Boaties from around the world will soon be banned from stopping at one of the Bay of Islands’ most important anchorages, as the Government and mana whenua move to fight New Zealand’s second-biggest caulerpa infestation.

The anchoring and fishing ban at Omakiwi Cove comes as the Government caulerpa response ramps up and a Northland-based national biosecurity leader warns it could cost millions to battle the pest.

The ban will be a first for caulerpa on mainland New Zealand.

It comes after the equivalent of almost 23 rugby fields of the invasive superspreader seaweed was confirmed around Omakiwi Cove on the edge of larger Parekura Bay in the eastern Bay of Islands. The ban came at a hui at Te Rawhiti marae on Wednesday.

Caulerpa has also been found spreading from its mainland stronghold out into the Albert Channel towards Urupukapuka Island.

Biosecurity New Zealand deputy director general Stuart Anderson and Rana Rewha, whose May 3 Omakiwi Cove caulerpa find has resulted in a huge response aimed at getting rid of the invader. Photo / Susan Botting

Mana whenua will also be placing a rāhui at Omakiwi Cove.

Taumata Moka Puru said Rawhiti hapū Ngati Kuta and Patukeha were fully in support of the Government ban.

Deputy director general of MPI’s biosecurity arm, Stuart Anderson, said the Bay of Islands’ caulerpa infestation was a sizeable problem.

Caulerpa has been found in 20 per cent of the almost 90 sites urgently checked by Northland Regional Council and Niwa divers in the week leading up to Wednesday’s hui.

Anderson said mana whenua, the community and all organisations involved needed to work together to develop a plan of attack to put to the Government for funding. There was not a bottomless purse, but nothing was off the table in considering how to wrangle the invasion.

Ministry for Primary Industries (MPI) national caulerpa response head John Walsh said the quantity of caulerpa found around Omakiwi Cove to date was sobering.

“It’s a wicked problem. It’s not easy to solve,” Walsh told the large hui.

Walsh said the Government’s controlled area notice for the Omakiwi area would be in place for 10 days from May 31. This would mean bans on any boats anchoring in an effort to stop the spread of even tiny fragments of the bright green seaweed that covers the sea floor.

The weed smothers seagrass, cockles and interrupts ecosystems. Fishing and seafood gathering will be prohibited under the ban, too.

Bay of Islands is a national and international boating mecca and attracts more than 1000 boats a year, and this season 38 cruise ships.

Boat anchors are a major caulerpa spreader as boaties anchoring in infected locations unknowingly pick up tiny pieces of the pest, which can live in the anchor well for up to 10 days and then spread to new locations as boats shift.

Caulerpa was first identified on Great Barrier Island and then Great Mercury Island in July 2021. The first piece of Bay of Islands’ caulerpa was found on Omakiwi Cove beach on May 3.

Walsh said the density of much of the Omikiwi infestation meant caulerpa had been there for at least a couple of years.

Bay of Islands marine tourism participants Luke Treadwell and Rachael Biggins, with their daughter Hazel Treadwell, were among community members at the Te Rawhiti marae caulerpa hui. Photo / Susan Botting

It had been thought Great Barrier Island was New Zealand’s first caulerpa presence, but the week’s caulerpa reconnaissance ahead of the hui had indicated the Bay of Islands’ infestation had been around longer, and was therefore likely the first.

Biosecurity NZ’s Anderson told the hui a plan of attack needed to be developed before the Government committed to putting money towards the Bay of Islands’ situation.

Meanwhile, Walsh said the next step was to get a full handle on caulerpa’s Bay of Islands’ distribution.

Northland Regional Council (NRC) and Niwa divers have checked 88 sites across the eastern Bay of Islands. Further urgent checks are continuing.

Deputy chair Jack Craw said the NRC was spending $5000 a day on caulerpa.

Walsh said the work would inform exactly where the anchoring ban’s outer boundary was.

This MPI map shows the transects dived by the NRC and Niwa checking for caulerpa presence in the week leading up to the Te Rawhiti caulerpa hui. Caulerpa has been found on all orange or red transect lines. Photo / MPI

Divers will check along the mainland coast towards another important boat anchorage at Opunga and Assassination Cove.

Caulerpa has been found in 18 locations to date around Omakiwi Cove and out into the Albert Channel, about halfway between the mainland Omakiwi and Urupukapua in the Ipipiri Islands.

There has been no caulerpa found on these islands.

Matauranga Māori and maramataka principles will be part of trials to get rid of the pest, with those at the helm warned to make sure the most qualified tohunga were chosen for this role.

This kaupapa potentially included the use of raupō and flax mats atop the caulerpa. The timing of eradication options would also be matched with traditional knowledge.

Great Barrier Island caulerpa governance group deputy chairman and mana whenua representative Martin Cleave said MPI was moving more quickly on the Bay of Islands find than it had on the island.

Rawhiti’s Rana Rewha reveals New Zealand’s first mainland caulerpa infestation

Reluctant hero Rana Rewha (Ngati Kuta) has been roaming the coastline of Bay of Islands’ Rāwhiti and surrounds for 40 years.

He wears almost more environmental restoration-themed potae (hats) than the fingers of both hands can count. So when he saw a seaweed he didn’t recognise washed up on Omakiwi Cove’s slightly stony beach at low tide on May 3, he started wondering.

Coincidentally, the next day hapū member Bob Willoughby sent out an email to hapū about the new seaweed caulerpa. Rewha instantly recognised what he had seen and photographed on the beach at Omakiwi Cove.

Caulerpa at Omakiwi Cove. Photo / Susan Botting

The rest was a flurry, his until-then unknown seaweed photo emailed to the Ministry for Primary Industries then identified by Niwa scientist Dr Irene Middleton. Middleton went to the beach with Rewha on a visit from Whangārei.

For Rewha, it was a lightbulb moment that made him realise what he was seeing anew. Rewha’s environmental potae are alongside others he wears that include being a kaitiaki of the history of his people in their ko iwi and artefacts.

“Now I don’t just look for ko iwi and artefacts, I look for caulerpa too,” Rewha said.

Rewha’s mandate is to collect ko iwi and artefacts for historical authorities and his Ngāpuhi hapū Ngati Kuta and Patukeha respectively.

Climate change-induced sea level rise is contributing to growing erosion of the beaches and shoreline he roams, exposing ancient burial areas and long-hidden artefacts.

Finding out the unusual seaweed was caulerpa made him feel lost. He wondered where to from here.

Omakiwi Cove is a place that holds special significance for his people. It is tapu and its history is filled with stories.

The reluctant hero’s eagle-eyed spotting has been praised by many in his community.

His find has led to the identification of caulerpa in dense mats across Omakiwi Cove and beyond, 16ha to date, in New Zealand’s second-biggest caulerpa infestation.

Rewha is among those now playing a key role in local mana whenua anti-caulerpa efforts.

■ Local Democracy Reporting is Public Interest Journalism funded through NZ On Air