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Our coastal waters, harbours, and estuaries

Top issue – coastal habitats and ecosystems are degraded

Coastal marine habitats have critical functions in the wider ocean ecosystem – such as recycling nutrients and human wastes, trapping and stabilising sediments, producing oxygen that supports other marine life, and as nursery grounds for fish. The loss or degradation of these habitats can undermine these functions, with consequential impacts on ecosystems.

New Zealanders visit our coastlines, beaches, and harbours to fish, harvest shellfish, and enjoy a wide range of recreational activities. These opportunities are diminished when the marine environment is degraded – for example, by poor water quality and limited marine life. A degraded coastal ecosystem has implications for aquaculture and recreational and commercial fishing. For Māori, the degradation of coastal waters has been a source of grievance since early European settlement, undermining cultural values, including harvesting of fish and shellfish.

The most important pressures on coastal waters

On a national scale, data are sometimes limited, but we know from expert opinion and the scientific literature that the most important pressures are:

  • ocean acidification and impacts of climate change
  • excess sedimentation, which accumulates over decades and can directly affect shellfish and finfish species and destroy important habitats including fish nurseries
  • seabed trawling and dredging for fish and shellfish
  • marine pests, which can alter ecosystem processes and modify natural habitats, potentially causing biodiversity loss and threatening marine-based industries
  • excess nutrients carried down waterways, mostly from urban development and agriculture, which can reduce oxygen in seawater and contribute to algal blooms, harming marine ecosystems (see Future reporting).

The impact of pressures can accumulate over decades, and pressures can combine and interact in complex ways to cause harm. For example, the acidification of coastal waters can be exacerbated by nutrient loading.

Other pressures

Other pressures include other commercial and recreational fishing methods, dumping of dredge spoils, infilling of estuaries and harbours for building coastal infrastructure (reclamation), and other sources of pollution.

This includes pollution from:

  • sewage and waste water, although New Zealand’s sewage treatment improved markedly in the 1990s and most sewage is now treated before discharge into the ocean
  • plastic waste, which can injure or kill marine animals, remains in the ocean for hundreds of years, and can enter the food chain.

Key findings

Excess sedimentation is an important threat to coastal habitats

  • In 2012, marine experts ranked sedimentation as one of the top four threats to New Zealand’s marine habitats. Excess sedimentation is caused by activities such as forest harvesting, clearing land for agriculture, and urban subdivision. Coastal marine habitats such as rocky reefs, sandy beaches, pipi beds, seagrass meadows, and sand and mud flats, are particularly vulnerable to sedimentation.

The levels of heavy metals in monitored estuaries and harbours are mostly at levels unlikely to cause harm to seabed species

  • Heavy metals, from run-off from roads and other sources, are toxic to both animals and humans even at low concentrations. Heavy metal concentrations in estuaries and harbours are mostly at levels unlikely to cause harm to seabed species, based on data from 10 regions.

The threat from non-indigenous species in our coastal waters has increased

  • The number of non-indigenous marine species in New Zealand’s coastal waters has risen 10 percent since 2010. Between 2010 and 2015, 33 new non-indigenous species were recorded, of which 12 have established in New Zealand’s waters.
  • Non-indigenous marine species most likely enter our waters on the hulls of boats and ships, or in ballast water. Some of these species become marine pests. The economic costs to New Zealand of marine pests to aquaculture and other industries are poorly quantified but have been estimated to amount to millions of dollars a year.