Distribution and Abundance of the Toxic Dinoflagellate Gonyaulax excavata in the Bay of Fundy

Abstract

Water samples were collected for five consecutive summers (1980–84) in the Bay of Fundy at the surface and at 5 m to examine the distribution patterns of the motile stages of the toxic dinoflagellate Gonyaulax excavata, which has caused shellfish toxicity in this area for years, as well as occasional fish kills. In 1980 and 1981, 128 and 122 stations were sampled, respectively, and 84 and 41% of the samples contained G. excavata cells. Further sampling in 1982–84 was reduced to areas where most cells were observed in previous years. During this period, G. excavata was observed in 91–100% of the locations sampled. Despite variations in abundance of G. excavata cells from year to year, the overall distribution patterns were similar. The highest concentrations of cells occurred in the south-central and southwestern portions of the Bay in the area bounded by the Quoddy Region and Saint John, New Brunswick, and Digby, Nova Scotia. The distribution of various life cycle stages (plahozygotes, vegetative duplets, and sexually fusing cells) was similar to that of individual motile cells, suggesting that the annual blooms in this region behave as one large population. Few or no G. excavata cells were found at the head of the Bay or at the seaward approaches. Results suggest the prevailing circulation in the Bay and the presence of tidal fronts are dominant factors in retaining G. excavata and its life cycle stages in the south-central and southwestern portion of the Bay and that this accounts for its perennial occurrence in this area.