Coral connectivity between deep and shallow sites in the tropical western Atlantic (Caribbean): Deep water refugia as potential sources of replenishment following coral bleaching

In recent years, considerable attention has been paid to understanding reef resilience and identifying sites that may serve as potential sources of new recruitment. To date, most assessments of reef connectivity have emphasized long-distance horizontal dispersal of propagules from one shallow reef to another. However, an intriguing but yet untested possibility is that relatively short-distance vertical dispersal from deep reefs may represent a significant source of propagules for shallow reefs. This study aims to test this hypothesis by investigating the connectivity of coral populations at deep and shallow sites in different localities, including the Florida Keys, Bermuda, Puerto Rico and U.S. Virgin Islands. It will use a combination of new and established population genetic markers (DNA microsatellites) in 4 important scleractinian reef coral species with different life-history reproductive strategies and broad depth distributions (Montastraea faveolata, M. cavernosa, Porites astreoides and Agaricia agaricites). A nested sampling design will be used to assess population structure and estimate gene flow between depths. In addition, algal symbiont (Symbiodinium spp.) diversity will be assessed to help determine the functional potential for brooding corals at deep sites to colonize shallow environments. Overall, this approach will allow the assessment of the extent to which deep reefs might serve as sources of local recruitment for nearby shallow reefs. If we can demonstrate significant short-distance vertical connectivity, then there will be a critical need for policymakers to re-assess the current level of protection afforded to deep water reefs and potentially inform the design of MPAs, whose boundaries follow a depth isobath that potentially excludes significant deep water reef resources.