Aotea Great Barrier Island’s lonely fight against the seaweed threatening it’s livelihood
DAN MOSKOVITZ (HE/HIM)
Take a look at this map of the Hauraki Gulf . Up in the top right corner is Great Barrier Island, or Aotea. It’s at the fringe, straddling the gulf on one side and the Pacific on the other. But that's the point. It is the Great Barrier. Despite being New Zealand’s sixth-largest island, its population barely ticks over a thousand, and is the world’s only island dark sky reserve.
On Aotea, petrol can reach four dollars a litre. The island is almost totally reliant on solar power and generators, and Aotea’s own website talks about how toasters are a rarity because of how much power they draw. For many, but particularly the island’s mana whenua (Ngāti Wai and Ngāti Rehua), the sea remains a prime source of food.
All of this is under threat. Aotea Great Barrier Island is the site of what’s been called New Zealand’s worst marine biosecurity disaster.
Part One: The Invasion
Caulerpa is a genus of seaweed. It doesn’t really look like much, just your standard frilly green weed in the water.
But what makes Caulerpa special is the incredible speeds at which it can grow; up to a centimeter a day. This means Caulerpa can effectively smother the rest of the seafloor, stifling the growth of other seaweed, overtopping corals, and changing the all-round habitat. To make matters worse, it can also regenerate from fragments, meaning if a strand of Caulerpa snaps, those pieces could create two new patches. Hence anything which comes into contact with the seafloor—like an anchor or a net— becomes a biosecurity risk.
Caulerpa invasions have posed massive ecological problems overseas. But in 2021 two species (Caulerpa parvifolia and brachypus, collectively referred to as exotic Caulerpa) were discovered at Aotea, causing the Ministry of Primary Industries, through its Biosecurity wing, to launch its response.
Dives by NIWA confirmed the scale of the problem. In one patch, the seaweed’s coverage had expanded from 0.01 square meters to 1840m in just a few months.
Three years on, and most of Aotea’s west coast is coated by Caulerpa. For many on the island, it's borderline traumatic.
“Caulerpa covers nearly a quarter of the island’s sea-floor,” says Maurice Ngatai, a skipper on the island and a member of the Ngāti Rehua ki Ngāti Wai trust. “It’s smothered everything so nothing can grow. “It’s a noxious weed, but nobody knows how to deal with it.”
“We still rely on the ocean to provide sustenance for whanau and the community. We can’t go in there at all to get kai” said Kelly Klink, a member of Ngāti Rehua.
Barry Scott, a retired Massey University professor who moved to the island post-retirement, describes what the seaweed is doing to the seafloor as “heartbreaking.”
So how has Biosecurity NZ responded? Where there is Caulerpa, Biosecurity puts in place Controlled Area Notices (CANs). These forbid activities which come into contact with the seafloor, like net fishing or anchoring.
“We still rely on the ocean to provide sustenance for whanau and the community. We can’t go in there at all to get kai”
Throughout 2022 and 2023, Caulerpa crept up Aotea’s coast, trailed by extensions of the CANs. But this was it. This was about the extent of the Biosecurity response. For many of Aotea’s residents, it felt like abandonment.
“We’ve been abandoned since it came out,” said Klink. “We had been fighting Caulerpa for two years before anyone on the mainland had heard of Caulerpa, with no money.”
To top it all off, in May 2024, Biosecurity New Zealand allowed three crayfishing boats—two from Leigh, and one from Aotea itself—into Aotea’s CAN. This was a biosecurity risk; craypots could absolutely create Caulerpa fragments. Biosecurity said this was needed for the crayfisher’s livelihoods, but for those on the Barrier, sweltering under restrictions since 2021, this was an outrage.
“I asked Biosecurity if they had a code of ethics,” said Scott. “They put the rights of two or three fishermen above the rights of the whole island. What’s more, they created a biosecurity risk. It undermined our trust, our confidence, and our respect.” A few months later, Caulerpa was detected at Leigh.
Biosecurity admitted fault in the lack of consultation with the Barrier, but said the crayfishers were unlikely to be the source of Leigh’s Caulerpa, as Leigh’s Caulerpa was found in an area different to the boats and biosecurity measures were in place.
Three years on from Caulerpa’s detection in 2021, and all but the northern tip of Aotea’s west coast lies within a CAN. Just a single sheltered port—Fitzroy, thanks to an exception from the CAN—remains open for anchoring. For an island which relies significantly on Auckland's tourism, Fitzroy is a vital lifeline.
“Port Fitzroy is the Mecca for recreational boats,” says Scott. “If you don’t keep Fitzroy free of Caulerpa then the island faces very hard questions. Does it lockdown? Or does it let boats in, which will spread Caulerpa throughout the Gulf?”
Currently, a small patch of Caulerpa exists at Fitzroy’s mouth. As summer comes and the waters warm, there’s real concern about whether it will spread into the rest of the harbour. Scott and others on the island have set up the Aotea Caulerpa Response Team but, devoid of government funding, their options are limited.
Part Two: The Spread
The exotic Caulerpa incursion attracted little media attention until 2023, when it was discovered at Omakiwi cove in the Bay of Islands. There, a combined effort from council, iwi, and locals rapidly propelled the seaweed to national attention. This is a sore point for many Aotea.
