Sea Squirt (Clubbed Tunicate)

Styela clava

Sea Squirt (Clubbed Tunicate)

Sea Squirt (Clubbed Tunicate)

Legal Status: Unwanted Organism - MPI
Status in New Zealand: Established
Organism: Water snails, crabs, shellfish, starfish, and other aquatic

This pest is present in Whangarei Harbour, Maharangi Harbour, Whangaparoa, Waitemata Harbour, Waiheke Island, Half Moon Bay, Tauranga Harbour (historically- hasn’t been detected since 2011), Tarakohe, Porirua Harbour, Nelson Harbour, Picton, Lyttelton Harbour, Otago Harbour.


  • Styela clava is a club shaped sea squirt (marine animal).
  • Individuals appear as a tough, leathery skinned cylindrical form, tapering to a stalk with a holdfast that anchors them to surfaces.
  • The sea squirt is usually brown in colour, and underwater often appears fuzzy with secondary growth coating it.
  • Styela clava individuals can grow up to 16cm long.
  • Underwater two short siphons or openings are visible at the top of the organism.

This sea squirt prefers to settle on hard surfaces, particularly man-made structures. It is most commonly observed on jetty and wharf pilings, on aquaculture structures and equipment, on ropes and lines, and on the hulls of infested vessels.

They may also be found attached to rocks, seaweed and on shellfish.

Styela clava can be mistaken for a native New Zealand species, Pyura pachydermatina, as they both have a stalk.

Pyura pachydermatina - a New Zealand native
Pyura Pachydermatina - a
New Zealand native

However, the stalk of Pyura pachydermatina is much longer – 2/3 to 3/4 the overall length of the organism. It is also white/purple in colour.


The Styela clava sea squirt poses potential threats to New Zealand’s aquaculture industry and biodiversity.

Deloitte, in conjunction with New Zealand Institute of Economic Research, estimated the cost of Styela from 2006 and 2011 is between $.01 million and $9.4 million in negative impacts. Most of the expected economic damage between 2011 and 2020 will be felt in Auckland and Waikato. By delaying the entry of Styela to Marlborough, a high-value region for aquaculture, the impacts are estimated to reduce by between $1.6 million and $53.5 million.

Report: Styela clava: Economic Impact Assessment. August 2011. Deloitte Download Report Link to PDF document (200 KB) (199 KB) (26 pages)


Styela clava is now known to be widely spread throughout the Hauraki Gulf. It has also been confirmed to be widespread but in low densities in Lyttelton Harbour (Port of Lyttelton and Magazine Bay Marina), and in the Tutukaka and Marsden Cove marinas in Northland.

There have also been detections of this organism on individual vessels in Picton, Nelson, and Opua. 

Styela clava, as with other fouling organisms, can be spread on the hull of vessels. It is able to settle and grow on existing hull fouling material and thus be transported to new locations.

To prevent the spread of Styela clava, it is important vessel owners ensure their hulls are regularly cleaned and anti-fouled.

Locations of confirmed Clubbed tunicate finds:

Styela clava Position Statement

Styela clava was first reported in New Zealand in Auckland in September 2005, and was subsequently found to be present throughout the Hauraki Gulf and the port of Lyttleton. Since 2005 Styela has been detected in Waikawa Marina (Picton - single specimen removed), Wellington Harbour (small known infestation on boats removed), Port of Nelson (known infestation removed), Marsden Cove Marina (Whangarei Harbour – unsuccessful control attempt, now established), Opua Marina (established),Tutukaka Marina (known infestation removed) and (in February 2009) Otago Harbour.

MAFBNZ led an initial response to the incursion into New Zealand. However, in December 2005 a technical advisory group of marine experts from New Zealand, Australia and North America determined that eradication was not technically feasible. The group recommended measures to slow Steyla's spread to allow time for further research and for stakeholders to establish their capability to engage in any long-term management of this species.

In 2008 the decision was made by MAFBNZ to cease Styela-specific work and focus on moving towards pathway management measures to target vessels or equipment that might spread pests. The decision was made in light of research findings that further demonstrated the complexity of controlling Styela due to its ecology, distribution and available response methods.

The decision also reflected that Styela is just one risk organism that marine stakeholders are concerned about. Of as much, if not more, concern are the potential risk organisms that may be present or arrive, about which we know little or nothing.

The Styela Advisory Group was disbanded in March 2008 and the Top of the North Marine Biosecurity Partnership was set up to focus on operational activities based on pathway management. This allowed the partnership to address the spread of a range of known and unknown non-indigenous species in our waters, rather than focus energy on a single species.

A number of additional partnerships and programmes focus on managing international and domestic marine pathways.

Public education campaigns targeting boaties and other marine users and encouraging them to keep their vessels and equipment clean and anti-fouled have been carried out.

General Documents

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Page last updated: 9 June 2016