Nitzschia pseudodelicatissima - a source of domoic acid in the Bay of Fundy, eastern Canada

Circumstantial evidence is presented that domoic acid detected in softshell clams Mya arenana and blue mussels Mytilus edulis from the southwestern Bay of Fundy, eastern Canada, during July to October 1988 was obtained by feedlng on the pennate diatom Nitzschia pseudodelicatissima. T h ~s microalga was the most abundant organism observed in weekly samples collected at the surface, 10 m depth and bottom from nearly all of the 18 locations sampled during the same penod. Phytoplankton net hauls consisting principally of N, pseudodelicatissima contained levels of domoic acid up to 3.5 pg g-l Isolates of 9 dominant phytoplankton species occurring in the southwestern Bay of Fundy during July to October 1988 were cultured and tested for the presence of domoic acid; only N. pseudodelicatissima cultures produced the toxin at concentrations of 7.0 X 1 0 -l ~ to 9.8 X 10-l4 g cell-' Since cultures of N. pseudodelicatissima were not axenic, the possibility exists that either a n intra or extracellular microorganism is acting independently, or in association with the diatom, to produce domoic acid.