Download Role of mangroves in mitigating global warming

SUBMISSION on the
PROPOSED MANGROVE REMOVAL – WHANGAMATA HARBOUR
by the Royal Forest and Bird Protection Society of New Zealand Inc (Forest & Bird).
Submitter:
Forest & Bird
Contact person:
Alan Fleming (Central North Island Field Officer).
Address for service:
Forest and Bird
PO Box 70 171
TAURANGA 3155
Date:
Phone:
07 544 4987
Cell:
021 988 295
Email:
[email protected]
4 October 2010
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Introduction
Mangroves in the Whangamata harbour are an important natural ecosystem which
contributes to the ecosystem productivity of both the Whangamata harbour and
adjacent coastal waters.
They contribute nutrients to local fisheries and shell fisheries and provide wetland bird
habitat and feeding areas. They are part of Whangamata harbour’s natural landscape
signature.
Forest and Bird wish to oppose these applications on the basis of:

Unknown effects associated with mechanised mangrove removal in Tauranga
harbour.

Catchment management may not be reducing the amount of sediment entering
the Whangamata harbour1.

Unwise use of ratepayer’s resources.

The scale of the removal.
Forest and Bird are also requesting further information on:

Whether the increase in mangrove distribution is encroaching on other coastal
and marine habitats, and

The role of mangroves in mitigating global warming.
However if Environment Waikato (EW) does consent to these applications, or parts of the
applications, Forest and Bird is seeking a number of outcomes associated with mitigation
and monitoring of consents given.
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Forest and Bird would like to undertake an analysis of this plan and present that analysis to the hearings committee.
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Flooding in the Moanaanuanu Estuary/Wentworth River
Forest and Bird acknowledge concerns / effects expressed in the application about
flooding in this area associated with an increase in mangroves. This includes modelling of
future flood risk in the Wentworth River in 2080
Mechanised removal of mangroves in Tauranga harbour and unknown effects.
Forest and Bird opposed the use of mechanised removal of mangroves in Tauranga
harbour on the basis it may result in:

An increase in the number of resource consent applications for mangrove
removal within Tauranga and throughout the country.

An increase in both the rate and total area of mangroves removed.
We understand that monitoring of mangrove removal in the Tauranga Harbour:

Has been largely ‘observation based’.

Includes some sampling of the seabed to identify changes in the benthos
community.

Includes some bird counts.
We understand that the mulch created by this machine has not dispersed / decomposed
and that the council believes it will over time. We understand that an algae has been
observed growing on the mulch in Omokoroa estuary area (Tauranga harbour) and has
created an anaerobic environment that gives of hydrogen sulphide gas.
Given that tidal currents in Whangamata harbour are low compared with Tauranga
harbour this could result in mulch not dispersing, associated algae growth, high levels of
hydrogen sulphide and dispersal of nuisance algae onto Whangamata beach, i.e. similar
to the situation of sea lettuce on Mount Maunganui beaches.
We are unsure of nutrient levels in the Whangamata harbour.
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Use of ratepayers resources
Forest and Bird is concerned that the 4 ‘northern’ regional councils are using ratepayers
resources for ‘mangrove management’, i.e. staff time, funding, mechanized mangrove
removal ... and effectively reducing the regional councils ability to address catchment
erosion and associated sedimentation of freshwater and coastal environments.
Forest and Bird understand that the recent consent application to mechanically remove
mangroves in Tauranga harbor cost approx $90,000.
Whangamata Harbour and Catchment Management Plan
Forest and Bird understand that the proposed removal of mangrove is part of a wider
catchment management program aimed at reducing sediment input to the harbour and
restoring native biodiversity to the catchment and harbour. It has been promulgated
that the Whangamata Harbour and Catchment Management Plan will reduce the amount
of sediment entering the harbour over time.
A large percentage of the harbour catchment is exotic forestry. Forest and Bird wish to
undertake an assessment of the current district plan rules, proposed national standards
associated with harvesting of exotic forest and present this analysis to the hearing
committee.
Scale and necessity of mangrove removal
Forest and Bird does not oppose the removal of mangroves that are encroaching on bird
roost areas or to clear drains and stream outlets (where appropriate). However we do
have concerns with regard to the necessity and proposed scale of mangrove removal in
these applications.
We note that Environment Waikato’s website http://www.ew.govt.nz/Projects/Lookingforward-to-a-healthier-harbour-in-Whangamata/Whangamata-Mangrove-ManagementOptions-Report/#Heading2 states:
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“The rapid expansion of mangroves in the Whangamata catchment since 1944 slowed
in the late 1990s. Since then mangroves in Whangamata have increased in height but
not in area. In fact the area of mangroves has decreased by about four hectares.”
If EW does consent to this application, or parts of this application Forest and Bird are
seeking a significant reduction in the amount of mangroves removed in the Whangamata
harbour. This will be based on further analysis of the application and presentation to the
hearing committee.
Duration of consent
The applicant is seeking a consent of 35 years (for hand clearance). If during this period it
was determined that the pulling of mangroves was detrimental to the harbour, how
would EW stop residents pulling mangrove seedlings?
If EW does consent to this application, or parts of this application, Forest and Bird seek a
consent of 15 years so an assessment on whether continued hand pulling is warranted
can be done at that time.
Adverse effects of mangrove removal
There are several adverse effect associated with the removal of mangroves in
Whangamata harbour. These include:

