Auckland iwi and carpet company work to eradicate invasive seaweed caulerpa

An Auckland iwi and a carpet company have come up with a biodegradable solution to eradicate the invasive seaweed, caulerpa.

After growing impatient with a lack of Government action, Ngāti Paoa approached Bremworth to make wool mats to lay on the sea floor in an effort to smother the fast-growing pest.

"We weren't too keen on waiting on the Crown to lead its response, so Ngāti Paoa have taken the position that we will lead, so as to get some action," Ngāti Paoa spokesman Blair Anderson said.

Made by carpet company Bremworth, the mats are being spread over the exotic caulerpa seaweed in an area off Waiheke Island.

It's a pest which experts say is threatening to crowd out native species and reduce fish stocks.

Ngāti Paoa is already concerned about shrinking shellfish populations.

"It's important that before we look at regeneration, that we rid ourselves of the pest that's come into our midst," Anderson stressed.

There were 12 mats laid on the seafloor on Sunday, ranging from 10 to 15 metres long. They're made from 100 percent pure New Zealand strong wool and from black and brown sheep, which is hoped will further prevent sunlight from coming through.

It's an innovative use of wool that, if scaled up, could provide an income stream for an industry that's been in decline.

"You want to make sure that when you're putting something into the environment you're going to be enriching it, you're not going to be adding toxicity or anything like that," Bremworth GM of sustainability Kirstine Hulse said. 

"We didn't want to use plastic benthic matting. We didn't want to use the chlorine tablets that have been used elsewhere," Anderson added.

Brook McRae has become something of a caulerpa removal expert. His company welded an underwater vacuum that has been deployed across the Gulf.

He reckons the wool mats will kill the caulerpa within 10 to 14 days.

"I believe that we can evolve something where we can deploy a lot of these diver-less and cover a larger amount of ground and that makes the cost-benefit a lot better," he said.

How the exotic algae got here remains a mystery, but it's colonised hectares of the sea floor across the Hauraki Gulf - something McRae said could've been avoided.

"Now we're three years down the track, there's so much money being thrown at it, I just see it as a shame it wasn't done at the start. If it was done at the start, I think what's been thrown at it today would've got rid of it," he said.

The Ministry for Primary Industries has been testing methods to remove caulerpa, but those who have watched its spread say a much bigger, coordinated effort is needed.

"We consider this to be the mycoplasma bovis of the sea and it will have severe impacts on the ecology, biodiversity and the economic issues that will surround our fisheries," Anderson said.

It's a biodegradable solution to a problem that's spreading by the minute.