XVI International Botanical Congess
Spirolides, a recently described group of biologically active macrocyclic compounds, were found in concentrated plankton samples from southeastern Nova Scotia, Canada in late spring. The epidemiological profile of spirolide occurrence in shellfish has suggested a planktonic source. Analysis by liquid chromatography combined with ion-spray mass spectrometry (LC-MS) indicated that spirolides were concentrated within the 21 to 56 |m plankton size-fraction when gonyaulacoid dinoflagellates were dominant in the water column. Repeated attempts to isolate spirolide-producing taxa from enriched size-fractionated field samples produced numerous isolates of potential source organisms, including Alexandrium ostenfeldii, A. tamarense, Fragilidium subglobosum, Gonyaulax spinifera, Protoceratium reticulatum, and Scrippsiella trochoidea. Analysis of cultured species harvested in late exponential growth indicated only A. ostenfeldii produced spirolides. Morphological examination of field specimens and cultured cells of A. ostenfeldii by Nomarski and epifluorescence microscopy and by SEM showed that specimens from the western Atlantic coast closely resemble this species as described from Scandinavian waters.