Effect on fish species

Effect on birds

A reduction in the uptake of mangrove-derived material within the mangrove
forest and export to adjacent habitats.

Potential mobilisation of sediments and smothering of adjacent seagrass and
shellfish beds.

Role of mangroves in mitigating global warming.
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
Potential effect on the Whangamata surf break.
Effect on Fish Species
We note that the applicant has not conducted a fish survey within the mangel or
harbour.
Whangamata harbour may be an important juvenile nursery for a number of common
estuarine species including yellow eyed mullet (Aldrichetta forsteri), parore (Girella
tricuspidata) and short finned eel (Anguilla australis).
Research on fishes in temperate mangroves has focused strongly on the role of
mangroves as fish nurseries (Morrisey et al. 2010). Since 2002 eleven studies have been
published (10 in temperate Australia and 1 in New Zealand). An earlier Australian study
identified mangels as important juvenile nursery areas (Bell et al. 1984).
Morrisey et al. 2007 found that parore was common only in eastern coast estuaries.
Short finned eels (Anguilla australis) were a common component of the fish–mangrove
assemblages on both coasts.
There may also be connectivity between fish populations within the Whangamata mangel
to surrounding habitat mosaics including seagrass habitat. Jelbart et al. (2007), working
in the Pittwater Estuary just north of Sydney, found seagrass beds closer to mangroves
had greater fish densities and diversities than more distant beds, especially for juveniles.
This study included Parore.
The removal of mangrove in the harbour would reduce this size of this potentially
important fish nursery area.
Effect on Birds
Morrisey et al 2010 concludes that available evidence suggests that there are no New
Zealand birds that are exclusively found in mangroves, but that many species make
extensive use of them for roosting, feeding or breeding. This report also states that
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Beauchamp (n.d.) noted that mangroves are “the only northern habitat of the banded rail
… and are a substantial breeding habitat for New Zealand kingfisher”.
Shaw et al 2010 states:
“The scale of the area being proposed will represent a significant loss of feeding
habitat for banded rail”.
This will result in a reduction of the current banded rail population in the Whangamata
mangel.
Uptake of mangrove-derived material within the mangrove forest and export to adjacent
habitats.
Morrisey et al 2010 found that information on nutrient and energy flows between
mangroves and other habitats in temperate estuaries is relatively limited, but identifies
that recent studies, such as that in Matapouri Estuary, northern New Zealand (Alfaro et
al. 2006), suggested that estuarine consumers exploit a range of sources of primary
production (seagrasses, mangroves, benthic microalgae and macroalgae) rather than
being dependent on one particular source.
Fresh mangrove and seagrass material appears to play a relatively minor, local role in the
overall estuarine food web, but detritus derived from these plants and exported via tidal
movement may play a more significant role via the detrital pathway. Macroalgae, such as
Hormosira banksii, can be an important source of organic material to estuarine food
webs and is abundant year round among mangrove pneumatophores and seagrass beds,
indicating an additional, indirect role for these habitats.
Shaw et al 2010 mentions the relationship of mangrove derived material to adjacent
habitats and coastal environment.
“Potential cumulative adverse effects of this clearance scenario are as follows:
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A reduction by approximately 36% of the contribution that mangroves and their
associated biota (e.g. Neptunes necklace) make to the estuarine food chain.
If
seagrass or shellfish beds fail to establish within cleared areas, the contribution that
these areas make to the estuarine food may be permanent”.
Role of mangroves in mitigating global warming
Catchment erosion and climate warming are prime drivers of mangrove expansion in the
Whangamata harbour.
The increase in mangroves plays a role in moderating these impacts on the coastal
ecosystem; by growing on sediment in estuaries, utilising additional nitrogen from run-off
and regulating rising carbon dioxide concentrations by converting carbon dioxide into
biomass and substrate sinks.
There is no assessment in this application on how much sequestered carbon would be
lost as a result of mangrove removal. Forest and Bird recommend that the 4 northern
regional councils undertake an assessment of the role of mangroves in mitigating global
warming including the amount of carbon sequestered in mangels. The LUCAS (Land Use
Carbon Analysis System) project may assist regional councils in this assessment.
Encroachment of other coastal and marine habitats
Forest and Bird is concerned if mangroves are encroaching and threatening other marine
habitats. For example several studies show that seaward expansion of mangrove habitat
onto accreting intertidal flats is a feature of New Zealand estuaries. These flats are often
important bird roosts and feeding areas.
In addition tidal creeks and drainage channels can provide conduits for mangrove
propagules to penetrate into saltmarsh habitats. We note that mangrove encroachment
into salt marsh is not well documented in New Zealand estuaries (Morrisey et al. 2007).
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Shaw et al 2010 identifies that sedimentation and the spread of mangroves has resulted
in the loss of seagrass beds in Whangamata harbour. This is on the basis of 1944 aerial
photographs showing areas of seagrass in the Moanaanuanu Estuary within an area that
is now mangrove shrubland. I have also been shown earlier photos of an estuary in
Tauranga harbour where mangel is now found in areas where seagrass was once found (B
Rowson pers comm.)
However the question I ask is has the mangrove displaced the seagrass or has the
seagrass been smothered by sediments. I have been unable to find any documented
research which shows that mangroves displays seagrass and request any information on
this matter.
Forest and Bird also note the following:

