DIEL FLUCTUATIONS IN DISSOLVED FREE AMINO-ACIDS AND MONOSACCHARIDES IN CHESAPEAKE BAY DINOFLAGELLATE BLOOMS

The accumulation of phytoplankton biomass in recurring summer dinoflag ellate blooms of Chesapeake Bay is accompanied by large pools of disso lved organic matter (DOM). Two fractions of the DOM, free amino acids (DFAA) and monosaccharides (MONO), were measured at 3 h intervals in m ixed species dinoflagellate blooms (Katodinium rotundatum, Gymnodinium spp.) and related to productivity, biomass and photoperiod. Peak chlo rophyll levels for the three blooms were 28, 65 and 938 mu g l(-1). In general, DFAA and MONO concentrations increased with increasing bioma ss of bloom-forming species, reaching 203 and 844 mu g l(-1). MONO app eared to accumulate during the ay while there was no consistent patter n for DFAA. The accumulations of DFAA and MONO in blooms indicate that bloom production might stimulate microheterotrophy, thereby enhancing carbon and nutrient cycling in bloom-impacted regions.