Invader threat to oyster farms

New Zealand's mussel and oyster industry is being threatened by the arrival of a Korean pest known as the sea squirt.

The clubbed tunicate styela clava was discovered in Lyttelton harbour by Biosecurity New Zealand.

It was also found recently in Auckland's Viaduct Harbour by a British marine scientist.

The sea squirt can grow up to 16cm long. It is a prolific breeder, spawning every 24 hours.

While Korea is its homeland, it is spread throughout the world, including parts of Australia, Biosecurity NZ said yesterday.

It was most likely to have arrived in New Zealand on the hull of a boat.

Biosecurity NZ senior marine adviser Brendan Gould said the consequences were potentially significant if it became established here.

"Clubbed tunicates can settle on lines and grow over shellfish cultures, including mussels and oysters," he said.

"They compete for food and space and also predate on shellfish larvae."

It tended to settle in sheltered areas such as bays and harbours.

Mr Gould said Biosecurity NZ would survey the Viaduct Harbour and nearby Freemans Bay to find out how widespread the sea squirt problem was.

"We should know the extent of the problem within a month."

Lyttelton Harbour would also be surveyed and treatment options investigated. Overseas the sea squirt had proved difficult to manage.

- NZPA