Caulerpa is an algae that blankets the sea floor, smothering everything from kelp to shell fish.
Nicola MacDonald is chief executive of the Ngati Manuhiri settlement trust. The iwi’s territory includes Kawau island and Little Barrier Island, two of the 11 areas where the seaweed pest is present.
“When caulerpa first got here, government really struggled with how to address caulerpa and take real proactive action, and we saw what happened at Great Barrier Island. It went from 60 hectares to now it’s well and truly over 2000 hectares. So that’s an absolute indication of how we take it seriously. And government isn’t taking it as seriously as they need to.”
Ngati Manuhiri recently produced a short film highlighting the concerns of iwi from the Hauraki gulf and Coromandel to the Bay of Islands.
“We certainly don’t want to leave the Hauraki Gulf in a much worse state for our mokopuna, our grandchildren and our children that inherit from us. So for all of those iwi that have been battling the invasive species such as caulerpa, that has been the single uniting moment”
A national caulerpa strategy was recently sent to Biosecurity Minister Andrew Hoggard.
“My understanding is that he was taking it through to Cabinet and there may be further budget, well there will have to be, further budget in order to deliver on those milestones that the strategy recommends,” said MacDonald.
MPI director of readiness and response John Walsh said $25 million was spent before this year on the fight against caulerpa.
“I think we’re actually in quite a good place through some good planning and some good management and also some good luck.”
The good luck came in the form of significant caulerpa dieback in some of the sites that NIWA monitors – including Great Barrier island and Omakiwi cove in the Bay of Islands.
But he said there had been no consistent pattern to why caulerpa had retreated in some of the sites. “It’s a bit of a mystery, we’ll still be continuing to examine it this year.”
There was also no guarantee the dieback will continue.
“This summer will be very telling,” Walsh said. “The waters are starting to warm up already. Warm waters mean more growth, unfortunately.”
Chlorine, UV-C light technologies trialled
New technologies are being developed in the fight against caulerpa.
Brook McRae runs Commercial Dive Specialists and has a background in biosecurity. His company expanded on an technique where mats treated with chlorine were used to kill caulerpa.
They did away with the mats, creating a submersible chamber , known as a ‘rehabitat’ chamber, that can be moved along the sea floor. Chlorine is pumped into the chamber, and once treatment is complete is removed, making sure no chlorine escapes into the sea.
“They’re actually just like an inflatable bouncy castle. But they’re inflated with water, and that allows them to contour to the shape of the seabed,” McRae said.
The chambers have proven effective in killing caulerpa, but signoff is needed before the ‘rehabitat’ enclosure can put higher levels of chlorine into action
Another tool to tackle caulerpa is being developed by Craig Thorburn of Advanced Aquarium technologies. His team is using UV-C light to treat caulerpa.
“I ended up talking to a chap in the USA, John Pelluccio, in Lake Tahoe. He was using UVC light to manage freshwater plants in Lake Tahoe. So that kind of set us on that journey of looking at is there an application here? No one had tried it in salt water. No one had tried it with a plant like caulerpa.”
Tests run with the University of Auckland showed UV-C light was effective in killing caulerpa, but then came the complex task of developing a vehicle that could operate on the sea floor.
“We like to think of it, it’s still a bit of a Model T Ford. The frame of it and its workings are still off our original prototypes. We’re building another unit in China at the moment that is another step towards something that would be a production model.”
Both McCrae and Thorburn’s projects have received government funding.
After bringing Californian experts to New Zealand in 2023, Ngati Manuhiri continue to look offshore for solutions.
“Having recently attended Aqua Nor in Norway, I saw a lot of technology that I think could be applied in New Zealand,” said MacDonald.
“Those are some of the conversations that I’ve had with Biosecurity New Zealand, that there’s some tech overseas that I think we need to bring here and we really need to get on the job of getting rid of this stuff”
But whether caulerpa can be eliminated completely remained unknown.
“I think the chances of managing it, particularly in our anchorages and our open sandy shellfish habitats are quite high”, said Thorburn.
“I think there’s a range of tools now that are available and they’re not well practised by any means, but they exist and the knowledge exists to say yes, that could be tackled in response and we didn’t have any of those possibilities, three or four years ago. We really would love to acknowledge that incredible leadership shown by iwi and local communities in tackling exotic caulerpa and from my experience, right from the very, very start, iwi have been right at the heart of this response”
And with summer beckoning, the message to boaties from MPI remains unchanged.
“If you’re in the top of the North Island, if you pull up seaweed on your gear, on your anchor, on your fishing gear, no matter what it is, no matter where you are, it’s really good practice to get into the habit of storing it safely on your boat, in a bag, in a bin, in a bucket, taking it ashore and disposing of it safely,’ said Walsh.
Originally published on RNZ, written by ,
