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The Hauraki Gulf Forum has been told that without adequate controls, it is just a matter of time before the pest seaweed Caulerpa spreads further into the gulf.
Biosecurity New Zealand director of readiness and response, John Walsh, said it had been about two years since Caulerpa first established in New Zealand waters and it had since spread across 90 hectares in Blind Bay at Aotea/Great Barrier Island.
“We think it probably arrived from Australia, possibly on an anchor chain,” Walsh said. “The Caulerpa are showing early signs of being successful invaders and displacing native species, with potentially wider ecosystem impacts.”
A Controlled Area Notice (CAN) and rahui were placed on three harbours at Aotea Island, which prevented fishing, seafood gathering or dropping anchor.
In July, NIWA surveillance divers positively identified Caulerpa at four new locations on the western coast of Aotea/Great Barrier, near Whangaparapara Harbour. These were discovered as a result of a report from a member of the public.
“We are quite concerned about it because of the speed at which it’s growing. We are unlikely to be able to eradicate it so we have focused on minimising the spread.”
In recent surveys, Caulerpa had not been found further inside the Hauraki Gulf, but Walsh said without adequate controls, it would spread. He said one surprising method of pest control, which had been effective, was to apply salt directly to the Caulerpa.
“Who would have thought you would use salt to kill something in the sea but apparently it works,” Walsh said. “The downside is the ‘monstrous’ volume of salt needed.”
Aotea local board member Valmaine Toki said restrictions on fishing had distressed the community. She described the engagement from the Ministry for Primary Industries as lacklustre and generic.
The CAN at Aotea Island expired in June, but Biosecurity New Zealand has extended it until the end of this month.
