Biosecurity New Zealand Moves to Contain Sea Squirt

21 March 2006

Biosecurity New Zealand is moving into a longer-term phase of its response to the invasive sea squirt, Styela clava.

The unwanted organism was first detected in New Zealand in August last year and subsequent surveillance of high risk locations around the country revealed its widespread presence in Auckland's Hauraki Gulf and smaller populations in Lyttelton Harbour and Tutukaka in Northland.

Senior Marine Adviser Brendan Gould says Biosecurity New Zealand has taken advice from some of the world's leading marine biosecurity and ascidian experts (the biological class the sea squirt belongs to) and the best scientific information available says it is not feasible, with today's available technologies, to eradicate it from New Zealand waters.

"The sea squirt is in such numbers in the Hauraki Gulf that you would never be able to accurately say you'd found the last one," Brendan Gould explains.  "You could have vast teams of divers working perpetually removing Styela clava from marine structures and you'd never complete the task.  Eradication on a national scale is simply not feasible."

Mr Gould says Biosecurity New Zealand has evidence that the sea squirt has been in the Auckland area for several years, and anecdotal stories indicate it may have been around for as long as ten years.

Over the remaining three months of this financial year (to end of June) the agency is putting in place a number of research initiatives.  These will look at ways to hold back the spread of Styela clava to high value areas such as the aquaculture-intense Marlborough Sounds, to gain a wider picture of where it is, and to better understand how the organism operates in the New Zealand environment.

"We're kicking off research into small-scale control measures in the two satellite locations of Tutukaka and Lyttelton.  In the case of Lyttelton, the aim is to scope the actual size of the population there and investigate treatments and controls that could reduce the risk of spread from there," says Brendan Gould.

Biosecurity New Zealand is also planning to survey a handful of additional marinas and ports that were not checked in the 24-location surveillance programme in November and December 2005.

"These additional locations will be selected on the basis of their proximity to high-value locations and the degree of vessel movements through to high-value locations," says Mr Gould.

Biosecurity New Zealand says raising public awareness of how the sea squirt is spread remains the most effective means of slowing its spread to non-infested areas. 

Imposing movement controls on vessels travelling from infested areas or into non-infested areas was investigated, but has been ruled out as impractical by both Biosecurity New Zealand and those involved in boating and transport.

"In the end, it is the responsibility of marine users, whether they're boaties, marine farmers, shipping companies, fishing boats… to ensure the sea squirt and other marine pests that could arrive here are not spread around the country," says Brendan Gould.

"Keeping vessel hulls clean of fouling is going to have to become as second nature as clicking your seatbelt."

Biosecurity New Zealand will continue to target the boating public and other marine users with information on how to prevent the spread by ensuring vessel hulls are cleaned and treated with anti-fouling paints where appropriate.

Since the sea squirt incursion was detected, Biosecurity New Zealand has spent approximately $1.5 million on researching the organism, surveillance for its geographical spread, following up more than 300 public calls about suspicious finds and undertaking public education and awareness.

A proposal for the long term management of Styela clava after the financial year ending June 2006 is being finalised.

Information about the seasquirt is available at:

Media contact:

Lesley Patston
Senior Communications Adviser
Biosecurity New Zealand
027 2051418



Last Updated: 23 September 2010

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