17 Sep 2021

Invasive seaweed detected on Aotea/Great Barrier Island

8:33 pm on 17 September 2021

Aotea/Great Barrier Island mana whenua say biosecurity officials must eradicate an invasive seaweed species detected in the area.

Caulerpa brachypus growing under water.

Caulerpa brachypus growing under water. Photo: Supplied by Ministry for Primary Industries

Caulerpa brachypus, which can spread rapidly and create dense mats, was found in July in Blind Bay and Tryphena Harbour. This was the first time the pest species had been detected in New Zealand.

The Ministry for Primary Industries (MPI) said it would issue legal controls on Monday, known as a Controlled Area Notice, which would make it illegal to take seafood from Blind Bay or Tryphena Harbour. Anchoring in the two areas would also be banned without a permit.

The local mana whenua governance group for the biosecurity response on Aotea were supporting a dual response by imposing a rāhui over the same areas, MPI said.

Governance group deputy chair Martin Cleave (Ngāti Wai representative) said the discovery of Caulerpa brachypus in Aotea waters and the extent of the infestation had been upsetting for mana whenua (Māori authorities over the land).

He said the incursion posed a significant threat to kai moana, including scallop beds in the area which could be smothered and suffocated by the seaweed.

"We're talking pristine kai moana here, because of the water quality that we have, these mats [of seaweed] prevent any of that from happening."

Cleave said he had been clear to the MPI that it needed to get rid of the weed and containment was not a solution.

"Kai moana, particularly for Māori and mana whenua, I mean, that's our food basket right? So if that [incursion] affects that, effectively, you're extinguishing our customary fishing rights."

Cleave said his role was to ensure that it can work collaboratively with MPI, to fix the problem.

"The biggest thing that is going to stop this from happening, is going to be money. Well, money shouldn't be an issue when it comes to eradicating this Caulerpa brachypus as far as we, the mana whenua, are concerned.

"We're upset about what's happened. But we're also very optimistic on what we can do collaborating with MPI," he said.

Cleave said Niwa staff would be on Aotea this week, to continue surveillance work to establish the spread of the seaweed.

Maps showing the controlled areas on Tryphena Harbour (left) and Blind Bay on Great Barrier Island.

Maps showing the controlled areas on Tryphena Harbour (left) and Blind Bay on Great Barrier Island. Photo: Supplied / Ministry for Primary Industries

MPI biosecurity response director John Walsh said the Controlled Area Notice aimed to protect the island's wider coastline while trying to not be too onerous for mana whenua and local people.

"People can still swim, dive, paddle or use a vessel in the Controlled Areas, so long as they don't drop anchor.

"It's the movement of equipment along the seabed which poses the risk of picking up fragments of Caulerpa and moving it elsewhere," Walsh said.

The Controlled Area Notice will be in place until at least the end of November.

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