DIFFERENTIAL AGGREGATION OF DIATOMS

The relative species composition of diatom flocs formed in the presenc e of 2 diatom species was studied in a series of laboratory experiment s. The aim of this study was to investigate whether species compositio n in flocs reflected initial species composition or whether certain sp ecies were enriched in aggregates. In each experiment, 2 species with differing aggregation behavior were combined and aggregated. These exp eriments elucidate several mechanisms controlling aggregation of diato ms. Cells of Nitzschia angularis aggregated preferentially due to thei r high cell stickiness, which is a function of cell surface properties . Species such as Chaetoceros gracilis cause aggregation indirectly, b y generating transparent exopolymer particles (TEP) which, in turn, sc avenge cells into aggregates. Thalassiosira weissflogii did not form f locs itself, but was included in flocs formed by other species. Differ ential aggregation may lead to species succession during the bloom, an d to sequential sedimentation. Flocculation behavior Like that initiat ed by C. gracilis will most Likely result in 1 mass sedimentation puls e, scouring of the water column and the end of the bloom.