“Mana whenua and the Regional Council went ballistic and caused so much noise that MPI felt embarrassed,” said Chris Olliver, a member of the Aotea Caulerpa Response Team about Omakiwi.
“They sat on the minister's desk and thumped the table and as a result the minister gave them $2,000,000. Unless you can get that sort of impetus, you are working within the slow bureaucracy.”
The incursion at Omakiwi is ⅙ the size of Aotea.
Three years on, and much of the Hauraki Gulf and Northland are feeling the effects of Caulerpa. This has brought upside of there now being more groups invested in the incursion, but means Aotea, already struggling to gain traction in its response, is now fighting with other affected areas for funding.
That’s apparent at both Omakiwi, and at Waiheke Island, the site of the second-largest infestation. There, while Blair Anderson of Ngāti Pāoa (the iwi of Waiheke), is quick to acknowledge Aotea’s suffering, he still describes Biosecurity as “responsive,” and is upbeat about their response to the Waiheke incursion.
For comparison, exotic Caulerpa covers 820 hectares of Aotea’s seafloor. Waiheke’s incursion measures at 410, Omakiwi’s at 240.
All of this led to Klink taking Biosecurity New Zealand to the Waitangi Tribunal, a move she herself admitted was to draw attention to the situation on Aotea. Because Aotea, at this point, is desperate. Many on the island wish to just speak with the Biosecurity minister, and plead their case, hoping to try and show him the personal struggle on the island.
But again, their pleas have been ignored.
“They sat on the minister's desk and thumped the table and as a result the minister gave them $2,000,000. Unless you can get that sort of impetus, you are working within the slow bureaucracy.”
Part Three: The Minister
The appointment of Andrew Hoggard as Biosecurity minister probably raised eyebrows.
The former Federated Farmers president turned ACT MP is as fresh as can be. Elected in 2023, a month after becoming an MP he was Minister of Biosecurity.
Yet Hoggard has done well with Caulerpa. Throughout 2024, in the most austere government in living memory, he reallocated $15 million from elsewhere in MPI to the Caulerpa response and has incentivised research into new technologies.
But Aotea is still at the periphery. While Biosecurity officials were hopeful of using the funding to support on-island suppression efforts, so far just $200k has gone to the island with the largest infestation. So why is Aotea getting such a paltry response compared to Waiheke, Omakiwi, and more?
According to Hoggard, Aotea is still part of the plan, but Biosecurity’s main focus right now is R & D. Only a small lagoon in California has ever been able to eradicate Caulerpa before, and certainly nothing at the scale of NZ’s incursion, which is why Hoggard hopes to scale up new technologies.
“We really need our technologies sorted before we go in there [Aotea],” said Hoggard when interviewed by Salient. “It's the worst spot and trying to tackle it without everything firing on all cylinders will be, quite frankly, wasting money.”
Scott worries this is too much linear thinking. Caulerpa will continue to spread while this research occurs, meaning interim suppression could make things cheaper down the line. Similarly, as Olliver points out, having a nest of untouched Caulerpa could provide a nursery for it to spread to the rest of the gulf.
And while there's probably some validity in Hoggard’s points, none of this was communicated to Aotea; Hoggard has no plans on visiting.
“I'm not one that’s just doing token visits,” he said. “If I'm visiting somewhere, it's to check in on progress and solutions.
“And from the surface, there's not a whole lot to see. I suck at swimming. I’m not going to put on a wetsuit and go underwater. No way in hell you’re getting me diving.”
Part Four: The Future
So what are these new technologies? If there’s a case for hope, it's here. Caulerpa is now taken seriously across the board, meaning there is now a slate of iwi, ministries, councils, and researchers all throwing the kitchen sink at the problem.
Suction dredging has gained the most attention. Imagine a vacuum cleaner powered at the seafloor, sucking up Caulerpa, sand, and anything else unlucky enough to be in its path. This can take the form of driver directed—a handheld vacuum cleaner—or a mechanical ship-bound dredge.
The cost of this is enormous. NIWA estimated such dredging to cost hundreds of thousands of dollars per hectare of Caulerpa cleared.
A potentially more cost-effective solution is being trialled by Ngāti Pāoa. They’re placing woollen mats (whāriki) over Caulerpa, which suffocates everything under them. Meanwhile, researchers at the University of Auckland are working on a UV light treatment, and kina have also been tested as biocontrol.
No matter what gets used—most likely a combination of what’s already been mentioned—it’s going to be ecologically damaging. Suction dredging sucks up seafloor alongside Caulerpa. Whāriki suffocate everything under it. UV light is a big unknown. As Klink herself puts it, “to save the ocean, we’re going to have to kill the ocean.”
And science takes time. Making things scaleable takes time. But Caulerpa spreads fast, and Aotea is teetering. Fitzroy is the only major port left for anchoring, but summer is coming, and with it comes the faster spread of Caulerpa. Whether Fitzroy will hold is another matter entirely.
The consequences of inaction cannot be overstated—modelling suggests Caulerpa could proliferate between Northland and Hawkes Bay.
Maurice Ngatai grew up on Aotea, living off the kai moana. For him, it's about his tamariki, and whether they will be able to experience the same life he did.
“The sea floor is the beginning of the food chain for us. But in ten years time, this stuff’s gonna take over. I’m going to have to tell my kids they better get used to having no food.”
The barrier has been breached. Whether it will be fully broken is yet to be seen.
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