People gather for a meeting to discuss the invasive weed caulerpa in the Coromandel area. Photo / Alison Smith
People gather for a meeting to discuss the invasive weed caulerpa in the Coromandel area. Photo / Alison Smith
The Californian team that successfully eradicated a killer algae is imploring the Coromandel community to pull together and fight the invasive seaweed caulerpa while being wary of bureaucratic processes.
Eric Noel Munoz, consultant and author of the book Caulerpa Conquest, was among the team brought to New Zealand by Ngāti Manuhiri Settlement Trust, which took immediate action to find solutions in eradicating the invasive weed caulerpa.
He told a roadshow audience in Whitianga on August 9 that indigenous people and local knowledge were of huge benefit here.
“You don’t have time for your normal bureaucratic processes. We planned meetings, got the dive teams together and were out within 15 days mapping it while we figured out the funding,” he said of the Californian incursion.
Munoz said early detection and rapid response helped their eradication.
“Don’t wait and study how fast it grows. Kill it while you figure out how fast it grows. You go out and kill it.”
He said a possible source of caulerpa was aquariums, even those on board mega-yachts.
The tropical seaweed Caulerpa brachypus and Caulerpa parvifolia have been found growing up to 38m deep in New Zealand waters. It was found off the Coromandel at Ahuahu (Great Mercury Island) more than a year ago.
MPI and Niwa are extensively surveying and have removed caulerpa through a multi-agency response, with Ngāti Manuhiri and Northland Regional Council in Northland. Other community and iwi leaders are proactively acting in their areas.
Biosecurity New Zealand director of response services John Walsh said at Great Mercury Island off the Coromandel, government agencies would continue monitoring but plan no removal or smothering of the algae until learning from trials on containment methods elsewhere.
Members of the Coromandel business and resident community mobilised in response, with divers, collection and potential processing facilities getting ready.
They include AgriSea in Paeroa, which is investigating how to handle and potentially safely utilise caulerpa, Dive Zone Whitianga, Ngāti Hei, Ngāti Tamatera and Hauraki iwi.
An explanatory poster hangs on the wall at a meeting to discuss the invasive weed caulerpa in the Coromandel area. Photo / Alison Smith
Dive Zone Whitianga owner Darrell Bird offered a boat and divers.
“We went to a hui here in 2022 and we’re in the same place, not much has changed. If they’re going to cut off Great Mercury Island to boats, that’s about our customers, and it’s way better for us to do something.”
AgriSea chief innovation officer Tane Bradley said it was a Māori-owned business that had been working with seaweed for the past 27 years.
“We have institutional knowledge of developing biostimulants and hydrogels from a variety of seaweed. We are, and would be, happy to explore opportunities for utilising caulerpa for this purpose.
“Alongside iwi and other stakeholders, we believe together we can find the most positive outcome for this outbreak. We are happy to run pilot studies on caulerpa to see its suitability for this purpose, and from this we hope to be able to provide funds back into the eradication project.”
Walsh said caulerpa was “not all that hard to kill”, but at scale was a huge challenge.
The first 40ha infestation, discovered on Aotea in 2021, was estimated to have been there at least three years when it was found.
Not long after, the weed was discovered off Great Mercury Island, Te Rāwhiti inlet in the Bay of Islands in May this year, Kawau Island and most recently, Waiheke.
Caulerpa was in 200ha of Aotea, and in the corner of Omakiwi Cove, 16ha is now 99 per cent covered in Caulerpa, MPI revealed at the August 9 meeting.
The incursion was of “moderate density” in Waiheke where surveillance to find the perimeter of the incursion continues.
On Great Mercury Island the algae was mostly found in 6-10cm patches and about 2 or 3 per cent coverage.
In early July divers were in the Ahuahu area, where a Controlled Area Notice (CAN) ban on anchoring was due to expire at the end of October.
“The patch we have out there has shrunk and grown and not behaved like we’ve seen the caulerpa behave in terms of rapid growth and big mats at Aotea and Te Rāwhiti.”
A suction dredging trial in Northland would start by manawhenua and Northland Regional Council in September, based on studies grounded in the Californian experience of removal, in combination with benthic mats — essentially giant underwater heavy tarps laid over the weed.
Kawau removal efforts begin in mid-August, and would inform removals at Waiheke next.
“Getting rid of the seaweed will take years, if we can do it. We can only achieve all of this by working together, everybody committed, egos out of the way, removing obstacles as we go,” Walsh said.
He said fragmentation of the weed remained a risk, and all tools had an ecological impact.
“Those are some of the things we’ll be testing in these trials — understanding the effectiveness, ecological impact, disposal. We’re going to be removing at least a hectare, hopefully 5ha in these trials and we’ve got to work out how we’re going to dispsose of that on a remote island.”
Under the Controlled Area Notices where caulerpa has been found, it is illegal to remove any marine life (fish, seaweed, shellfish or crayfish) and all equipment used for marine activities — footwear, wetsuits, cray pots, dredges, and boat trailers — cannot be removed from those zones without first checking for seaweed and removing it, leaving it in the area it came from.
Anyone wanting to move a boat that has been anchored out of the affected bays can do so only with a permit.
Munoz was critical of the Government’s public messaging to “chuck it back” if found on a fishing line or anchor.
However, John Walsh said controlled area notices meant boaties couldn’t anchor or fish where caulerpa was known to exist.
“What we didn’t want was boaties pulling out a little [caulerpa identification] card and having to make a positive decision to do something with it. We thought that was too hard for people. You’ve got to get people to care, and the smaller [we] ask of people, the easier to get them to do something.
“At the time, in those circumstances we felt there’s a good chance it wasn’t caulerpa when people aren’t in a CAN area.”
The public messaging was now being re-evaluated.
“Caulerpa is laughing at you for having a policy that allows you to put it back,” said Munoz.
In California, divers worked a metre apart every day for three months to remove it — the initial $50,000 budget growing to a cost of $1 million a year for three years. Monthly detection surveys have been made but were challenging at scale.
“If I had to do it again in a small area I would suction dredge and still put the [benthic] barrier on,” Munoz said.
As part of its border patrol, MPI inspects boats including superyachts and ships, which carry and release ballast, and some ships are sent away.
