Caulerpa invader seaweed found in Bay of Islands, Northland

Metres-long giant caterpillar-like swathes of bright green invasive caulerpa seaweed washed ashore at Okupu Beach in Great Barrier's Blind Bay. Photo / Sid Wales

The invasive seaweed caulerpa has been found at Rāwhiti in the Bay of Islands, just days after Northland authorities slammed the Government for being too slow to deal with what it calls the world’s worst marine seaweed pest.

The find is the first time the “foot and mouth” of marine seaweed pests has been found in the country outside of its Great Barrier Island stronghold.

Several of the island’s key harbours have been shut to boat anchoring since October in an effort to halt the spread of the seaweed, and traditional kaimoana cockle beds have died.

Caulerpa has also been found in a small presence to the south on the southwest of Great Mercury Island, where crayfish pots are banned in some spots as a result.

This week a member of the public found the 20 centimetre clump of suspected caulerpa brachypus washed up on the beach at Rāwhiti, a small beachfront town roughly 27km from Russell in the Bay of Islands.

The person took a photo and sent it to the Ministry for Primary Industries (MPI) which has indicated it is likely the exotic caulerpa.

Niwa scientists from Whangārei, who have worked on the Great Barrier Island caulerpa response, visited Rāwhiti to help identify the seaweed.

Northland Regional Council (NRC) earlier this week criticised the Government for being too slow to adequately deal with the Great Barrier Island infestation.

MPI national caulerpa response lead John Walsh will travel to Rāwhiti on Wednesday for an urgent hui about the find.

New Zealand's caulerpa response leader MPI's John Walsh at NRC in Whangārei. Photo / Susan Botting

NRC deputy chairman Jack Craw said the Government should have a proactive plan in place to deal with any new outbreaks.

He said it was the “foot and mouth” of marine pests and the worst of pests in the marine habitat that he had seen in 40 years of biosecurity management.

Meanwhile, NRC biosecurity working party chairman Geoff Crawford said the alarming Rāwhiti find was the worst kind of news to hear.

He said it would likely have come to the Bay of Islands in a boat anchor well. Great Barrier Island is only 100km from the Bay of Islands by sea and caulerpa is spread more so by boat anchors than hulls.

Crawford said caulerpa had the potential to devastate the Kiwi way of life for those who lived, worked or played in areas such as Rāwhiti where it was found. The find posed a huge threat to the Bay of Islands’ environmental, economic, social and cultural features.

Seventy per cent of New Zealand’s boats are found along the coasts of Waikato, Auckland and Northland. Boaties from Auckland and beyond often head north to the Bay of Islands, many calling into Great Barrier Island en route.

Caulerpa can spread rapidly, growing from a fragment as small as a freckle to cover an area the size of a rugby field in just a few weeks in the right conditions. It forms a carpet across the seafloor that smothers all in its path, killing traditional shellfish and kaimoana gathering areas.

Cyclone Gabrielle saw 100 tonnes of caulerpa wash up in Great Barrier Island’s Blind Bay – just 18 months after the pest was first identified there.

NRC has become so worried about the invader’s threat it set up a new emergency response unit two weeks ago, to swing into action, should caulerpa be found. This includes suction pipes to vacuum the pest off the sea floor.

Caulerpa was first found in New Zealand in 2001, the outbreak managed by the Government’s MPI.

MPI’s Walsh said the risk area for the new exotic marine pest ran from Cape Reinga to the East Cape - a 1000km stretch.

Crawford said NRC would be out at selected coastal locations on Saturday urgently checking for caulerpa in Tūtūkākā, Whangaruru and Whangaumu.

Their work would be subject to getting the all-clear after Friday’s tsunami beach threat alert triggered by a 7.7 earthquake in the Loyalty Islands about 2000km north-west of New Zealand.

Northland Regional Council biodiversity and biosecurity working party chair Geoff Crawford. Photo / Susan Botting

He said this urgent NRC work was being done in support of MPI’s Rāwhiti mission and is being funded by MPI.

Crawford said NRC’s view was that caulerpa should be eradicated not simply contained. Quick action was essential to make this happen.

A Delaware, United States, community got rid of a new caulerpa infestation in just 17 days by swinging into action with a pre-organised plan of attack.

Meanwhile, however, the pest covers 30,000 hectares in the Mediterranean after a small piece of caulerpa escaped from a university in Monaco and nothing was done.

Crawford represented New Zealand in the world spearfishing championships in the Mediterranean in 2014 so has seen the consequences of doing nothing after its arrival.

He said there was “bugger all” fish and that he’d had to go down to 45 metres deep to find any.

Caulerpa thrives on sandy seafloors but is spreading over rocky areas and up kelp stems on Great Barrier Island.

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