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 t he Chesapeake Bay. Studies have shown that environmental factors such as temperature, salinity, light intensity, nutrient availability and p hysical mixing can affect the seasonal and vertical distribution of mo tile dinoflagellates. Furthermore, these environmental factors can aff ect the life history of cyst forming dinoflagellates by inducing the f ormation of dormant cysts in unfavorable conditions and by inducing cy st germination in favorable conditions. A generalized, dynamic model, developed in Stella II, is proposed to examine combined effects of env ironmental processes on the life history and transport of a cyst formi ng dinoflagellate, Gyrodinium sp., in the Chesapeake Bay. The proposed model is arranged as a one-dimensional vertical column with no latera l migration or emigration to examine the role of local cysts in the fo rmation of blooms. Two sampling stations provided by the EPA Chesapeak e Bay Program, one at the mouth of the Potomac River (LE2.3) and the o ther in the main stem of the Chesapeake Bay (CB5.2), were used for com parison. Calibration was attempted using the Maryland Phytoplankton Ta xon Survey, also provided by the EPA Chesapeake Bay Program, at MLE2.2 (a location upstream from station LE2.3). Observed cell concentration s for the winter and fall did not coincide with the cell concentration s calculated from the model for station LE2.3. This discontinuity sugg ests 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 concentrati ons at CB5.2 were the result of cell migration alone, due to the prese nce of a permanent pycnocline that inhibited cyst transport to the sur face. The results of the proposed vertical transport model suggest tha t a three-dimensional model incorporating migration and emigration may be necessary in examining bloom formation. (C) 1998 Elsevier Science B.V. All rights reserved.