A 2004 survey of Whangamata Harbour (Shaw et al 2010) has shown that of the
410 Ha of harbour, 101 is Mangrove with approximately 100 Ha in other plant
species. Only 3 Ha is sand beaches with the remainder is classified as intertidal
flats or subtidal channels. Comparison with a similar study in 1996 shows a slight
increase in seagrass, static mangrove areas and a slight decrease in saltmarsh, i.e.
during the period 1996 to 2004 both mangrove and seagrass habitat increased?

Shaw et al 2010 identifies that the removal of mangroves may result in the
potential mobilisation of sediments and smothering of seagrass and shellfish beds
in as an intermediate effect
Monitoring and monitoring conditions
A report on the success of the Whangamata Harbour and Catchment Management Plan
in terms of sediment reduction should be undertaken by EW prior to any consideration
being given to removal of mangroves.
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However if EW does consent to these applications, or parts of the applications,
monitoring conditions should address the adverse effects identified in this submission
both prior to and post any clearance. This includes:

Effect on fish species

Effect on birds

Transfer of mangrove-derived material within the mangrove forest and export to
adjacent habitats.

Potential mobilisation of sediments and smothering of adjacent seagrass and
shellfish beds

Recolonisation of seagrass beds in areas of mangrove removal
Forest and Bird support Shaw et al 2010 recommendations that monitoring conditions
should:

Include monitoring of mitigation measures, e.g. control of weeds and pest
animals within saltmarsh, and that restoration works need to be successful, and
in some cases ongoing, if the effects of habitat loss due to mangrove removal are
to be adequately mitigated and compensated for.

