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CONTEXT
Invasive tunicates or ‘sea squirts’ are a type of aquatic invasive species (AIS), which pose a serious threat to the environment, economy or society. When AIS become established in a new habitat, they can exert serious ecologic and economic effects on the ecosystem.
Also known as the sea squirt, this marine animal (with a heart, stomach, intestines, etc) looks more like a blob of jelly. Its bag-like body is filled with water that will sometimes squirt out, hence the name. It is continuously processing water and extracting its nourishment and excreting waste. It gets its tunicate name from its thick skin which is compared to a tunic.
Since 1970, a new invading tunicate species has been reported every five years in Atlantic and/or Gulf waters. The clubbed tunicate (Styela clava) was initially established in an estuary of eastern Prince Edward Island (PEI) in 1998. This invasive species is causing significant problems for the mussel aquaculture industry by overgrowing mussels, reducing yields and increasing costs of harvesting and processing mussels. The spread and establishment of the clubbed tunicate into other mussel growing areas of PEI, Nova Scotia, New Brunswick and Quebec could have devastating effects.
The clubbed tunicate (Styela clava),
violet tunicate (Botrylloides violaceus), golden star tunicate (Botryllus
schlosseri), and vase tunicate (Ciona intestinalis) have been
discovered in waters in and around the Maritime Provinces. Although the
pathways leading to successful invasions are not well understood, tunicates may
be introduced into new aquatic ecosystems through ballast water, hull fouling
and transport on fishing gear. One other sea squirt, the colonial tunicate,
Didemnum, has been found west of Nova Scotia, on George’s Bank, between Nova
Scotia and New England.
CASE STUDY
The goal of the ‘Case Study of Tunicates in Maritime Canada,’ is to conduct targeted research and provide strategic science advice to help reduce the introduction and spread of tunicates throughout maritime Canada through prevention, early detection and rapid response mechanisms.
In one part of the Case Study, the Government of Canada is contributing $350,000 and the Province of PEI and the mussel industry $240,000 in dollars and kind for risk assessment, biological research, monitoring the incidence of tunicates in PEI, as well as local co-ordination of research efforts.
In a second part of the Case Study, Canada will provide an additional $400,000 to federal researchers for the monitoring of tunicates and other invasive species in the maritime areas of Newfoundland, Nova Scotia and New Brunswick, and Quebec.
This research is part of the framework document on AIS (Proposal for a Canadian Action Plan to Address the Threat of Aquatic Invasive Species) approved in September 2004 by the Canadian Council of Fisheries and Aquaculture Ministers (CCFAM).
Prevention
Once established, it is very difficult and expensive to control or eradicate AIS. Therefore, preventing new introductions and controlling the further spread of established species are the most effective means of addressing the threat of these organisms to aquatic ecosystems.
A number of activities will be undertaken including risk assessments and economic analyses to determine ecologic and economic impacts. As well, pathways of entry and spread will be examined, and the factors affecting the establishment of tunicates in aquatic systems will also be studied.
Early Detection
A high priority monitoring and surveillance program will be designed with stakeholders (e.g., mussel growers, recreational fishers, divers) especially at high risk locations and pathways of introduction.
Rapid Response
Rapid response is essential to minimizing the impact of AIS and controlling their spread. The effectiveness of existing mitigation measures will be studied and new measures will be developed.
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