ENVIRONMENTAL-EFFECTS ON THE GROWTH AND DEVELOPMENT OF EASTERN OYSTER, CRASSOSTREA-VIRGINICA (GMELIN, 1791), LARVAE - A MODELING STUDY

The effects of temperature, food concentration, salinity and turbidity on the growth and development of Crassostrea virginica larvae were in vestigated with a time-dependent mathematical model. Formulations used in the model for larval growth are based upon laboratory data. Simula tions were done using temperature conditions characteristic of Laguna Madre, Galveston Bay, Apalachicola Bay, North Inlet and Chesapeake Bay . These simulations show that the duration of the planktonic larval ph ase, which is determined by larval growth rate, decreases at lower lat itudes in response to warmer water temperatures. Also, oysters in the more southern locations have a longer spawning season during which the oyster population can produce more larvae. Simulations were done for Galveston Bay and Chesapeake Bay using idealized time series of food s upply that included higher concentrations in the spring, summer or fal l. Additional simulations considered the effects of increased food sup ply in both spring and fall seasons. The results show that shifting th e period of enhanced food supply from March-April to April-May, when t emperatures are warmer, reduces the minimum larval planktonic period f rom 44 to 34 days. Shifting the fall bloom from August-September to Se ptember-October, however, does not appreciably change the minimum larv al planktonic period. The final set of simulations considered the effe ct of low salinity events and turbidity on the planktonic period of th e larvae of Crassostrea virginica. By imposing a simulated low salinit y (5 ppt) event of one month duration in August, the larval planktonic time is increased by about 39% over normal August salinities. Turbidi ty concentrations less than 0.1 g l-1 result in slightly decreased pla nktonic times. These model results show clearly the importance of ambi ent environmental conditions in determining the planktonic time of lar vae of Crassostrea virginica, and hence their ultimate recruitment to the adult oyster population.