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Feature

Shoring Up the Beaches

What can be done to fix the damage done to our shorelines?

Stephanie Turner

In New Zealand, many shallow-water coastal and estuarine ecosystems have been adversely affected by human activities such as pollution from urban stormwater run-off and industrial point sources, coastal engineering works, poor management of catchment sediments, overfishing and inappropriate harvesting practices. The result is the degradation or loss of habitat and a corresponding decline in the natural biological resources, including recreational and commercial fisheries and traditional Maori food-gathering sites. Degradation of these ecologically valuable and sensitive areas is cumulative, and likely to accelerate as populations grow and as pressure on natural resources increases.

The widespread degradation of shallow-water coastal and estuarine systems, as well as the increasing focus of public concern regarding the environment and its sustainable management, has led to a growing interest in the repair of degraded marine ecosystems.

Scientists and resource managers are increasingly considering the effectiveness of restoration as a means of mitigating the effects of environmental disturbance on coastal resources, thereby enhancing their sustainability, as well as increasing their cultural, recreational and commercial value.

The Resource Management Act (1991) places an obligation on those responsible for developments to avoid, remedy or mitigate any effects on the natural environment. As a result, restoration of habitats that have been degraded or destroyed will become an increasingly important tool in conservation and, for developers, in complying with the RMA.

While the restoration of natural communities is an established method in land and freshwater management, restoration of marine systems has only recently received attention. In the past, the focus of marine ecosystem restoration has been to identify what has been causing the degradation, and then attempting to stop or control the source or sources of the degradation.

Typically, the impacted systems have been left to recover naturally. In many cases, however, there may be no simple solution to finding the source of the problem or controlling it. In addition, natural recovery of degraded areas can be very slow -- even non-existent -- as many species may take a long time to recolonise degraded areas and to attain natural population densities, size and age structures.

Ecosystems often do not recover from human disturbance without additional management or manipulation, and active intervention may be necessary. With restoration or enhancement, degraded sites can recover sooner than would occur naturally.

Restoration and Enhancement

Restoration is the active re-establishment of a species, community or ecosystem, in an area where it used to be important, following a decline in quality or quantity arising from natural or human-induced disturbance.

Enhancement is the active increasing of one or more of the functions or attributes of an existing species, community or ecosystem, such as the productivity or habitat value.

Restoration and enhancement are distinct from creation, which is the establishment, by some action of humans, of a desired species or community or ecosystem at a site that is not documented to have supported a similar species, community or ecosystem in the recent past (100-200 years).

Although replacing the target species (such as shellfish, seagrass, mangroves) is often the immediate restoration objective, the ultimate goal of any enhancement or restoration project should be the enhancement or replacement of natural, functional and persistent communities. In most cases, however, we simply do not know the extent to which restoration compensates for the loss of natural habitat, the trade-offs that occur if out-of-kind restoration is undertaken, or the rate of functional replacement if restoration is successful.

There is a growing body of information regarding the restoration of impoverished marine ecosystems overseas, and work of this type is progressing rapidly. Unfortunately, the technologies and information are not necessarily directly transferable to degraded marine ecosystems within New Zealand without further evaluation and modification.

While techniques do exist to restore saltmarshes, seagrass beds, mangroves, kelp forests, coral reefs and temperate reefs, the science of habitat restoration is still "young, imperfect and experimental".

Over the last four years, scientists at the National Institute of Water and Atmospheric Research (NIWA) have been developing and testing techniques to restore degraded marine ecosystems (in particular intertidal shellfish and seagrass beds) within New Zealand. Fundamental questions that are being addressed include:

  • can practical, cost-effective techniques be developed which enable species to be transplanted and/or encouraged to recruit and survive?
  • what factors limit the establishment and growth of transplanted species in degraded systems?
  • what are the medium-to-long term consequences of restoration at the population and community levels?
  • can we identify systems which would benefit from enhancement procedures augmenting natural recolonisation processes?
  • under what conditions is restoration an ecologically defensible policy?

Many of the problems associated with restoration projects highlight a lack of information on the basic ecological requirements of transplant species, as well as a poor understanding of how biological and environmental factors in degraded systems may limit the establishment, growth, and survival of the species concerned. Proper site selection, species selection and the timing of restoration effort are of paramount importance to the success of restoration projects.

Only an understanding of the functioning of marine ecosystems, coupled with a knowledge of the species' ecology, will enable effective, long-term restoration of these systems.

Saving Shellfish Beds

Shellfish beds are an essential part of healthy coastal waters and estuaries, with shellfish -- pipis, cockles, scallops, tuatuas -- playing an important role in the ecology of these habitats. Some shellfish filter large volumes of water, extracting phytoplankton and detritus, and may thereby have a role in limiting phytoplankton blooms and increasing water clarity in shallow water.

