Efforts are ramping up to fight the spread of exotic caulerpa at scale, after it was detected within 400 hectares of seafloor around Onetangi Bay and Thompsons Point. Government, iwi and community groups are scrambling to secure funding and organise its removal as it threatens to smother marine life around Waiheke.

Ngāti Paoa Iwi Trust has placed a rāhui on areas one nautical mile (1.8km) from both Onetangi Bay and Thompsons Point, urging people to avoid sailing, kayaking, fishing, scuba diving or paddling in the area. Meanwhile, boaties are asked to deep clean their boats and gear to avoid spreading the invasive seaweed to other bays.

Speaking at a public meeting at the Old Blackpool School last week, Biosecurity New Zealand’s director of readiness and response John Walsh underscored his support for the rāhui and said millions of dollars are currently being spent on the caulerpa response.

“The volume of work that is going on in this space is enormous,” he says. “I have a very large, broad job but all I do at the moment is caulerpa. That is an insight into the resource and effort that our agency is putting into caulerpa.”

The Ministry of Primary Industries, along with Auckland Council, is planning another surveillance of the Hauraki Gulf, with a focus on high-risk sites.

Meanwhile, this week Biosecurity NZ will start a trial involving diver-assisted suction dredging at Aotea/Great Barrier Island where 88-hectares of exotic caulerpa was discovered back in August 2021 at Okupu/Blind Bay. 

Biosecurity NZ established Controlled Area Notices (CANs) at the time and has monitored the outbreak since then.

“Rightly or wrongly, and many people tell us wrongly, we took the initial approach which was the best that we can do (because killing it at that scale, at that depth, in those environments is really, really difficult) the best we can do is try and hold it there; so that’s what we did for a couple of years,” said Walsh

• Liza Hamilton

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