Biosecurity New Zealand is planning immediate actions after the find of small patches of exotic Caulerpa seaweed in an area close to Te Kawau Tūmaro ō Toi Kawau Island in the Tāmaki Auckland region, says director of response services John Walsh.

"We’ve talked to the Ngāti Manuhiri Settlement Trust, and the Auckland Council today and will meet with them next week. With their agreement, we plan to begin some control work as soon as possible as well as further surveillance in the area," says Mr Walsh.

"Ngāti Manuhiri Settlement Trust is committed to protecting our rohe moana and putting all efforts to remove and eradicate the invasive pest from our beautiful waters," says Ngāti Manuhiri Settlement Trust's chief executive Nicola MacDonald.

Mr Walsh says Biosecurity New Zealand is considering the use of chlorine pellets beneath tarpaulins, as is currently being tested in the Bay of Islands by Northland Regional Council, or suction dredging to remove the seaweed.

"Divers found small 20 centimetre to 30 centimetre patches of the seaweed in the North Channel, north-west of Kawau. Finding exotic Caulerpa in another area of Tāmaki is disappointing but not unexpected given the nature of the seaweed.

"Caulerpa can easily be spread to new locations as it’s commonly caught up as tiny pieces of seaweed on vessel anchors and fishing gear.

"For the past 2 years, we’ve been working with partners, including mana whenua, local authorities and communities to address exotic Caulerpa at Aotea Great Barrier Island, Ahuahu Great Mercury Island and, most recently, in Te Rāwhiti Inlet in the Bay of Islands.

"This has been a sustained, thorough and collaborative effort to contain Caulerpa to known locations, better understand the pest and its challenges, trialling treatments, and working to prevent its spread.

"This includes legal controls on risk activities and widespread campaigns involving local communities, mana whenua, regional councils and others to educate people about Caulerpa."

Mr Walsh says work continues on exploring and trialling treatment methods. Aside from immediate work in the Kawau Island area, new in-water treatment trials will start in the Bay of Islands, Aotea and Ahuahu from July and will run through to the early summer period.

"People in those areas want Caulerpa eliminated. This will be very challenging given the many hectares of Caulerpa involved, but these trials are geared towards that.

"We are supporting the Ngāti Manuhiri Settlement Trust, mana whenua and mandated iwi authority, to bring experts from California to Aotearoa New Zealand early next month to provide first-hand insights about using suction dredge techniques to remove Caulerpa.

And we’ve also set up another expert technical advisory group to revisit the latest information on this suction technique.”

Mr Walsh says exotic Caulerpa is challenging to deal with.

"Internationally, Caulerpa has not been successfully eradicated from areas the size of the finds in New Zealand, and climate change and warming oceans also present a tough biosecurity challenge for everyone.

"All marine users can play a part in preventing the spread of exotic Caulerpa. We’re asking people to be vigilant by keeping boats and other aquatic equipment clean to reduce the risk of introducing or spreading any exotic seaweeds.

"Check your gear, especially anchors and chains. If you see any seaweed on your equipment, chuck it straight back in the waters it came from.

"And if you think you've seen exotic Caulerpa, note the location, take a photo and report it to Biosecurity New Zealand on 0800 80 99 66 or online at report.mpi.govt.nz "

Find out more about the seaweed

Exotic Caulerpa seaweeds at Great Barrier, Great Mercury, Kawau Island, and Bay of Islands (Te Rāwhiti inlet)