Carpet sea squirt

Carpet sea squirt grows attached to hard surfaces and often looks like yellowish wax or paint dripping over structures such as ropes, mooring lines or mussel lines.

It can usually be distinguished from native sea squirts by its colour and by the fact it doesn’t feel slimy to the touch.

Carpet sea squirt can occur from the intertidal zone down to depths of at least 65 metres, in waters with salinity greater than about 25 PSU. It’s most commonly found on artificial structures, including wharves, mooring lines, and vessel hulls.

While it has also been recorded growing on natural surfaces like rocks, seaweed and seagrass in tide pools, estuaries, lagoons and open coastal areas, in New Zealand it appears to have only a limited ability to establish in natural habitats.

Carpet sea squirt is highly adaptable, reproduces quickly, and can build dense populations due to the lack of natural predators or diseases outside its native range. It can overgrow other marine organisms and releases chemicals that hinder the settlement of larvae, giving it a strong competitive advantage.

It spreads both sexually, by releasing larvae into the water, and asexually, through fragments that break off and form new colonies. In New Zealand, its breeding season is unusually long, lasting at least nine months of the year.

Larvae and fragments can be carried by water currents and ballast water, while human activity plays a major role in its spread through hull fouling and the movement of aquaculture stock and marine equipment between harbours.