Long distance dispersal and vertical gene flow in the Caribbean brooding coral Porites astreoides

<jats:title>Abstract</jats:title><jats:p>To date, most assessments of coral connectivity have emphasized long-distance horizontal dispersal of propagules from one shallow reef to another. The extent of vertical connectivity, however, remains largely understudied. Here, we used newly-developed and existing DNA microsatellite loci for the brooding coral <jats:italic>Porites astreoides</jats:italic> to assess patterns of horizontal and vertical connectivity in 590 colonies collected from three depth zones (≤10 m, 15–20 m and ≥25 m) at sites in Florida, Bermuda and the U.S. Virgin Islands (USVI). We also tested whether maternal transmission of algal symbionts (<jats:italic>Symbiodinium</jats:italic> spp.) might limit effective vertical connectivity. Overall, shallow <jats:italic>P. astreoides</jats:italic> exhibited high gene flow between Florida and USVI, but limited gene flow between these locations and Bermuda. In contrast, there was significant genetic differentiation by depth in Florida (Upper Keys, Lower Keys and Dry Tortugas), but not in Bermuda or USVI, despite strong patterns of depth zonation in algal symbionts at two of these locations. Together, these findings suggest that <jats:italic>P. astreoides</jats:italic> is effective at dispersing both horizontally and vertically despite its brooding reproductive mode and maternal transmission of algal symbionts. In addition, these findings might help explain the ecological success reported for <jats:italic>P. astreoides</jats:italic> in the Caribbean in recent decades.</jats:p>