Molecular Genetic Assessment of Dispersal Potential, Population Connectivity, and Biodiversity in Coral Reef Organisms: Application to Marine Protected Area (MPA) Design

ISSUE: Establishment of marine protected areas (MPAs) is widely advocated for conservation, recovery, and management of coral reef ecosystems. Selection of biologically optimal MPA sites and delineation of their spatial boundaries by the management community require a robust understanding of the dynamics of population connectivity among reef tracts and identification of biodiversity hotspots. This information is largely lacking for most U.S. reefs. To provide this information for the management community, NCRI is developing and using new molecular genetic approaches to assess dispersal potential, population connectivity, and biodiversity in a variety of reef organisms.

Female amphipod brooding a juvenile.

PROJECT AND FINDINGS: NCRI's initial focus has been on assessing population connectivity and genetic biodiversity in three coral reef invertebrates that are cryptic in their habitat: two brooding amphipods and a broadcast-spawning brittle star, which display a commensal life history in association with the common branching vase sponge (Callyspongia vaginalis). The vastly different reproductive life-histories of these species overlaid on their commensal nature and their occurrence in the same microhabitat (i.e., the sponge C. vaginalis) provide a unique opportunity to examine the influence of life-history on reef connectivity dynamics without the potentially confounding influences of different habitats that are subject to the additional environmental variables of different currents and other water circulation patterns. DNA sequence data from the mitochondrial cytochrome oxidase subunit one (COI) gene reveal high gene flow (i.e., extensive reef connectivity) along 400 km of the SE Florida coastline for all three species. Although this result was not surprising for the brittle star, which disperses via pelagic larvae, it was unexpected for the two amphipod species that brood their young and lack pelagic larvae. Subsequently, the project was expanded into the Caribbean where the genetic data show that expanses of deep open water create substantial barriers to gene flow and many populations of all three species are reproductively isolated. Furthermore, one amphipod species is divided into six morphologically identical but genetically highly divergent lineages, suggesting multiple cryptic species are present.

Parsimony network depicting the genetic relationships among individual amphipods from one species along the SE Florida coastline. Circles represent individuals with identical gene sequences and the colors indicate different geographical sampling locations. The absence of any significant geographic (color) partitioning indicates extensive genetic connectivity between SE Florida reefs for this species, despite its brooding reproductive life history.

IMPLICATIONS FOR MANAGEMENT: These results show that assumptions regarding the dispersal potential of reef invertebrates based simply on life history characteristics may be misleading and need to be empirically tested. In addition, there is a need to integrate traditional morphological taxonomy with new genetic techniques in order to reveal the full extent of coral reef biodiversity.

PARTNERS:
NCRI via NOAA-CSCOR
Guy Harvey Research Institute