Bay of Islands invasive caulerpa battle gears up with $10 million boost

The main Bay of Islands caulerpa eradication barge with a smaller vessel alongside for bagged waste, which will take the bags to shore while the main barge keeps working. Photo / Northland Regional Council

Northland’s world-leading caulerpa eradication trials are taking a major step forward with a new national $10 million research funding boost, Northland Regional Council chairman Geoff Crawford says.

Research trials on the eradication of the invasive exotic pest at Bay of Islands’ Omākiwi Cove epicentre are already removing three tonnes of caulerpa from the seafloor daily.

Crawford said many people around New Zealand were eagerly awaiting the trial’s outcome.

New signage at Whangārei Harbour's Onerahi boat ramp reminds boaties to keep an eye out for exotic invasive caulerpa. Photo / Susan Botting

The goal was to use the new government funds to significantly improve the mechanical eradication efficiency and expand towards doing this work on industrial scale.

The New Zealand-first eradication method could eventually be used around the country and overseas.

NRC chairman Geoff Crawford on the caulerpa eradication barge with its South Island gold mine-sourced trommels in Omākiwi, Bay of Islands. Photo / Northland Regional Council

“This is a race. There is tremendous pressure to get this all moving,” Crawford said.

“We have no choice but to step forward with this new technology development. If we do nothing, the invasive pest will continue to grow and smother ecosystems, as is already happening at Omākiwi and around New Zealand,” Crawford said.

The research funding will be used towards adding a large underwater tractor unit that travels over the sea floor to the mechanical dredging trials, which began in Omākiwi Cove at the start of this year.

This will enhance the already internationally groundbreaking caulerpa eradication dredging barge technology.

The tractor unit has been designed by the same local Ōpua-based dredging and marine construction company, Johnson Bros, that developed initial mechanised eradication technology trialled at Omākiwi Cove with the support of earlier government funding.

This has now evolved to include two giant rotating cylinders called trommels, brought north from South Island gold mining operations to add to the trial’s caulerpa eradication efficiency.

Former South Island gold mine filtering cylinders, called trommels, are the latest addition in the eradication fight against caulerpa. Photo / Northland Regional Council

Crawford said all stages of the procedure worked towards making sure caulerpa fragments were not breaking off and therefore spreading the pest.

A piece of exotic caulerpa, the size of a freckle, is capable of spreading to cover the equivalent of a rugby field within a few weeks in the right conditions.

Crawford said there was no time to waste. Some of the Omākiwi Cove ecosystem where the exotic pest was first identified in May last year was now denuded of life as the invasive caulerpa infestation deepens in places.

“There’s bugger-all biodiversity.

“There’s nothing living underneath the [Omākiwi Cove] caulerpa, everything is dead. It has thickened up since last year.”

A boat anchoring ban is now in place across more than 1000ha in the Bay of Islands to fight caulerpa’s spread. In November, a similar ban around Aotea/Great Barrier Island was expanded to 10,000ha. The invasive pest has also been found at Great Mercury Island, the Mokohinau Islands, Kawau Island, Waiheke Island and not far from Leigh Marine Reserve.

Exotic caulerpa’s major threat area runs from Cape Reinga to East Cape and councils are now working more closely together, along with iwi and other community members, in what is a fight for traditional kaimoana gathering areas and New Zealand’s traditional “boatie” way of life.

Crawford said the upgrade of including the underwater tractor unit in the Northland-developed eradication technology was part of working towards an outcome that would have national and international implications.

Portland’s Carolyn and Steve Wells say protecting important kaimoana sources is an essential aspect in the fight against invasive caulerpa seaweed, which has been boosted with new education signage at boat ramps, including one behind them at Onerahi, Whangārei Harbour.

It would be the first effective, large-scale mechanical harvesting for the invasive pest on sandy-bottomed infestations in the world.

Crawford said he expected the trial to shift to a full operation scale within 18 months.

Former Portland fire chief and avid kaimoana gatherer Steve Wells said the boost for caulerpa eradication science research was essential.

Wells dives, fishes and gathers kaimoana with his wife Carolyn, something they have been doing for decades.

He said the growing threat of caulerapa invasion in harbours such as Whangārei is of major concern.

Scientific research trials towards eradication in the Bay of Islands were essential to finding an urgent solution.

Wells has started spreading the word among his diving mates as part of doing his bit in the caulerpa fight.

■ LDR is local body journalism co-funded by RNZ and NZ On Air.