Encystment in a Dynamic Environment: Deposition of Dinoflagellate Cysts by a Frontal Convergence

Abstract

The dinoflagellate Gyrod~n~urn uncatenum forms massive summer red tides in Chesapeake Bay (USA) and tributary estuaries These blooms are delimited in the downstream direction by estuanne fronts which may serve to concentrate and recirculate the population Toward the end of the bloom cycle, G uncatenum sexual stages accumulate in the frontal convergence and are transported downward along the frontal interface These stages are retained below the pycnocline in net upstream flowing bottom waters and settle out into the sediments along the subsurface transport pathway Examination of s e d ~ m e n t s indicates that major deposits of cysts of G uncatenurn are bounded in an upstream direction by a b e n t h ~ c front (where the pycnocllne intersects the bottom) Above this area, motile cells and sexual stages are absent from the water column and cysts are absent from the sediment Streamflow-induced variations in the location of the estuarine front in 1979 and in 1980 result in deposition of cysts in different regions predictable from examination of the location of the convergence Thus it IS proposed that the convergence zone of the estuarine front and the associated pycnocline serve to transfer encysting dinoflagellate forms from surface waters to their ultimate seed-bed locations