water; large aquatic plant
LWM
Low water mark
MCM
Marine and Coastal Management Directorate, Department of
Environmental Affairs and Tourism.
NPA
National Ports Authority
Pollution
The introduction of unwanted components into waters, air or
soil, usually as result of human activity; e.g. hot water in rivers,
sewage in the sea, oil on land
Population
Population is defined as the total number of individuals of the
species or taxon
PSSA
Particularly sensitive sea area
Recruitment
The replenishment or addition of individuals of an animal or
plant population through reproduction, dispersion and
migration
SANCCOB
Southern African National Foundation for the Conservation of
Coastal Birds
SEA
Strategic Environmental Assessment
Sediment
Unconsolidated mineral and organic particulate material that
settles to the bottom of aquatic environment
Species
A group of organisms that resemble each other to a greater
degree than members of other groups and that form a
reproductively isolated group that will not produce viable
offspring if bred with members of another group
Taxon (Taxa)
Any group of organisms considered to be sufficiently distinct
from other such groups to be treated as a separate unit (e.g.
species, genera, families)
Toxicity
The inherent potential or capacity of a material to cause
adverse effects in a living organism
Toxicity test
The means by which the toxicity of a chemical or other test
material is determined. A toxicity test is used to measure the
degree of response produced by exposure to a specific level of
stimulus (or concentration of chemical).
Trigger values
These are the concentrations (or loads) of the key performance
indicators measured for the ecosystem, below which there
exists a low risk that adverse biological (ecological) effects will
occur. They indicate a risk of impact if exceeded and should
‘trigger’ some action, either further ecosystem specific
investigations or implementation of management/remedial
actions.
UCT
University of Cape Town
UWC
University of the Western Cape
Vulnerable
A taxon is vulnerable when it is not Critically Endangered or
Endangered but is facing a high risk of extinction in the wild in
the medium-term future.
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Port of Cape Town SEA – Table Bay Marine Ecology
Table of Contents
1. Introduction
2. Rationale and Approach
3. Environmental Description
3.1 Physiography
3.2 Oceanography
3.3 Ecology
3.3.1 Table Bay Benthos
3.3.2 Pelagic Communities in Table Bay
3.3.3 Table Bay Harbour Communities: Benthos
3.3.4 Table Bay Harbour Pelagic Communities
3.3.5 Seabirds
3.3.6 Marine Mammals
4. Resources and Commercial and Recreational Fisheries in Table Bay
4.1 Abalone
4.2 Rock Lobster
4.3 Periwinkle
4.4 White Mussel
4.5 Snoek and Hottentot Commercial Fisheries
5. Biogeography and Unique Biodiversity Resources
6. Current Pollution Status of Table Bay
6.1 Table Bay
6.1.1 Enrichment from Sewage
6.1.2 Pollution from Industrial Sources
6.1.3 Hydrocarbons
6.1.4 Biological Community Responses
6.2 The Port of Cape Town
6.2.1 Enrichment from Sewage
6.2.2 Pollution from Industrial Sources
6.2.3 Hydrocarbons
6.2.4 Biological Community Responses
7. Trends in Table Bay Pollution and Ecological Status
7.1 Pollution
7.2 Ecology
8. Risks Posed by Port Development and Operations to Table Bay
Ecology, Impacts and Mitigation
8.1 Risks
8.2 Impacts and Mitigation
9. Table Bay Marine Ecology Constraints to Port Development
and Operation
10. Table Bay Ecology Sustainability Indicators
11. Monitoring
11.1 Precautionary Monitoring
11.2 Effects Monitoring
12. Conclusions and Recommendations
13. Acknowledgements
14. References
APPENDIX 1
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Port of Cape Town SEA – Table Bay Marine Ecology
List of Figures
Figure 1: Examples of some of the ‘free’ natural functions (goods and services)
provided by the marine ecosystem in Table Bay (within the NPA’s area of
jurisdiction). These functions need to be sustained to avoid serious opposition to
Port activities. Red arrows indicate activities that may impact on Table Bay marine
ecology and green arrows show activities that draw advantages from the natural
system.
Page 2
Figure 2: Table Bay bathymetry, outfall pipelines and storm
water discharges
Page 5
Figure 3: Sediment and bedrock distribution in Table Bay
(after Woodborne 1983).
Page 6
Figure 4: Distribution of rocky shores, sandy beaches, kelp beds, seabird
colonies and seal populations in Table Bay
Page 8
Figure 5a: Typical species zonation patterns on a South African West
Coast rocky shore (modified after Lane and Carter, 1999)
Page 11
Figure 5b: Typical species zonation patterns on a South African West
Coast sandy beach (modified after Lane and Carter, 1999)
Page 11
Figure 6: Comparisons of the distribution of the major benthic
macrofauna taxa and sediment structures at a depth of 30 m on a
cross-shelf transect off Lamberts Bay, South Africa (modified from
Christie 1974).
Page 15
Figure 7: Mussel Watch sampling sites in Table Bay (data from MCM)
Page 29
Figure 8: Outfalls discharging into the Port of Cape Town
Page 32
List of Tables
Table 1: Mean nematode, harpacticoid copepod and flatworm densities
per 100 cm3 in Table Bay in relation to grain size categories. Modified after
Bartlett et al. (1985), standard deviations were not reported.
Page 16
Table 2: Average percentage cover and wet biomass (± standard error)
of benthic organisms at the outer harbour wall and at Mouille Point.
Percentage cover includes secondary cover (e.g. barnacle cover) and
can thus exceed 100% (after Mayfield 1998).
Page 18
Table 3: Common whales and dolphins found in inshore waters of the
Southern African West Coast (from Lane & Carter 1999).
Page 20
Table 4:. Abalone (Haliotis midae) densities at selected sites at
Robben Island at different depths. (Modified after Zoutendyk 1982).
Page 21
Table 5: Site, time, mean count (counts of lobsters in the traps) or
density (numbers per 40 m2), sample size and the proportion of the
sample greater than 75 mm carapace (% legal) for rock lobsters caught
using small, baited mesh traps on long lines or counted by diving
surveys (modified from Mayfield & Branch 1999)
Page 22
Table 6: Averaged rock lobster density, the proportion of female rock
lobsters, area of concern, number of eggs from that area and the proportion
of egg production this area had contributed to the total production of eggs
per region (modified after Mayfield & Branch 1999).
Page 23
Table 7: Landings (kg) of snoeks and hottentots in the Cape Town
area (Llandudno to Koeberg Power Station) from 1997 to 1999 (data
provided by C. Wilkie, Linefish Section, MCM).
Page 24
Table 8: Proportion of sediment trace metal analyses for Table Bay
that exceed the Australian interim sediment quality trigger values
(ANZECC 2000).
Page 27
Table 9: Mean mussel flesh trace metal (Cadmium, Copper, Lead
and Zinc) concentrations (mg/kg Dry mass) for samples collected
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Port of Cape Town SEA – Table Bay Marine Ecology
from the Table Bay sites (Figure 7) over the periods 1985-2000
(data from MCM).
Table 10: Numbers of African Penguins treated by SANCCOB for
oiling in the period 1994-2000. (Data from SANCCOB and MCM).
Table 11: Proportion of sediment trace metal analyses for the Port of
Cape Town that exceeded the Australian interim sediment quality trigger
values (ISQG, ANZECC 2000) in 1985 (Henry et al 1989) and 2000
(Monteiro and Scott 2000). The selected trace metals are Cadmium (Cd),
Copper (Cu), Lead (Pb) and Zinc (Zn). Note: Calculations are based on
measurements for the sediment surface only and exclude Henry et al's
(1989) deeper portions of sediment cores.
Table 12: Assessment of the potential impacts that may arise from
Port of Cape Town development and operation and mitigation where
appropriate.
Table 13: Sustainability indicators for selected biological communities
in Table Bay.
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Port of Cape Town SEA – Table Bay Marine Ecology
Strategic Environmental Assessment for the Development of the Port of Cape Town
Marine Ecological Aspects
by
Dr R Carter, Dr N Steffani and Ms S Lane
1. Introduction.
The Port of Cape Town lies in Table Bay and, in the South African context, has a long
developmental history. The first jetty was constructed in 1656, the Alfred basin in 1870, with
the port reaching its present configuration in 1977 (NPA 2002). Up to this point little
cognisance had been taken of the overall environmental effects of the port on the Table Bay
marine and coastal environments aside from providing coastal protection from wave attack
along the shores of Paardeneiland to south of the Diep River mouth (Quick and Roberts
1993). This situation has improved in response to South African environmental legislation
and the acceptance by the National Ports Authority (NPA) of environmental responsibilities
inherent in sustainable management as stated in their corporate environmental policy (NPA
2001).
Development within the Port of Cape Town over the next two decades as described in the
Port Development Framework Document (NPA 2002) is anticipated to focus mainly on
relocation and consolidation of services provided by the port. Major construction should be
limited to the expansion of the container berth (addressed in a separate Environmental
Impact Assessment) and the development of 'dolphin' berths on the southern side of Ben
Schoeman dock. Subsequent to this it is possible that the port may extend its harbour area
towards Milnerton.
Prior to any significant development NPA has commissioned a Strategic Environmental
Assessment (SEA) to provide guidance for the Port of Cape Town development. The overall
aim of the SEA is to define the influences that the Table Bay biophysical and socio-economic
environment may or should have on port development. A schematic of these is shown in
Figure 1. Here the influences are defined as the activities that depend upon a functioning,
biologically diverse and unpolluted Table Bay marine environment and activities that may
compromise this. The former includes tourism, conservation and recreation and associated
commercial developments. The activities that may jeopardise the natural system include
physical modification, pollution and other disturbances associated with shipping and the port.
Accordingly the strategic issues focussing this specialist study are the:
 The rights all interested and affected parties have to a healthy, well functioning
environment, in this case specifically the coastal marine environment.
 The 'ecological' requirements of retaining Table Bay in as near a natural state as possible
to ensure its natural function in the local and regional marine environments.
Both of these issues are integral parts of the requirements of ecological sustainability
inherent in NPA's environmental policy.
This specific specialist study is designed to assist NPA in meeting these requirements by
identifying the constraints and opportunities, in terms of maintenance of Table Bay marine
ecological structure and function, that need to be taken account of in the planned
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Port of Cape Town SEA – Table Bay Marine Ecology
World
Heritage
Site
Rock
Lobster
Sanctuary
Recreation
and Tourism
Tourism
2.5 km
Robben
Island
Light
te r
Wes
Ecological
it of P
n Lim
Vessel Traffic
Management
Areas
ort
Structure
&
Function
Residential
Areas
Tanker
Services
Green
Point
Light
World
Heritage
Site
Marine
Park
Ramsar
Site
Northern Limit of Port
Tourism
Storm Water
Drainage from
City
Storm Water
Drainage
From
Industry &
Suburbs
Intermodal Logistics
Nodes
Research
Figure 1: Examples of some of the ‘free’ natural functions (goods and services) provided by the
marine ecosystem in Table Bay (within the NPA’s area of jurisdiction). These functions need to
be sustained to avoid serious opposition to Port activities. Red arrows indicate activities that
may impact on Table Bay marine ecology and green arrows show activities that draw
advantages from the natural system.
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
developments of the port and its routine operations. The study includes assessments of
potential impacts on important marine ecology components in Table Bay and recommends
monitoring programmes that can track actual impacts and allow appropriate management
intervention(s).
2. Rationale and Approach
This specialist assessment of Table Bay marine ecology describes the environment,
identifies the 'risk factors' for the Table Bay marine environment that may arise from the
proposed development(s), identifies potential impacts and, where appropriate, mitigation.
Due to the high level of assessment (i.e. strategic) the mitigation is essentially precautionary
in nature. Monitoring requirements are also defined, an important aim being to provide a
more informed base against which specific effects can be evaluated.
The study was limited to a 'desk top' assessment based on the available published and
unpublished scientific reports and data, supplemented by discussions with scientists,
engineers and NPA staff with direct experience of Table Bay and/or the port and its
operations. The assessment is structured on:
 A description of the affected environment (i.e. Table Bay marine ecology). This includes
summaries of physiography, oceanography, ecology and fisheries with as much detail as
possible on the biological communities that inhabit or occur in Table Bay. The purpose of
this was twofold, firstly to identify unique biodiversity resources and/or communities, if
any, and secondly to determine suitable ecological sustainability indicators. The latter
could be biological communities, individual species or key ecological processes, damage
to which may have significant deleterious effects on sustaining important biological
communities or the ecological functioning of Table Bay.
 An assessment of the current pollution status of Table Bay, identification of the important
contaminant sources and determination of trends.
 Identification of the environmental disturbances associated with port development and
operations.
 Determination of the potential impacts of these environmental disturbances and
assessments of their severity in terms of sustainability and requirements, if any, for
mitigation.
 Identification of constraints, or opportunities, that Table Bay marine ecological structure
and function may pose to port development and operation.
 Identification of Table Bay ecology sustainability indicators, and
 Recommendations on monitoring requirements.
It should be noted that this assessment assumes that there are no significant changes in the
macro-environment within which the Port of Cape Town operates. The study therefore does
not assess potential effects of sea level rise or more intense or frequent large storms that
may be associated with global warming. Nor does it address the implications of political,
social or economic changes that may alter the current relationship between the City and Port
of Cape Town and Table Bay. Should such changes arise or be expected to arise then
specialist assessments and evaluations should be undertaken to guide NPA's responses.
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3. Environmental Description
Quick and Roberts (1993) have given a general description of Table Bay, including
overviews of oceanography, biology and ecology and human uses. The description given
below follows the structure provided by these authors but departs from their report in that
more detailed information is provided on biology and ecology and incorporates results from
more recent publications.
3.1 Physiography
Table Bay is a log spiral bay anchored by rocky headlands at Mouille Point in the south and
Blouberg in the north and contains Robben Island and the important Port of Cape Town.
The bathymetry of Table Bay is shown on Figure 2. Maximum depth in the centre of the bay
is 35m with an important feature being the topographic high between Robben Island and the
mainland immediately north of Bloubergstrand.
The seabed is characterised by large portions of partly exposed bedrock, which in places
may be covered by a thin layer of coarse sediment. Fine sand is generally confined to the
eastern nearshore region between Blouberg and the harbour. However, a tongue of fine
sediments extends from the nearshore zone seaward to a depth of approximately 25 m
between Table View and Rietvlei. Smaller pockets of fine sand are found at the bay entrance
and on the eastern shore of Robben Island. Medium sand covers the remaining areas of
Table Bay (Figure 3) (Woodborne 1983; Monteiro 1997). The major sources of the sand in
Table Bay are seasonal (mainly winter) inputs from the Diep and Salt rivers and local erosion
of Malmesbury shales (Quick and Roberts 1993). There does not appear to be any
significant sediment supply from wave driven longshore transport from the south. Sediment is
transported out of Table Bay by local wave and storm driven transport and the overall
residence time for surficial sediments is estimated at 2-3 years (Monteiro 1997).
The shoreline of Table Bay (Figure 4; from Blouberg to Mouille Point) consists of 3 km of
rocky shore (at Blouberg and at Mouille Point), 13 km sandy beach (between Blouberg and
Table Bay harbour) and 4 km of artificial shore protection and breakwaters comprising the
Port of Cape Town (CMS 1998). Robben Island has a total shoreline of 9 km, of which 91%
is rocky (CMS 1998).
3.2 Oceanography
Table Bay is located within the southern Benguela upwelling system and its circulation and
water properties are characteristic of this region. Surface currents are mainly wind driven
with velocity generally decreasing with depth. Quick and Roberts (1993) quote typical
velocities as being 20 – 30 cm/s at the surface and near bottom flows being generally less
than 5cm/s. Summer circulation is mainly clockwise. Nearshore currents are wave driven;
waves approach the coast obliquely (200 - 260 predominantly) generating northward flow.
Due to generally low current velocities flushing periods in Table Bay are generally long with
an average period of 4 days (96 hours) (Quick and Roberts 1993). This particularly applies to
the bottom waters where van Ieperen (1971, cited in Quick and Roberts 1993) noted that
currents were undetectable in 80% of the measurements made over an annual cycle. This
contrasts with recent estimates of comparatively short residence times for surficial sediments
in Table Bay (above). It would therefore appear that the main drivers for sediment turnover
are episodic winter storms (cf Hill et al 1994), which probably also completely flush the water
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Port of Cape Town SEA – Table Bay Marine Ecology
3735000
Stormwater Outfall
Small Stormwater Outfalls
Industrial & Sewage Outfalls
Bloubergstrand
3740000
Blouberg Rocks
Robben
Island
Table View
3745000
Milnerton
3750000
Diep
River
Mouille
Point
Green Point
Sea Point
3755000
Salt
River
Cape Town
Harbour
Clifton Beach
-45
-50
Camps Bay
0 km
3760000
65000
60000
55000
2.5 km
5 km
50000
45000
Figure 2: Table Bay bathymetry, outfall pipelines and storm water discharges.
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Port of Cape Town SEA – Table Bay Marine Ecology
3735000
Very Fine Sand (0.063-0.125mm)
Fine Sand (0.125-0.250mm)
Medium Sand (0.250-0.500mm)
Coarse Sand (0.500-1.0mm)
Very Coarse Sand (1.0-2.0mm)
3740000
Bedrock
Blouberg Rocks
Robben
Island
Table View
no data
on bedrock
no data
on bedrock
3745000
Diep
River
no data
on bedrock
3750000
Milnerton
Mouille
Point
Green Point
Cape Town
Harbour
Salt
River
Sea Point
3755000
Clifton Beach
Camps Bay
0 km
3760000
65000
60000
55000
2.5 km
5 km
50000
45000
Figure 3: Sediment and bedrock distribution in Table Bay (after Woodborne 1983).
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Port of Cape Town SEA – Table Bay Marine Ecology
mass held in Table Bay. This being the case Table Bay may not be as prone to build up of
anthropogenic waste, such as sewage, as proposed by Quick and Roberts (1993).
