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CONTRIBUTION FROM AZTI
- Dredging disposal and aquaculture:
Both dredging and disposal of marine sediment (polluted and unpolluted) can affect the
water column features, the physical and chemical nature of the seabed, and the benthic
communities. The impact can be observed at short- or long-term.
The potential impact of these activities could be observed in:
- A deterioration in the overall quality of the marine system
- A reduction in the socio-economic aspects (fishery, aquaculture, tourism,…)
- An interference with other uses (recreation, navigation, aquaculture,…)
- A reduction in the aesthetic qualities of the location.
The inputs of suspended materials, dissolved pollutants, organic matter, etc., from
sediment disposal, can produce increase of turbidity, oxygen demand, toxicity, and algal
blooms, and subsequent impacts on the aquaculture. These impacts can lead to an
increase of diseases, mortality or productivity, within the cages.
- Impact of the introduction of alien species:
Aquaculture is the second cause of transfer of marine species from different areas of the
world. It has been described that aquaculture impacts on Posidonia beds, favouring the
establishment of Caulerpa sp. (alien species).
The main impact of the introduction of alien species is the community structure change
by means of the alteration in trophic nets and biodiversity, outcompeting local
fauna/flora and threatening diversity. They can also involve an increase in the use of
biocides in order to control their populations. But there are other impacts related to
physicochemical variables which depend on the kind of species we are talking about:
 Benthic species: They can impact on dissolved oxygen in bottom waters
(negative impact) and nutrients concentrations in sediment
(positive/negative impact) by consumption. Besides, if they are filter
feeding species they can decrease suspended particulate matter
(positive/negative impact).
 Planktonic species: If they are phytoplanktonic species, they can impact on
dissolved oxygen by increasing it (positive impact) and on algal toxins by
incorporating new toxins into the area (negative impact).
 Fishes: If they are fishes they can bring with them new diseases that affect
autochthonous species, including those cultured (negative impact).
An increase in algal toxins, a decrease in dissolved oxygen, an increase in the use
of herbicides/pesticides/biocides, an increase on some pollutants (e.g. metals and
organo-metals, hydrocarbons, synthetic organics, pharmaceuticals, etc.), nutrients, or
diseases could impact negatively on alien species by eliminating them or positively by
eliminating autochthonous competitor species. Changes in community structure, trophic
nets and biodiversity could also favour the success of alien species.
- Environmental Effects of Mineral Extraction affecting Aquaculture
Mineral extraction results in furrows on the sea floor or crater-like pits.
Assuming that extraction is not performed within aquaculture sites, the effects of
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mineral extraction affecting the surrounding sea bottom have been summarized. In most
cases, wave climate and currents are only changed in the direct vicinity of the extraction
area. The removal of a significant thickness of sediment by trailer or anchor suction
dredging may cause a localized drop in current strength associated with the increase in
water depth. This results in reduced strength of the bottom currents and hence the
deposition of finer sediments than originally present in the surrounding substrate.
Erosion at the upper shoreface and beach zone can result from infill of pits, situated
onshore of the -25 depth contour (van Rijn et al., 2005). In some cases the created
extraction pits migrate slowly in the direction of the dominant current. The fastest
migration observed was more than 25 m/year (Boers, 2005). The creation of a sand pit
may even trigger the development of morphological irregularity at the sea bottom,
resulting in alternating sand dunes and depressions, (Roos, 2004; van Rijn et al., 2005).
The pit itself deepens and the pattern spreads out and migrates at a rate of 10 to 100
m/year.
Extraction activity leads to an increase in turbidity in the water column through
the production of plumes of suspended material (Boyd et al., 2004) mainly issued
through outwash from spillways of the vessel. A further source of suspended material
may result from the rejection of unwanted sediment fractions by screening activities.
Both sources have been termed surface plumes and their spatial extent and excursion are
dependent on the sediment particle size, total quantity of material suspended, velocity of
discharge and the local hydrodynamics (Hitchcock and Drucker, 1996). Suspended
material can also arise from the mechanical disturbance of the seabed sediment by the
draghead, an increase in organic matter possibly derived from fragmented benthos
discharged during the dredging process. Large increases on the suspended solid
concentrations are short-lived and localised, i.e. close to the operating dredger.
Therefore, the potential negative impact on plankton is supposed to be insignificant.
Negative implications for fish like avoidance of the turbid area by visual feeders such as
mackerel and turbot exist, but sometimes positive consequences such as attractiveness
of some fishes by the “odour stream” of crushed benthos are observed (de Groot, 1979).
More recently, “non visual” avoidance threshold was demonstrated for some species,
with effects at very low sediment concentration (3-10 mg.l-1) on the buoyancy and
mortality of cod eggs and larvae (Westerberg et al., 1996). Nevertheless, the effects of
suspended fines in the water column are temporary, while changes are generally longerterm on bottom fauna, mainly in case of damage to spawning grounds for some shellfish
and fish species.
