MODELING THE VERTICAL-DISTRIBUTION OF OYSTER LARVAE IN RESPONSE TO ENVIRONMENTAL-CONDITIONS

A size-structured, time and vertically-dependent model was used to inv estigate the effects of water column structure on the distribution of larvae of the oyster Crassostrea virginica. Formulations used to model larval growth and behavior are based upon laboratory studies. Simulat ed vertical larval distributions obtained for conditions representativ e of a well-mixed, partially stratified and strongly stratified water column illustrate the effect that salinity and temperature gradients h ave on moderating larval swimming and hence on larvae vertical locatio n. For well-mixed conditions, smaller larvae are dispersed throughout most of the water column. For strongly stratified conditions, the smal ler-sized larvae cluster within the region of strong salinity change. Intermediate-sized larvae cluster within or directly below the region of strong salinity change. The oldest larvae are found near the bottom for all salinity conditions since their location is determined primar ily by sinking rate. Additional simulations show that diurnal salinity changes interact with larval behavioral responses to create patchy la rval distributions. Finally, simulations show that the inclusion of an upwelling or downwelling velocity can overwhelm the behavioral respon ses of smaller larvae and result in much different vertical distributi ons. The simulated vertical larval distributions show that changes in larval migratory behavior which are brought about by changes in the ve rtical salinity gradient can significantly alter larval distribution p atterns. These, when combined with horizontal advective flows, have im portant implications for larval dispersal.