The influence of mixing processes and behavior on larval transport and mortality estimates in a stratified wind- and tidally-forced system

Coupled biological-physical models have been used to enhance understanding of fisheries recruitment, identify marine protected areas, and, in this case, determine the potential to establish or restore a self-sustaining population of oysters. The overall objective of our research program is to determine the potential distance and rate of larvae dispersal for two oyster species, Crassostrea virginica (native) and C. ariakensis (non-native), in Chesapeake Bay using a coupled biological-physical model. Predictions of the fate of larvae in coupled models may be highly dependent on simulated circulation patterns and mixing processes as well as biological factors like larval behavior. The goal of this paper is to assess the influence of these factors on predictions of larval transport. We used a particle-tracking model and output from a 3D hydrodynamic model (Regional Ocean Modeling System) implemented in Chesapeake Bay, a stratified windand tidally-forced estuary. We conducted two sets of model scenarios that focused on 1) turbulent processes and 2) larval behavior. Results of the turbulence sensitivity studies demonstrated that simulated vertical or horizontal turbulent particle motion resulted in both horizontal and vertical dispersal of particles. In addition, particle transport estimates were quite sensitive to the value of horizontal diffusivity used to parameterize sub-grid scale turbulence in the particle-tracking model. Model scenarios that included larval behavior demonstrated that even the particles with the slowest swimming speed (0.5 mm s) influenced the direction of transport such that their distribution was significantly different from that of passive particles. In addition, there were stage-specific differences in particle dispersal, the magnitude of which differed between behavior types. Results indicate that proper parameterization of turbulent processes (for passive organisms like eggs) and behavior (for active organisms) is critical for predicting larval dispersal. In addition, results suggest that knowledge of the influence of stage-specific larval behaviors on transport is important for accurate estimates of mortality rates from field collections.