Within mulched areas, monitoring should document the dispersal pathways
and/or in-situ decomposition of mulchate and, if mulchate is dispersed to other
communities (e.g. seagrass beds), the health of those communities. Monitoring
needs to document any mobilisation and redistribution of sediment, and this
should be undertaken at sites both immediately adjacent to and well removed
from tidal channels. The monitoring programme needs to whether adverse
effects have occurred and whether adverse effects have been adequately
addressed, prior to any second clearance stage being approved.
In addition we are seeking that a fish survey of the mangroves be undertaking prior to
any mangrove removal.
Low J 2010 (Beca report) proposes that:
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“The results of monitoring should be reported to the consent authority at least one
month prior to Stage 2 commencing, with stage two contingent on the effects of stage
1 being confirmed to be minor with evidence of species recovery consistent with the
adjacent Mangrove-free habitats.”
This does not give the community, stakeholders and interested parties sufficient time to
assess and make submissions to EW on whether stage 2 should proceed or not. A
monitoring report should be sent to all stakeholders and available to the community 2
months prior to EW given consideration as to whether stage 2 should commence or not.
There should also be the ability for persons to make submissions on this report for the
council’s consideration.
It is also proposed that mangrove clearance occur over two years, with clearance in the
second year dependant on the initial clearance not resulting in significant adverse effects.
EW should take an adaptive management approach as some of the anticipated results
may not have occurred in the 1st year, e.g. decomposition / dispersal of mulch. Any stage
2 removals should not commence until mulchate is complete dispersed / decomposed.
Inappropriate use of ratepayers resources
Forest and Bird understand that improvement of the areas marked “A” on the map and
“D” in the photo provided by EW was supposed to be the responsibility of the
Whangamata Marina Society as mitigation for a destroyed wetland, and has yet to be
enhanced to a satisfactory level in regard to the loss of the original wetland for the
benefit of the marina development.
Forest and Bird are concerned at the apparent externalising of costs onto ratepayers for
something that is the responsibility of the marina developers.
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Mulcher head
If EW does consent to these applications, or parts of the applications they should
considered use of a finer mulcher head.
Mitigation measures
If EW does consent to these applications, or parts of the applications, mitigation
measures should include:

pest control, i.e. to mitigate direct predation on birds and competition for food
(invertebrates).

Restoration of terrestrial margins.

Control of pest plants in all remaining areas of saltmarsh throughout the
harbour.
Outcomes sought
Forest and Bird are seeking the following outcomes:

That these resource consent applications are declined.

That EW undertake an investigation of reports that an algae has been observed
growing on the mulch in Omokoroa estuary area (Tauranga harbour) and has
created an anaerobic environment that gives of hydrogen sulphide gas.

That monitoring results from mechanised removal of mangroves in Tauranga
harbour are considered by EW prior any further consideration of mangrove
removal in Whangamata harbour.
If EW do consent to this application, or parts of this application Forest and Bird are seeking:

A significant reduction in the amount of mangroves removed in the Whangamata
harbour.
This will be based on further analysis of the application and
presentation to the hearing committee.
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
A consent duration of 15 years so an assessment on whether continued hand
pulling is warranted can be done at that time.
Forest and Bird wish to speak to this submission.
References
Alfaro, A.C. 2006. Benthic macro-invertebrate community composition within a
mangrove/seagrass estuary in northern New Zealand. Estuarine Coastal and Shelf Science
66, 97–110.
Beca Carter Hollings & Ferner Ltd (Beca) in association with Wildland Consultants and the
Isthmus Group.
Jelbart, J.E., Ross, P.M. & Connolly, R.M. 2007. Fish assemblages in seagrass beds are
influenced by the proximity of mangrove forests. Marine Biology 150, 993–1002.
Low, J. 2010. Whangamata Mangroves- Assessment of Effects of Removal. Beca Carter
Hollings & Ferner Ltd.
Morrisey, D., Beard, C., Morrison, M., Craggs, R. & Lowe, M. 2007. The New Zealand
mangrove: review of the current state of knowledge. Auckland Regional Council Technical
Publication No. 325. Auckland, New Zealand: Auckland Regional Council.
Morrisey, D.J. & Swales, A. & Dittmann, S. & Morrison, M.A. & Lovelock, C.E. & Beard, C.M.
2010. The ecology and management of temperate mangroves. Oceanography and Marine
Biology: An Annual Review, 2010, 48, 43-160.
Shaw, W. & Martin, T. & Long J. 2010. Ecological assessment of proposed mangrove
clearance at Whangamata. Wildlands Consultants Ltd Report No. 2310
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