During summer upwelling cold water (9 - 13C) invades Table Bay from the Oudekraal
upwelling centre, south of Table Bay. Temperatures can increase rapidly to > 20C during
relaxation phases of the upwelling cycle as water flows into Table Bay from the north and
north west (Monteiro 1997). Winter temperatures are more uniform than those of summer
and fall in the narrow range of 14 - 16C. This is a result of no upwelling and strong mixing
driven by storms.
3.3 Ecology
The major force driving the ecology of the region containing Table Bay is coastal upwelling.
This is forced by equatorward winds which, at the latitude of Table Bay, predominantly occur
in the austral spring/summer period (e.g. Shannon 1985). The upwelling process supplies
inorganic nutrients to the euphotic zone and results in rich blooms of phytoplankton and
dense stands of macroscopic algae such as the kelps.
These directly and indirectly provide food sources for the well-developed biological resources
on the west coast including pelagic (pilchards, anchovy) and demersal (hakes, kingklip) fish
stocks, near shore fisheries (linefish, rock lobster, abalone), mammals (seals and whales)
and seabirds (penguins, gannets, cormorants etc).
This review on the biological communities in Table Bay and their ecology draws on various
published scientific studies and general reviews, non-published reports from several
institutions, and discussions with specialists in relevant fields. It has to be noted, though, that
there is a general paucity of information regarding the biota
specific to Table Bay, and thus some of the descriptions of the different biological
communities are based on information drawn from the wider West Coast.
Marine ecosystems comprise a range of habitats each supporting a characteristic biological
community. Figures 3 and 4 show that Table Bay habitats comprise:
 Sandy beaches extending from the Salt River mouth north past Blouberg
 Rocky shores extending south of the harbour past Sea Point, at Blouberg Rocks and at
Robben Island
 Artificial surfaces of the harbour itself plus the shore protection extending towards Salt
River
 Subtidal sand substrata and
 Subtidal rock substrata in the bay itself
 The water body in Table Bay, and
 The water body in the port.
The biological communities in each of these habitats are described below focusing mainly on
the macrobenthos, mammals and resident seabirds. The reason for this is that these are the
components that will face the largest risks from the port and its development. For
completeness, however, short descriptions on pelagic communities are also provided.
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Port of Cape Town SEA – Table Bay Marine Ecology
3735000
Non-breeding Seal Colony
White Mussel Beds
Intertidal Sandy Shores
Intertidal Rocky Shores
Bank Cormorant Colony
African Penguin Breeding Colony
Bloubergstrand
Kelpbeds
3740000
Blouberg Rocks
Robben
Island
Table View
3745000
Milnerton
3750000
Diep
River
Mouille
Point
Green Point
Cape Town
Harbour
Salt
River
Sea Point
3755000
Clifton Beach
Camps Bay
0 km
3760000
65000
60000
55000
50000
2.5 km
5 km
45000
Figure 4: Distribution of rocky shores, sandy beaches, kelp beds, seabird colonies and seal
populations in Table Bay.
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Port of Cape Town SEA – Table Bay Marine Ecology
3.3.1 Table Bay Benthos
3.3.1.1 The intertidal rocky shore community
Intertidal rocky shores on the West Coast can be divided into four zones (Figure 5a):
uppermost is the supralittoral fringe, also called the Littorina zone, followed by the upper
midlittoral zone (or ‘upper balanoid’ zone), the lower midlittoral zone (or ‘lower balanoid’
zone), and lowermost the sublittoral fringe or Cochlear/Argenvillei zone. These four zones
and the actual biomass of species present in them can be modified by a number of factors,
the most important being wave action (McQuaid & Branch 1984, Branch & Griffiths 1988).
The following description of the ‘typical’ inhabitants of these zones is based on the review by
Lane & Carter (1999), with supplements from other reviews (Branch & Branch 1981, Branch
& Griffiths 1988, McQuaid et al. 1985).
Supralittoral fringe (Littorina zone) - Highest on the shore, in the Littorina zone, species
diversity is low, and macroscopic life is almost entirely constituted by high densities of the
tiny snail Littorina africana and variable cover of the red alga Porphyra spp.
Upper midlittoral (‘upper balanoid’) – The upper midlittoral is dominated by animals, with
the limpet Scutellastra (=Patella) granularis being the most characteristic species. Other
grazers such as the trochid gastropod Oxystele variegata and the limpets Helcion
pectunculus and Cymbula (=Patella) granatina, and the thaid gastropod Nucella dubia occur
in variable densities. Barnacle cover (Chthalamus dentatus, Tetraclita serrata and Octomeris
angulosa) is low. The green alga Ulva spp. is usually present.
Lower midlittoral (‘lower balanoid’) – Towards the lower shore, the biota is determined by
the degree of wave exposure. On sheltered and moderately exposed shores, algae become
more important, particularly the red algae Champia lumbricalis, Gigartina radula, G. stiriata,
Aeodes orbitosa, Iridea capensis, the green algae Codium spp. and the brown algae
Splachnidium rugosum and Bifurcaria brassicaeformis. The limpet Cymbula granatina and
the whelks Burnupena spp. and Nucella cingulata are also common, as is the reef building
tube-worm (polychaete) Gunnarea capensis. Shores experiencing greater wave action are
almost completely covered by the alien invasive mussel Mytilus galloprovincialis or at more
sand inundated shores by the indigenous black mussel Choromytilus meridionalis.
Sublittoral fringe (Cochlear/Argenvillei zone) – Lowermost on the shore is the unique
Cochlear/Argenvillei zone, which has no counterpart anywhere else in the world. At shores
with moderate to strong wave action, this zone is dominated by dense populations of the
limpet Scutellastra (=Patella) cochlear, which can exceed densities of 450 m-2. At such
densities it excludes most other species from this zone. When limpet densities are lower, the
flora and fauna composition resembles that of the lower midlittoral zone accompanied by the
anemone Bunodactis reynaudi, other patellid limpets and numerous whelks. Further north on
the West Coast S. cochlear is replaced by S. argenvillei. Shores with very high exposure are
again dominated by the mussels M. galloprovincialis and C. meridionalis and/or the tunicate
Puyra stolonifera. The Cochlear/Argenvillei zone is then absent. However, at shores covered
by mussel beds, usually all the species normally occurring on the rock surface can be found
living on the shells using the mussel bed as substratum. These animals are, however, often
smaller than those found on rock (Hockey & Van Erkom Schurink 1992, Steffani & Branch
2002). On very sheltered shores, both limpets and mussels are absent and the shore is
dominated by the limpet C. granatina and the polychaete G. capensis, which can build reefs
more than 30 cm thick, thereby excluding most other species from the shore.
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Rocky shore communities are strongly influenced by physical factors of which wave action is
one of the most important. Generally, biomass is greater on exposed shores, which are
dominated by filter-feeders. Sheltered shores support lower biomass and algae form a large
portion of this biomass (McQuaid & Branch 1984, McQuaid et al. 1985, Bustamante et al.
1995, Bustamante & Branch 1996a, b). Most of the shores at the West Coast including Table
Bay are exposed to moderate to heavy wave action and are thus dominated by filter-feeders.
Important filter-feeder species in the intertidal are the mussels Mytilus galloprovincialis and at
more sand inundated shores Choromytilus meridionalis (McQuaid & Branch 1984,
Bustamante et al. 1995). Next to their importance in terms of biomass and percentage cover,
they are also good indicators for water quality since they filter the water and may accumulate
any trace metals or hydrocarbons occurring in the water column. This makes them suitable
for monitoring programmes.
Intertidal rock pools form a specialized habitat on rocky shores where salinity, oxygen and
temperature may fluctuate greatly over tidal cycles and between day and night (Huggett &
Griffiths 1986). The composition of communities in the pools depends on the height on the
shore and three different assemblages can be found: one below low water neaps, a second
between low and high water neaps, and a third above high water neaps (Huggett & Griffiths
1986). The species richness in rock pools generally declines towards the top of the shore but
usually remains higher than that of the surrounding rocks. Pools are often dominated by
algae. The sea urchin Parechinus angulosus, anemones such as Pseudoactinia flagelifera
and Bunodosoma capensis and small chitons are frequently abundant. Sea stars (particularly
Patiriella exigua), ophiuroids, small limpets (Helcion pruinosu and Crepidula porcellana) and
small winkles such as Tricolia spp. are also common (McQuaid et al. 1985).
Species diversity and abundances of rock pool fish are low on the West Coast, and
represented by two families, the Clinidae (klipfish, 13 species) and the Gobiesocidae (gobies,
two species). Most of these are endemic to South Africa and restricted to the intertidal zone
(Prochazka 1994, Glassom et al. 1997). Typical fish species include various klipfish (Clinus
superciliosus, C. heterodon, C. acuminatus and C. agilis) and the sucker fish
(Chorisochismus dentex). Densities of fish are around 5-8 fish m-2 (Prochazka & Griffiths
1992, Bennett & Griffiths 1984).
3.3.1.2 The subtidal rock substratum community
Along the West Coast of South Africa, kelp beds are the dominant communities on subtidal
rocky reefs (= Sublittoral zone, Figure 5a). The main species in these beds are the kelps
Ecklonia maxima and Laminaria pallida. The more delicate rope-like Macrocystis angustifolia
can be found at more sheltered localities (Branch & Griffiths 1988).
Below the sublittoral fringe, the inshore zone is generally dominated by small E. maxima
plants and supports few animals. At intermediate depths, algal biomass is maximal with large
E. maxima plants forming a canopy, beneath which L. pallida and understorey algae grow.
Animal species diversity and biomass are, however, still low. Further offshore the kelp plants
thin out and give way to a dense faunal community dominated by sea urchins, filter-feeding
mussels, sponges and holothurians (Velimirov et al. 1977, Field et al. 1980, Branch &
Griffiths 1988).
Detailed maps of the exact distribution and width of kelp beds in Table Bay are presently not
available (Dr R Anderson, Seaweed Research Unit, MCM, pers. comm.) and thus only a
general distribution can be given here. In the Table Bay area, kelp beds can be found off the
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Burnupena spp.
Porphyra capensis
Nucella spp.
Scutellastra granularis
Oxystele variegata
Ulva spp.
Cymbula granatina
Aeodes orbitosa
Gigartina spp .
Splachnidium rugosum
Gunnarea capensis
ROCKY SUBSTRATA
Mytilus galloprovincialis
Choromytilus meridonalis
Pyura stolonifera
Scutellastra cochlear
Bunodactis reynaudi
Parechinus angulosus
2m
Ecklonia maxima
Laminaria pallida
Epymenia obtusa
Aulacomya ater
Pentacta doliolum
Haliotis midae
Jasus lalandii
Plagusia chabrus
Porifera
Pachmetopon blochii
0m
Typically found on shores
Found on more exposed shores
-10m
-40m
Supralittoral
Upper Midlittoral Lower Midlittoral Sublittoral Fringe
Sublittoral
Figure 5a: Typical species zonation patterns on a South African west coast rocky shore
(modified after Lane & Carter 1999).
Niambia sp.
Coleoptera
Diptera
Tylos granulatus
SANDY SUBSTRATA
Eurydice kensleyi
Excirolana natalensis
Pontegeloides latipes
Scololepis squamata
Donax serra
Cumopsis robusta
Cerebratulus fuscus
Gastrosaccus spp.
Bullia digitalis
2m
Cunicus profundus
Orbinia angrapequensis
Nephtys spp.
Lumbrineris tetraura
Cirriformia tentaculata
0m
-2-4m
Virgularia schultzi
Pectinaria capensis
Bullia laevissima
Ovalipes punctatus
-5-12m
INTERTIDAL
SURF ZONE
BREAK POINT
Eulittoral
Inner Turbulent Zone
Transition Zone
-20-40m
Outer Turbulent Zone
Figure 5b: Typical species zonation patterns on a South African west coast sandy beach
(modified after Lane & Carter 1999).
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rocky shores at Blouberg and from Mouille Point southwards and around Robben Island. On
the eastern side of Robben Island exists a dense Macrocystis bed extending down to a depth
of about 10 m (Dr R Anderson, Seaweed Research Unit, MCM, pers. comm.) (Figure 4).
Field et al. (1980) have surveyed transects across kelp beds at Sea Point (south of Mouille
Point) and Melkbosstrand (north of Blouberg), which due to their close proximity are likely to
be similar to those found in Table Bay. At both sites, the inshore is dominated by E. maxima,
giving way to L. pallida with increasing depth.
Kelp densities decline rapidly at a depth of 5-6 and 10 m for Melkbosstrand and Sea Point
respectively, which is attributed to relatively high turbidities at these sites.
Representative understorey algae include Bifurcariopsis capensis, Botryoglossum
platycarpum, Desmarestia firma, Epymenia obtusa, Gigartina radula, Neuroglossum
binderianum, Plocamium corallorhiza, P. maxillosum and Trematocarpus fragilis.
Epiphytically on kelp growing algae include Carpoblepharis flaccida, Carradoria virgata and
Suhria vittata. At both sites, but especially at Sea Point, filter-feeders form the largest trophic
group, notably the ribbed mussel Aulacomya ater, the holothurians (sea cucumbers)
Pentacta doliolum and Thyone aurea, Porifera (sponges) and to a lesser degree the tunicate
Puyra stolonifera and barnacles.
Carnivores, particularly the rock lobster Jasus lalandii and anemones, are fairly abundant
and prey almost exclusively upon filter-feeding mussels. This high abundance is probably
again attributable to the turbid waters, providing more food for mussels, which grow faster
and provide more food for rock lobsters. Grazers and debris feeders are less common and
include the sea urchin Parechinus angulosus, some patellid limpets, the giant periwinkle
Turbo cidaris, the abalone Haliotis midae and some isopods and amphipods. Other faunal
members include the whelks Burnupena papyracea and Argobuccinum argus, the starfish
Marthasterias glacialis, the crab Plagusia chabrus and polychaetes. The fish fauna is
dominated by the endemic hottentot (Pachymetopon blochii), but also includes twotone
fingerfin (Chirodactylus brachydactylus), redfinger (Cheilodactylus fasciatus), blacktail
(Diplodus sargus capensis), galjoen (Dichistius capensis), maned blennies (Scartella
emarginata), and various klipfish.
The kelps Ecklonia maxima and Laminaria pallida are the main primary producers in this
system. Few species feed directly on them but the main energy conversion pathway is by
means of detritus- and particularly filter-feeders feeding on the detritus derived from the kelp
plants. This detritus is also an important food source for filter-feeders in the rocky and sandy
intertidal (Bustamante & Branch 1996b, Soares et al 1997). The main filter-feeders in the
kelp beds are the mussels Aulacomya ater, Mytilus galloprovincialis and Choromytilus
meridionalis and the top predator on this species is the West Coast rock lobster Jasus
lalandii. The kelps, the mussel and the lobster are thus very important in this system.
3.3.1.3 Intertidal sandy beaches communities
The properties of the intertidal portion of sandy beaches and consequently the composition
of their biota are related to the degree of wave energy, sand particle size and beach slope
(McLachlan et al. 1993). These factors interact to produce three general beach
morphodynamic types: dissipative, reflective, or intermediate beaches. Generally, dissipative
beaches are characterised by fine sand and flat intertidal beach gradients. The wave energy
is generally dissipated in the surf zones, so that the conditions experienced in the intertidal
are less exposed/turbulent. These beaches are considered benign and harbour the richest
intertidal faunal communities. Reflective beaches, on the other extreme, are coarse grained
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(mean particle size >500 µm) with steep intertidal beach faces. The relative absence of a surf
zone causes all the wave energy to travel into the intertidal and the waves to break directly
on the shore. This causes a high turnover of sand, which is considered a harsh intertidal
climate. The result is depauperate faunal communities. Intermediate beach conditions exist
between these extremes and have a very variable species composition (McArdle &
McLachlan 1991, McLachlan et al. 1993, Jaramillo et al. 1995). This variability is mainly
attributable to the amount and quantity of food available. Beaches with a high input of e.g.
kelp wrack have a rich and diverse drift-line fauna, which is sparse or absent at beaches
lacking a drift-line (Branch & Griffiths 1988, Field & Griffiths 1991).
The West Coast of South Africa is almost linear, and virtually all beaches are exposed to
strong wave action, and are thus of the intermediate or reflective type. Typical of exposed
beaches, they are usually relatively steep and narrow with well-sorted fine to medium-sized
sediments, but some of the steepest beaches can have coarse sands (Branch & Griffiths
1988).
Macrofauna
The entire Benguela region from the Cape Peninsula right up the West Coast to northern
Namibia has a remarkably consistent sandy beach fauna (Field & Griffiths 1991). Although
very few data exist on the species compositions of the Table Bay sandy beaches
(Bloubergstrand and Milnerton Beach), data from other beaches are very likely to be
applicable to them. Lane & Carter (1999) have recently reviewed the composition of the softbottomed benthic macrofauna (invertebrate animals >1 mm) communities of the West Coast,
and the following description of the beach zones and their invertebrate beach macrofauna is
based on their document, supplemented by data from other studies and reviews (Christie
1976, Bally 1983, 1987, Branch & Griffiths 1988, Jaramillo et al. 1995).
The sandy beach intertidal is divided into the following zones (Figure 5b):
Supralittoral zone - The supralittoral zone is situated above the high water spring mark
(HWS), and receives water input only from large waves at spring high tides or through sea
spray. This zone is characterised by air-breathing Crustaceans, particularly the amphipods
Talorchestia capensis and T. quadrispinosa, the giant isopod Tylos granulatus and the
terrestrial isopod Niambia sp. The giant isopod T. granulatus, however, is very sensitive to
disturbance (e.g. driving and walking on the beach) and has almost completely disappeared
from Table Bay beaches (P. Nel, Marine Biological Research Unit, UCT, pers. comm.) A
diverse array of insect species (Coleoptera and Diptera) can also be found, which are almost
all associated with, and feeding on, wrack or other debris deposited along the drift-line.
Oligochaetes can also be abundant, again particularly under seaweed debris. Community
composition depends on the nature and extent of wrack, in addition to the physical factors
structuring beach communities, as described above.
