| Abstract | During the summer in the southeastern Gulf of St. Lawrence, various species of Dinophysis occur in significant numbers near the thennocline in stratified coastal waters. These organisms also appear sporadically in inshore shellfish aquaculture and harvesting sites, possibly as a result of periodic meteorologically forced advection of the offshore populations into these locations. However, the evidence for the occurrence of diarrhetic shellfish poisoning (DSP) toxicity in shellfish from this region is weak, and, despite many tests, we have been unable to demonstrate significant levels of these toxins in the Dinophysis populations themselves. Nitrate is often not detectable at the depths where the maximum concentrations of Dinophysis are present in offshore waters, and this led us to try to induce DSP toxicity by nutrient enrichment experiments in microcosms. Although considerable growth was obtained by bath nitrate and ammonia enrichments, this did not lead to the production of DSP toxins. |
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