Styela clava, commonly known as the clubbed tunicate, can form dense colonies of up to 1500 individuals per square metre, competing for space and food with native species such as mussels and oysters. They are highly effective filter feeders, preying on larvae of commercially important fisheries species and impacting native biodiversity. Styela clava can grow rapidly on marine farming lines, vessel hulls, and other structures, increasing maintenance, harvesting, and fuel costs.

This pest spreads via vessels, either as larvae in ballast water or as hull fouling, and can also be dispersed as larvae carried by water currents.

It has been detected in Otago, found on artificial structures in Otago Harbour. Styela can impact marine farms, reduce native biodiversity, and increase maintenance costs for vessels and infrastructure. It has not been detected in Southland, and efforts are focused on preventing its spread further South.

• Size: Up to 160 mm long.
• Appearance: Long, club-shaped body on a tough stalk with a leathery, knobbly surface. Color ranges from brownish-white, yellowish-brown, to reddish-brown. It often appears fuzzy underwater.
• Distinctive Features: Two closely spaced siphons at the top of the body, usually surrounded by warty little bumps.
• Habitat: Found up to 25 m deep, attaching to rocky coastlines, reefs, boat hulls, piers, pontoons, and aquaculture structures. Prefers sheltered sites but can be found in semi-exposed waters.

Late summer to early autumn (January to April in Southern Hemisphere). This period often coincides with peak settlement and when individuals are most visible. Growth is typically rapid during warmer months, making colonies more prominent.

It is an offence to breed, knowingly communicate, exhibit, multiply, propagate, release, or sell, an unwanted organism (Biosecurity Act 1993).