Caulerpa at Te Rawhiti's Omakiwi Cove in the eastern Bay of Islands. Photo / NRC
Caulerpa at Te Rawhiti's Omakiwi Cove in the eastern Bay of Islands. Photo / NRC
Northland is facing at least a 10-year-long battle to eradicate the new marine seaweed superspreader, caulerpa.
“People might think it doesn’t affect them but it sure as hell does because everything is connected. The problem affects absolutely everybody,” Tūtūkākā-based ocean ecologist Glenn Edney said.
New Zealand’s first mainland infestation of the exotic pest was found at Omākiwi, Te Rawhiti in the Bay of Islands on May 3, and the Bay is gearing up for the annual influx of yachties and boaties.
The new pest is greatly concerning to those who live, work and play along Northland and New Zealand’s coast – including mana whenua, councils, boaties, divers, recreational and commercial fishers and tourist operators.
More than 1000km of New Zealand’s northeastern coastline from Cape Reinga to East Cape are at risk.
Caulerpa expert and Niwa’s national marine biosecurity research programme leader Graeme Inglis, who is based in Nelson, has shed more light on what the arrival of the pest seaweed means.
New Zealand is the first and only country on the globe to have a pest caulerpa brachypus infestation. There was no research that might help with understanding how it might behave here, Inglis said.
Inglis, who has been leading Niwa’s marine research programme for 20 years, said there are about 100 different species of caulerpa globally but New Zealand has nine native caulerpa. Native meaning they had evolved naturally within their own complex local food web that has its own checks and balances.
Three of the nine caulerpa are in the North Island and another in the South Island, which includes Stewart Island, the subantarctic Snares Islands and the Chatham Islands.
Problems arose when caulerpa jumped to new places overseas where it was not native and became an invasive pest, he said.
This happened predominantly through human activity as the pest caulerpa in New Zealand mostly spreads via fragments. Tiny pieces easily break off a plant in storms or through boat anchors, divers’ actions or fishing equipment.
Caulerpa spreads by breaking off from larger clumps, as seen here. Photo / Susan Botting
It is illegal to shift caulerpa from the beach.
Inglis said New Zealand had evolved in isolation from the rest of the world for centuries, meaning much of its marine ecosystems were unique. That in turn made the new arrivals an even bigger threat.
He said caulerpa grows and changes the environment in which it lives by carpeting everything in its path and turning it into a monoculture. The seaweed likes sea temperatures averaging above 15C.
The country’s native caulerpa was not a problem, Inglis noted.
Aotearoa now has two exotic pest caulerpas, caulerpa brachypus and caulerpa parvifolia. They are found naturally in Lord Howe Island, Norfolk Island, central and western Pacific including Tonga, and in Australia. In Indonesia and the Philippines, they are also farmed and harvested.
Tūtūkākā-based ocean ecologist Glenn Edney, who has been working with exotic caulerpa-affected communities on Great Barrier Island/Aotea, warned exotic caulerpa are capable of spreading from a piece the size of a freckle to cover the equivalent of a rugby field within a few weeks if conditions are right.
The two types of exotic caulerpa in New Zealand form messy, thick short carpets marching across the sea floor. Depending on the type, caulerpa is typically bright apple green as it grows, but can become yellowish if sunburnt in shallow water.
The Ministry for Primary Industries (MPI) said caulerpa, once established in Northland and New Zealand, would potentially reduce the nursery habitat for fish by crowding out native marine plant species. Caulerpa’s dense clumps can block fish from finding their food such as bottom-dwelling crabs, clams and worms.
Aotea/Great Barrier Island's Tryphena Harbour is now shut to anchoring boats due to caulerpa infestation in the key anchorage. Photo / NZME
Edney said the local fishery has the potential to be seriously affected by major caulerpa infestation as the quantity and variety of fish declined in heavily caulerpa-infested areas.
Traditional cockle-harvesting areas on Great Barrier Island have already died off under smothering exotic caulerpa carpets.
The invasive seaweed may affect tourism too. Rāhui and Controlled Area Notice bans in the Bay of Islands and Great Barrier Island/Aotea and Great Mercury Island/Ahuahu stop boaties anchoring in those areas, impacting tourist operators who rely on healthy coastal marine ecosystems for their business.
Edney said Northland’s regional climate is already being affected by the breakdown in natural ecosystems, including the increased quantity of rain Northland had been experiencing over the past six months. Ecosystem health is a key defence against human-induced climate breakdown.
Anyone who thinks they have come across caulerpa is encouraged to take a photo, note the exact location and complete MPI’s online reporting form at report.mpi.govt.nz/pest/ or contact Biosecurity New Zealand on 0800 80 99 66.
■ Local Democracy Reporting is Public Interest Journalism funded through NZ On Air