Midlittoral zone - The intertidal or midlittoral zone has a vertical range of about 2 m. This
mid-shore region is characterised by the isopods Pontogeloides latipes, Eurydice longicornis
and Excirolana natalensis and the polychaete Scololepis squamata. In some areas, e.g.
Bloubergstrand, the white mussel Donax serra is also present in considerable numbers.
In the Table Bay area, the shoreline is characterised by strong coastal erosion. The
construction of the docks at Table Bay harbour caused the wave energy to be reflected from
the hard vertical harbour structure, which in turn resulted in the regression (erosion) of the
shore to the north and east, particularly at Milnerton Beach (Quick & Roberts 1993, Smith et
al. 2000). At the most common swell direction (west-south-west) waves approach the
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coastline at an angle close to normal with wave heights ranging from 1.0 to 2.0 m (Smith et
al. 2000). The headland at Mouille Point and the harbour are the only structures having a
wave sheltering effect, but only on the lee (Salt River mouth) of these structures. The erosion
and the strong impact of wave action are likely to result in relatively coarse sand at Milnerton
Beach, which in turn would suggest a relatively low macrofaunal diversity and abundance
there. A study by Orren et al. (1981b), who have sampled low intertidal beach sediments and
macrofauna from the Salt River mouth 4 km northwards along the beach, supports this. They
recorded a general northward increase in mean particle size from 200-250 µm near the
mouth to around 350 µm 4 km north of the mouth, reflecting the increase in wave energy.
Accordingly, they found a very low species diversity and density, comprising mainly of the
ribbon worm Cerebratulus fuscus and the polychaetes Lumbrineris tetraura and Nephtys
homburgi. The white mussel D. serra was not found. Pollution and/or fresh water effects from
the Salt River discharge might also be responsible for the low diversity. However, Orren et al.
(1981a) working on unpolluted beaches noted a general paucity of macrofauna along this
stretch of coastline due to the general high wave energy.
Meiofauna
The well-oxygenated beaches of the West Coast support also a rich and often diverse
meiofauna (invertebrate animals <1 mm), which can penetrate to at least 1 m below the
sediment surface, although overall densities decline with depth. Upper intertidal levels are
typically dominated by nematodes and harpacticoid copepods, whilst mystacocarids,
archiannelids, nematodes, harpacticoid copepods and sometimes oligochaetes are abundant
at mid-tidal levels. At lower, more turbulent tidal levels the meiofauna is sparse (Orren et al.
1981a, Branch & Griffiths 1988). Abundances and distribution of species can vary greatly
from beach to beach, and along the same beach, depending on sediment particle size,
patchiness of food sources, dissolved oxygen and organic content and wave energy (Orren
et al. 1981a). For example Orren et al. (1981a) observed a negative correlation between the
nematode/harpacticoid copepod density ratio and grain size. Finer sediment traps more
organic material but reduces oxygen penetration thereby supporting relatively higher
numbers of nematodes than does the more oxic but less organically rich coarse sediments.
3.3.1.4 Subtidal sand substratum community
Macrofauna
Subtidally, three zones are defined in the turbulent depths zone, each with a defined
macrofaunistic grouping:
Inner turbulent zone - The inner turbulent zone extends from the low water spring mark
(LWS) to a depth of about 2 m. The mysid Gastrosaccus spp., the ribbon worm Cerebratulus
fuscus and the cumacean Cumopsis robusta are typical of this zone, although they generally
extend partially into the intertidal above. In areas where a suitable swash climate exists (both
Milnerton Beach and Bloubergstrand), the scavenging gastropod Bullia digitalis is present in
considerable numbers, ‘surfing’ up and down the beach in search of carrion. Adults of the
white mussel D. serra can also be present in this zone (e.g. at Bloubergstrand, above).
Transition zone - The transition zone spans approximately the depth range 2-5 m. Extreme
turbulence is experienced in this zone, and as a consequence it typically harbours the lowest
diversity. Typical fauna of this zone include amphipods such as Cunicus profundus and deep
burrowing polychaetes such as Cirriformia tentaculata and Lumbrineris tetraura.
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Outer turbulent zone - Below 5 m depth extends the outer turbulent zone, where turbulence
is significantly decreased and species diversity is again much higher. Next to the polychaetes
of the transition zone, other polychaetes in this zone include Pectinaria capensis, Sabellides
ludertizi, Nephtys capensis and Orbinia angrapequensis. The sea pen Virgularia schultzei is
also common as is the whelk Bullia laevissima and a host of amphipod species. Relatively
large numbers of the three spotted swimming crab Ovalipes punctatus were noted during a
survey off Melkbosstrand (north of Bloubergstrand), and they are likely to occur further south
as well (S. Brouwer, Rock Lobster Section, MCM, pers. comm.). Similar to the intertidal
portion of the sandy beaches, the most important factors regulating the distribution of species
are the degree of turbulence and the sediment texture (Christie 1976). Christie (1974)
compared the distributions of the major benthic macrofauna taxa and sediment structures at
selected depths on a cross-shelf transect off Lamberts Bay (Figure 6). He found that the
outer turbulent zone up to a depth of 30 m was dominated by fine sands, and harboured
mainly molluscs, polychaetes and cnidarians. The important cnidarian species was the filterfeeding sea pen Virgularia schultzei. In Table Bay, fine sands with presumably similar faunal
composition to that described by Christie (1974), are distributed along the eastern nearshore
region between Blouberg and the harbour, and between Table View and Rietvlei, where a
tongue of fine sediments extends seawards to a depth of ~ 25 m. Smaller pockets of fine
sand occur at the bay entrance and on the eastern shore of Robben Island (Figure 3).
SEDIMENT TEXTURE
VCS CS
MS
FS
Legend:
VCS – Very coarse sands
CS – Coarse sands
MS – Medium sands
FS – Fine sands
VFS – Very fins sands
SC – Silts and clays
VFS
BENTHIC FAUNA
SC
CN
POL
CR
MOL ECH OTH
Legend:
CN – Cnidaria
POL – Polychaeta
CR – Crustacea
MOL – Mollusca
ECH – Echinodermata
OTH - Other
Figure 6: Comparisons of the distribution of the major benthic macrofauna taxa and
sediment structures at a depth of 30 m on a cross-shelf transect off Lamberts Bay, South
Africa (modified from Christie 1974).
Meiofauna
Bartlett et al. (1985) determined subtidal meiofauna distributions from 60 subtidal stations
covering large areas of Table Bay. They recorded generally high nematode numbers in the
sediments, with largest numbers near Green Point and north of the Kynoch outfall.
Harpacticoid copepod numbers were generally low but higher densities were distributed
offshore of the Diep River mouth and off Green Point. High numbers of flatworms occurred
offshore of Table View and Green Point. Table 1 lists nematode, harpacticoid copepod and
flatworm densities in relation to grain size. Whereas nematodes had highest densities in fine
and coarser sands, harpacticoid copepod densities increased with grain size. This is in
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Port of Cape Town SEA – Table Bay Marine Ecology
contrast to the findings of Orren et al (1981a) at intertidal beaches, which have shown
decreases in densities for both nematodes and harpacticoid copepods with increasing grain
size.
Table 1: Mean nematode, harpacticoid copepod and flatworm densities per 100 cm3 in Table
Bay in relation to grain size categories. Modified after Bartlett et al. (1985), standard
deviations were not reported.
Sediment size (µm)
Nematodes
Harpacticoid
copepods
Flatworms
0 - 180
644
9
181 - 300
93
16
301 – 700
507
382
10
23
23
3.3.2 Pelagic Communities in Table Bay
The pelagic communities are typically divided into plankton and ichthyoplankton and fish.
Table Bay forms part of the southern Benguela ecosystem and, as there are few barriers to
water exchange, pelagic communities are typical of those of the region. Brief descriptions are
given below, again with emphasis on communities, or components of communities that may
be affected by port development and operation.
3.3.2.1 Plankton and ichthyoplankton
The phytoplankton is generally dominated by large celled organisms. The most common
diatom genera are Chaetoceros, Nitschia, Thalassiosira, Skeletonema, Rhizoselenia,
Coscinodiscus and Asterionella whilst common dinoflagellates are Prorocentrum, Ceratium
and Peridinium (Shannon and Pillar, 1985). Harmful algal bloom (HAB) species (e.g.
Ceratium furca, C. lineatum, Promocentrum micans, Dinophysis sp, Noctiluca scintillans,
Gonyaulax tamarensis, G polygramma, Alexandrium catanella, Mesodinium rubrum) also
occur episodically and dense HABs have been observed in Table Bay (Pitcher and Calder,
2000). Mean phytoplankton biomass ranges between 3 and 4 µg chla/litre but varies
considerably with phases in the upwelling cycle and in HABs (Brown et al, 1991).
Zooplankton comprises predominantly crustacean copepods of the genera Centropages,
Calanoides, Metridia, Nannocalanus, Paracalanus, Ctenocalanus and Oithona (Shannon and
Pillar, 1985). Larger zooplankton commonly occurring in the nearshore area (e.g. Table Bay)
are the two Euphausiid species Euphausia lucens and Nyctiphanes capensis (Hutchings et
al, 1991, Shannon and Pillar, 1985). The zooplankton generally graze phytoplankton and
therefore biomass and biomass distributions depend upon this component of the plankton.
Ichthyoplankton in the southern Benguela area comprises mainly fish eggs and larvae. The
most significant contributors to this are the epi-pelagic shoaling species anchovy Engraulis
japonicus and pilchard Sardinops sagax (Shannon and Pillar, 1985). Other species including
hakes and mackerel are also represented but generally to a far lesser extent. Table Bay falls
within the main recruitment areas for these commercially and ecologically important species
and therefore it is likely that relatively high densities of fish eggs and larvae can be present in
the plankton (Crawford et al, 1989).
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Port of Cape Town SEA – Table Bay Marine Ecology
3.3.2.2 Fish
Nearshore and in the sandy beach surf zones of the southern Benguela region the structure
of fish communities varies greatly with the degree of wave exposure. Species richness and
abundance is generally high in sheltered and semi-exposed areas but typically very low off
the more exposed beaches (Clark 1997a, b). Beach seine catches from the shore have
resulted in a total of 29 species. Dominant species include harders (Liza richardsonii),
silverside (Atherina breviceps), white stumpnose (Rhabdosargus globiceps), False Bay
klipfish (Clinus latipennis) and two species of goby (Psammogobius knysnaensis and
Caffrogobius nudiceps) (Clark 1997a, b).
In the offshore environs of Table Bay all of the commercially important fish species occur,
some of which are fished (below). As pointed out above Table Bay falls in an important
recruitment area for the epi-pelagic species and is also in the seasonal migration pathway of
these fish to spawning grounds south of Cape Point and on the western Agulhas Bank
(Crawford et al, 1991). However, the absolute or relative importance of Table Bay to these
fish is not known but is probably not significant due to the relatively small area encompassed
within Table Bay compared to that of the overall recruitment and foraging habitat of these
species.
3.3.3 Table Bay Harbour Communities: Benthos
Macrofauna
The Table Bay harbour communities were recently surveyed, specifically in the Victoria and
Alfred Basins, and the inner dock walls of Duncan Dock (CMS 1995a, b). The fouling
communities on the dock walls near the harbour entrance in the Victoria Basin and on the
inner Duncan Dock walls were relatively diverse and included the barnacles Octomeris
angulosa, Austromegabalanus cylindricus and Notomegabalanus algicola, sea squirts (Ciona
intestinalis), large polychaetes (Syllis spp., Pseudonereis variegata, Nephtys spp. and
Platynereis dumerilii), the tunicate Pyura stolonifera (red bait), spiral fanworm Spirorbis spp.,
anemones (mainly Bunodosoma capensis, but also Anthothoe stimpsoni, Actinia equina and
Cerianthus spp.), bryozoans, sponges, feather stars (Comanthus wahlbergi), chitons,
nudibranchs, few amphipods and the algae Porphyra capensis, Aeodes orbitosa, Laurenica
flexuosa and in some places E. maxima. Klipfish were common and a few crabs (Plagusia
chabrus) and small lobsters Jasus lalandii (at the harbour entrance) were reported. The walls
were 100% covered with a 7.5 - 35 cm thick fouling community. Interestingly, no bivalves
(mussels) were found on any of the walls. The reason for this is not known. Despite the
absence of bivalves, the community structure was found to be reasonable healthy for this
type of environment (CMS 1995a, b) with an acceptable level of species diversity.
Further into the harbour, however, species diversity declined drastically. In addition to a few
barnacles, sea squirts and green algae (Ulva spp. and Enteromorpha spp.) the alien
anemone Metridium senile (Griffiths et al. 1996) was found near the bottom and in the bottom
sediments. The crab Plagusia was replaced by the alien European shore crab Carcinus
maenas, which could occur in great numbers. The sites with the lowest diversity and
sparsest cover were near the dry dock and the synchro-lift in the Alfred Basin. Here were
only some green algae, very few barnacles, the low growing hydroid Tubularia warreni and
some C. maenas present.
Outside the harbour, large numbers of juvenile rock lobsters can be found on the vertical
faces of the outer harbour wall (Hazell et al. 2002). Other major components of the wall
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Port of Cape Town SEA – Table Bay Marine Ecology
community are encrusting corallines, the barnacle Notomegabalanus algicola, the sea urchin
Parechinus angulosus, the ribbed mussel Aulacomya ater, and sponges (Mayfield 1998).
The relatively low coverage and biomass of mussels and the high cover of encrusting
corallines at the wall contrast with nearby natural subtidal rocky shores, for example at
Mouille Point, where mussels cover approx. 80% of the rocks and encrusting coralline cover
is low (Mayfield 1998, Table 2).
Table 2: Average percentage cover and wet biomass (± standard error) of benthic organisms
at the outer harbour wall and at Mouille Point. Percentage cover includes secondary cover
(e.g. barnacle cover) and can thus exceed 100% (after Mayfield 1998).
Benthos
Coralline algae
Foliar algae
Sponges
Parechinus angulosus
Aulacomya ater
Notomegabalanus algicola
Harbour Wall
% / g wet mass m-2 ± SE
75 / 2235 ± 289
<1 / <1 ±0.29
10 / 36 ± 7
70 / 334 ± 75
50 / 826 ± 391
40 / 81 ± 34
Mouille Point
% / g wet mass m-2 ± SE
20 / 506 ± 192
<1 / 1 ± 0.21
3 / 16 ± 8
5 / 259 ± 51
80 / 3303 ± 279
2 / 10 ± 7
Harbours are a typical place for the introduction of alien species. Ships calling at the port
may transport organisms on their hulls or in their ballast waters, which can be released at the
port. The European shore crab Carcinus maenas is such an example. It probably arrived in
the early 1980’s and is now well established in Table Bay harbour, from were it has spread
north and south (Le Roux et al. 1990). Another introduced exotic is the anemone Metridium
senile, which grows on loose, silt-laden boulders or other objects, and on the soft sediments
on the floor of the Victoria and Alfred Basins. It has not been recorded from outside the
harbour (Griffiths et al. 1996). Another recent introduction to the harbour is the red algae
Schimmelmannia elegans, which is currently restricted to small areas in the harbour (De
Clerck et al. 2002).
Meiofauna
The CMS (1995a) surveys included limited investigations into meiofauna inhabiting harbour
sediments. The meiofauna typically consisted of harpacticoid copepods, nematodes and
oligochaetes with very variable densities. Almost no meiofauna was for example found near
the dry dock area. This and the low species diversity on the dock walls there suggest that the
region at the dry dock and the synchro-lift is polluted, particularly by oil but also probably by
trace metals and antifouling agents from ship repair and maintenance operations.
3.3.4 Table Bay Harbour Pelagic Communities
There is apparently no published information on communities inhabiting the water column in
the harbour. It is known that euphausiids do occasionally occur in the port reaching densities
sufficiently high to clog the Two Oceans Aquarium seawater intakes (Mr D Vaughan Two
Oceans Aquarium Curatorial Staff, pers comm). Small shoals of mullet (Mugil sp.) are
common in the outer harbour area, particularly along the seawalls between the entrance to
Duncan Dock and the western breakwater (own observations). As pointed out above there is
also a resident or semi-resident fur seal population that utilises the port apparently as a
foraging area.
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3.4 Seabirds
Important seabirds in the Table Bay area include the African penguin Spheniscus demersus
and the Bank cormorant Phalacrocorax neglectus. In 1983, African penguins recolonized
Robben Island starting with a breeding population of nine pairs. By 1996, the colony had
grown to about 3100 breeding pairs. Counts from April to June 2000 at Robben Island
revealed a breeding population of 5705 pairs (Crawford et al. 2000), which, assuming a ratio
of 3.2 adults per breeding pair (Crawford & Boonstra 1994), amounts to an estimated
population of 18 000 adult penguins. Robben Island harbours thus the 3rd largest colony of
this species in the world (Figure 4). The African penguin is endemic to southern Africa and its
numbers have decreased throughout the 20th century, recently at a rate that has led to its
classification as Vulnerable under IUCN criteria (Crawford 1998, Barnes 2000).
Satellite tracking data indicates that penguins forage mainly north and offshore of Robben
Island generally within 20km of the island itself (MCM unpublished data).
Next to the large penguin colony, Robben Island supports the 3rd largest colony of Bank
cormorants (120 breeding pairs in June 2000), which are also endemic to southern Africa.
The 2nd largest colony is at Clifton Rocks, just south of Table Bay (Crawford et al. 2000,
Figure 4). The global population of Bank cormorants have decreased drastically in the last
three decades, from 8 672 breeding pairs to 4 888 pairs between 1995 – 97, and they are
also considered as Vulnerable (Barnes 2000).
Other seabirds, which might breed at Robben Island, are the Cape, crowned and great
cormorant (Phalacrocorax capensis, P. coronatus and P. carbo, respectively), kelp and
Hartlaub’s gull (Larus dominicanus and L. hartlaubii, respectively), and swift tern (Sterna
bergii). Cape and crowned cormorants and Hartlaub’s gull are endemic to southern Africa,
and the races of kelp gull and swift tern in this region occur nowhere else (Crawford et al.
