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Biodiversity Effects

A Pacific oyster farm may alter an area’s marine habitats, species abundance and diversity, and ecosystems through a variety of ways. However, the Resource Management Act requires both central and local government to ensure that aquaculture does not occur in high sensitivity areas.

Farms are generally not approved if they are proposed over reefs or complex habitats with a high diversity or abundance of species.  Planning for new aquaculture sites takes into account the likely ecological effects on the environment, including effects on fisheries resources (particularly important spawning or nursery habitats) as well as general biodiversity.

Marine farming may also result in a decrease in the abundance of some species that are relatively intolerant of the organically enriched conditions that can develop below farms.  Typically changes are evident as a displacement of some species with others that perform similar ecological functions, such as deposit feeders. 

A review by Forrest et al 2007 reports that a study of a New Zealand oyster-farming harbour showed relatively mild effects typical of those described for oyster cultivation overseas.

The presence of farms will likely aid the establishment and spread of wild Pacific oyster populations. This is not considered to be an issue, however, as the Pacific oyster has already spread itself widely around the New Zealand coastline in places where there are no oyster farming activities (e.g. Manukau Harbour).

Habitat Creation

Oyster farm structures can support a much greater biomass and density of organisms than adjacent natural habitats. And communities living on farm structures can be quite different from those in adjacent rocky areas.

Several studies have highlighted the possible beneficial role that can be played by artificial structures, in terms of enhancing the biodiversity and productivity of an ecosystem. Such roles are recognised for seabed oyster reef habitats, but are not well understood for elevated rack and longline culture oyster farming systems.

Fish

Oyster farms and other artificial structures can offer shelter, habitat complexity and a food source for fish.

The aggregation of various fish species around such structures is well recognised, particularly for mussel farms; however, virtually nothing is known of the significance of fish associations with New Zealand intertidal oyster farms.

Seabirds

Effects on seabirds have been considered for mussel and finfish farming developments in New Zealand, and some effects may be applicable to oyster farming.

Farming structures can offer resting spaces that may attract some bird species. Also, small fish and other organisms associated with the structures may provide a food source for predatory seabirds.

Marine mammals

The potential effects of oyster farming on marine mammals (seals, dolphins and whales) are unknown. But it is likely that habitat or foraging area displacement effects would be minimal for intertidal farms.  Dolphins and whales are unlikely to be common visitors to sheltered intertidal muddy areas, and most oyster farms in New Zealand are in the northern part of the country where seals are not found.

New oyster farming applications usually provide a description of the proposed location and any known interactions by marine mammals or seabirds in the area, and an assessment of the likely effects of the proposal on such species.