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Diplosoma, the only time this species was observed on the Islands, in summer 2008

M. Desraspe

In summer 2008, a private-sector diver observed an unknown aquatic species at the Havre-Aubert marina on the Magdalen Islands. This experienced and knowledgeable diver, able to detect the presence of non-native species, immediately reported his discovery to the biologists at the Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec (MAPAQ) and the Department of Fisheries and Oceans (DFO) involved in monitoring invasive species on the Magdalen Islands.

Analyses showed that they were dealing with a new invasive species, the sea squirt Diplosoma listerianum, an invasive colonizing sessile tunicate. Sea squirts are filtering organisms that feed primarily on phytoplankton, bacteria and organic particles suspended in the water. Colonies of this particular Diplosoma form thin gelatinous layers that can cover up to 20 cm.

Diplosoma has been observed along the American east coast since 1993 and is now present from Cape Cod, Massachusetts to Casco Bay, Maine. This was the first time this species was observed in Canadian east coast waters. Although it is nearly impossible to affirm with any certainty how this tunicate was introduced to the Islands, fouling on ships’ hulls is the most plausible introduction vector.

Because of the major ecological and economic impacts associated with invasive tunicates, this discovery was of considerable concern to scientists. To measure the scope of the situation, a 14-member joint DFO and MAPAQ scientific team conducted an evaluation of the Havre-Aubert marina, fishers’ wharf and harbour in summer 2009. Divers equipped with underwater cameras surveyed Diplosoma listerianum and characterized the site (other species present and environmental conditions).

No observations in 2009

No D. listerianum specimens were observed in Island waters in 2009. This may mean that the specimens observed in 2008 failed to survive the winter and that the species is no longer present or that there are not enough individuals present to be detected by means of the sampling methods used so far. During the next few years, regular monitoring and the use of new detection methods should allow us to learn more.

In fact, genetic detection tools are being developed at the University of Prince Edward Island. A genetic probe could be used as early as the summer of 2010 to improve our detection capability, strengthen our ability to take action quickly and thus, prevent the establishment of new invasive species on the Magdalen Islands.

Nathalie Simard, Science
Selma Pereira, Magdalen Islands Area
Madeleine Nadeau, MAPAQ, Magdalen Islands