2000). However, none of these birds had nested at Robben Island in 2000 (Crawford et al.
2000).
Another endemic seabird, the African black oystercatcher (Haematopus moquini), classified
as Near-threatened (Barnes 2000), had in 2000 a breeding population of about 35 pairs at
Robben Island (Crawford et al. 2000).
All of these seabirds are seriously at risk from oil spills, such as happened after the Apollo
Sea sank on 20 June 1994 between Dassen and Robben Island, or more recently the
Treasure oil spill on 23 June 2000, which sank as well between Dassen and Robben Island.
3.5 Marine mammals
A number of resident, semi-resident and migrant cetaceans (dolphins and whales) occur in
the waters of the southern African West Coast (Table 3), and have been sighted in Table Bay
(Best 1981, Findlay et al. 1992).
The most common is the Southern right whale which undergoes a seasonal (May –
October/November) migration into South African coastal embayments where females bear
and raise calves and may mate with males (Best 1989). Highest densities occur between
Cape Point and Mossel Bay but the whales also extend onto the west coast and are regularly
reported in the Table Bay to St Helena Bay region (Best 2000). Southern right whales are
classified as vulnerable under the IUCN criteria due to precipitous population declines
attributable to industrial whaling. This reduced the population in the southern African region
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Port of Cape Town SEA – Table Bay Marine Ecology
from ~20 000 to ~400 individuals by 1935, completely eradicating the Namibian and
Mozambican components (Richards and Du Pasquier 1989). Following the cessation of
'legal' whaling off South Africa in 1960's and 1970's the Southern right whale population
migrating to South African coastal waters began recovering and now stands at about 3000
whales (~15% of the 'pristine' population; Dr P Best, South African Museum, pers comm.).
With the cessation of whaling the main threat to Southern right whales during their presence
in South African waters is considered to be disturbance by vessel traffic and ship strikes and
Table Bay with its port related shipping obviously represents a potentially high risk area for
this. Some protection is afforded to these whales under South African Law which prohibits
any vessel from approaching closer than 300m from all whales. Unfortunately this is not
always enforceable (resources for surveillance are limited) or achievable (ships navigating at
night or in fog conditions). However, adequate controls on ship speeds can significantly
reduce risks here (see DEAT/SAMSA (2002) proposals on the designation of Particularly
Sensitive Sea Areas and associated protective measures for South African continental shelf
waters). Also, any such disturbance should only affect a minor proportion of the Southern
right whales that visit the South African coast due to most whales being located east of Cape
Point. Further, although philopatry to the South African coast must be quite strong fidelity to
specific coastal embayments is apparently not as well developed (Best 2000) and thus
disturbance at one site should not have strong negative affects on the whales that occur
here.
Table 3: Common whales and dolphins found in inshore waters of the Southern African West
Coast (from Lane & Carter 1999).
Common Name
Scientific Name
Notes
Common Dolphin
Cephalorhynchus
heavisidii
Lagenorhynchus
obscurus
Delphinus delphis
Killer whale
Orcinus orca
Endemic to the West Coast of
South Africa. Form small schools.
Often accompanies ships. Form
schools of up to 300 individuals.
Resident, forming schools of up to
5000 animals.
Cosmopolitan along entire South
African Coast, hunting in packs of
up to 30 individuals.
RESIDENT
Heaviside’s Dolphin
Dusky Dolphin
SEMI-RESIDENT
Humpback whale
MIGRANT
Southern Right
Whale
Megaptera
novaeangliae
Migrate past coast during
midwinter and spring.
Eubalaena australis
Most common between June and
December whilst breeding in
southern African waters. Occurs in
Table Bay.
Four species of seals are found in South African waters of which the Cape fur seal
(Arctocephalus pusillus pusillus) is the most common, and can often be seen in Table Bay.
There is a non-breeding population in the harbour itself, mainly occurring in the Victoria
Basin. The size of this population fluctuates greatly depending on food availability in and
around Table Bay, and because they leave the harbour during the breeding season (M.
Meyer, Mammal Section, MCM, pers. comm.). The nearest breeding colonies are at Seal
Island in False Bay and at Robbensteen between Koeberg and Bok Punt on the West Coast
(Wickens 1994). The survival of seal pups at Seal Island is, however, low due to the flat
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Port of Cape Town SEA – Table Bay Marine Ecology
topography of the island. Big waves often wash pups out to sea (M. Meyer, Mammal Section,
MCM, pers. comm.). Historically, there was also a seal colony at Robben Island, but along
with many other colonies it was destroyed due to disturbance and sealing by the early 20th
century, and so far seals have not returned to any of them (Shaughnessy 1984).
Far less common on the West Coast are the subantarctic fur seal (Arctocephalus tropicalisa),
the leopard seal (Hydrurga leptonyx) and the southern elephant seal (Mirounga leonia).
Vagrant individuals may occur in Table Bay.
4. Resources, and commercial and recreational fisheries in Table Bay
Several vertebrate and invertebrate fisheries operate either in Table Bay or in adjacent
waters. These are described briefly below.
4.1 Abalone
The abalone (perlemoen) Haliotis midae is an important resource in South African waters,
supporting a commercial fishery since 50 years. Although the fishery is small-scale, with
small Total Allowable Catch (TAC) of around 600 tons per annum, it is economically
important. Abalone is also fished recreationally and this sector having increased in recent
years. The greatest current threat, however, to the abalone stocks is the increase in illegal
catches (Dichmont et al. 2000, Tarr 2000).
Three commercial fishing zones exist on the West Coast: one from Cape Point to Mouille
Point (zone E), one from Blouberg to Cape Columbine (zone G) and one at Robben Island
(zone F) (Tarr 2000). Current quotas are 13, 20 and 20.5 tons for E, F, and G respectively
(Tarr, Abalone Section, MCM, pers. comm.). The quotas have been gradually reduced over
the years, due to declining catch rates. This is probably due to the fact that successful
recruitment at the West Coast is occurring only intermittently (very 2-4 years) in contrast to
the regular annual recruitment cohorts found on the southwest Cape coast (Tarr 2000, Tarr,
Abalone Section, MCM, pers. comm.). Recreational fishing is only allowed from the shore
and by snorkelling and thus does not occur, or is at least very restricted, at Robben Island.
Most abalones are found on rocky reefs shallower than 10 m and are closely associated with
kelp beds. Counts at Robben Island in 1981 revealed densities ranging from 0.4 to 2.8
individuals per m2 in the depth zone 1-6 m and 0.2 m-2 at 6-9 m depth (Zoutendyk 1982,
Table 4). New fishery-independent abalone surveys (FIAS) were initiated in 1995 to provide
an index of relative abundance (Dichmont et al. 2002). However, at present no data of these
surveys are published or prepared in such a way that they can be made available for use in
this review (Tarr, Abalone Section, MCM, pers. comm.).
Table 4:. Abalone (Haliotis midae) densities at selected sites at Robben Island at different
depths. (After Zoutendyk 1982).
Sites
Tantallon Castle – north-west of the island
Tantallon Castle – north-west of the island
Asgate – north-east of the island
Asgate – north-east of the island
Robben Island South
SEA Port of Cape Town
Depth (m)
1–6
6–9
1–6
6–9
1–6
No. m-2 (Mean)
0.7
0.2
2.8
0.2
0.4
21
Port of Cape Town SEA – Table Bay Marine Ecology
4.2 Rock lobster
The whole of the Table Bay area is a rock lobster sanctuary. Neither commercial nor
recreational fisheries are therefore taking place there. No actual data on poaching exist, but
in comparison to other areas poaching seems to be low there (S. Brouwer, Rock Lobster
Section, MCM, pers. comm.).
No regular surveys on rock lobster densities take place in Table Bay since this a non-fishing
area (S. Brouwer, Rock Lobster Section, MCM, pers. comm.). In 1998/99, however, a
number of diving surveys in <10 m depth and between 20-30 m depth were conducted. In
addition, lobsters were caught using small, baited mesh traps on long-lines at 20-30 m and
60-70 m depths (Table 5; Mayfield & Branch 1999). This survey revealed very low numbers
of lobsters in the Table Bay sanctuary below 60 m (mean = 1.11 lobsters/trap) and higher
numbers of lobsters caught further inshore at 20-30 m depths (31.60 - 54.84 lobsters/trap).
During the diving surveys, average numbers of lobsters counted at depths between 20-30 m
ranged from 0.25 to 20.71 per 40 m2. Highest densities were recorded at Camps Bay and
around Robben Island. In shallower waters (<10 m) the densities decreased again (Mayfield
& Branch 1999).
Compared to trap catches from 20-30 m depths outside the sanctuary at adjacent or nearby
exploited areas, traps in the Table Bay sanctuary yielded significantly smaller numbers of
lobsters. Densities obtained during the diving surveys, however, showed similar densities of
lobsters within the sanctuary compared to non-sanctuary sites (Mayfield & Branch 1999,
Table 6).
Table 5: Site, time, mean count (counts of lobsters in the traps) or density (numbers per 40
m2), sample size and the proportion of the sample greater than 75 mm carapace (% legal) for
rock lobsters caught using small, baited mesh traps on long lines or counted by diving
surveys (modified from Mayfield & Branch 1999)
Site
Table Bay (offshore)
Robben Island
Sea Point
Camps Bay
Llandudno
Robben Island
Robben Island
Robben Island
Sea Point
Sea Point
Sea Point
Camps Bay
Llandudno
Llandudno
Llandudno
Small baited mesh traps on long lines
Time
Depth
Mean count ± SE
1998
60-70 m
1998
20-30 m
1998
20-30 m
1998
20-30 m
1998
20-30 m
Diving surveys
Time
Depth
1998
1999
1999
1998
1999
1999
1998
1998
1999
1999
20-30 m
20-30 m
<10 m
20-30 m
20-30 m
<10 m
20-30 m
20-30 m
20-30 m
<10 m
% legal
1.11 ± 0.43
31.60 ± 3.74
42.20 ± 7.56
54.84 ± 8.27
9.80 ± 1.68
Sample
size
42
71
31
41
34
Density
(per 40m2) ± SE
8.59 ± 1.46
15.23 ± 3.58
3.09 ± 0.84
6.80 ± 2.18
0.25 ± 0.19
5.28 ± 1.33
20.71 ± 3.89
14.30 ± 3.94
12.13 ± 2.17
3.41 ± 0.66
Sample
size
32
30
32
26
32
32
32
29
32
29
% legal
100
0
2.4
not recorded
19.2
not recorded
not recorded
not recorded
not recorded
not recorded
not recorded
not recorded
not recorded
not recorded
not recorded
The proportion of legal-sized (>75 mm carapace length) rock lobsters caught in the Table
Bay sanctuary (in 20-30 m depth) was relatively low with a maximum of 19.2% at Llandudno,
at the southern end of the sanctuary (Table 3.5). Compared to areas north (Dassen Island,
median size 71-75 mm) and south (Kommetjie, median size 71-75 mm) of the sanctuary, the
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Port of Cape Town SEA – Table Bay Marine Ecology
median size of rock lobsters in Table Bay was also markedly lower falling in the size category
of only 51-55 mm carapace length (Mayfield & Branch 1999).
Furthermore, the Table Bay sanctuary does not appear to contribute more eggs per area to
the total egg production in the West Coast region than other areas, including other
sanctuaries (Table 5).
Table 6:. Averaged rock lobster density, the proportion of female rock lobsters, area of
concern, number of eggs from that area and the proportion of egg production this area had
contributed to the total production of eggs per region (modified after Mayfield & Branch
1999).
Region
South Coast
South Coast
West Coast
West Coast
West Coast
Site
South Coast
Betty’s Bay reserve
West Coast
Table Bay sanctuary
Saldanha sanctuary
Density
(m2)
0.667
0.577
0.456
0.315
0.657
%
female
73.7
87.6
30.9
44.1
50
Area
(km2)
60
5
800
45
14
No. eggs
1.41 x 1012
1.18 x 1011
6.1 x 1012
2.5 x 1011
2.1 x 1011
% of
total
92.2
7.7
92.9
3.8
3.2
The harbour wall of the Table Bay port and subtidal rocky reefs at Mouille Point act as
nursery reefs for the rock lobster. An average of 323 juvenile rock lobster were caught during
nine dives of 40 –60 minutes at the harbour wall, and 291 in eight dives at Mouille Point
(Hazell et al. 2002). Juvenile rock lobsters at the harbour wall grow, however, slower than
those at Mouille Point (Hazell et al. 2002). This is probably due to the difference in the
benthic community structures since lobsters at the harbour wall have to forage for longer and
thus spend more energy to find favoured food species (e.g. mussels), which are less
represented in the community there (see Table 3; Mayfield 1998).
4.3 Periwinkle
In the kelp beds at Sea Point and Melkbosstrand, Field et al (1980) found very low numbers
of the giant periwinkle T. cidaris. This was confirmed by a more recent survey ranging from
Yzerfontein to Quoin Point (Pulfrich & Penney 2000). In this survey greatest biomass of T.
cidaris in the total surveying area was found in the kelp beds on the leeward site off Robben
Island with an average biomass of 170.4 wet mass per m2 and densities of up to 72.5
individuals per m2. It is suggested that the Robben Island population is the result of an
historic migration of larvae around Cape Point and subsequent larval settlement and survival
of recruits on the sheltered side of the island. Despite the high numbers a commercial fishery
of the periwinkle at Robben Island was thus not recommended (Pulfrich & Penney 2000). No
recreational fishery takes place, because harvesting is only allowed from the shore.
4.4 White mussel
Along the West Coast, the white mussel Donax serra has a typical distribution pattern
according to size, changing from small to large down the beach from the mid-water to the
low-water mark and below. A large portion of the adult stock is usually located subtidally
below the low water mark. This is in contrast to the populations on the South Coast, where
the entire population occupies the mid to upper intertidal (De Villiers 1975, Donn 1990,
Farquhar 1995).
A large population of D. serra occurs at Bloubergstrand (Big Bay) just north of the rocky
shores at Blouberg. A survey in 1994/1995 revealed average densities of adult mussels (>50
mm) of 68 animals m-2 or 2.0 x 106 km-1 of shoreline. This was considerably lower than for
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
example at Yzerfontein (97 m-2 or 2.9 x 106 km-1) or at Elands Bay (156 m-2 or 4.7 x 106 km-1)
(Farquhar 1995). Including recruits (<15 mm) and juveniles (15-50 mm), densities of D. serra
at these beaches could reach up to 400 m-2. More recent sampling at Bloubergstrand,
however, suggests that the Donax population has increased significantly to the point where it
currently supports one of the highest densities of adults along the South African West Coast
(P. Nel, Marine Biology Research Unit, UCT, pers. comm.). D. serra also occurs at the
northern end of Milnerton Beach. A survey in 1994 revealed densities of approx. 400 animals
per m2 (all sizes classes) (P. Nel, unpublished data).
D. serra is harvested recreationally for bait and consumption and is thus an important
resource species in the area. In 1995, it was estimated that on a stretch of 900 m along
Bloubergstrand 15.8 tons of white mussel were collected annually, which was much higher
than at Yzerfontein (11.3 tons) or at Elands Bay (2.7 tons) (Farquhar 1995).
No data exist for white mussel populations along the southern stretch of Milnerton Beach, but
it is likely that this species does not occur there or only in very low numbers, since the grain
size at this beach is too coarse (P. Nel, Marine Biology research Unit, UCT, pers. comm.). D.
serra prefers particle sizes between 200 to 300 µm (Nel 1995).
4.5 Snoek and hottentot commercial fisheries
Table Bay supports a small commercial linefishery for hottentot (Pachymetopon blochii)
(Pulfrich & Griffiths 1988) and large numbers of snoek (Thyrsites atun) are also sometimes
caught in the bay, particularly around Robben Island (M. Griffiths, Linefish Section, MCM,
pers. comm.). Table 7 lists the landings of snoek and hottentot between 1997 to 1999 in the
Cape Town area, which reaches from Llandudno to the Koeberg Power Station. It is not
known, however, what proportion of the landings were caught in Table Bay.
Table 7:. Landings (kg) of snoek and hottentot in the Cape Town area (Llandudno to
Koeberg Power Station) from 1997 to 1999 (data provided by C. Wilkie, Linefish Section,
MCM).
Year
1997
1998
1999
Snoek
634 898
781 494
932 667
Hottentot
39 582
62 435
59 571
5. Biogeography and Unique Biodiversity Resources.
The South African coastline can be divided into three biogeographic provinces, the cold
temperate West Coast, the warm temperate South Coast and the subtropical East Coast.
Table Bay falls within the cold temperate West Coast province. A study by Bolton and
Stegenga (2002) on the diversity of seaweeds along the South African coast (divided into
contiguous 50-km coastal sections) has shown that the number of species occurring in the
Table Bay area is typical for the West Coast, thus not separating this area from the rest of
the West Coast. Another survey done by Emanuel et al. (1992) on the zoogeographic
patterns around the Southern African coast also groups Table Bay within the West Coast
province, not showing significant differences between rocky shore communities along the
West Coast other than related to physical factors such as for example wave action. Their
survey, however, was done on a relatively broad scale (coast divided into 100-km stretches),
but comparisons of data from varies studies on rocky shore communities (or specific
organisms within these communities) in the Table Bay area show a similar set of species
compositions as found for other areas at the West Coast (McQuaid & Branch 1984, McQuaid
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
et al. 1985, Van Erkom Schurink & Griffiths 1990, Bustamante & Branch 1996a, Kruger &
Griffiths 1998, Harris et al. 1998). Similarly, the sandy beach fauna is remarkable consistent
in the entire Benguela region from the Cape Peninsula all the way up the West Coast to
northern Namibia (Field & Griffiths 1991), which also includes the Table Bay area. This
suggests that the communities in Table Bay are typical for the West Coast and not unique to
Table Bay. The only exception to this - though not in terms of species uniqueness but rather
in terms of high density and thus importance - is the D. serra population at Bloubergstrand
(Big Bay), which is the densest population of this species at the West Coast (P. Nel, Marine
Research Unit, UCT, pers. comm., see 3.2).
