The effect of seasonal variability on the germination and vertical transport of a cyst forming dinoflagellate, Gyrodinium sp., in the Chesapeake Bay

Seasonal dinoflagellate blooms frequently occur in estuaries such as the Chesapeake Bay. Studies have shown that environmental factors such as temperature, salinity, light intensity, nutrient availability and physical mixing can affect the seasonal and vertical distribution of motile dinoflagellates. Furthermore, these environmental factors can affect the life history of cyst forming dinoflagellates by inducing the formation of dormant cysts in unfavorable conditions and by inducing cyst germination in favorable conditions. A generalized, dynamic model, developed in Stella II©, is proposed to examine combined effects of environmental processes on the life history and transport of a cyst forming dinoflagellate, Gyrodinium sp., in the Chesapeake Bay. The proposed model is arranged as a one-dimensional vertical column with no lateral migration or emigration to examine the role of local cysts in the formation of blooms. Two sampling stations provided by the EPA Chesapeake Bay Program, one at the mouth of the Potomac River (LE2.3) and the other in the main stem of the Chesapeake Bay (CB5.2), were used for comparison. Calibration was attempted using the Maryland Phytoplankton Taxon Survey, also provided by the EPA Chesapeake Bay Program, at MLE2.2 (a location upstream from station LE2.3). Observed cell concentrations for the winter and fall did not coincide with the cell concentrations calculated from the model for station LE2.3. This discontinuity suggests that cell migration from other portions of the Chesapeake Bay and the Potomac river could have contributed to the majority of observed winter and fall concentrations. Furthermore, observed cell concentrations at CB5.2 were the result of cell migration alone, due to the presence of a permanent pycnocline that inhibited cyst transport to the surface. The results of the proposed vertical transport model suggest that a three-dimensional model incorporating migration and emigration may be necessary in examining bloom formation.