Metres-long giant caterpillar-like swathes of bright green invasive caulerpa seaweed washed ashore at Okupu Beach in Great Barrier's Blind Bay. Experts fear the seaweed would devastate Northland’s harbours when it gets here.
Metres-long giant caterpillar-like swathes of bright green invasive caulerpa seaweed washed ashore at Okupu Beach in Great Barrier's Blind Bay. Experts fear the seaweed would devastate Northland’s harbours when it gets here.
Northland boaties will soon be able to have their say on a proposed new Biosecurity Act-backed top-of-New Zealand clean hull plan, aimed at fighting the spread of two new, highly invasive seaweeds on Great Barrier Island – and other marine pests.
The invasive seaweed species caulerpa brachypus and caulerpa parvifolia were first found by members of the public on Great Barrier Island in October 2021 and have also been discovered about 65 kilometres south of that location on Great Mercury Island off the Coromandel Peninsula.
Northland Regional Council (NRC) marine biosecurity manager Kaeden Leonard said it was hoped the proposed plan would be out for public consultation before the end of the year.
It would look at the way different marine pests were spread and address interrupting these with a range of rules. The Government has already put in place a ban on boaties accessing several Great Barrier Island harbours and bays to try to fight the spread of caulerpa brachypus and caulerpa parvifolia.
February’s Cyclone Gabrielle resulted in 40 tonnes of the seaweed washing ashore at Okupu Beach in Great Barrier Island’s Blind Bay – just 18 months after the marine pest was first identified in a small area on the island’s seafloor. Locals had to collect the seaweed in wheelbarrows and put it into wool bales.
Great Barrier Island is a year-round stopping-off point for boaties from around the top of New Zealand. It is less than 100km by sea from Northland’s Whangārei, the Bay of Islands, Mangawhai and many other Northland harbours now at risk.
This bright green invasive caulerpa seaweed, which is smothering the delicate marine ecosystem at Great Barrier Island, is a major risk to Northland’s east coast harbours.
Leonard said the new clean hull plan was being put together by New Zealand’s Top of the North Marine Biosecurity Partnership (TON) alliance between Northland, Auckland, the Waikato, Bay of Plenty Regional Council, the Department of Conservation and Biosecurity New Zealand.
The area accounted for 70 per cent of New Zealand’s maritime vessels, with boaties highly mobile and consistently travelling around this area. It also includes overseas boaties and international shipping.
Leonard said public consultation around TON’s proposed clean hull plan would likely happen before the end of the year. The plan included a rule controlling the spread of marine pests such as caulerpa on Great Barrier Island - via requiring all gear and equipment on moving boats to be clean and without fouling, something that was expected to start later this year.
He said the seaweeds had the potential to hit Kiwis’ core environmental, cultural, economic and social values.
“... we’re really aware that with caulerpa being in Great Barrier, it’s not far from our [Northland] doorstep, and early detection and a rapid response are key to successful management of new pests,” Leonard said.
Northland ocean ecologist Glenn Edney said even a tiny piece of the seaweed could grow to cover an area the size of a rugby field “within weeks”, and its arrival into Te Tai Tokerau would devastate Whangārei and other Northland harbours.
Edney, a founder of Te Wairua O Te Moananui Ocean Spirit Trust, said it was only a matter of time before the seaweed made its way to Northland, and a plan was needed before this happened. Eradication rather than control was needed, he said.
The short, bright green seaweed pest forms vast verdant fields on sandy harbour floors. At Great Barrier Island, it is also growing on rocky surfaces as well as up kelp stems. It is spread via fishing gear, boat anchors and wave action.
Tūtūkākā-based Edney said caulerpa brachypus and caulerpa parvifolia could live in less than ideal conditions for some time. Boat hulls were not as much of a problem for the pest’s spread. It was more about anchoring, or fishing gear.
The seaweeds could stay alive on anchors and anchor chains used in an infected area. They survived in damp anchor wells before anchors were once again brought out as boaties arrived in the next spot to stay. It could also spread via fishing gear.
Glenn Edney, founder of Te Wairua O Te Moananui Ocean Spirit Trust.
Edney said the whole of Northland’s east coast was at risk.
Anybody seeing the bright green seaweed on the sea floor should take photographs and note GPS co-ordinates, then call Biosecurity New Zealand’s exotic pest and disease hotline 0800 80 99 66. Information about the new seaweed invaders and what to do if finding them is available on NRC’s online pest hub: www.nrc.govt.nz/environment/weed-and-pest-control/pest-control-hub/?pwsystem=true&pwid=1055.
