In estuaries of New Jersey and James River, early-stage oyster larvae were randomly distributed throughout the water column and late-stage larvae were found frequently near the bottom. In New Jersey estuaries and Prince Edward Island, Canada, differential vertical distributions of oyster larvae were observed in relation to variations in biological movement with tidal phases and stratification. Biological movement of larvae has been suggested to explain observed patterns of oyster larval distribution in several estuaries.

Biological movement, defined as larval movement in the vertical direction influenced by larval characteristics such as larval size, density, and behavior, includes sinking and swimming of larvae, that is, all vertical transport except that due to vertical advection and turbulent mixing. Similarly, tidal currents, wind-driven circulation, and gravitational circulation promote transport of blue crab larvae into estuarine nursery areas and enhance their retention near settling areas in the northern Gulf of Mexico. Andrews suggested that the ultimate fate of bivalve larvae is strongly dependent on current regimes and flushing rates of estuaries. In the James River estuary, horizontal and vertical circulation and turbulent mixing associated with a frontal system combine to enhance upstream transport of oyster larvae and, thus, contribute to larval retention. Physical transport processes that enhance larval retention play a critical role in successful recruitment of larval organisms within outflux-dominant estuaries.

Physical transport, defined as larval transport not affected by larval characteristics but solely determined by physical processes, includes advection and turbulent mixing. Larval supply is influenced by a combination of physical transport and biological movement of larvae. For most marine invertebrates and fish this influx occurs during the planktonic larval stage and is a function of both concentrations of larvae in the water column and horizontal advection into the region, that is, larval supply.

Persistence of exploitable populations of marine invertebrates and fish is dependent on a high influx of new recruits into a population. Inclusion of biological movement, however, caused little change in the overall patterns of larval transport and still resulted in a west-east gradient, presumably because of frequent destratification in the shallow Mobile Bay system. Biological movement increased larval retention near the spawning area, thus providing a favorable condition for local recruitment of oysters. A persistent gradient decreasing from west to east in the model results at time scales of overall average, season, and each survey in 2006 suggests that the larval supply may be responsible for the corresponding gradient in oyster spat settlement observed over the past 40 years. The model reasonably reproduced the observed gradient in oyster spat settlement and bivalve larval concentration, although the model results were less dynamic than the data, probably owing to the simplified biological conditions employed in the model. Site- and larval-specific conditions, including spawning location, spawning stock size, spawning time, and larval period, were determined based on the previous studies. A hydrodynamic model was used to simulate physical transport, and biological movement was parameterized as a function of swimming and sinking velocity of oyster larvae. A three-dimensional larval transport model accounting for physical transport, biological movement of larvae, and site- and larval-specific conditions was developed.

Here we conducted a field and modeling study to investigate the larval transport of eastern oyster, Crassostrea virginica, in Mobile Bay and eastern Mississippi Sound, Alabama. Among the various factors affecting recruitment of marine invertebrates and fish, larval transport may produce spatial and temporal patterns of abundance that are important determinants of management strategies.

Size of oyster spat