Shellfish are also important in the cycling of nutrients through filtration and excretion, as well as modifying sediment dynamics (i.e., deposition, erosion and transport). Filter-feeding shellfish can be adversely affected by increases in the amount of sediment in the water affecting their ability to feed.

Shellfish are an important food resource for fish, birds and crabs, and at high densities they can be very important in stabilising the seabed and channels in harbours. Shellfish are also a natural food resource that have been harvested by people throughout New Zealand since the earliest Maori settlement. This harvesting of shellfish from shallow water coastal and estuarine areas continues to be a culturally, recreationally and economically important activity.

Degraded shellfish beds are an increasingly common ecological problem throughout New Zealand. Poor catchment management has lead to increases in water-borne sediment loads in coastal and estuarine areas, with serious consequences for the resident shellfish. There is increasing evidence that declines in shellfish beds may constitute a major factor contributing to deterioration in water quality and shifts in the abundance of species inhabiting these areas.

Te Moana o Whaingaroa (Raglan Harbour) is a small (33 km2), shallow estuary on the west coast of the central North Island. Traditionally, Whaingaroa was a significant area of Maori settlement. Today the harbour provides many recreational opportunities, including shellfish gathering, whitebaiting and fishing.

Tangata whenua have strong ancestral and spiritual ties with the harbour, allied in part to the gathering of food. Historically, the harbour offered a wide variety of fish and shellfish, serving as the food basket for the hapu of the area.

In the past 10 years however, shellfish have been significantly depleted in some areas and the fin-fish catch is low. Although over-fishing and inappropriate gathering methods may have contributed to the decline of shellfish beds, other factors affecting shellfish habitat and resources are also likely to have played an important role. For example, changing land-use patterns in the harbour catchment over the past 10-20 years may have contributed to changes in water quality and sediment loading.

Local Involvement

Scientists at NIWA are collaborating with the coastal marae surrounding the harbour (represented by Tainui Awhiro te Po, Ngunguru te Ao Management Committee) to develop an iwi-driven demonstration shellfish enhancement and restoration project. The programme is jointly funded by the Ministry for the Environment's Sustainable Management Fund and NIWA.

The programme combines local and tribal knowledge of the harbour with scientific expertise in the culturing of shellfish seed-stock and the development, testing and application of techniques to restore degraded marine environments. This partnership provides a rare opportunity to adopt a holistic approach to the management of coastal resources, while enabling the tangata whenua to take a proactive role with respect to kaitiakitanga (guardianship of resources).

Wherever possible, we are looking towards the application and integration of both traditional and scientific methods. The Whaingaroa project will also act as a demonstration of the process of community groups working with scientific groups to achieve their resource management aspirations.

Scientists are presently assisting tangata whenua to establish small, temporary, low-technology and low-cost shellfish nursery facilities in Whaingaroa to rear juvenile shellfish to a size suitable for out-planting. This will ensure that cost-effective technologies are formulated under field conditions and will lead to estimates of the costs and yields that best reflect what a community can expect from the implementation of such projects.

The next stage will be to transplant nursery-reared shellfish into areas of the harbour selected as suitable for re-seeding. It is anticipated that transplanting dense populations of seed shellfish to shellfish beds having suitable habitat conditions but relatively sparse populations, will provide for increased shellfish recruitment and growth over subsequent years.

Further work will be directed towards monitoring and quantifying the survival, growth and reproductive condition of the transplanted shellfish.

The goal of the shellfish restoration project in Whaingaroa Harbour is to enhance sustainable natural productivity, rather than a programme of "put-and-take" whereby seed shellfish are transplanted into depleted areas and the adult shellfish harvested one or two years later, without any additional enhancement. To achieve this goal, the management of the areas that are re-seeded must also be addressed, including future harvesting and disturbance, so as to prevent subsequent decline.

Wide-ranging Benefits

Restoration and enhancement of shellfish beds will provide environmental benefits that extend beyond replenishment of the beds themselves, including increased water column filtration, increased sedimentation and nutrient recycling.

Indeed, restoration of shellfish populations is regarded by some scientists and resource managers as imperative to the restoration of healthy coastal ecosystems. However, these projects need to be part of a multifaceted programme addressing the issues causing environmental degradation.

The restoration of degraded marine ecosystems is one of the most challenging problems in coastal management. Because of a fundamental lack of understanding of the ecology and dynamics of natural habitats and their biological resources, restoration of marine ecosystems has not yet evolved into a reliable management tool.

Nevertheless, successful restoration projects, aimed at enhancing the biological resources of our shallow coastal and estuarine environments will help to ensure both the sustainable use and pertinent management and development of these ecologically sensitive and important ecosystems.

The development of effective and successful restoration projects will be of direct benefit to the many New Zealanders who use the shallow coastal and estuarine environments for recreation, relaxation, nature reserves and scenic respites, or for whom they have cultural and spiritual significance.

Stephanie Turner worked for NIWA while carrying out this project.