The Clubbed Invader: Spotlight on Styela clava
Lurking quietly in sheltered harbours and bays, Styela clava – the clubbed tunicate – has made itself at home in our waters. Tough-skinned and leathery, this sea squirt makes its home on hard surfaces like wharf piles, mooring lines, and aquaculture gear.
Photo / Northland Regional Council
Originally from the northwest Pacific, Styela clava thrives in calm waters, from the low tide mark to depths of 25 metres, tolerating a wide range of temperatures and salinity. Once settled, it competes with native species and can clog marine infrastructure.
Confirmed regions where Styela clava has been reported include:
Auckland – widely established in Waitematā Harbour and many marinas
Northland – found in harbours including Whangārei
Waikato - West coast of the Coromandel Peninsula
Bay of Plenty – including Tauranga Harbour
Wellington – present in parts of the harbour
Lyttelton Harbour (Canterbury)
Otago Harbour – found near Dunedin
Eradicating this pest is no longer realistic – it’s simply too widespread. But all is not lost. Localised removal is still possible, especially in areas where its arrival could damage marine farming, biodiversity, or treasured recreation spots.
Because of its ability to spread via vessel hulls, equipment, and even shellfish movements, it’s considered a high-risk pest for uninfested areas. Monitoring and controlling its spread is a key focus for regional councils and Biosecurity New Zealand.
Interesting fact:
Marine pests like Styela clava can hitch a ride on store-bought shellfish—and spread if shells are dumped in the sea. That’s why we worked with supermarkets to help stop the spread. You can help by always putting shells in the landfill, not on the beach or in the water.
Styela on an oyster / Northland Regional Council