Dinoflagellate distribution in the Southeastern Kattegat during an autumn bloom

Distribution and density of selected dinoflagellates in relation to the salinity distribution was studied in Laholm Bay, southeastern Kattegat in the autumn 1985. Obvious heterogeneity and patchiness was observed on four sampling occasions during an autumn bloom. During strong west winds some dinoflagellate species accumulated along the salinitygradients towards the coast, while one showed a gradient perpendicular to the salinity gradient. During calm and sunny conditions the dinoflagellates appeared in well defined patches, coinciding with areas of slightly lower salinity. This supports the viewthat.patchiness is size-determined by salinity gradients. The distinct patches formed in the central Laholm Bay covered an area of 21.4 and 8.3 km2 for Proroeentrum minimum (PAV.) SCHILLER and Ceratium furca (EHR.) CLAP. et LACHM. respectively. The calculated patch stability revealed critical patch lengths ranging from 1.2 to 9 km, depending on diffusion scales used. During the stable weather conditions prevailing the Ceratium furca patch was not large enough to be stable and withstand dissemination unless the diffusion scale was below 3 km, whereas the Prorocentrum minimum patch would be stable under all conditions tested.