Survival of dinoflagellate blooms in the western English Channel

Abstract

DURING the summer of 1976, for the second successive year, blooms of the dinoflagellate Gyrodinium aureolum Hulburt have occurred at the western entrance to the English Channel. The influence of tidal mixing on the temperature structure of the water column and the availability of light and nutrients for phytoplankton growth in this region have already been described^1,2. Here we report a frontal movement in response to the cycle of tidal mixing induced by the alternation of neap and spring tides, and suggest that plant populations both in surface water on the stratified side of the front and in the thermocline are dependent on the associated periodic release of nitrate and inorganic phosphate from the cold, nutrient-rich, bottom layer. We also describe the effects of phytoplankton on nutrient gradients across the thermocline.