DECIMETER SCALE HETEROGENEITY IN THE PLANKTON DURING A PYCNOCLINE BLOOM OF GYRODINIUM-AUREOLUM

Vertical heterogeneity of pelagic organisms in a subsurface bloom of Gyrodinium aureolum (Hulburt) was studied on the decimeter scale by a high resolution sampler in the Kattegat, Denmark, during August 1990. Maximum concentrations of 3.25 x 10(6) G. aureolum 1(-1) and 72-mu-g chlorophyll a 1(-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.