Recreational boaties asked to stay vigilant for marine pests

Recreational boaties are being asked to stay vigilant for marine pests to prevent them from taking hold in other parts of the country as we head into summer.

Mediterranean fanworm and the exotic seaweed caulerpa have become established around parts of the country's coastline in Auckland, Northland and Canterbury but have been kept out of others.

Biosecurity Minister Andrew Hoggard launched the Protect our Paradise campaign in Picton on Monday, asking boaties to undertake good biosecurity practices this summer, to avoid accidentally spreading invasive weeds or pests.

"Marine pests are really challenging for us, in some cases it may not even be possible for us to eliminate them, we can only control them, so limiting the spread is key.

"It's potentially a really costly invasive species that if we were to do nothing could cover a huge area and disrupt aquaculture, businesses and people's recreational enjoyment."

Hoggard said marine pests were often moved between regions on boat hulls and in bilge water, so paying attention to boat fouling and keeping vessels clean helped limit the spread.

"If you pull up anything on your anchor, put it in a bag and put it in the bin."

Hoggard said there had been some Mediterranean fanworm incursions in the Marlborough Sounds, but they had so far been able to prevent it from becoming established and the government was concerned about the potential impact on the aquaculture industry.

"We've got a great opportunity to create a lot more wealth from aquaculture, so keeping on top of marine pests will help that industry grow."

Marine pests in Marlborough

Biosecurity New Zealand, Marlborough District Council and Marlborough Sounds Marinas have spent the past decade working to keep the fouling pest Mediterranean fanworm from becoming established in the region's waters.

Port Marlborough is the largest New Zealand marina operator outside of Auckland with marinas at Picton, Waikawa and Havelock providing around 1050 berths and Mediterranean fanworm was first found in Marlborough in 2014 on a visiting recreational vessel in Waikawa Bay.

Marlborough Sounds Marinas manager Anouk Euzeby said vigilance was needed to ensure the region remained free of such pests and to protect the unique marine ecosystems of the Marlborough Sounds.

"At the marinas we ensure all vessels requesting a berth are screened and informed of biosecurity protocols. This proactive approach is vital for managing risks posed by incoming vessels from areas of the country where incursions are already established."

Marlborough Sounds ward councillor Barbara Faulls said that with warmer weather and Labour Weekend coming up, there would be more boaties out on the water.

"The Marlborough Sounds is a very popular boating area, with 1700km of coastline. We have a lot to protect here including tourism, aquaculture and our unique environment that we all want to continue to enjoy."

What is Mediterranean fanworm?

The Mediterranean fanworm, Sabella spallanzanii, is a tube-dwelling worm that can grow up to 80 centimetres in length and has a spiral crown of feeding tentacles that extends out of the tube and appears like a golden flower in the water.

The highly invasive marine pest has the potential to smother native species and disrupt marine farming.

It can form dense beds (up to 1000 individuals per square metre) that out-compete other species including native filter-feeding organisms for food and space. It can also clog fishing gear and dredges.

It was first discovered in Lyttelton in 2008 and an eradication programme using divers was launched. Two years later, it had become established the Waitemata Harbour and Biosecurity New Zealand said it was too established to be eradicated.

Surveillance work occurs in locations where Mediterranean fanworm has not yet established (Coromandel, Tauranga, Nelson and Picton), with small populations eradicted as they appear.

What about exotic caulerpa?

Exotic caulerpa are pest seaweeds - with two almost identical species of exotic caulerpa now in New Zealand waters - Caulerpa brachypus and Caulerpa parvifolia.

It was first found in New Zealand in July 2021 at Aotea Great Barrier Island. It has since been confirmed at Ahuahu Great Mercury Island, Te Rāwhiti Inlet in Northland, Kawau Island, Waiheke Island, Mokohinau Islands, Rakino Island, Fantail Bay, Coromandel Peninsula.

The two species now cover more than 1500 hectares of the upper North Island seabed. Density ranges from thick carpets in some areas to sparsely distributed plants in others.

More than 1000 kilometres of New Zealand's north-eastern coastline from Cape Reinga to East Cape are at risk.

It can compete with other species for space and upset the balance of local ecosystems which presents a risk to recreational, cultural, and commercial marine activities.

Exotic caulerpa can get snagged on anchors, chains and dive and fishing gear and be accidentally moved to new locations.

This year, the government allocated $5 million for an urgent work programme to develop technology to locate exotic caulerpa and get rid of it where possible, followed by another $10m to develop new tools aimed at removing the invasive seaweed.

There are legal restrictions on some anchoring and fishing activities in parts of Aotea Great Barrier Island, Ahuahu Great Mercury Island, and Te Rāwhiti Inlet in the Bay of Islands due to the high risk of spreading exotic caulerpa from areas of infestation.

How should I be cleaning my boat to prevent the spread of marine pests?

• All types of boats: check and clean any gear, the anchor and chain before you move during a trip
• Trailer boats: drain the bilge and clean when you get home
• Moored boats: keep your hull clean and maintain antifouling