Clubbed Tunicate
Styela clava
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The Clubbed Tunicate is an invasive solitary tunicate from the Western Pacific. It is one of the worst invasive alien species in the world. © DFO, St. Andrews Biological Station.
Origin and distribution
Observed distribution of Clubbed Tunicate in subregions of Canada's Maritime provinces.
Note: Observation within a subregion does not mean the species is found throughout it. Lack of observation within a subregion does not mean the species is absent from that subregion. It means that it has not been observed there.
The Clubbed Tunicate, native to the western Pacific, is invasive in many parts of the world. It has been present in Pacific Canadian waters since at least 1994 when specimens were collected in British Columbia in:
- Nanaimo
- Vancouver Island
- many areas in the Strait of Georgia
In Atlantic Canada, Clubbed Tunicate has been reported in:
- Prince Edward Island in the Gulf of St. Lawrence since 1997, where it is now found in several bays
- Nova Scotia on the southwest shore since 2012 and now from Cape Breton Island to the Bay of Fundy
- New Brunswick in the Bay of Fundy
Identifying features
- Body firm and wrinkled with little bumps, shaped like a water-filled wineskin
- Presence of a solid stalk
- Leathery texture
- Measures up to 18 centimetres, the stalk accounting for one third of its length
- Colour: brown
- Solitary, but may grow in very dense clumps
Similar species (native)
Among native species, Sea Potatoes and Sea Peaches are other solitary tunicates, but they are found growing alone or in small groups. The Sea Potato is shaped like a rattle and has a stalk that can reach 13 centimetres. The Sea Peach's body is firm and rounded and its skin is rough.
Stalked Tunicate (Styela montereyensis)
On the west coast, Clubbed Tunicate can be confused with Stalked Tunicate, but the latter can be distinguished by its regular longitudinal grooves and 1 recurved siphon.
Habitat
Clubbed Tunicate typically occurs between depths of 15 to 25 metres but has also been recorded at 40 metres. When located in some micro-habitats (e.g., under rocks) or sheltered habitats with low wave action (e.g., inlets, bays, harbours and marinas), Clubbed Tunicate can resist tidal immersion. This species can be found attached to a range of artificial substrates, including:
Clubbed Tunicate
- pier pilings
- jetty walls
- concrete structures
- submerged ropes
- buoys
- floating docks
- vessel hulls
Ecological and economic impacts
This species' ability to settle on a range of artificial surfaces causes dense fouling of fishing gear, moorings, and ropes and is difficult and time-consuming to remove. In Prince Edward Island, mussel lines and floating docks have been weighed down by heavy growth of Clubbed Tunicate, making them difficult to remove from the water. The tremendous density and abundance of this species in Prince Edward Island is considered a serious threat to the long-term economic viability of the shellfish industry.
Mode of arrival and dissemination
East coast
It is believed that Clubbed Tunicate has been introduced to the Atlantic coast of North America by commercial shipping and then spread through a number of potential vectors, including:
- aquaculture activities
- fisheries gear fouling
- commercial shipping
- recreational boating
West coast
It has been hypothesized that Clubbed Tunicate was introduced to Pacific North America with Japanese oyster shipments or hull fouling in the mid-20th century and then dispersed through intra-regional vectors such as aquaculture activities or hull fouling on commercial or recreational watercraft.
Government action
Scientific research
Fisheries and Oceans Canada is monitoring the distribution of invasive biofouling species (that is, aquatic species that live attached to hard surfaces) on the Atlantic and Pacific coasts to detect new invasions and track the spread of Clubbed Tunicate.
For further information
- Canadian Science Advisory Secretariat (CSAS) Publications
- Invasive Tunicate - Fact Sheet
- Biological Synopsis of the Invasive Tunicate Styela clava (PDF, 1,415 KB) Canadian manuscript report of fisheries and aquatic sciences 2807, 2007 - Fisheries and Oceans Canada
- Science advice from a risk assessment of five sessile tunicate species (CSAS SAR - 2012/049)
References
Vercaemer B. and Sephton D., 2014. Rapid assessment and biofouling monitoring of Halifax Harbour and Bedford Basin following the detection of three new invasive ascidians in Nova Scotia. Can. Tech. Rep. Fish. Aquat. Sci. 3063: v + 28 p.
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