The above indicates that the benthic communities in Table Bay are typical for the West
Coast, are not unique to Table Bay and cannot be classified as locally, regionally or
internationally important biodiversity resources. This rationale also applies to the pelagic fish
and marine mammals occurring in Table Bay as these are widespread on the South African
west (and south) coast. Further Table Bay itself does not appear to be critically important
either as a foraging or breeding area for these fauna.
The resident seabird community is a strong exception to this, especially the endemic African
penguin and Bank cormorant. It is estimated that approximately 36% of the global population
of penguins forage in continental shelf waters adjacent to Table Bay. These birds coming
from the breeding sites at Dassen and Robben Islands and, to a lesser extent, Boulders
beach in False Bay. Robben Island is an important breeding site for Bank cormorants as it
represents the third largest breeding colony for this species. Both of these species have
undergone severe declines in population size over the last century and are currently
classified as vulnerable under the IUCN criteria (Crawford et al 1998). Due to their population
size, endemism and conservation classification these seabirds represent internationally
significant biodiversity resources.
6. Current Pollution Status of Table Bay.
Table Bay receives effluents and contaminants from a number of sources. These range from
sewage and industrial pipelines, through point and diffuse stormwater outfalls, spillages and
discharges from shipping in and outside of the Port of Cape Town, ship repair activities in the
port, to atmospheric deposition (Henry et al 1989, Bartlett et al 1988, Monteiro 1997). The
complexity of the situation as far as point source outfalls are concerned is illustrated in Figure
2.
The variables employed in this status assessment are organic loading derived from sewage,
trace metal and hydrocarbon concentrations, derived from industrial activities and responses
in the biological communities, especially the benthos. Due to circulation and water
exchanges the water bodies in the larger Table Bay and the port are considered separately.
6.1 Table Bay
6.1.1 Enrichment from Sewage
Table Bay receives domestic sewage effluent from the Green Point outfall (~30 000m3/d,
Quick and Roberts 1993), minor outflows from the Salt and Diep rivers and from shipping.
Quick and Roberts (1993) considered Table Bay to be vulnerable to organic enrichment due
to measured low velocities of bottom currents and correspondingly long flushing periods.
Monteiro (1997) tracked deposition of sewage derived organic matter in Table Bay sediments
on the basis of organic carbon and stable isotope ratios of carbon and nitrogen. This study
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
showed that organic carbon content in sediments was low (< 0.1% in bulk sediments) and
that areas of highest concentrations were characterised by marine as opposed to terrestrial
(= plant plus sewage) derived carbon and nitrogen. Terrestrial derived organic matter was
restricted to nearshore areas adjacent to the Salt and Diep river mouths where sediment
organic carbon concentrations were particularly low. This is ascribed to continuous advection
out of the system due to wave driven currents.
The low organic enrichment accords with the absence of any significant depositional area,
characterised by fine sediments (< 63µm silts and clays), the general paucity of sediment in
the system (Woodborne 1983), and the apparent short residence time of surficial sediment in
Table Bay (2-3 years, Monteiro 1997). There is little biogeochemical evidence to support the
contention that Table Bay has or is being negatively impacted by sewage discharged from
the Green Point outfall. There are indications that the bay is more exposed to water quality
problems emanating from the Salt and Diep rivers.
6.1.2 Pollution from Industrial Sources.
Table Bay hosts two industrial outfalls, both of which are located on the eastern side of the
bay (Figure 2). The Nitrogen Products (formerly Kynoch) outfall was discharging 825 m 3/d
but has now closed down and Caltex discharges 2883 m3/d (CMC 2001). Both of these
discharged trace metals into Table Bay with the Caltex outfall also releasing relatively large
amounts of oil and grease (~ 9.5 tonnes/year). Other sources of trace metals are the Salt and
Diep Rivers, the Green Point sewage outfall and the harbour itself. Bartlett (1985) calculated
the total flux (i.e. supply) of the trace metals copper, cadmium and lead to be 16000, 1000
and 7000 kg/year respectively. Despite these large supplies there is no convincing evidence
of build ups in Table Bay sediments which led Monteiro (1997) to conclude that the bay is in
steady state with its supply. In short, trace metal contaminants are transported out of Table
Bay more or less at the same rate they are supplied.
Trace metal distribution maps compiled by Monteiro (1997) do, however, show areas where
trace metal concentrations are elevated. Notable amongst these are high copper
concentrations at the Green Point outfall, peaks in cadmium associated with the Caltex and
Green Point outfalls, and two areas of elevated concentrations of lead. One of the latter two
areas is located in the centre of Table Bay and the other on the western boundary. Of these
the western boundary peak appears anomalous and may have been due to an isolated
source of lead, e.g. weights or ingots, as the typical association with other trace metals such
as copper did not apply here.
Table 8 lists the proportion of measurements made by Bartlett et al (1985) and Monteiro
(1997) where Table Bay trace metal concentrations exceed ANZECC (2000) Interim
Sediment Quality Guideline trigger values for the protection of benthos. This table indicates
that Table Bay sediments are not significantly contaminated with trace metals. Indeed it
shows that in the bulk of the Table Bay area trace metal concentrations are well below the
ANZECC (2000) trigger values implying that biological communities would not be negatively
impacted by these contaminants, nor that they would constitute any significant risks in terms
of trace metal remobilisation if dredged (DEA&T 1998).
Water column trace metal concentration data for Table Bay are limited to those of Bartlett et
al (1985) who measured copper, iron, mercury, manganese, nickel and zinc concentrations.
Distribution maps show that highest concentrations were generally distributed nearshore
particularly around the Green Point – Harbour – Salt and Diep River and towards Blouberg.
Bartlett et al (1985) ascribed these elevated concentrations to the various outfalls in the area,
notably Caltex near Blouberg, and outflows from the harbour.
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
Table 8: Proportion of sediment trace metal analyses for Table Bay that exceed the
Australian interim sediment quality trigger values (ANZECC 2000).
Trace Metal
Cadmium
Copper
ANZECC ISQG Trigger
concentration (mg/kg)
1.5
65
% Exceedance 1985
4.7%
0%
(n = 64)
% Exceedance 1997
1.7%
0%
(n = 60)
* Includes anomalous high levels recorded from western side of Table Bay.
Lead
50
0%
*5%
Comparison of the Bartlett et al’s 1985 data with the RSA target values for the beneficial use
of the maintenance of marine ecosystems (DWAF 1995) indicate that only mercury exceeded
the set limits. This occurred at the Green Point outfall, while all other stations had values an
order of magnitude less than the target value. Although limited in temporal coverage these
data indicate that the water mass in Table Bay does not, in the main, contain significantly
increased trace metal concentrations from industrial effluents discharges.
6.1.3 Hydrocarbons
Formal data on oil spill observations are held by MCM, these being compiled from their own
observations from routine patrols and call outs and are supplemented by reports from
SAMSA, NPA etc. Over the period August 1991 to October 1999 (~ 8 years) 11 spills or
discharges of oils from shipping were recorded in Table Bay. The estimated total volume
discharged to the sea was 135 tonnes with an average spill size of 12.3 tonnes and an
average occurrence of 1.4 spills/year The largest spill observed was 113 tonnes from the
'Afrikander' which ran aground on Robben Island in March 1993. Note that the MCM spill
data is probably an underestimate of the actual frequency of discharges of oil by shipping as
the observations are limited in time and space due to budgetary constraints and are solely
conducted during daylight. Thus deliberate 'illegal' discharges of oils made at night would go
undetected.
The recorded spills/discharges are relatively small when compared with larger spills
associated with sinking of larger ships immediately outside of Table Bay such as the 'Apollo
Sea' (June 1994, ~2 600 tonnes) and MV 'Treasure' (June 2000, ~1 260 tonnes). However,
the minor spills and discharges contribute to chronic oiling of the coastline and specifically
impact African penguins.
Other contributors of hydrocarbons to Table Bay are oil spills and discharges within the
confines of the harbour. Normal tidal exchanges will lead to the incorporation of proportions
of the harbour water body into Table Bay, along with any oils (and other contaminants) it may
contain. An example occurred in May 1998 when 150 tonnes was accidentally discharged
into the harbour. Whittington (1998) estimates that 5 tonnes of this escaped into Table Bay
resulting in ~ 500 oiled penguins. The relative amounts and frequencies of such events is not
known, however.
6.1.4 Biological Community Responses
There are no published data or analyses suitable for identifying pollution impacts on the
various benthic biological communities in Table Bay. Bartlett et al (1985) focused on
meiofauna and identified areas of apparently anomalously high nematode abundance,
attributing these to organic enrichment from sewage. This may be so but unfortunately no
SEA Port of Cape Town
27
Port of Cape Town SEA – Table Bay Marine Ecology
convincing statistical analyses were provided in support of this aside from abundance
comparisons with Belgium's southern bight (North Sea). The lack of statistical rigour also
applies to the other conclusions drawn by Bartlett et al (1985), and so they cannot be used to
show pollution impacted areas within Table Bay. Field et al (1980) showed that filter feeder
biomass (i.e. mussels, sea cucumbers and barnacles) was relatively high in Sea Point kelp
beds compared to other areas surveyed such as Oudekraal, south of Camps Bay. A reason
advanced for this was higher particulate organic matter concentrations emanating from the
Green Point sewage outfall. However, there has been no objective test of this and so it is
impossible to exclude other potential causes such as variations in predation and/or larvae
settlement dynamics. Thus, similar to the meiofauna case (above) pollution effects remain
moot.
Pollution impacts on individual species or species groups are better known than those on
communities. Trace metal and hydrocarbon body burdens in mussels collected from sites
distributed around Table Bay have been measured regularly since 1985 by MCM as part of
their 'mussel watch' programme. MCM has also monitored penguin and other seabird
population levels and breeding success at Robben Island since penguin recolonisation in
1983 (above), as well as collecting oiled birds for rehabilitation.
The mussel watch programme Table Bay sampling sites are shown on Figure 7. Table 9 lists
mean concentrations of selected trace metal body burdens for these sites.
Table 9: Mean mussel flesh trace metal (Cadmium, Copper, Lead and Zinc) concentrations
(mg/kg Dry mass) for samples collected from the Table Bay sites (Figure 7) over the periods
1985-2000 (data from MCM).
Sample Site
Blouberg Beach
Black River
Paardeneiland
Ben Schoeman
Dock Customs
shed
Ben Schoeman
Dock breakwater
Duncan Dock
Victoria Basin
Granger Bay
Green Point
SEA Port of Cape Town
Cadmium
Mean(+/-sd), n
8.25 (5.77), 26
4.50 (4.61), 25
5.84 (6.36), 25
Copper
Mean(+/-sd), n
5.78 (4.16), 26
6.80 (2.07), 25
6.32 (5.25), 24
Lead
Mean(+/-sd), n
5.36 (16.80), 25
6.01 (5.02), 24
5.58 (12.33), 23
Zinc
Mean(+/-sd), n
159.42 (71.01), 25
185.46 (125.61), 24
144.13 (68.76), 23
7.28 (4.86), 24
5.85 (3.79), 24
9.63 (17.45), 23
228.79 (135.21), 23
7.13 (6.24), 26
3.62 (2.00), 25
4.36 (2.76), 24
5.95 (4.24), 26
9.75 (7.78), 26
6.21 (4.09), 26
6.11 (3.56), 25
5.48 (1.85), 24
7.63 (5.09), 26
6.74 (5.62), 26
6.71 (15.40), 25
3.68 (3.03), 24
3.98 (2.60), 23
10.96 (14.94), 25
5.48 (12.66), 25
180.49 (93.19), 25
254.04 (152.16), 25
212.55 (79.34), 24
304.20 (223.33), 24
251.84 (138.14), 25
28
Port of Cape Town SEA – Table Bay Marine Ecology
3736000
3738000
3740000
Blouberg
3742000
3744000
3746000
3748000
3750000
1)
h.
(2)
Sc
Be
nS
Be
n
P. Island
ch
.(
D.
an
Du
nc
Green Pt.
sin
Ba
3752000
ra
ng
er
B.
.
Vic
G
Black R.
3754000
3756000
0m
2500m
5000m
7500m
10000m
3758000
3760000
64000
62000
60000
58000
56000
54000
52000
50000
48000
46000
Figure 7: Mussel Watch sampling sites in Table Bay (data from MCM).
SEA Port of Cape Town
29
Port of Cape Town SEA – Table Bay Marine Ecology
The underlying assumption in monitoring contaminant concentrations in sentinel organisms
such as mussels is that they reflect the availability of contaminants in the environment
(Widdows and Donkin 1992). Due to differential uptake and elimination rates mussels can
bioconcentrate inorganic (trace metals) and organic (e.g.hydrocarbons) contaminants and
body burdens represent a time integrated estimate of environmental contaminant levels.
Thus the gradients evident in Table 9 reflect environmental gradients in the availability of
trace metals. Important sources of trace metals to Table Bay are therefore:
 Cadmium – primarily marine origin but supplemented by Green Point sources (e.g Green
Point outfall),
 Copper – Granger Bay, Green Point and Black River,
 Lead – Granger Bay and Ben Schoeman Dock in the Customs shed region, and
 Zinc – Granger Bay, Green Point and Duncan Dock.
The mussel watch data generally indicate a relatively lower contribution of trace metals from
the harbour (Duncan Dock and Victoria Basin) than the adjacent coastlines. This despite the
ship repair activities in the harbour and their known contribution of trace metals, especially
copper and zinc, to ports (e.g. Pacific Northwest Pollution Prevention Resource Centre,
1999; www.pprc.org) and the high trace metal concentrations measured in the port by Henry
et al 1989. This notwithstanding mussel flesh trace metal concentrations throughout Table
Bay are indicative of trace metal pollution in the system when compared to non-industrialised
areas in South Africa, e.g. False Bay (MCM mussel watch data) and internationally (Widdows
and Donkin 1992; Fowler 1990, lead only). This is a strong contrast to measured trace
metals in sediments and the water column in Table Bay (above).
As part of the MCM mussel watch programme Mason (1988) measured body burdens of
petroleum hydrocarbons in Table Bay mussels during 1985 and 1986. Concentrations
ranged from 10 – 937 µg/g (dry weight) for polar and 20 – 5171 µg/g for aromatic
hydrocarbon compounds. For both years and both compounds highest concentrations were
measured at Ben Schoeman Dock, Duncan Dock, Victoria Basin (Figure 6) and on the
western breakwater. Mason (1988) notes that surface slicks of oil were either present or oil
was liberated from the clumped mussels during collection at the sampling sites immediately
adjacent to the port. From this he concludes that the high concentrations measured from
these sites were due to frequent or semi-permanent exposures to oil slicks. Mason's data
also indicate that storm water is an important contributor of hydrocarbons to Table Bay.
Another animal that has been well researched and reported on in terms of oil pollution is the
African penguin (e.g. Crawford et al 2000). The effects of oiling on penguins (and seabirds in
general) are mainly deaths of adults through hypothermia during foraging, decreased
breeding success due to oiling of one or both parents during egg incubation and/or chick
rearing and mortalities of fledged juveniles during first excursions to sea around breeding
sites. Oiled penguins do come ashore, usually at islands or mainland breeding sites and may
be collected for rehabilitation at SANCCOB (Table 10). This has been shown to be
successful in that only 2 000 of the ~19 500 adult and sub-adult oiled penguins collected for
rehabilitation after the 'Treasure' oil spill died (Crawford et al 2000). However, total deaths
were much higher as it was estimated by Crawford et al (2000) that 4 350 penguin chicks
died due either to oiling or nest desertion by parents (presumably one or both parent birds
having been oiled or caught for translocation away from the oiled areas). These losses from
the penguin population would have been exacerbated by reduced breeding success amongst
rehabilitated birds which has been estimated at 30% lower than in unoiled birds (Avian
Demography Unit, University of Cape Town, unpublished data).
The Robben Island population prior to the 'Treasure' oil spill was estimated at 18 000 adults.
Assuming that ~80% of the 2 000 adult birds that died due to the spill were resident on
SEA Port of Cape Town
30
Port of Cape Town SEA – Table Bay Marine Ecology
Robben Island indicates a 9% loss for the Robben Island population. Penguin breeding
success, gauged by the number of fledged chicks produced per breeding pair per year,
ranges between 0.32 and 0.59 (Ellis et al 1998). Using the mid-point value of 0.46, it is
calculated that the loss of adults is equivalent to the annual breeding output of ~3 500 pairs
which represents approximately 62% of the known breeding population on the island.
Therefore despite the apparent successes in dealing with disasters such as the 'Treasure' oil
spill, oiling represents a significant threat to the penguin population and may contribute to
these birds becoming extinct in the wild.
Table 10: Numbers of African penguins treated by SANCCOB for oiling in the period 19942000. (Data from SANCCOB and MCM).
Year
1994
1995
1996
1997
1998
1999
2000
Penguins
>10 000
>1 332
1021
287
>563
584
19 500
Comment
'Apollo Sea' oil spill
Port of Cape Town spill
'Treasure' oil spill
6.2 The Port of Cape Town
6.2.1 Enrichment from Sewage
The port receives stormwater from a large number of outfalls (Figure 8) that drain the city
catchment. None of these are apparently linked to any of the city's sewage lines or overflow
systems. However, faeces have been observed adjacent to some of the outlets in the port
and faecal pollution, as shown by faecal coliform bacteria, has been shown to be associated
with fresh water in the port (CMS 1995 a & b). The other potential source of sewage is
discharge from vessels in the port. Due to harbour regulations this is considered to be a
minor contributor of sewage.
Elevated nitrate-nitrogen concentrations are associated with the stormwater flows (CMS
1995) and, coupled with the organic enrichment implied by the widespread faecal pollution in
the port, some level of eutrophication may result. However, Probyn (in CMS 1995) notes that
total nitrogen (nitrate+ammonium nitrogen) in the port may be similar to that in unpolluted
West Coast water. From this it can be concluded that sewage and/or stormwater derived
nitrogen will probably not lead to eutrophication of port waters with associated algae blooms
followed by anoxia.
