TOXIN ACCUMULATION AND FEEDING-BEHAVIOR OF THE PLANKTONIC COPEPOD CALAMUS-FINMARCHICUS EXPOSED TO THE RED-TIDE DINOFLAGELLATE ALEXANDRIUM-EXCAVATUM

The planktonic copepod Calanus finmarchicus is a dominant member of th e zooplankton community in the lower St. Lawrence Estuary in eastern C anada. Blooms of the toxic marine dinoflagellate Alexandrium excavatum which produces high cellular levels of paralytic shellfish poisoning (PSP) toxins, occur during the period of high C. finmarchicus producti on in summer in this region. To study the feeding behaviour of C. finm archicus in the presence of Alexandrium spp., experiments were conduct ed in which female adult copepods collected from the St. Lawrence Estu ary between May and September 1991 were exposed under controlled condi tions to two toxic isolates of A. excavatum (Pr18b and Pr11f) from the estuary and to a non-toxic control (PLY173) of a closely related spec ies, A. tamarense isolated from the Tamar Estuary, Plymouth, U.K. Clea rance rates on non-toxic A, tamarense cells averaged 5.5 mi ind(-1) h( -1) but were near-zero with either toxic isolate. When presented with a mixture of A. excavatum and the non-toxic diatom Thalassiosira weiss flogii in varying proportions, C. finmarchicus fed upon the diatom but avoided the toxic dinoflagellate. Although feeding rates on A. excava tum were very low, toxin analysis by high-performance liquid chromatog raphy with fluorescence detection (HPLC-FD) revealed that the PSP toxi ns were accumulated in copepods exposed to toxigenic dinoflagellates. The toxin composition in copepods was similar to that of the toxic din oflagellate, but not necessarily identical, particularly after short-t erm (2-h) exposure, when relatively elevated levels of N-sulfocarbamoy l toxins were detected. The evidence suggests that C. finmarchicus ing ests toxic dinoflagellate cells, either mistakenly or during explorato ry bouts of feeding, and accumulates PSP toxins in its gut system and perhaps in other tissues.