Waikato Regional Council’s regular surveys of the region’s coastal marine areas will help support Biosecurity New Zealand to determine if exotic Caulerpa species is spreading throughout the Waikato region.

Divers started their annual surveys to determine the presence and extent of marine pests along the Coromandel Peninsula coastline in August and will then move to the west coast harbours of Port Waikato, Raglan and Kāwhia, where surveys are done every three years.

Senior Biosecurity Officer Danielle Kruger said to date, the divers had checked 573 vessels, 908 piles, 10,900 metres of pontoon and 15.51 hectares of benthic area or popular mooring sites in Tairua, Whitianga, Whangamatā, Whangapoua and Ahuahu/Great Mercury Island.

Marine pests are mainly spread by heavily fouled vessel hulls, so the dive team checks the pathways of boats and check vessels, marine structures (marinas, wharves, jetties and moorings), popular anchoring spots and mussel and oyster farms.

“We do these surveys to prevent the spread of marine pests through biofouling,” said Mrs Kruger.

“If infested vessels are found then we may request that owners remove and antifoul them.

The council started its coastal biosecurity surveillance programme in 2017, particularly to target marine pests Mediterranean fanworm (Sabella spallanzanii) and clubbed tunicate (Styela clava), which are found in the Coromandel Peninsula.

Mrs Kruger said since then, however, there was also concern about two exotic Caulerpa species after their discovery in Aotea/Great Barrier Island in 2021.

Caulerpa grows rapidly and can form thick mats or meadows over just about any underwater surface.

It is mostly spread via fragments and can easily break up during storms or by boat anchors, divers' actions or fishing equipment.

“Caulerpa has since been discovered in the Bay of Islands, Waiheke Island and Ahuahua/Great Mercury Island, which is in the Coromandel Peninsula, so it is a great concern,” said Mrs Kruger.

“Our dive team is very experienced and have a good knowledge of all marine pests, so if it’s in our survey areas then they will see it.”

Thames-Coromandel councillor Warren Maher says marine biosecurity is incredibly important for marine health and to maintain recreational and customary values.

“We need to protect our marine environment from invasive species which can outcompete our native species, reduce overall biodiversity and have a major impact on the economy.”

Please help prevent the spread of marine pests: make sure your hull has been checked, cleaned and antifouled before heading away and that you clean your anchor and gear before moving.

Don’t know what a marine pest is? Check out marinepests.nz for some of the pests we look out for.

Controlled Area Notice and rāhui at Aotea Great Barrier Island and Ahuahu Great Mercury Island

To minimise the spread of Caulerpa species, Biosecurity New Zealand has placed a Controlled Area Notice (CAN) on three affected harbours at Great Barrier Island (Blind Bay, Tryphena Harbour, and Whangaparapara) and the western bay of Ahuahu Great Mercury Island. Mana whenua have imposed a rāhui in the same areas. The CAN and rāhui are in place until 31 October 2023.

Biosecurity New Zealand is reviewing all information gathered on Caulerpa brachypus and Caulerpa parvifolia since they were discovered in New Zealand. The review will inform future controls to best manage the risk of spread, while taking into account the effect of any requirements on communities and other marine users.

To find out more about Biosecurity New Zealand’s Caulerpa response and what the CAN and rāhui mean for recreational water users, or to subscribe to updates about the response, click here.

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