A modeling study of oyster larval transport in Mobile Bay and eastern Mississippi Sound, Alabama

Oysters and oyster reefs are very important components of estuarine and coastal ecosystems and economies. Among various factors affecting recruitment of oysters, larval transport may produce spatial and temporal patterns of abundance that are important determinants of management strategies. This study involving both field and modeling components investigated the characteristics of larval transport of eastern oyster, Crassostrea virginica, in Mobile Bay and eastern Mississippi Sound, Alabama.;A three-dimensional larval transport model accounting for physical transport, biological movement of larvae, and site- and larvae-specific conditions was developed for eastern oyster. The model reasonably reproduced the observed gradient decreasing from west to east in oyster spat settlement and bivalve larval concentration at time scales of overall average, season, and each survey.;Local-recruitment of larvae released at Cedar Point Reef, which contributes over 90% of oyster harvest in Alabama, is likely responsible for the persistent gradient decreasing from west to east in oyster spat settlement over the past 40 years. Efficient flushing through Main Pass prevents larval exchange between the west and east side of the Bay, resulting in negligible connectivity between the two basins separated by about 30 km. Seasonal and spatial variations in oyster spat settlement are explained in terms of variations in larval supply in response to seasonal wind and river discharge. Flooding events, which occur at any time during the oyster larval recruitment period, reduces larval retention substantially in CP and EMS. Retention of early-stage larvae mostly determined by physical transport plays a critical role in overall transport and retention of larvae in the Mobile Bay system. Net sinking of late-stage larvae shortens downstream dispersal range of larvae and increases larval retention near spawning area, thus providing a favorable condition for local-recruitment of oysters. However, biological movement of oyster larvae does not change overall patterns of larval transport by physical transport only.;This study have enhanced our understanding of the controlling processes for larval transport and retention and provided fundamental knowledge for restoration and management of oyster population.