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Biosecurity authorities are scrambling to get on top of an invasive seaweed species that threatens tourism and native species after it was spotted by divers near Te Kawau Tūmaro ō Toi Kawau Island.
Tourism operators and scientists have already sounded the alarm about the incursion of the fast-spreading caulerpa seaweed was found in areas around the Bay of Islands in May.
But divers have now found small, 20cm to 30cm patches of the underwater plant growing in the Hauraki Gulf near Kawau Island.
The seaweed is fast-growing and is known to smother shellfish beds and reduce diversity of fauna in the sea.
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Biosecurity New Zealand boss John Walsh said it was no surprise given the nature of the fast-spreading seaweed, his team is already planning a containment operation.
Working together with the Ngāti Manuhiri Settlement Trust and Auckland Council they will look to start control work “as soon as possible”.
Glenn Edney/Supplied
Boaties have been stopped from dropping anchor at harbours on Aotea/Great Barrier Island where caulerpa was found.
As a starting point they are considering the use of chlorine pellets under tarps, which is being tested in the Bay of Islands by Northland Regional Council. Also on the radar is suction dredging to remove the seaweed.
Walsh said they had been fighting to keep the seaweed under control for the past two years after it was found near Aotea/Great Barrier.
“This has been a sustained, thorough and collaborative effort to contain Caulerpa to known locations, better understand the pest and its challenges, trialling treatments, and working to prevent its spread,” he said.
“This includes legal controls on risk activities and widespread campaigns involving local communities, mana whenua, regional councils and others to educate people about Caulerpa.’’
Caulerpa can easily be spread to new locations and commonly caught up as tiny pieces of seaweed on vessel anchors and fishing gear.
Glenn Edney
The seaweed is fast-growing and is known to smother shellfish beds and reduce diversity of fauna in the sea.
On Aotea/Great Barrier, boats are banned from dropping anchor in three affected harbours as a means to stop the spread.
Walsh said that no overseas attempts to eradicate Caulerpa had yet been successful in areas the size of the finds in New Zealand.
In May, Te Rawhiti environmental restoration and pest control specialist Rana Rewha (Patukeha) said caulerpa had the potential to impact cultural, social, environmental, economic and spiritual aspects of life for mana whenua and everybody in the Bay of Islands.
Meanwhile, Ngāti Manuhiri Settlement Trust chief executive Nicola MacDonald said they are committed to protecting their rohe moana and “putting all efforts to remove and eradicate the invasive pest from our beautiful waters”.
Walsh told sailors to check their gear, especially anchors and chains, and people found any seaweed on their equipment, they should chuck it straight back in the waters it came from.
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