The abovementioned screening activities can also contribute to the fining or
coarsening of sediments over time. Assuming the intention is to increase the gravel
content, fine material will be returned to the sea and may lead to a higher fine sediment
content than originally present.
Boers, M., 2005. Overview of historical pits, trenches and dump sites on the
Netherlands’ Continental Shelf. In: van Rijn, L.C., R.L. Soulsby, P. Hoekstra, A.G.
Davies (Editors), 2005. SANDPIT: Sand transport and morphology of offshore sand
mining pits – Process knowledge and guidelines for coastal management (end
document April 2005 - EC Framework V Project No. EVK3-2001-00056)
Boyd, S.E., K.M. Cooper, D.S. Limpenny, R. Kilbride, H.L. Rees, M.P. Dearnaley, J.
Stevenson, W.J. Meadows & C.D. Morris, 2004. Assessment of the re-habilitation
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of the seabed following marine aggregate dredging. Science Series Technical
Report, CEFAS Lowestoft, 121: 154 pp.
de Groot, S.J., 1979. The potential environmental impact of marine gravel extraction in
the North Sea. Ocean Management, 5: 233-249.
Hitchcock, D.R. & B.R. Drucker, 1996. Investigation of benthic and surface plume
associated with marine aggregates mining in the United Kingdom. Oceanology
International 96. The Global Ocean – towards operational oceanography.
Conference Proceedings, vol.2.
van Rijn, L.C., R.L. Soulsby, P. Hoekstra, A.G. Davies (Editors), 2005. SANDPIT:
Sand transport and morphology of offshore sand mining pits – Process knowledge
and guidelines for coastal management (end document April 2005 - EC Framework
V Project No. EVK3-2001-00056)
Roos, P. C., 2004. Seabed pattern dynamics and offshore sand extraction. UT
University Twente, 167 pp. (Enschede: University of Twente) (ISBN 90-365-20673). Prom./ coprom.: Hulscher, S. J. M. H., & Vriend, H. J. de
Westerberg H., P. Rönnback and H. Frimansson. Effects of suspended sediments on cod
egg and larvae and other behaviour of adult herring and cod. ICES C.M. 1996 (E:26
(Marine Environmental Quality Committee)), 13 pp.
- Wind, storms, hydrography
The influence is double:
Influence of the ocean-meteorological variables on aquaculture:
The water dynamics and meteorological conditions are key factors in order to
select the aquaculture sites. Indeed, they affect directly to:
(a)
(b)
the quality of elaborated product and sustainability of aquaculture.
Hence, low water renewal rate could produce oxygen depletion and
mortality of fishes,
the security of installations: (i) Bathymetry: a sufficient water depth
is needed to avoid wave breaking and ensure a good dilution and
dispersion, (ii) wave and wind regime: these factors can destroy the
installation, produce damage to the fish stock, reduce the feed ratio,
reduce the access to the farm, etc., (iii) storm return period, which can
be critical in the production scheme of the farm, etc., and
Influence of the aquaculture on ocean-meteorological variables:
Whatever structure installation in the coastal area can impact the previous
dynamical conditions. Aquaculture can affect the local system by modifying the
bathymetry, the current velocity or the wave regime. Some little changes can induce
huge variations in a complex system, including for the original water dynamics
conditions witch were the factors of the site selection. The close link between wave,
hydrodynamics, sediment transport and morphology make some systems very sensible
to interferences like the ones created by aquaculture structures.
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- Comments on Table
We have some comments, but I think it is better to discuss them in our next meeting (if
you have an electronic version of the table it should be better).
- Major environmental factors affecting aquaculture in Spain
One important problem in Spanish aquaculture comes from the competence of uses with
other marine activities (see Table below).
Table. Interactions between aquaculture and other marine activities. (-): negative
interaction; (+): positive interaction; (-/+): both. (Adapted from Dosdat et al., 1996; and
Borja, 2002).
