Clubbed Tunicate


[Image: Jeannine Fischer, MPI]


The clubbed tunicate (Styela clava, Herdman, 1881)

Status in New Zealand

Present in some areas of New Zealand

Legal status:

Under management


The clubbed tunicate is an ascidian that grows on both natural and artificial hard marine surfaces. It is most commonly observed on wharf pilings, aquaculture structures, ropes and vessel hulls. They may also be found attached to rocks, seaweed and on shellfish. The clubbed tunicate is found in low energy environments such as ports and harbours and it has wide physiological tolerances. It has been found to reach high densities of 500-1500 individuals per square metre and is an efficient suspension feeder. Because of these two features it can outcompete other species for habitat and food.

Why is it a problem?

The clubbed tunicate can outcompete other species due to it reaching such high densities and being an efficient suspension feeder. As a fouling organism it can decrease the productivity of cultured species and increase aquaculture processing and harvesting costs. It also results in higher fuel and maintenance costs for vessels. In Japan it has caused asthmatic symptoms in individuals who shuck fouled oysters in poorly ventilated areas.

A vessel discovered by Marlborough District Council with significant numbers of Styela clava present on the hull.

What do they look like?

Key Features

The clubbed tunicate has as a long, tough, leathery skinned cylindrical form, tapering to a stalk with a disc shaped holdfast that anchors them to hard surfaces. The sea squirt ranges in colour from yellowish to reddish to brownish and can grow up to 160mm in length. Underwater it often appears fuzzy with secondary growth coating it. Under water, two short siphons or openings are visible at the top of the organism. Similar looking native New Zealand species such as Pyura pachydermatina also have a stalk, however, their stalk is much longer.


[Image: Chris Woods, NIWA]


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