Resting Cysts of the Toxic, Red Tide Dinoflagellate <i>Gonyaulax excavate</i> in Bay of Fundy Sediments

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<jats:p> During the winter of 1980–1981 sediment samples were collected from 115 stations throughout the southern Bay of Fundy to determine the distribution and abundance of Gonyaulax excavata resting cysts. An improved, semiquantitative method of cyst enumeration was developed for this purpose. Resting cysts of G. excavata were widely dispersed in the Bay, occurring both offshore and inshore, including the intertidal zone. The great majority of cysts occurred in a large, extremely rich deposit located offshore in the southwestern Bay of Fundy in a zone of fine brown mud at depths of 80–160 m. The location of this deposit was consistent with hydrographic and sedimentary processes in the Bay. Cyst concentrations ranged from 2000 to 8000 cysts∙cm<jats:sup>−3</jats:sup> wet sediment at many stations in the approximately 2000-km<jats:sup>2</jats:sup> deposit. Mouse bioassay tests of cyst extracts (prepared by sonication or boiling) indicated that the cysts were toxic, containing 2–5 × 10<jats:sup>−5</jats:sup> μg saxitoxin (STX) equivalent per cyst — the same range as for G. excavata motile cells in culture. Results support the view that the wintertime acquisition of G. excavata toxins by offshore and inshore molluscan shellfish is caused by ingestion of cysts. Results suggest that the offshore seed bed serves as the primary source of the motile cells which initiate the annual G. excavata bloom in the Bay of Fundy.Key words: cysts, Gonyaulax excavata, dinoflagellate blooms, red tide, paralytic shellfish toxins, shellfish toxicity, sediments, Bay of Fundy </jats:p>

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