Invasive seaweed detected on Aotea, Great Barrier Island

Mana whenua of Aotea say that biosecurity officials need to eradicate an invasive species of seaweed found on the motu.

Caulerpa brachypus was found in Blind Bay and Tryphena in July, 2021. It can spread quickly and form thick mats. This was the first time the pest species had been found in New Zealand.

The Ministry for Primary Industries (MPI) says it will issue a Controlled Area Notice on Monday, which makes it illegal to take seafood from Blind Bay or Tryphena Harbour. Without a permit, it would also be illegal to anchor in the two areas.

MPI said that the Biosecurity Response Group for Mana Whenua on Aotea was supporting a dual response by putting a rāhui over the same areas.

Martin Cleave, who represents Ngāti Wai on the Governance Group, said that the discovery of Caulerpa brachypus in Aotea waters and the size of the infestation were upsetting for mana whenua.

He said that the invasion was a big problem for Kai Moana because the seaweed could smother and kill scallop beds in the area.

"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 told RNZ.

Cleave says he told the MPI that it needed to get rid of the weed and that containment was not an option.

"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 that it was his job to make sure mana whenua could work with MPI to solve 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." Cleave told RNZ.

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

John Walsh, who is in charge of biosecurity response for MPI, said that the Controlled Area Notice was meant to protect the island's wider coastline without being too hard on mana whenua and other locals.

"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.

-Additional reporting, RNZ