A new to mainland New Zealand red seaweed - Asparagopsis taxiformis - has been found at Tamaterau in Whangārei Harbour and at Iris Shoal, Kawau Island.

Northland Regional Councillor Jack Craw, who chairs the council’s Biosecurity and Biodiversity Working Party, says the seaweed was first spotted at Tamaterau recently by his regional council colleague, Cr Amy Macdonald, an ecologist.

Councillor Craw says Asparagopsis taxiformis is considered native to the Rangitāhua/Kermadec Islands and is similar to - and can grow among - New Zealand’s red seaweed Asparagopsis armata.

Officials suspect it has been at both the Whangārei Harbour and Kawau Island locations for some time - likely finding its way there on a vessel either associated with biofouling, on an anchor, anchor chain, or dirty equipment - and is likely to be in other spots.

"We don’t know how this weed will react in the mainland New Zealand marine environment and at this stage there is no evidence to suggest that the seaweed is affecting biodiversity in these areas. However, internationally it has been shown to outcompete and displace native species, impacting biodiversity."

Councillor Craw says as a new species, any decisions regarding control (if any) will be made by Biosecurity New Zealand in the first instance.

"Currently Biosecurity New Zealand is completing a risk assessment, but in the meantime, the regional council urges all vessel owners to be extra vigilant and ensure hulls are clean before moving."

"It’s also important to make sure that anchors and all top side gear are also clean, free of fouling and if possible dry before moving."

Councillor Craw says the seaweed is difficult to identify and specialised testing had been required to confirm its presence.

He says red seaweeds have been researched by scientists both in New Zealand and overseas for their properties that can reduce methane emissions when used in feed for ruminants.

The seaweed was first spotted by NIWA staff during a pre- dredging exotic caulerpa survey at Iris Shoal, where it was in water around 11 metres deep and mixed in with other red seaweeds.

More of it was found washed up in large amounts at Tamaterau.

Councillor Craw says anyone spotting what they thought might be Asparagopsis taxiformis outside the Whangārei Harbour could freephone the MPI exotic pest and disease hotline on 0800 80 99 66, or use the online report form http://report.mpi.govt.nz/pest/

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