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Coastal pests

Introduced plant and animal pests have invaded much of the Waikato region’s coastal environment. These pests can have important environmental, economic, social and cultural impacts. There is the potential for the arrival of further pests in ship ballast water and attached to ships’ hulls.


Spartina, Whaingaroa Harbour On this page: Plant pests, Animal pests, Marine hitchhikers, Ballast water, Ballast water controls, Ships' hull fouling, Hull cleaning controls

Plant pests

Many introduced plant pests are affecting the natural character of our coastal environment. Some plant pests invade our coastal forests, dunes and the margins of estuaries. These plants include:

An introduced marine species of Paspalum is spreading in some eastern Coromandel Peninsula estuaries (including Tairua, Wharekawa and Otahu). This plant has invaded nearly six per cent of the total estuary area in Wharekawa Harbour.

Another grass, Spartina, has invaded estuaries throughout New Zealand, covering large areas of mudflat and displacing native plants and animals. Through deliberate planting and natural spread, Spartina is now present in a number of estuaries in the Waikato region including:

  • Kawhia Harbour
  • Aotea Harbour
  • Raglan Harbour
  • streams and mudflats around Waitakaruru in the Firth of Thames
  • at least six sites on the Coromandel Peninsula.

Check out our Extent of Coastal Habitats indicator.

Find out about the region’s plant pest control programmes in our Pest Management Strategy.

Animal pests

Introduced animals are damaging the native plants and animals in some coastal areas.

Rabbits graze on native dune plants. Wild goats eat many coastal forest plants. Possums eat coastal forest plants such as pohutukawa and puriri, as well as native birds and their young. Rats also eat both plants and animals. Feral cats and mustelids (ferrets, stoats and weasels) prey on native coastal animals.

One of our best known introduced marine animals is the Pacific oyster. The Pacific oyster arrived in New Zealand in the 1960s. It is not known whether it was brought to New Zealand intentionally or accidentally.

Although the Pacific oyster has become a successful aquaculture organism, it is regarded as a pest in some areas. Pacific oysters may form ‘oyster reefs’ on intertidal shores. These ‘reefs’ displace native species, accumulate sediment, change hydrology and can affect recreation.

We have little information on the distribution and impacts of other introduced marine plants and animals in our region. Surveys and monitoring will help us to learn more.

Marine hitchhikers

For as long as people have been navigating between islands and continents, marine plants and animals have been hitching a ride on our boats.

Increased trade, faster ships and more frequent visits to every part of the world have increased the opportunities for these hitchhikers. Some marine hitchhikers have successfully colonised new areas in coastal areas around New Zealand.

Marine hitchhikers have the potential to:

  • adversely affect our aquaculture and fishing industries
  • threaten human health if exotic species enter the food chain via shellfish and fish
  • displace our native marine plants and animals.

Under the Biosecurity Act, regional councils can have responsibility for controlling introduced marine pests.

Ballast water

Ballast water is seawater used in ships to assist with stability, steerage, safety and fuel efficiency. Water is usually taken on in one port, carried to another, and discharged when cargo is loaded onto the ship. Ballast water may contain plants and animals found in the water under the ship. When ships de-ballast in a port, organisms that were taken up in the ballast water from a previous port may be introduced and become established. The seaweed Undaria was probably bought to New Zealand in ballast water of ships from Asia.

Although the Waikato region does not have a major port, it is vulnerable from ships passing through on their way to Auckland and Tauranga, as well as from shipping at Taharoa on the west coast.

Ballast water controls

In May 1998 voluntary controls for ballast water were replaced with an Import Health Standard, which requires all ships to exchange their ballast with mid-ocean water (without putting the ship and crew at any risk), which is less likely to contain organisms that thrive in a coastal environment.

Ships' hull fouling

Many plants and animals have been introduced into New Zealand coastal areas (especially ports and harbours) attached to the hulls of commercial ships, fishing vessels, recreational boats, barges and drilling rigs. These organisms may become dislodged (for example, during hull cleaning) or release juvenile (young) stages into the coastal environment where they may become established.

Hull cleaning controls

In March 2002 the proposed Biosecurity (Hull Cleaning) Regulations were put out for public consultation. These set out to regulate hull cleaning activities to reduce the risk of undesirable marine organisms being introduced.