Scientists working on methods to eradicate sea squirt

Scientists at Nelson's Cawthron Institute are working on developing a method to eradicate a marine pest which poses a huge risk to marine farming in New Zealand.

Aquaculture scientist Kevin Heasman said the independent foundation had been contracted by Biosecurity New Zealand for the project, and would be looking at finding the best way of getting rid of the sea squirt styela clava.

He said scientists had to consider environmental issues, the effectiveness of potential methods or solutions, and how well they could be used on man-made structures such as wharves and mooring lines.

The Fisheries Ministry last year commissioned development of a hydraulic-powered cutter head to gather and shred sea squirts, while minimising the escape of particles or spores which might grow elsewhere. Water and waste sucked up from underwater were passed through three sets of filters to prevent larvae draining back into the sea.

It was bult by NZ Diving and Salvage Ltd in stainless steel and tested on a native sea squirt species, didemnum vexillum, on a barge at Picton in 2002.

It was judged "largely successful".

The cutter cleaned up the barge hull, but only about half of the sea squirts on the seabed under the barge, because pebbles and other material were also sucked in to the cutter. It was also used as a stationary "waste disposal" by divers who gather the sea squirt manually and dropped armloads into the cutter housing. In other places, the vacuum hose alone was found to be effective at stripping the pest from the hull.

Plans for the suction device and cutter were passed to Biosecurity New Zealand before the current outbreak was recognised.

Mr Heasman said the team working on Cawthron's project, headed by biosecurity scientist Ashley Coutts, could not take too long to find a solution, and he expected initial trials would take three to four weeks.

Marine farmers in Canada used a vinegar solution to help control the sea squirt, and it was possible that vinegar could be a component of whatever Cawthron developed, because it was environmentally friendly, Mr Heasman said.

He said it would be challenging to find a solution for the leathery and tough organism, which was a prolific breeder.

Mr Heasman is working with Biosecurity NZ on the project. He said it was still trying to find out how far the sea squirt had spread.

The pest has been found in various sites, including Auckland's Viaduct Harbour, Lyttelton Harbour, and Kaiaua in the Firth of Thames.

- NZPA