Posted on March 3, 2025
The invasive seaweed caulerpa has been found in six new locations in a Northland tourist hotspot.
The discovery was made the same week the Government announced more than $6 million toward developing world-first industrial-scale technology to fight the seaweed.
Biosecurity Minister Andrew Hoggard said big strides were being taken with the $6.2 million development of the new technology at Omākiwi Cove and $3.8 million for other technology at two other New Zealand locations to control the invasive exotic seaweed.
Biosecurity Minister Andrew Hoggard.
Hoggard said funding was based on earlier project success.
Northland Regional Council (NRC) confirmed this week that caulerpa had been found in six places in the eastern Bay of Islands Ipipiri island group, about 6km from Paihia.
It has been found at Urupukapuka Island’s major boating anchorages Paradise Bay and Otiao Bay (Entico Bay) and Moturua Island’s Army Bay as well at two locations around adjacent Motukiekie Island.
NRC chair Geoff Crawford said the new finds were disappointing, but there had always been the potential for them to happen.
Caulerpa eradication was still possible – with the help of technology being developed in the Bay of Islands’ Ōmakiwi Cove.
Five of the new sites are outside the Bay of Islands 1000ha caulerpa anchoring ban area in June 2021.
It is the first confirmed caulerpa spread since New Zealand’s only mainland caulerpa infestation was confirmed at Ōmākiwi Cove, Te Rāwhiti, about three kilometres away, in May 2023.
A new infestation has also been identified on the northern edge of the anchoring ban area, close to the islands.
Ōmākiwi Cove has been the site of groundbreaking eradication trials since May 2023.
Newly-discovered dense caulerpa meadow on sandy shoal at Motukiekie Island, Bay of Islands.
Crawford said the new government funding was essential in the race to develop robust tools to fight caulerpa, even as the invasive pest seaweed had spread to the Ipipiri Islands.
He said it was important to stay focused in the face of this spread.
“It’s disheartening to hear. But unfortunately, until we develop these tools, eradication isn’t likely.
“Without technology like the underwater tractor unit we wouldn’t have anything to fight invasive caulerpa,” Crawford said.
NRC chair Geoff Crawford says continuing to develop caulerpa eradication tools is essential.
He said there had always been the chance that caulerpa would spread outside the anchoring ban area.
The Government money will go towards upscaling successful Omākiwi Cove caulerpa removal trials to an industrial scale.
“At present we’re capable of harvesting 30 tonnes of caulerpa a day,” he said.
“We’re hoping to be able to expand that to 600 tonnes a day. That quantity’s about the same in volume as a typical three-bedroom house.”
New Zealand’s first mechanical caulerpa suction dredge in action in Omākiwi in the Bay of islands
Johnson Bros’ Angus Johnson can be seen with the dredge head’s distinctive red counteracting brushes, surrounded by sealed walls enclosing the area where caulerpa dredgings will go into a large filtering bag atop the loose foundation material he is standing on.
One of the biggest challenges would be working through how to deal with the increased quantity of caulerpa brought up on to the vessel in the new regime, Crawford said.
NRC would continue linking with Ōpua-based marine contractor Johnson Bros, which had been working with the council and local mana whenua partners Ngāti Kuta and Patukeha hapū to remove exotic caulerpa in Omākiwi Cove.
The new tool called a “submersible dredge planer” would operate remotely on the seafloor and aimed to remove exotic caulerpa in a single pass.
Exotic caulerpa can be recognised by its oar shaped leaves – Pictured here washed up on a beach.
It would be part of a new larger system including the remotely operated planer, upsized dredge head, pumping arrangements, GPS position system, dredge spoil processing plant and disposal system.
Crawford said the new technology was eradicating caulerpa on soft sandy seafloor.
Other work to control it on surrounding rocky areas along shorelines also needed developing.
NRC will also be supporting two other $3.2 million Government-funded projects – developing an ultraviolet light irradiation tool to kill the pest seaweed and a chlorine treatment chamber that will hover over the seabed.
Exotic caulerpa has been found in nine different locations in the upper North Island since being discovered on Aotea Great Barrier Island in July 2021.