Activity
Industry and ports
Spatial resources
Urbanization
Agriculture
Terrain necessity (-)
Navigation (-)
Terrain necessity (-)
Marinas (-)
Artificial reefs (-/+)
Navigation, bathing, fishing (-)
Fishing areas (-)
Military use (-)
Coastal land (-)
Fishing
Land use (-)
Dredging (-)
Environmental
quality
Tourism
Land necessity (-)
Hatchery & nursery areas (-)
Historical sites (-)
Contaminants (-)
Discharges (-)
Ballast water (-)
Warm water (+)
Antifouling paints (-)
Fertilizers (-)
Disease transmission (-)
Organic Matter (-)
Pesticides (-)
Genetic loss (-)
Bacteria and viruses (-)
Organic matter (-)
Nutrients (-)
Suspended Solids (-)
Freshwater (-/+)
Infrastructures (+)
Markets (+)
Invest attraction (-/+) Infrastructures (+)
Economy
Habitation areas (-)
Social resources
Regulation
Invest Attraction (-/+)
Infrastructures (+)
Invest Attraction (-/+)
Employment (-/+)
Markets (+)
Local markets (+)
Infrastructures (+)
Infrastructures (+)
Aquaculture feed (+)
Eco-tourism (+)
Education (+)
Wildlife (-)
Internal Competence (-)
Nearby areas (-)
Regional/local (-)
Protected areas (-)
Fishing reserves (-/+)
Port reservation (-)
Policies (-/+)
Wild fauna & flora (-)
Military areas (-)
Environmental standards (+)
Other important environmental factors are:





Pollution: submarine and surface discharges (both urban and industrial): probably
the most important.
Dredging disposal: from harbours and navigation channels
Tanker accidents: this problem is especially important in Galicia, where in the last
10 years at least 3 tankers sunk in the coast.
The aquaculture itself: synergy between two or more farms.
Sand extraction for beach nourishment
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Borja, A., 2002. Los impactos ambientales de la acuicultura y la sostenibilidad de esta
actividad. Boletín del Instituto Español de Oceanografía, 18(1-4): 41-49.
Dosdat, A., M. Héral, I. Katavic, M. Kempf, J. Prou and C. Smith. 1996. Approaches
for zoning of coastal areas with reference to Mediterranean aquaculture. Priority
Actions Programme Regional Activity Centre (PAP/RAC). PAP-10/EAM/GL.1. Split,
Croacia: iv + 37 pp.
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- Site selection and incompatibilities between uses in Spain:
This information has been extracted from:
Bald, J., A. Borja, A. Uriarte and M. González, 2002. Environmental impact assessment
of open sea cages for aquaculture in the Mediterranean coast of Spain. Extended
abstracts and short communications. Aquaculture Europe 2002. Trieste (Italy).
European Aquaculture Society Special Publication No. 32: 137-138.
Bald, J., A. Borja, A. Uriarte and M. González, 2002. Site selection protocol for open
sea cages for aquaculture in the mediterranean coast of Spain. Extended abstracts and
short communications. Aquaculture Europe 2002. Trieste (Italy). European Aquaculture
Society Special Publication No. 32: 139-140.
Borja, A., 2002. Los impactos ambientales de la acuicultura y la sostenibilidad de esta
actividad. Boletín del Instituto Español de Oceanografía, 18(1-4): 41-49.
Site selection for the installation of open sea cages for aquaculture in Spain is based
upon the Guidelines developed by AZTI and approved by JACUMAR (Spanish
Advisory Council for Marine Aquaculture) in November 6th, 2000 (Borja, A, 2000.
Protocolo a utilizar para el establecimiento y seguimiento medioambiental de jaulas de
cultivo en mar en España. Junta Asesora Nacional de Cultivos Marinos (JACUMAR).
Aprobado con carácter definitivo por la 49ª JACUMAR de 6 de noviembre de 2000).
Other important tool are the requirements established in the main legislative body for
EIA in Spain, the 1302/1986 Royal Decree for Environmental Impact Assessment,
modified latter by the 9/2000 Royal Decree.
The Guidelines are divided into two parts, according with issued recommendations of
different regional governments before is approbation: (1) Guidelines for site selection of
open sea cages for aquaculture; and (2) Guidelines for Environmental Impact
Assessment (EIA) of open sea cages for aquaculture.
The main tasks for site selection are:
1. Site selection guidelines is based upon several factors:
a. Those who affect the quality of elaborated product and sustainability of
aquaculture:
i. Good quality of waters: avoiding contaminated areas. The
dissolved oxygen concentration should be high (more than 70%).
Several parameters such as temperature, salinity, dissolved
oxygen, turbidity, suspended solids and contaminants should be
controlled before the installation.
ii. Good renewal of waters: water currents in the area should be
enough to provide good dispersal of feed and faecal wastes,
avoiding enclosed or semienclosed areas, with low current
velocity. Tides (if applicable), freshwater inputs and current
velocity and direction should be controlled, during a minimum
period of 30 days.
b. Those who affect the security of installations:
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i. Wave regime: it is related with the resistance of cages. It should
be controlled that frequency and maximal height of wave regime
do not exceed the fixed resistance standards of cages. The
parameters to be controlled are: prevalent wave direction, wave
period, significant and maximal wave height, wave threshold to
storm conditions, fetch and wave regime (sea or swell).
ii. Bathymetry: in areas affected by tides, the control of bathymetry
is especially related to the security of cages. In other cases, is
essential for a good dispersion of pollutants. As reference, a
minimum depth for cage installation should be of the order of 20
m (preferably >30 m).
iii. Wind regime: it is recommended to have, at least, ten years of
data from the nearest station available.
c. Those who affect the competition with other uses of the coastal zone:
i. The uses clearly opposed with aquaculture development should
be avoided e.g. protected areas, beaches, ports and harbours,
sewage disposal areas, military uses, etc.
ii. In this sense, it would be necessary to collate data about
biodiversity and community structure in the area subject to
aquaculture development, in order to avoid the alteration of
biological communities of interest or protected species.
