Predicting the export of retention-oriented larvae from their natal population using coastal features: a modelling study on the Pacific oyster

Larvae from many marine coastal species deploy ecological strategies that promote their arrival to geographically close or distant populations. Some larvae adjust their vertical positions in response to the tidal cycle, which, in combination with coastal features, helps keep them relatively close to their natal population instead of being advected offshore (retention-oriented larvae). However, a few of these larvae are transported away from their natal population and spread further afield. In this study, we aimed to better understand the environmental mechanisms that influence the export of retention-oriented larvae by modelling the transport of tidal larvae and using a species distribution model to predict that export rate. The larval transport model was parametrised with ecological data about the Pacific oyster Magallana gigas and tidal larval behaviour from 2 Irish coastal regions. The simulated dispersal of retention-oriented larvae showed that 55-60% of larvae were exported from the 2 regions. This export rate decreased to below 40% if the release occurred in protected and shallow coastal areas. The exportation of larvae occurred relatively early in a larva’s simulated pelagic life (when the larva began to have an active behaviour). When export rate was associated with the coastal features in the 2 Irish regions, wave exposure at the release sites was an important predictor for low (below 20%) and high (above 90%) export rates. The study has implications for the management of coastal grounds since export rates of retention-oriented larvae can be predicted based on knowledge of local hydrodynamics. Our approach could be applied to predict the export rate of other coastal larvae with retention-oriented behaviour.