| Résumé | Spirolides are pharmacologically active macrocyclic imines discovered in plankton size-fractions and shellfish from the eastern toast of Nova Scotia, Canada. The gonyaulacoid dinoflagellate Alexandrium ostenfeldii was recently found to be the cause of spirolide toxicity. Analysis by liquid chromatography-mass spectrometry (LC-MS) showed that spirolide profiles were similar over time and depth within a site, but composition was markedly different among sites. The spatio-temporal distribution of spirolides in the water column is usually confïned to late spring (May and June), following the decline in the spring diatom bloom. Highest spirolide concentrations were found in the 26-56 pm plankton size- fractions, during periods when large (>20 pm) thecate dinoflagellates, such as Alexandrium, Dinophysis. Gonyaulax and Scrippsiella, were dominant. Spirolide concentrations in plankton at Graves Shoal were highly correlated with abundance of cells of Alexandrium spp. (r2=0.93), but attribution to A . ostenfeldii was complicated by the co-occurrence of A. tamarense, a morphologically similar species that does not produce spirolides. |
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