With all this information and a validated hydrodynamic model (handled by expert
personnel), several modelizations should be realised to define the extent of the pollutant
dispersion, and to determine the affected areas, pollutant loads, carrying capacity, etc.
All these modelizations should be realised using the dominating wind regimes of the
area, and dominating waves and currents. Adequate sedimentation rates should be
employed consistent with feed and faeces size particles. The obtained conclusions
should be very useful for the subsequent Environmental Impact Assessment (if
necessary). This study will establish the possible influence of fish farming structures
with other uses, as well as the minimum distance between cages, in order to avoid
synergic effects between them and the carrying capacity of the area.
The following table summarizes the main environmental factors and the ranges in which
they can be considered good, medium or bad for aquaculture development (Adapted
from PAP-RAC, 1996, and Borja, 2002):
FACTOR
Exposition
Wave regime
Bathymetry
Current Velocity
Water contamination
Maximum temperature
Minimum temperature
Average salinity
Salinity (fluctuation)
Dissolved oxygen (%)
Slope (%)
Substrate
Trophic condition
Fouling
Predators
GOOD
Partial
1 to 3 m
>30m
>15 cm·s-1
Low
22 to 24ºC
12ºC
25 to 35
<5
>100
>3
Sand or gravel
Oligotrophic
Low
No
MEDIUM
Sheltered
<1m
15 to 30 m
5-15 cm·s-1
Medium
24 to 27ºC
10ºC
15 to 25
5 to 10
70 to 100
1 to 3
Mixed
Mesotrophic
Moderate
Some
BAD
Exposed
>3m
<15m
<5 cm·s-1
High
>27ºC
<8ºC
<15
>10
<70
<3<10
Mud
Eutrophic
High
Abundant
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IMPACTS
Species
Food
Chemical
products
Pesticides
Hormones
Faeces
Selected
Site
Aloctone
species
Antifouling
2. Guidelines for Environmental Impact Assessment (EIA) of open sea cages for
aquaculture, is based upon the previous study, and the following steps:
a. Description of all the activities for sea cage installation and exploitation,
especially those related with culture method, stocking density, feed type,
and husbandry practices.
b. Description of the environmental characteristics of the proposed area.
Using previous studies and field surveys for the establishment of water
dynamic (wave, current and wind regime), quality (temperature, salinity,
optical properties, contaminants, etc), and sediment and benthic
communities characterization.
c. Modelization of the pollutant dispersion by means of TRIMODENA©
software; a three-dimensional finite element model developed by AZTI
Foundation, which takes into account the current, wind and wave regime
of the proposed coastal area. This tool allows to quantify the spatial
extension of the plume and the loads of organic matter (feed wastes and
faeces) to the column water and bottom sediment.
d. Impact identification and description. Feed wastes, fish excretion, faeces
production and respiration are the main sources of impact usually
identified. The major impact is on the sea bottom, where, in some cases,
high sediment oxygen demand, anoxic sediments, production of toxic
gases and decrease in benthic diversity may result. Decreases in
dissolved oxygen and increases in nutrient levels in the water are also
evident but are normally confined to the vicinity of the farm. The
following table summarizes the main impact activities of aquaculture and
main affected factors. Black circles represent significant impacts, white
circles represent moderate impacts and lines represent no relation
(Adapted from Wu, 1995 and Borja, 2002).
Nutrient enrichment
Trophic chains
Oxygen consumption
Biodiversity
Fouling
Changes in benthos
Resistance to antibiotics
Wild life
Substrat changes
Non desirable species
Eutrophy
Marine species toxicity
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e. Correction and protection measures to minimize the main impacts of
farm activity specially, feed wastage, and a monitoring programme are
proposed. The objective of the programme is to check that environmental
impact of sea farm doesn't overcome the realised predictions, thus,
consequent correction measures should be applied.
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References:
PAP/RAC, 1996. Approaches for zoning of coastal areas with reference to
Mediterranean aquaculture. PAP10/EAM/GL.1 Split Croatia, 37 p.
Wu, R.S.S., 1995. The environmental impact of marine fish culture: towards a
sustainable future. Marine Pollution Bulletin, 31: 159-166.
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