Biosecurity New Zealand investigates ‘sea squirt’

6 October 2005

Biosecurity New Zealand is investigating a confirmed find of the exotic marine pest the ‘clubbed tunicate’ (sea squirt), Styela clava in two New Zealand locations.

The clubbed tunicate has been found in Auckland at the Viaduct Harbour and in Lyttelton Harbour in Christchurch. The Auckland find was made recently by a visiting UK marine scientist and the Lyttelton specimen was located as a part of routine baseline port surveys undertaken by Biosecurity New Zealand.

The clubbed tunicate is a tough, leathery club-shaped organism that grows up to 160 mm long. It is a prolific breeder, spawning every 24 hours or so from maturity. The tunicate tends to settle in protected areas such as bays and harbours, out of wave action. It is frequently found on wharves, aquaculture structures and equipment, boat hulls, mooring lines and other man made structures.

The clubbed tunicate originated in Korea, but is now spread throughout much of the world, including parts of Australia. It can travel on the hulls of boats (hull-fouling) or in bilge water. Hull-fouling is the most likely source of its arrival into New Zealand.

Biosecurity New Zealand’s Senior Marine Adviser, Brendan Gould, says there are potentially significant impacts if the clubbed tunicate becomes established in New Zealand waters – particularly for the aquaculture industry.

“Clubbed tunicates can settle on lines and grow over shellfish cultures, including mussels and oysters. They compete for food and space and also predate on shellfish larvae.”

Mr Gould says Biosecurity New Zealand’s initial response is to survey the Viaduct Harbour and nearby Freemans Bay to determine just how widespread the organism is.

“We’re moving quickly to set up this delimiting survey and we should know the extent of the problem within a month.”

If necessary, the survey will extend to the whole Waitemata Harbour. A survey of the Lyttelton incursion will also be carried out.

Brendan Gould says work is also underway to have the clubbed tunicate declared an unwanted organism, which will allow Biosecurity New Zealand to implement control measures under the Biosecurity Act.

Potential treatment options will be investigated once it’s established how just how widespread the pest is. Overseas experience, however, has demonstrated clubbed tunicate is difficult to manage.

Biosecurity New Zealand will be asking the aquaculture industry, boaties and wharf users for help identifying any further clubbed tunicate. Awareness material with photographs and information about the pest is being prepared and will be circulated to those most likely to come across the clubbed tunicate.

ENDS

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