Marine pest surveys by Waikato Regional Council support caulerpa response

Caulerpa grows rapidly and can form thick mats or meadows. Photo / NZME

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.

Divers started their annual surveys to determine the presence and extent of marine pests along the Coromandel Peninsula coastline in August.

Senior biosecurity officer Danielle Kruger said so far, the divers had checked 573 vessels, 908 piles, 10,900m of pontoon, and 15.51ha of benthic area or popular mooring sites in Tairua, Whitianga, Whangamatā, Whangapoua and Ahuahu/Great Mercury Island.

Marine pests are spread by mainly heavily fouled vessel hulls, so the dive team checks the pathways of boats and checks 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,” Kruger said.

“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.

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 spread via mostly 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 Kruger.

This bright-green invasive caulerpa seaweed is smothering the delicate marine ecosystem on Great Barrier Island. Photo / Glenn Edney

“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.”

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.

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