DOMOIC ACID PRODUCTION BY THE DIATOM ...

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In 1987, Pseudo-nitzschia multiseries was responsible for the domoic acid (DA) that resulted in the first ever incident of ASP and the closure of mollusc ...

Book of abstracts, p. 23. Xth International Conference on Harmful Algae, Oct. 2002, Florida

DOMOIC ACID PRODUCTION BY THE DIATOM Pseudo-nitzschia seriata CAUSES SPRING CLOSURES OF SHELLFISH HARVESTING FOR THE FIRST TIME IN THE GULF OF ST. LAWRENCE, EASTERN CANADA Stephen S. Bates*, Claude Léger, John M. White, Neil MacNair, James M. Ehrman, Maurice Levasseur, Jean-Yves Couture, Roger Gagnon, Esther Bonneau, Sonya Michaud, Gilbert Sauvé, Kevin Pauley and Joël Chassé *Fisheries and Oceans Canada, Moncton, New Brunswick, Canada In 1987, Pseudo-nitzschia multiseries was responsible for the domoic acid (DA) that resulted in the first ever incident of ASP and the closure of mollusc harvesting in eastern Prince Edward Island (PEI), located in the southern Gulf of St. Lawrence (sGSL), eastern Canada. Since then, there have been sporadic closures in PEI due to the presence of DA produced by P. multiseries, but always in the fall. On April 5, 2002, there was a closure due to DA, for the first time ever during the spring, of mollusc harvesting in 9 bays of northern PEI. Closures were expanded to portions of the Baie des Chaleurs (Quebec) and to the entire coast of eastern New Brunswick on April 19, then to portions of Cape Breton Island (Nova Scotia) on May 1, when it was discovered that the presence of the DA was more widespread. Such a broad extent of closures, encompassing most of the sGSL, suggests a wide-spread bloom of toxic diatom cells. The bloom was likely distributed throughout the sGSL by the prevailing water currents, which move towards the southeast. Water samples collected at each affected site showed that Pseudo-nitzschia seriata (identified by SEM) was the only potentially toxic diatom present, at concentrations up to 403,100 cells L-1. The highest toxicity in mussels was 200 µg DA g-1. Pseudo-nitzschia seriata, known as a “cold-water” diatom, is found only in northern latitudes. It is normally present at low concentrations year round in the Gulf of St. Lawrence, and was associated with high levels of DA in Magdalen Island sea scallops and with trace levels in soft-shell clams, since 1998. Twelve clones of P. seriata were isolated from several sGSL sites, and were grown in culture at 8°C. Initial tests showed that the clones are capable of producing DA during mid-stationary phase (day 25) in batch culture, although at low levels (< 1 pg DA cell-1). In late-stationary phase (day 51), levels had increased to ca. 7 pg DA cell-1. Further studies will determine the growth and toxicity of P. seriata at different temperatures.

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