The above notwithstanding Henry et al (1989) and Monteiro and Scott (2000) show that
sediments within the port are considerably enriched in organic carbon compared to
sediments in the adjacent Table Bay (<1% - >10% vs <1%). Obviously the port has
considerable protection from wave energy compared to that outside and thus deposition of
allocthonous and autocthonous organic matter is higher in the port. Supporting evidence is
the overall smaller particle size of the sediments in some areas of the port (>50% < 75µm =
silts and clays) than offshore and higher organic carbon concentrations at the heads of the
basins (Henry et al 1989).
SEA Port of Cape Town
31
ou
Harb
Do
ck
Sm
a
Ba ll C
sin raf
t
Du
nc
an
Do
ck
Ta
n
Be
n
ke
rB
as
in
St
ur
ro
ck
Sc
ho
em
an
D
oc
k
El
lio
tt
Ba
s
in
Port of Cape Town SEA – Table Bay Marine Ecology
Vi
Ba ctor
si i a
n
Co
nfe
r
en
ce
ce
nt
re
ll
r Wa
Syncrolif
t
red
Alf
Robinson
Dry Dock
Stormwater (&
canal?) Overflow
Intake &
discharge from
Roggebaai
Canal (was
cooling water
si n
Ba
Roggebaai
Canal
Aquarium
Proposed
marina
Figure 8: Outfalls discharging into the Port of Cape Town
SEA Port of Cape Town
32
Port of Cape Town SEA – Table Bay Marine Ecology
6.2.2 Pollution from Industrial Sources.
The major sources of trace metals in the port are the ship repair facilities and storm water
systems (Henry et al 1989; Monteiro and Scott 2000) and trace metal concentrations in the
harbour sediments are high. For instance the latter authors recorded cadmium concentration
ranges of <0.4 – 2.4 µg/g, copper 14.3-1804.9 µg/g, lead 7.7- 600.7 µg/g and zinc 15.41549.3 µg/g. These values are generally an order of magnitude larger than those recorded in
Table Bay (see above). Other trace metals such as manganese, chromium, nickel and
arsenic also show high concentrations. Highest trace metal concentrations were recorded at
the heads of the basins, especially at ship repair facilities and storm water inlets, and
generally declined towards the entrance of the port. Port of Cape Town trace metal
concentrations generally exceed those of other South African ports (Henry et al 1989),
despite the fact that ore shipments through the port are limited , underlining the roles of the
local ship repair industry and storm water flows.
Comparisons of selected Port of Cape Town sediment trace metal concentrations with the
ANZECC (2000) sediment quality trigger values (Table 11) show that substantial proportions
of the sediments contain levels considered to be potentially deleterious to benthos.
Consequently dumping of spoil dredged from the harbour may have implications in terms of
the London Dumping Convention (DEA&T 1998) as well as negative effects on the marine
environment.
Table 11: Proportion of sediment trace metal analyses for the Port of Cape Town that
exceeded the Australian Interim Sediment Quality trigger values (ISQG, ANZECC 2000) in
1985 (Henry et al 1989), 1999 (Monteiro 1999), 2000 (Monteiro and Scott 2000) and 2001
(Monteiro and Scott 2001). The selected trace metals are Cadmium (Cd), Copper (Cu), Lead
(Pb) and Zinc (Zn). Note: Calculations are based on measurements for the sediment surface
only and exclude Henry et al's (1989) deeper portions of sediment cores.
Trace Metal
ANZECC ISQG Trigger
concentration (mg/kg)
% Exceedance 1985
(n = 50)
% Exceedance 1999
(n = 15)
% Exceedance 2000
(n = 15)
% Exceedance 2001
(n = 15)
Cd
Cu
Pb
Zn
1.5
65
50
200
35%
52%
66%
46%
20%
53%
67%
53%
20%
67%
67%
60%
20%
67%
73%
47%
Contamination by biocide (antifouling) compounds, tributyl tin (TBT) and Igarol-15, may also
be a problem in the Port of Cape Town. Measurements are sparse and apparently limited to
analytical method trials for TBT conducted by CSIR in 1999. These yielded concentrations of
384 ng/l adjacent to the Royal Cape Yacht Club and 380 ng/l at Bertie’s Landing.
Comparative values in Saldanha Bay were 1.5 ng/l (A Pascall, CSIR, pers comm.). TBT is
toxic at 100 ng/l (0.1 µg/l) and the guideline water quality trigger value applied in Australian
marine waters is 0.006 µg/l (ANZECC 2000). Consequently the measured levels indicate that
TBT in the Port of Cape Town is probably exerting toxic effects on the biota. The scales of
this are unknown, however. There are no reported measurements on Igarol-15.
6.2.3 Hydrocarbons
Hydrocarbons enter the port waters directly from spills during ship bunkering, leaks from
piping infrastructure supplying bunkers, minor losses of hydraulic fluids from cranes and
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
other machinery and indirectly from road washings via storm water. NPA recorded 250 spill
events in the period 1999 – 2001 (NPA harbour oil spill records, unpublished). The total
volume of these spills was 707 tonnes. Four large spills accounted for 645 tonnes; included
here are 500 tonnes from the 'Treasure' that later sank between Robben and Dassen
Islands. The balance of the spills were obviously small with average volumes of 250 litres.
In the harbour hydrocarbons are incorporated into sediments through attachment to fine dust
particles and sinking and deposition in low turbulence areas (Henry et al 1989).
Consequently peak sediment hydrocarbon concentrations (8.0 – 11.7 mg/kg) occur in the
inner parts of Duncan Dock, between the 'Repair Pier' and K, L and M berths and in the
Alfred and Victoria Basins (Henry et al 1989). Low concentrations characteristically occurred
at the entrances to Duncan and Ben Schoeman Docks where turbulence would have been
higher. Fluorescence spectra indicate that fuel and lubricating oils comprise the bulk of the
hydrocarbons in the harbour sediments (Henry et al 1989).
From the overall distributions of hydrocarbons in the sediments Henry et al (1989) surmised
that contamination arises from small and/or continuous spills, not necessarily from sporadic
or episodic large spills. This is borne out to an extent by the common observation of oil
sheens on the water surface (e.g. Mason 1988; CMS 1995b) and the NPA harbour oil spill
records (above).
6.2.4. Biological Community Responses
The harbour wall (biofouling) community was characterised by low species diversity and
biomass and sparse cover (<50%) in the inner port areas such as the dry dock and the
Synchro-lift facility in the Alfred Basin (above). CMS (1995a) attributed this to higher pollution
impacts, primarily hydrocarbons but this may include biocides, at these sites compared to
dock walls at the entrances to the Victoria Basin and Duncan Dock. Here species diversity
and biomass was high as was coverage by the fouling community (>100%). A contributing
factor may be reduced water turnover rates in the inner harbour areas and thus lower food
supplies to the filter feeding community. Direct toxicity assays using sea urchin eggs,
however, underlined the importance of pollution in causing the observed distributions (CMS
1995c).
There are no reports of macrofauna in harbour sediments and information on meiofauna is
limited to the study by CMS (1995b) which investigated distributions in the Victoria and Alfred
Basins. Meiofauna were reduced in sediments adjacent to the dry dock in the Alfred Basin
but increased towards the Victoria Basin. This mirrors the gradients in sediment hydrocarbon
concentrations reported by Henry et al (1989). It is likely that meiofauna are similarly reduced
in other hydrocarbon impacted areas such as adjacent to the ship repair pier in Duncan
Dock.
7. Trends in Table Bay Pollution and Ecological Status.
7.1 Pollution
Generally the most suitable indicator for detecting long term trends in pollution status are
contaminant concentrations in sediments and indicator species such as mussels.
Long term signals in the sediments are confounded by the relatively short residence times of
the surficial sediments in Table Bay (above). However, the available information does
indicate that the contaminant deposition rate to the sediments does not exceed the supply
SEA Port of Cape Town
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Port of Cape Town SEA – Table Bay Marine Ecology
rate of new sediments to the system, hence the apparently steady state in contaminant
concentrations. Similar arguments can be applied to contaminant concentrations in mussels.
Although there are horizontal gradients with mussels collected from point sources of
contaminants showing higher concentrations than those collected from more distant stations
(above), there is no consistent build up in any of the contaminant levels over time except for
Cadmium (CMC 2001). The cadmium appears to be of a 'natural' marine origin and the
increases may not be attributable to anthropogenic sources (Monteiro 1997; CMC, 2001).
Oil pollution in Table Bay arising from operational and small-scale accidental discharges also
appears to be stable according to the spill records held by MCM. This is supported to an
extent by SANCCOB's records of oiled penguins received for rehabilitation. However, this
data set is complicated to an extent by the larger accidents that have recently occurred (e.g.
'Apollo Sea' and 'Treasure') as well as the fact that not all of the birds received would have
been oiled in the Table Bay area.
In summary, although the supply of contaminants to Table Bay may have increased over the
last two decades through increased industrialisation, increased stormwater and sewage
flows and larger shipping volumes, the physical dynamics of the system has apparently
precluded increases in contaminant concentrations in the system.
7.2 Ecology
Similar to the situation pertaining to pollution there are no data that allow the establishment
of trends in any of the identified communities, i.e. sandy beach, rocky shore, subtidal sand
habitat, subtidal kelp bed, and harbour wall in Table Bay. Also data for the species targeted
by commercial and recreational fishing is either non-existent or incomplete and a reliable
time series cannot be established.
In fact it is only seabirds that have received sufficient monitoring to establish trends in the
community. Here the two important species are the African penguin and Bank cormorant,
both breeding on Robben Island and both considered vulnerable under the IUCN criteria
(above). Apart from birds lost due to oiling from the 'Apollo Sea' sinking in 1994 and the more
recent loss due to the 'Treasure', breeding penguins on Robben Island have increased
steadily since 1983 when the colony was re-established ' (Crawford et al 2000). However, the
recorded increase appears to be the result of immigrating birds as opposed to increased
breeding success, at least up to the time of the 'Treasure' oil spill (June 2000, Underhill
2000). Subsequently penguin population growth may have been based more on increased
breeding success, related to increased availability of pilchards (Sardinops sagax) in the
southern Benguela region (Dr R Crawford, MCM, pers comm).
The Bank cormorant population in the Table Bay has decreased over the recent past (MCM
unpublished data) which may be a long-term effect of the 'Treasure' oil spill. However, this
may also be linked to an overall decline in numbers of this species in the southern Benguela
region (Dr J Cooper, ADU, pers comm) the underlying reasons for which are not yet clear. A
consequence of this is that Bird Life, South Africa are seeking to reclassify the species from
'vulnerable' to 'endangered' in terms of IUCN conservation status. Bank cormorants mainly
forage in kelp beds and shallow inshore waters where they prey on small fish and
invertebrates (Berruti 1989) so apparent increases in pilchard availability will probably not
help this species.
Unfortunately due to the large areas over which especially penguins forage (MCM,
unpublished satellite tracking data and observations) changes in Robben Island breeding
colonies do not necessarily reflect changes in Table Bay.
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Port of Cape Town SEA – Table Bay Marine Ecology
In summary, with the important exception of seabirds, the available data and information are
insufficient to establish trends in the important biological communities inhabiting or occurring
in Table Bay, or even the harbour. But equally there is no hard evidence that any of these
communities are showing significant declines or alterations in structure.
8 Risks posed by Port Development and Operations to Table Bay Ecology, Impacts
and Mitigation.
8.1 Risks
The risks that the port poses to Table Bay biological communities and ecology can be
categorised as those arising from port development and those due to the operational aspects
of the port. Development risks are those associated with the construction and expansion of
berths and associated activities such as capital dredging and construction. Operational risks
include those associated with spills and discharges of substances into the port and/or from
shipping that can affect water quality, maintenance dredging, shipping accidents and ship
operations. Development risks vary temporally along with the planned development phases
of the port. In the short term (0 – 7 years) the major physical development is expected to be
the expansion of the container berth into Table Bay. The next major expansion is expected in
15-25 years (long term) when there may be extension of the harbour area towards Milnerton
(NPA 2002). Operational risks, on the other hand, are inherent in the day to day activities of
the port, shipping, ship maintenance and cargo handling. These risks thus exist independent
of port development but, of course, may be modified by this.
The following risks are recognised:
Development Risks
 Permanent changes in the distribution of wave energy in Table Bay due to extension of
structures into the bay such as may arise from the expansion of the container berth and
potential extension of the harbour area towards Milnerton. Consequences include
changes to beaches on the eastern side of Table Bay. Examples are changes in beach
slope and sand particle size distributions attributable to changed wave conditions. This
can result in alterations to sandy beach intertidal community structure, particularly Donax
(white mussels) but also Bullia (plough snails).
 Temporary losses of seawall biota during construction or extensions of berths or
breakwaters.
 Removal or alteration of subtidal sand habitat through capital dredging.
 Short term (days) deterioration in water quality through elevations in turbidity at the
dredge and spoil dumps during capital dredging.
Operational risks
 Maintenance dredging carried out episodically throughout the life of the port with the
following potential consequences:
 Dumping of dredge spoil in Table Bay resulting in inundation of benthos,
 Remobilisation of trace metal and hydrocarbon contaminants during dredging and
from the dredge spoil with associated acute effects on biota, and
 Temporary increases in turbidity levels.
 Release or transfer of contaminants/pollutants into Table Bay through the port from port
or city operations.
 Release or transfer of contaminants/pollutants directly into Table Bay from operational
discharges from shipping or spills from shipping accidents.
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36
Port of Cape Town SEA – Table Bay Marine Ecology
 Release or transfers of alien species into Table Bay via ballast water discharges and/or
cleaning of ship hulls.
 General disturbances to the larger fauna in Table Bay from shipping.
8.2 Impacts and mitigation
The risks identified above are evaluated in terms of their expected impacts on Table Bay
marine ecology and the risk level they represent in Table 12. Twenty two separate impacts
are identified in this table, four are rated as medium significance and four as high. For NPA
to achieve the goal of minimal impact on Table Bay requires that the impacts rated as
medium and high be reduced through mitigation. Possible mitigation measures are included
in the table.
It should be noted that even with the application of mitigation, risks associated with oil spills
would not be significantly reduced in terms of their consequences because of the
conservation status of seabirds (penguins, cormorants and others such as gannets) that may
be affected. The suggested mitigation should, however, reduce the probability of spills
occurring.
SEA Port of Cape Town
37
Port of Cape Town SEA – Table Bay Marine Ecology
Capital Dredging –
Excavated area
modifying wave
energy distributions
SEA Port of Cape Town
Expansion
Outer and inner
harbour walls
Removes or changes
existing habitat
Table Bay subtidal
sand habitat
Modified beach slope or
particle size distributions
reducing Bullia populations
Modified beach slope or
particle size distributions
reducing Donax populations
Redistribution of sand
and/or modifications to
particle size distributions
Removal of habitat
Any effects should be short term (< 1 year) as
ambient waves and currents will transport sand
into the excavated area lessening wave energy
modification and its effects
Ambient waves and currents will transport sand
into the excavated area lessening wave energy
modification and its effects
This is short-medium term (<5 years) impact as
the excavated area will be recovered with
sediment and then be recolonised. Also it is
unlikely that the subtidal sand biota are
regionally unique and this habitat appears to be
regularly modified by storms etc anyway.
Medium significance
Low
Outer harbour walls
It is unlikely that the subtidal sand biota are
regionally unique and this habitat appears to be
regularly modified by storms etc anyway.
Expansion does offer more habitat for rock
lobster but this is apparently regionally
unimportant.
This is a medium term (<5 years) impact as the
new harbour walls will be recolonised.
N/A
Low
Blouberg beach currently hosts a large Donax
population. Loss or changed distribution may
have implications at the regional scale for the
southern Benguela Donax population.
Limit extensions to the eastern
(Milnerton) side of the harbour
within the wave shelter of the
existing western breakwater.
Demonstrate no or negligible
modifications to wave energy
distributions and Table View Blouberg beach characteristics by
appropriate modelling.
N/A
Low
Modified beach slope or
particle size distributions
reducing Donax populations
Suggested Mitigation
N/A
Low
Milnerton and Blouberg beaches are not
regionally important for the Bullia population
therefore this is a local effect.
Redistribution of sand
and/or modifications to
particle size distributions
Table Bay subtidal
sand habitat
Capital Dredging –
Sand removal
Modified beach slope or
particle size distributions
reducing Bullia populations
Table Bay subtidal
sand habitat
Table Bay intertidal
sand beaches
Rationale for estimation of the significance
N/A
Low
Breakwater and/or
berth construction
Table Bay intertidal
sand beaches
Nature of impact
N/A
Low
Breakwater or outer
harbour extensions
modifying wave
energy distribution in
Table Bay
Affected habitat or
biological community
N/A
Low
NPA activity and
aspect
Risk
Table 12: Assessment of the potential impacts that may arise from Port of Cape Town development and operation and mitigation where
appropriate.
N/A
38
Reduced light penetration,
decreases in filter feeding
efficiencies
Maintenance
Dredging – Harbour
dredge spoil disposal
Table Bay subtidal
sand habitat
Inundation by dredge spoil
and possible colonisation by
different fauna because of
altered particle size
distributions
Maintenance
Dredging – Harbour
dredge spoil disposal
- remobilisation of
contaminants and
pollutants in the
dredge spoil
All Table bay
communities and
habitats excluding
intertidal sand beaches
(distance), seabirds
and mammals.
Maintenance
Dredging – Harbour
dredge spoil disposal
- Elevations in
turbidity at dredge
and dump sites
Release or discharge
of contaminants and
pollutants into the
port and transfers to
Table Bay – Trace
metals
SEA Port of Cape Town
Table Bay and harbour
water column and
possibly harbour wall
community
All Table bay
communities and
habitats excluding
intertidal sand beaches
(distance), seabirds
and mammals.
