Spatial and temporal aspects of Gyrodinium galatheanum in Chesapeake Bay: distribution and mixotrophy

Gyrodinium galatheanum (Braarud) Taylor 1995 is a common bloom-forming, pot entially toxic photosynthetic dinoflagellate in Chesapeake Bay, USA. Abunda nce of this dinoflagellate achieved densities >4 x 10(3) cells ml(-1) in th e mid- and upper Bay during late spring and early summer of 1995 and 1996. Ingestion of cryptophytes by this dinoflagellate was detected in most sampl es collected from the Bay. During late spring and early summer, mean number of ingested cryptophytes per G.galatheanum was as high as 0.46 for dinofla gellate populations located in surface waters of the mid- and upper Bay whe re dissolved inorganic phosphorus was low. Observations on the distribution of G.galatheanum in Chesapeake Bay show that populations of this dinoflage llate were usually restricted to waters with salinities ranging from 7 to 1 8 psu, seasonally progressed up the estuary, and usually co-occurred with c ryptophytes. Correlation analysis indicates that abundance of G.galatheanum and incidence of feeding was negatively correlated with dissolved inorgani c phosphorus, and that incidence of feeding was positively correlated with abundance of cryptophyte prey. These results indicate that G.galatheanum is an important component of the Chesapeake Bay phytoplankton during the spri ng and summer. Our results suggest that the phagotrophic capability possess ed by this phototrophic dinoflagellate may contribute to its success in a v arying-resource environment like Chesapeake Bay.