An apparent lunar tidal cycle of phytoplankton blooming and community succession in the Gulf of Maine

Abstract

Concentrations of diatoms in the surface waters off Monhegan Island, Maine U.S.A., bloomed in phase with a lunar cycle during the summer of 1978. Highest abundances of diatoms were associated with the major spring tide of each month. Dinoflagellates were more abundant during the intervening minor spring and neap tides. Variations in vertical mixing during the spring to neap tidal cycle appeared to have influenced the vertical transport of chlorophyll upwards, thus causing an increase in the surface cell counts. Succession within the major phytoplankton communities was also related to the lunar tidal cycle. The community assemblages were most pronounced immediately before or after the spring tide diatom bloom, but not during. The transition from one community to another occurred during the more stable neap and minor spring tides. Epidemic blooms of the toxic dinoflagellate, Gonyaulax excavata (Braarud) Balech, occurred during major spring tides; prediction of the toxic blooms may be aided by using tidal data.