Coral reef fish have considerable larval behavioral capabilities that can lead to successful completion of the early pelagic life phase. In particular, vertical migration during ontogeny increases retention near natal reefs and decreases losses due to transport by currents. For those larvae that are not returning home, the relative influence of behavior (biology) and currents (physics) on their arrival pattern among adjacent and distant reefs is not known. Moreover, interactions of the naturally small-scale larval movements with those of larger-scale currents need to be evaluated with regard to the spatial patterns of recruitment. We used an offline Lagrangian stochastic modeling approach to explore the relative influence of physical (i.e. eddy perturbation, diffusion) and biological processes (i.e. vertical movement, mortality) on the connectivity of the coral reef fish population in the western Caribbean, a region with complex geomorphology and circulation. This study revealed that the impact of larval behavior extends beyond enhancing the process of self-recruitment by changing population connectivity patterns. Connectivity was significantly influenced by larval vertical movement, survival, and by the eddy field, all controlling arrival patterns near reefs. A sensitivity analysis was done to gauge the robustness of the results by varying the model parameters. We found that particle-tracking models with homogeneous parameterization of the sub-grid motion tended to bias dispersal from and along the reef track, which can be mitigated by using spatially explicit parameters calculated from the Eulerian velocity fields. Finally, larval survival emerged as a key component for connectivity estimates, the study of which poses a great challenge in tropical ecosystems.

Gene flow was shown to be limited between western and eastern Caribbean populations of the reef-building coral, Acropora palmata. However, some mixing was detected among populations near Puerto Rico. Our genetic analyses categorize A. palmata samples from the east coast of the Dominican Republic with the western Caribbean population, suggesting a filter to gene flow east of the Dominican Republic. To test the hypothesis of a present day bio-oceanographic filter occurring between Puerto Rico and the Dominican Republic (i.e., in the Mona Passage), we used a Lagrangian stochastic model (LSM) of larval dispersal, coupling coral life history characteristics with physical forcing. The model operated at two spatial scales: Caribbean-wide and focusing on the Mona Passage area. Results from the Caribbean-wide study showed no significant virtual larval exchange between the two populations. The small-scale model indicated that virtual larvae do not readily traverse the Mona Passage during the corals' reproductive season. Larvae released from Mona Island, in the center of the passage, are retained in the lee within topographically steered eddies, which act, together with the larval competency period, as a de facto filter to dispersal. Combined, our findings reveal the location of a seasonal filter to gene flow and its mechanism.

Rising sea temperatures cause mass coral bleaching and threaten reefs worldwide. We show how maps of variations in thermal stress can be used to help manage reefs for climate change. We map proxies of chronic and acute thermal stress and develop evidence-based hypotheses for the future response of corals to each stress regime. We then incorporate spatially realistic predictions of larval connectivity among reefs of the Bahamas and apply novel reserve design algorithms to create reserve networks for a changing climate. We show that scales of larval dispersal are large enough to connect reefs from desirable thermal stress regimes into a reserve network. Critically, we find that reserve designs differ according to the anticipated scope for phenotypic and genetic adaptation in corals, which remains uncertain. Attempts to provide a complete reserve design that hedged against different evolutionary outcomes achieved limited success, which emphasises the importance of considering the scope for adaptation explicitly. Nonetheless, 15% of reserve locations were selected under all evolutionary scenarios, making them a high priority for early designation. Our approach allows new insights into coral holobiont adaptation to be integrated directly into an adaptive approach to management.

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