Styela sea squirt
Styeladae - Styela clava

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 to white, though not to be confused with the native species that is white to 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 and Wong et al 2011).

Control Methods

You can help prevent the spread of marine pests by:

• Regularly cleaning your boat’s hull – ideally keep fouling growth to no more than a light slime layer.

• Applying a thorough coating of antifouling paint and keep it in good condition.

• Ensure your hull is clean and free of fouling before you travel to a new area.

• Clean and dry any marine equipment (e.g. ropes, lines and pots) before using in a new area.

• Inspect areas on your boat that retain water for signs of marine life.

• Check for aquatic weeds tangled around anchors, trailers and other equipment.

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