A potentially serious marine pest has been recorded in New Zealand for the first time.
The sea squirt clavelina oblonga has been found in the waters around Great Barrier Island, north-east of Auckland.
It was thought to have been introduced last summer and appeared to have established itself in a very short amount of time, Auckland Council says.
The council's biosecurity advisor, Samantha Happy, says they were working with Biosecurity NZ to find out more about the marine pest and how widespread it might be.
"It is difficult to know how a species will interact with our environment when it has not been observed here before," she says.
"Learning about the biology of introduced species is crucial in order to achieve successful management.
Samantha says the species was less visible in cold water and it may become more obvious closer to summer.
The council is asking boaties nearby to check and maintain their hulls to make sure the sea squirts are not hitchhiking, and to not wash their boats in Smokehouse Bay on the island.
The sea squirt is native to the southern Atlantic coast of North America and the Caribbean Sea, but has "invaded" Brazil, Cape Verde, and parts of the Mediterranean.