This will occur but should be transient (days),
very restricted in space to <200m radius from
dredger and spoil dump site and limited to the
dredging period.
Affected area will be small due to low volumes
of dredge spoil being removed from the harbour
and recovery will probably occur through
particle redistribution by ambient waves and
currents
Acute toxicity effects.
The effects of the contaminants can be
pervasive across all of the biological
communities and ecological processes but
should be temporary as the contaminants will
dilute or be immobilised through recombination
with sediments with time.
Reduced light penetration,
decreases in filter feeding
efficiencies
This will occur but should be transient,
restricted in space to <100m radius from
dredger and spoil dump site and limited to the
dredging periods which are short with long
intervals (years) between them due to the low
level of sedimentation in the port.
Acute and chronic toxicity
effects
The effects of the contaminants can be
pervasive across all of the biological
communities and ecological processes and can
be long term (> 5 years) through modification of
species assemblages and community structure.
Low
Table Bay water
column
Suggested Mitigation
N/A
Low
Capital Dredging –
Elevations in turbidity
at dredge and dump
sites.
Rationale for estimation of the significance
N/A
Medium
Significance
Nature of impact
Low
Affected habitat or
biological community
Medium
Significance
NPA activity and
aspect
Risk
Port of Cape Town SEA – Table Bay Marine Ecology
Prohibit dumping of any harbour
dredge spoil with contaminant
concentrations exceeding the
lower end of the action level
ranges for London Dumping
Convention Annex 1 Substances
and special care ranges for
Annex II Substances as listed in
DEA&T (1998).
N/A
Eliminate inputs to the port from
ship repair operations and, in cooperation with the City of Cape
Town improve the quality of storm
water inflows to the port.
39
Release of
hydrocarbons from
ships directly into
Table Bay through
accidental spills (=
large volumes >7
tonnes).
SEA Port of Cape Town
Table Bay intertidal and
subtidal bivalves
(mussels)
All Table Bay
communities
and seabirds.
All Table Bay
communities, and
seabirds.
Oiling and acute and
chronic toxicity
The most serious effect here is mortality and
reduced breeding success in African penguins,
Bank cormorants and, to a lesser extent other
resident seabirds. The implications are
international in scope through the Biodiversity
convention and IUCN conservation status
classifications
Human health aspects
Although not strictly an ecological issue for
Table Bay prevention of collection mussels and
sand mussels can lead to higher pressures
being placed on adjacent mussel populations.
Chronic toxicity, and oiling
of penguins, Bank
cormorants and other
seabirds.
Acute and chronic toxicity
for all Table Bay
communities, and oiling of
penguins and other
seabirds.
Chronic discharges of oils probably occur with
chronic effects in the various communities.
Large spills associated with shipping accidents
can have serious acute effects for all
components but especially penguins and Bank
cormorants. The latter have international
implications through the Biodiversity convention
and IUCN conservation classification.
High Significance
Rationale for estimation of the significance
Low
Release or discharge
of contaminants and
pollutants into the
port and transfers to
Table Bay –
Pathogens
Release of
hydrocarbons from
ships directly into
Table Bay through
operational (= small
<7 tonnes)
discharges.
All Table Bay intertidal
areas, kelp beds, outer
harbour wall
communities and
seabirds
Nature of impact
Medium
significance
Release or discharge
of contaminants and
pollutants into the
port and transfers to
Table Bay –
Hydrocarbons
Affected habitat or
biological community
High significance
NPA activity and
aspect
Risk
Port of Cape Town SEA – Table Bay Marine Ecology
Suggested Mitigation
Seal up or remove existing
pipeline system supplying bunker
fuel and diesel to berthed vessels
and replace with the proposed
bunker barge system. Ensure the
highest level of control on fuel
transfers to limit accidental
discharges and enforcement of
discharge prohibition by any ships
in the port area.
N/A
Through SAMSA and MCM seek
enforcement of existing legislation
prohibiting such discharges and
contribute to improving
surveillance to ensure
compliance.
Through SAMSA and MCM seek
to reduce probabilities of
accidental spills through
enforcement of traffic
management systems and
preventing entry to Table Bay of
ships that clearly represent
hazards (but observing SOLAS
requirements). However, due to
the devastating effects of even
one large spill significance would
remain high but mitigation can
help reduce probabilities of
accidents.
40
Resident seabirds and
marine mammals
Mortalities
Ballast water
discharges from
ships.
All habitats and/or
communities except
seabirds and mammals.
Discharge or dumping
of biological material
removed from ship
hulls during
maintenance cleaning
and/or painting.
All habitats and/or
communities except
seabirds and mammals
SEA Port of Cape Town
Transfers and
establishment of alien
species and/or pathogenic
organisms, Potential
modification of
communities through
species substitution.
Transfers and
establishment of alien
species and/or pathogenic
organisms, Potential
modification of
communities through
species substitution.
There is a potential disruption of penguin
behaviour and foraging during breeding and
avoidance of the area by specifically whales
This may occur but all of the species can avoid
shipping navigating at <10 kts.
Alien species can displace indigenous or local
species and/or disrupt or distort important
ecological processes.
Alien species can displace indigenous or local
species and/or disrupt or distort important
ecological processes.
Suggested Mitigation
Low
Disturbance and avoidance
Rationale for estimation of the significance
N/A
Low
Shipping disturbance
- collisions
Nature of impact
N/A
High
Significance
Shipping disturbance
- noise
Affected habitat or
biological community
High
Significance
NPA activity and
aspect
Risk
Port of Cape Town SEA – Table Bay Marine Ecology
Prohibit untreated ballast water
discharges in Table Bay and/or
the port if of distant origin (i.e.
outside of southern African
region). Follow recommendations
on ballast water controls in IMO
(2002).
Prohibit discharging or dumping
of biological material cleaned
from ship hulls in both the port
itself and Table Bay.
41
Port of Cape Town SEA – Table Bay Marine Ecology
9. Table Bay Marine Ecology Constraints to Port Development and Operation.
Table Bay is not ecologically unique in the context of the southern Benguela
ecosystem. Therefore port development, if restricted to that contemplated in the NPA
Port of Cape Town development framework document (NPA 2002) and given that
appropriate mitigation will be applied where necessary, should not have negative
ecological consequences at the regional scale. Various negative environmental
impacts at the local scale (i.e. restricted to Table Bay itself) have been predicted but
with mitigation all are considered to be of low significance and should not constrain
port development.
Most of the anticipated negative impacts associated with port operation are also
judged to be of low significance at the local scale given the application of appropriate
mitigation. Exceptions, however, are activities or accidents that may lead to African
penguins or Bank cormorants becoming oiled. These are classified as significant
negative impacts at the international scale because of the current conservation status
of these endemic seabird populations.. Although not expected to curtail or constrain
port operations mitigation and control measures need to be seen as being high
priority to ensure containment of the risks.
The NPA Port of Cape Town development framework does not specify development
scenarios apart from the implicit development and status quo alternatives (NPA
2002). The most serious impacts on Table Bay marine ecology are linked to port
operation and thus these may persist for either of the implicit alternatives. However,
the consolidation of particularly the ship repair industry in the Elliot Basin, Sturrock
Dock and small craft basin area of the port envisaged in the port development
framework may facilitate better control of this industry than is presently the case. This
should be an environmental benefit to the port and Table Bay as losses of
contaminants (e.g. trace metals, paints, oils etc) to the port water body should
decrease. This argument also applies to berth refurbishment inherent in the
consolidation of the various terminals in the port. It is expected that at least losses of
bunker and fuel oils through the fuel supply infrastructure in the port system should
diminish as upgrades or replacements are achieved (W Cilliers, NPA, pers. comm.).
Therefore aside from the strategic business, economic and commercial motivations
supporting the port development put forward by NPA (2002), there also may be an
overall environmental benefit for Table Bay. Consequently, this assessment does not
find any significant marine ecological constraints to the proposed development.
10. Table Bay Ecology Sustainability Indicators.
Important issues for Table Bay in terms of sustaining its overall ecological structure
and function are the prevention or limitation of degradation and/or loss of habitat,
reduction(s) in biodiversity, pollution and introductions of alien species (above and
"State of Environment Indicators", DEAT 2001).
Indications of changes caused by port development and/or operations will be seen in
the structure of the various biological communities that inhabit the bay. As described
above, and given that appropriate mitigation will be applied where predicted or
observed impacts were significant, it is expected that there should be only slight, if
any, modifications to community structure. This notwithstanding it is beneficial for
monitoring and management purposes to define relevant indicators for each of the
main communities and/or habitats that may be affected. Table 13 summarises these.
SEA Port of Cape Town
42
Port of Cape Town SEA – Table Bay Marine Ecology
An important additional indicator is the level of pollution in Table Bay, particularly
trace metal and hydrocarbon concentrations in sediments and selected biota.
Table 13: Sustainability indicators for selected biological communities/habitats in
Table Bay.
Biological community/Habitat
Important Taxa/species
Intertidal sandy beaches
Bullia and Donax
Intertidal rocky shores
Mussels – Mytilus galloprovincialis
and Choromytilus meridionalis
Intertidal rocky shore rock pools
Clinidae and Gobiesocibae
Subtidal Sand
Unknown (for Table Bay)
Subtidal Rock
Kelps (Ecklonia maxima and
Laminaria pallida), mussel
(Aulacomya ater) and rock lobster
(Jasus lalandii)
Barnacles (Octomeris angulosa,
Austromegabalanus cylindricus
and Notomegabalanus algicola)
and rock lobster
Resident, semi-resident and
migrant species
African penguin (Spheniscus
demersus) and Bank cormorant
(Phalacrocorax neglectus)
Alien species
Outer harbour walls
Marine mammals
Resident seabirds
All marine environments
Sustainability
Indicators
Presence/absence
(Bullia) and
population size
(Donax)
Trace metal
concentrations in
mussel flesh
Abundance (between
low and high water
neap tide levels)
Species diversity and
population structure
Kelp bed community
structure
Species diversity and
rock lobster
abundance
Presence/absence
Numbers oiled/year
Presence/absence
and population
distributions.
11. Monitoring
This specialist study has predicted low significance impacts on Table Bay ecology
and biological communities for all risk factors except releases of hydrocarbons,
mainly fuel oil and to a lesser extent diesel, that may lead to oiling of seabirds, given
that appropriate mitigation measures are applied where required. However, it still
behoves NPA to monitor contaminant/pollution levels and potential effects in selected
biological communities. The purposes of this are twofold: firstly to confirm the
predictions that have been made and secondly to act as a precautionary measure to
prevent specifically contamination and/or pollution levels emanating from the port
exceeding known safe limits. This falls into the two categories of precautionary and
effects monitoring.
11.1. Precautionary Monitoring.
The purpose of this monitoring category is to provide warning if concentrations or
frequencies of releases of pollutants or contaminants increase. This will allow
timeous management intervention to reduce discharges and/or spills of contaminants
or pollutants. Candidates are trace metal and hydrocarbon concentrations in Harbour
and Table Bay sediments and selected sentinel organisms such as mussels, oil spill
observations, and frequencies and numbers of seabirds (African penguins and Bank
cormorants) affected by oiling.
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Port of Cape Town SEA – Table Bay Marine Ecology
All of the identified variables are currently the subject of ongoing monitoring in Table
Bay. The Port of Cape Town conducts annual assessments of sediment quality in the
harbour to determine suitability for dredge spoil disposal (Monteiro 1999, Monteiro
and Scott 2000 and 2001). The Cape Town Metropolitan Council supports monitoring
of Table Bay sediments at approximately 6 year intervals (Monteiro 1997 and survey
commissioned for April/May 2003). MCM monitors mussel flesh trace metal
concentrations at sites around Table Bay (Mussel Watch programme). MCM and
SAMSA maintain oil spill records and MCM and SANCCOB track frequencies of
oiling in seabirds (e.g. penguins, cormorants, gannets etc). These established
monitoring programmes represent an extremely valuable resource for NPA to assess
and track distributions of contaminants in Table Bay that may be derived from the
port and associated activities. The focus point for NPA with these variables is
temporal change. Increasing trends with time should trigger investigation or research
to establish whether these are attributable to the port or its operations as well as
identifying relevant management interventions where appropriate. Additional to these
variables MCM monitors penguin and cormorant populations and breeding success
on Robben Island and also the frequency of HAB occurrences. Although both of
these are mainly controlled or affected by mesoscale (10 – 100 km) physical and
biological oceanographic features and processes (e.g. Randall 1989; Probyn et al
2000), the monitoring data can 'protect' the NPA from negative public perceptions on
the role of the port. Consequently we recommend that the port of Cape Town,
through NPA, actively and formally support these monitoring efforts by engaging with
the relevant institutions. 1
For these monitoring programmes to be useful to NPA requires that both the data
and information (i.e. analyses and interpretations) be incorporated into NPA’s
environmental monitoring and management information systems and be reported on.
The latter is probably best achieved by annual ‘state of the environment’ reports for
the Port of Cape Town and Table Bay. This allows both tracking of trends and
publicising of the Port’s (and NPA’s) efforts in reducing/controlling deleterious
environmental impacts.
Another requirement for effectiveness of the monitoring programmes is for the Port of
Cape Town to have a clear understanding of what management interventions may be
required should the monitoring indicate e.g. increasing amounts of contaminants in
Table Bay. This, in turn, requires that sources of contaminants are known, e.g. spills,
fuel supply system leaks, storm water flows, as well as how contaminants entering
the port water body or sediments are exported to Table Bay. Implicit here is an
understanding of transfers across the major interfaces of the port and city (mainly
storm water) and the port and Table Bay (tidal and other exchanges, effects of
storms and high wave conditions, etc). To our knowledge this level of understanding
has not yet been achieved. We therefore recommend that appropriate research,
incorporating model simulations and measurement programmes, be commissioned to
facilitate effective management interventions that will protect Table Bay ecology from
possible deleterious impacts emanating from or through the port.
1
Note: Trace metal and hydrocarbon concentration monitoring can be conducted in the water column (dissolved
forms) where they may have impacts on pelagic communities such as plankton, ichthyoplankton and/or fish.
However, this is complicated by a myriad of factors that can confound relating measured concentrations to sources.
Examples include tidal cycles, fresh water inflows affecting density distributions and thus currents, the upwelling cycle
on the adjacent continental shelf and coastline affecting circulation, etc. The main effect of these is to cause
significant short term variability which indicates that, to achieve statistically reliable estimates of dissolved
contaminant/pollutant concentrations, extensive and intensive measurements are required. This is an expensive
approach in terms of manpower, resources and time, and is not recommended here.
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11.2 Effects monitoring
The purpose of this monitoring category is to demonstrate whether port development
and/or operations are affecting important biological communities in Table Bay.
Detection of effects indicates that management intervention is required to reduce the
stressor(s) driving the change(s) in the respective community. Similar to the above
this requires that, for this class of monitoring to be effective in generating appropriate
intervention, the links between the observed response(s) and the project activities
and specific aspects thereof are known or are demonstrable. Clearly if this is not the
case then there is no point in monitoring apart from just to observe change which, in
a lot of cases, may be due to natural variability.
The development of the port has potential consequences for specifically the intertidal
sandy beach biological community whilst port operations may affect all of the
biological communities in Table Bay through chronic toxicity effects of contaminants
and pollutants and imports and releases of alien organisms. Convenient indicators of
this are the outer harbour wall and kelp bed communities. The former because of its
proximity to the areas where contaminants, pollutants and alien species may be
introduced into the Table Bay environment and role as a rock lobster habitat and the
latter because of critical roles in nearshore ecology in the Benguela Current
ecosystem.
The important indicators for the sandy beaches (Donax and Bullia, Table 13) are
sensitive to changes in beach slope and particle size distributions. Changes in the
respective populations will therefore indicate or confirm such changes. The
respective monitoring variables are population density and age structure for Donax
and abundance for Bullia. The focus point in this monitoring is change over time from
a baseline established either from historical data (depending on quality) or
observations prior to capital dredging and container berth expansion. An outline
monitoring framework is set out in Appendix 1.
The premise underlying monitoring of harbour wall and kelp bed communities is that
chronic toxicity effects will modify community structure through, for example,
reducing recruitment rates of some components (Gray et al 1991). Invasive alien
species also have the potential to modify these communities through competitive
replacement or elimination of components of biota. Both of these effects can result
either in subtle or gross community changes and the latter, at least, may have
significant consequences for trophic relationships and ecological functioning.
Baseline information on the outer harbour wall community is available from CMS
(1995b), monitoring surveys would examine changes in overall community structure,
presence of alien species and rock lobster abundance over time.
There is no recent survey data suitable for creating a baseline against which changes
in kelp bed communities can be measured. Velimirov et al (1977) represents the
most recent comprehensive study for the Sea Point area and is clearly out of date.
Thus the monitoring for this component would have to obtain suitable baseline data
from an initial survey and then measure change against this over time. This is
expensive but there are possibilities of co-operation with the Cape Peninsula
National Park authorities who have initiated a programme to monitor key indicators of
community structure for the whole of the Cape Peninsula Coastline (kelp, sea
urchins, rock lobster, abalone, alikreukel and reef fish).
Outline monitoring frameworks for the harbour wall and kelp bed communities are set
out in Appendix 1.
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Port of Cape Town SEA – Table Bay Marine Ecology
12. Conclusions and Recommendations
Seven different ecological habitats are recognisable in Table Bay:
 Sandy beaches extending from the Salt River mouth north past Blouberg,
 Rocky shores extending south of the harbour past Sea Point, at Blouberg Rocks
and at Robben Island,
 Artificial surfaces of the harbour itself plus the shore protection extending towards
Salt River,
 Subtidal sand substrates and
 Subtidal rock substrates in the bay itself,
 The water body in Table Bay, and
 The water body in the port.
The available local and regional information indicates that each of the identified
habitats support biological communities characteristic of the region except for the
artificial surfaces associated with the Port of Cape Town. There is no natural
analogue to port breakwaters and harbour walls but species occurring there are
common in the region even though the overall community structure may be different.
