What does it look like?
Styela sea squirts have a long, club-shaped body on a short, tough stalk. Its surface is tough, leathery, rumpled, and knobbly, ranging in colour from brownish-white through Not to be ocnfused with the native species that is white/purple with a much longer stalk (2/3 to 3/4 the overall length of the animal).
The styela sea squirt has been found from the low intertidal zone to water about 40m deep, but is most common at depths of less than 25m. In addition to growing on rocks, shell fragments and other organisms (e.g. oysters) it can also grow on a wide range of artificial surfaces such as pylons, buoys, mussel lines, wharves and jetties. In New Zealand, it has a preference for sheltered sites but overseas also is found in semi-protected waters on more exposed coasts.
Why is it a problem?
The styela sea squirt is able to colonise a variety of hard surfaces and tolerate wide ranges of salinity and temperature. It is also a highly efficient filter feeder, straining food particles from the water. These features make it a strong competitor and it is capable of forming monospecific stands and potentially out-competing native species.
The styela sea squirt is a hermaphrodite but is not considered to be self-fertile, except possibly by mechanical disturbance (McClary et al 2009). Animals release eggs and sperm into the water and the larvae are free-swimming for a 12-24h period before settling on suitable surfaces and metamorphosing into sessile adults. Spawning is believed to occur in waters above 15°C (McClary et al 2009; Wong et al 2011).
Please contact the Northland Regional Council if you think you have seen this pest.