Decimeter scale heterogeneity in the plankton during a pycnocline bloom of Gyrodinium aureolum

Abstract

Vertical heterogeneity of pelagic organisms in a subsurface bloom of Gyrodinium aureolum was studied in the Kattegat during August 1990. Maximum concentrations of 3.25 × 106 G. aureolum l-1 and 72 μg chlorophyll a l-1 were recorded in the pycnocline at a depth of 14 m with 5% of surface irradiance. Dinoflagellates were confined to a 1 m thick layer which contained more chlorophyll than the rest of the water column. In situ primary production rates suggested a phytoplankton turnover time of 1 d. Bacterioplankton production and turnover rate and microzooplankton abundance were significantly reduced in the dinoflagellate layer. -Authors