Conclusion #1: Overall the benthic communities in Table Bay are typical for the
West Coast, are not unique to Table Bay and cannot be classified as locally,
regionally or internationally important biodiversity resources. This also applies to the
pelagic fish species and populations occurring in Table Bay as these are widespread
on the South African west (and south) coast. Despite some of the marine mammals
that occur in Table Bay, particularly the whale component, being internationally
important from the perspectives of conservation and conservation status, the bay
itself does not appear to be critically important as either a foraging or breeding area.
Further Table Bay is not important for industrial, commercial, artisanal or recreational
fishing.
Conclusion #2: The resident seabird community is an internationally important
biodiversity resource as it contains the endemic African penguin and Bank cormorant
which are considered vulnerable under the IUCN criteria. Approximately 36% of the
global African penguin population forages in continental shelf waters adjacent to
Table Bay and Robben Island currently hosts the third largest breeding population of
this species in the world. The island also supports the third largest breeding colony of
Bank cormorants in South Africa with the second largest colony breeding at Clifton
Rocks, immediately south of Table Bay.
Conclusion #3: Despite the fact that Table Bay receives effluents and contaminants
from pipelines, storm water outfalls, spills and discharges from shipping, ship repair
facilities in the Port of Cape Town and atmospheric deposition there is no clear
evidence of a systematic contaminant build up. There is also no evidence of any
marked distortion in biological community structure outside of the harbour area due
to pollution. This is attributed to the absence of depositional areas within the Bay and
regular flushing during winter storms.
Conclusion #4: In marked contrast to Table Bay there is evidence of contamination
build up in the port itself with sediments in the inner port areas being characterised
by high trace metal and hydrocarbon concentrations. Sewage derived human
pathogens are present in the water along with oil. Harbour water toxicity levels to
marine organisms has been assessed as being high. Benthos in port sediments is
depauperate and that on the harbour walls shows strong gradients in community
structure between the inner port and outer port areas, consistent with the distribution
of contaminants.
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Port of Cape Town SEA – Table Bay Marine Ecology
Conclusion #5: Both development of, and normal operations associated with, the
Port of Cape Town pose risks to Table Bay marine ecology. Nine main classes of
risks were identified in these two categories:
Development Risks
 Permanent changes in the distribution of wave energy in Table Bay due to
extension of structures into the bay arising from the expansion of the container
berth and potential extension of the harbour area towards Milnerton.
Consequences include changes to beaches (slopes and/or sand particle size
distributions) on the eastern side of Table Bay with related effects on the intertidal
sand beach community.
 Temporary losses of seawall biota during construction or extensions of berths or
breakwaters.
 Removal or alteration of subtidal sand habitat through capital dredging.
 Transient deterioration in water quality through elevations in turbidity at the
dredge and spoil dumps during capital dredging.
Operational risks
 Maintenance dredging carried out episodically throughout the life of the port with
the following potential consequences:
 Dumping of dredge spoil in Table Bay resulting in inundation of benthos
 Remobilisation of contaminants during dredging and from the dredge spoil
with associated acute effects on biota, and
 Transient (days) increases in turbidity levels.
 Release or transfer of contaminants/pollutants into Table Bay from the port and
its operations.
 Release or transfer of contaminants/pollutants from operational discharges from
shipping or spills from shipping accidents.
 Release or transfers of alien species in Table Bay via ballast water discharges
and/or biological material transported on ship hulls.
 General disturbances to the larger fauna in Table Bay from shipping.
Conclusion #6: Evaluations of these risks identified 22 potential impacts on Table
Bay ecology or associated ecological sustainability indicators. Eight of these were
considered to be of medium or high significance as shown below:
 Risk - Breakwater or outer harbour extensions modifying wave energy and
distribution in Table Bay causing alterations to beach slope and particle size
distributions on the sand beaches extending from Milnerton northwards.
Impact - Potential alteration to or loss of intertidal sand beach biota, particularly
white mussel (Donax) and plough snails (Bullia).
Impact Significance - medium.
 Risk – Disposal of harbour dredge spoil.
Impact – Acute toxicity for biota from remobilised contaminants (e.g. trace metals)
in the spoil.
Impact Significance - medium
 Risk – Release or discharge of trace metals into the port and transfers to Table
Bay.
Impact – Chronic and acute toxicity for Table Bay biological communities.
Impact Significance - medium
 Risk – Release of hydrocarbons from ships directly into Table Bay through small
volume operational discharges.
Impact – Chronic toxicity for all Table Bay biological communities and chronic
oiling of seabirds.
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Port of Cape Town SEA – Table Bay Marine Ecology
Impact Significance - medium.
 Risk – Accidental large volume oil spills from ships into Table Bay.
Impact – Acute and chronic toxicity for all Table Bay biological communities but
especially acute oiling of penguins, cormorants and other seabirds.
Impact Significance – high
 Risk –Release or discharges of hydrocarbons into the port and transfers to Table
Bay.
Impact – Oiling and acute and chronic toxicity for Table Bay intertidal
communities, kelp beds, harbour wall communities and seabirds
Impact Significance – high
 Risk – Ship's ballast water discharges transferring alien species to Table Bay.
Impact – Modifications to Table Bay biological communities.
Impact Significance – high
 Risk - Discharge or dumping of biological material removed from ship hulls
during maintenance cleaning and/or painting transferring alien species to Table
Bay.
Impact – Modifications to Table Bay biological communities.
Impact Significance – high
All except the risks derived from oil/hydrocarbon discharges and spills can be
mitigated to the extent that their respective significance ratings are reduced to 'low'.
Because of potential effects on specifically African penguins and Bank cormorants
even chronic oil discharges in the port can have serious consequences for these
seabirds in Table Bay. Large volume spills either within or advected into Table Bay
can have disastrous consequences for the survival of these species. It is considered
that, at best, mitigation can reduce the probabilities of occurrence of spills but not
remove the possibility. Hence the threats remain and potential impacts cannot be
classified as 'low' significance.
Conclusion #7: Risks associated with planned port development can be mitigated
and hence there is no apparent constraint posed to development by Table Bay
marine ecology, and
Conclusion #8: Port development through consolidation of the terminals,
rehabilitation and repair of berths and associated service infrastructure, especially
bunker supplies, offers the opportunity of reducing current levels of operational
contaminant and pollutant discharges to the port. This should assist in maintaining
the ecological structure and functionality of the Table Bay marine system.
Following on from the above three recommendations are made:
Recommendation #1: Develop and apply appropriate mitigation to each of the risks
identified as having potential impacts rated higher than low significance. As pointed
out above this will reduce all but those associated with oils to the acceptable
significance levels.
Recommendation #2: Collaborate with and support existing monitoring programmes
run by the City of Cape Town, MCM, MCM and SAMSA and the port itself to ensure
that the identified stressors to marine communities remain below trigger levels (=
precautionary monitoring). Establish baselines for effects monitoring and institute
appropriate effects monitoring programmes. Where necessary commission
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Port of Cape Town SEA – Table Bay Marine Ecology
appropriate research to clearly identify sources of the various environmental
stressors to facilitate management interventions when required.
Recommendation #3: Ensure that all stakeholders and interested and affected party
groups are adequately informed about the environmental performance of the Port of
Cape Town during all development phases and also regularly in terms of operational
issues. This is probably best achieved through a combination of forums and
newsletters.
Implementation of these recommendations should result in the following benefits for
NPA in the Port of Cape Town development and operation and improve the
sustainability of future port and port-city planning through:
 Reductions in negative environmental effects from current port operations.
 Guidance on screening out inappropriate developments or projects at an early
stage.
 Gaining the co-operation of others with influence or jurisdiction over activities
impacting Table Bay marine ecology (City of Cape Town, SAMSA, MCM, DWAF)
to reduce risks.
 And, minimise risks that port development and operation may encounter serious
opposition from stakeholders, interested and affected parties and the general
community due to natural or social environmental considerations.
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13 Acknowledgements
We thank staff of the Port Planning and Environmental departments of NPA for
information, data and advice given during this project. MCM provided essential data
on mussel contamination concentrations through their mussel watch programme,
information on port maintenance dredging and seabird populations. Dr Barry Clark of
Anchor Environmental Services CC provided constructive comments on an initial
draft of this assessment.
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Port of Cape Town SEA – Table Bay Marine Ecology
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APPENDIX 1
Outlines of Recommended Effects Monitoring Programmes
1. Sandy Beaches
Sand beaches extending from Milnerton to Blouberg may be modified due to
changes in the distributions of wave and current forces in Table Bay caused by the
extension of harbour seawalls and wave protection structures into Table Bay. The
modifications may be expressed in gross changes to beach morphology, e.g. erosion
of the shoreline, or more subtle changes in beach slope and sand particle size
distributions. The biological effects of such changes may include modifications to
population density and distributions on the beaches of both white mussel Donax
serra and plough snail Bullia digitalis. For white mussel this can have regional scale
implications due to the apparent importance of specifically the Blouberg beaches in
terms of overall biomass distributions for this species. Disappearance or reduction in
population density may also affect the current recreational fishery for this species in
Table Bay.
1.1 Monitoring of Donax serra
Two linked hypotheses are put forward for testing in the monitoring programme:
(i)
Donax population biomass (tonnes/km of shoreline) on Table Bay beaches
will decrease from its current (pre-construction) level in response to modified
distributions of wave and/or current forces in Table Bay caused by harbour seawall
and/or breakwater extensions.
(ii)
The overall variability in Donax population biomass (tonnes/km shoreline) is
reduced or increased due to corresponding changes in distributions of wave and
current forces in Table Bay attributable to harbour seawall and/or breakwater
extensions. Reductions in variances will indicate that the distributions of beach
modifying events such as storm waves have reduced, vice versa applies.
The above are testable with routine surveys of Donax distributions such as those
conducted by Cook and Birkett (1984 & 1986). Survey beaches should be Milnerton,
Tableview and Blouberg. Surveys should be conducted annually in the period April –
May. The monitoring period should initially be set at six years but this needs to be reevaluated towards the end of this period. The initial, pre-construction survey must be
conducted prior to any capital dredging or other activities that may, however
indirectly, affect specifically wave energy distributions in Table Bay.
The survey format and data outputs should be discussed with MCM as they require
such data for management of the recreational fishery. The most appropriate service
providers for the monitoring surveys are UCT or UWC as the work is amenable to
honours level projects and/or training (field plus statistics) of graduate students under
staff supervision.
Estimated costs for these surveys are R40 000 per year (2003 prices) with a total
cost of ~R240 000 (plus inflation) for the overall programme.
1.2 Monitoring of Bullia digitalis
The hypothesis to be tested here is that Bullia abundance will reduce in response to
modified beach slopes and wave swash zones caused by changes in wave energy
distribution in Table Bay.
Bullia are mobile and therefore quantitative monitoring in terms of absolute, or even
relative, numbers per length unit of beach will present significant logistical problems.
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To determine effects it should suffice to synoptically assess Bullia abundance in
terms of absent, rare, common or abundant. These categories should be defined in
the initial, pre-construction survey. Survey beaches should be as for Donax and
survey units at least 200 m of shoreline with at least 3 replicates per beach. Sampling
points with their replicates should be randomly assigned with the caveat that similar
types of shoreline should be covered on each of the beaches. Survey intervals
should be seasonal to account for this level of variation in the data. The monitoring
period should extend for three years at this intensity after which review of the
monitoring results should indicate appropriate levels for continuance. Survey data
should be logged in spreadsheet (e.g. excel) format.
Similar to Donax monitoring the most suitable service providers are UCT and/or
UWC. The Bullia monitoring should be combined with that for Donax to reduce costs.
Estimated costs are R18 000 per year (2003 prices) with an overall cost of ~R50 000
(plus inflation) for the three year programme.
2. Outer Harbour Wall Biofouling Community and Rock Lobsters
Outer harbour wall biofouling communities together with rock lobster Jasus lalandii
densities have been described by Mayfield (1998) and Hazell et al (2002).
Considered in relation to observations inside the harbour (CMS 1995a) there is clear
gradient in biofouling community attributes, e.g. % cover, biomass, species
composition and diversity, from the inner to the outer reaches of the port. CMS
(1995a) attributed gradients in their observations to pollution but other factors
including water, and thus food, exchange may have also contributed (above). If
pollution incidences in the port and frequencies and intensities thereof increase
effects on biofouling community attributes may extend to the outer harbour areas, in
particular the outer harbour seawalls. If so, then impacts may also be realised in the
local rock lobster community.
Two linked hypotheses are to be tested here:
(i)
The outer seawall biofouling community will reduce in terms of % cover,
biomass, species diversity etc and experience modified species community structure
over time in response to increased levels of contaminants and pollution associated
with increased shipping and related port activities.
(ii)
Rock lobster densities on the outer seawall will reduce in response to
diminished or altered food value of the biofouling community.
These two hypotheses are testable against biofouling and rock lobster distribution
data gathered by standard marine benthos and rock lobster survey techniques (e.g.
Velimirov et al 1977).
Biofouling community attributes can be derived from combinations of underwater
photography of quadrats and biomass and community structure determinations on
cleared quadrats. The sampling site should be the outer seawall of the western
breakwater. Samples should be derived from 5 replicates of randomly spaced
quadrats in each of three depth zones corresponding to upper, middle and bottom
depths. Species community/structure analysis should meet the requirements of the
Primer suite of computer programs.
Rock lobster population density should be estimated from belt counts along the
seawall and size structure from trapping or other non-biased technique.
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Sampling intervals should be bi-annual (mainly to reduce autocorrelation between
samples and monitoring duration should be initially set at 10 years, i.e. five individual
surveys.
Observations and reporting on presence/absence of alien species should be included
in this monitoring programme as part of the biological community analyses.
Suitable agencies for managing and conducting these surveys are consultancies in
the Western Cape possibly in cooperation with academic institutions such as UCT
and/or UWC. Estimated costs for the surveys are R100 000/survey (2003 prices)
giving an overall cost of R500 000 (plus inflation) over the ten year monitoring period.
3. Kelp Bed Communities
Kelp beds are large and diverse biological communities including the kelps
themselves, understorey algae, grazers, filter and suspension feeders, benthic
carnivores, fish and even avian predators (e.g. Bank cormorants) (see Velimirov et al
1977). Biological surveys of kelp beds sufficient to detect changes or variability
caused by non-natural causes are complex and labour intensive and accordingly
expensive. An alternative to general surveys of biological structure is to focus on
specific habitats within kelp beds such as kelp holdfasts. These contain a diverse
fauna (Velimirov et al 1977), constitute convenient sampling units and kelp holdfast
communities have been shown to be reliable indicators of anthropogenic impacts
(e.g. Smith 1996 and references therein). Accordingly kelp holdfast communities are
the focus of biological effects monitoring as proxies for the larger kelp bed ecological
unit.
The hypothesis to be examined here is that biological community structure within
kelp holdfasts in kelp beds adjacent to the port of Cape Town will be modified over
time in response to pollution from increasing port and shipping operations.
The hypothesis is testable against temporal distributions of kelp holdfast biological
community structure across a kelp bed.
A candidate sample site for monitoring is the kelp bed off Green Point. Sampling
units for monitoring are kelp holdfasts with their entire biological communities.
Sampling locations are appropriate discrete depth horizons extending across the kelp
bed, e.g. depth ranges 2-4m, 6-8m, 10-12m, 14-16m, >18m. Such a sampling range
will incorporate Ecklonia maxima and Laminaria pallida holdfasts and the depth
zonation of kelp bed fauna (Velimirov et al 1977). Five replicate samples randomly
spaced should be taken to resolve variability within each of the chosen depth
horizons. Biological analyses of the samples should be sufficient for compilation of
univariate and multivariate statistics as set out in the Primer suite of computer
analysis programs.
Sampling should be carried out at three year intervals for an initial period of 12 years,
giving five sets of samples. Temporal trends in these should provide sufficient
justification for extending, modifying or terminating the monitoring programme.
Cooperation with the surveys planned for the Cape Peninsula National Park should
provide the larger kelp bed context for the kelp holdfast biological community
monitoring programme and assist in identifying anthropogenic effects.
Suitable agencies for managing and conducting these surveys are consultancies in
the Western Cape possibly in cooperation with academic institutions such as UCT
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Port of Cape Town SEA – Table Bay Marine Ecology
and/or UWC. Survey costs are estimated at R250 000/survey (2003 prices). Overall
costs for the monitoring programme are therefore estimated at R1 250 000 (plus
inflation) over the 12 year period.
4. Establishment of Alien Species
Sources of alien species associated with shipping transported and released into
Table Bay or the port of Cape Town are ballast water or ballast tank sediment
discharges or biological material scraped from ship hulls during cleaning. Generally
the numbers of taxa and/or individuals released in this process are low. Further, most
commonly the life stages released are spores (algae) or larvae or juveniles.
Consequently only the most extensive, intensive and assiduous sampling or
observation programme has any acceptable probability of detecting imported alien
species before they become established in the receiving environment. In some cases
once established finding exotic species becomes easier, examples are the Spanish
mussel Mytilus galloprovincialis here as it became the base of commercial mussel
farming and zebra mussels Dreissena sp. in NE USA (e.g. Dermott and Keree 1995).
Such established alien species would probably be observed in monitoring
programmes directed at harbour seawall and kelp bed communities (above). Species
that do not reach such dominance or remain fugitive and cryptic would probably
remain undetected.
Therefore to complement the proposed systematic effects monitoring programmes
described above it is proposed that field observational diving surveys be undertaken
to check the establishment of alien species at a specific location or locations in the
harbour, e.g. eastern mole and/or A berth in Duncan Dock, elbow and/or east pier in
Victoria Basin. The surveys should be conducted by marine biologists with in-depth
knowledge of the range of species expected to be found in these environments to
facilitate recognition of alien species. UCT has a suitable pool of expertise for these
surveys. Surveys should be conducted at least once every three years but shorter
intervals may be appropriate. No cost estimates are provided here as these depend
on which experts would be best, or available, to conduct the surveys.
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