12. Biogeography, Biodiversity and Connectivity of Bermuda’s Coral Reefs

As the most northern ecoregion within the Tropical Northwestern Atlantic biogeographic province, Bermuda’s reef biodiversity is a reduced complement of that found within the other ecoregions of the TNA. A characteristic of the Bermuda marine fauna is the absence of species otherwise ubiquitous in the TNA province (i.e., Acropora spp.). Notable differences in Bermuda’s species diversity is attributed to both geographic and physical forcing agents that include isolation, temperature, currents, bathymetric or coastal complexity, and environmental seasonality. Pleistocene sea level changes also may have been important to the development of Bermuda’s current diversity. Shallow-water scleractinian and octocorallian species diversity is currently considered well documented, however information is still lacking on the depth limits of many species, including in and extending beyond the mesophotic zone. The shallow-water azooxanthellate coral, Rhizopsammia bermudensis, is the only endemic scleractinian. Bermuda’s Symbiodinium diversity is comparable to the Caribbean in that clades A, B and C predominate in anthozoan hosts, but there is a notable absence of Clade D which has been recorded from several Caribbean conspecifics. In Bermuda, octocorals harbour only clade B. Most fishes in Bermuda have a western Atlantic distribution, but amphi-Atlantic and more widely distributed species are also common. High levels of genetic variation and unique Bermudian haplotypes have been determined for several species, spanning several higher taxa – not just cnidarians and fishes. Studies indicate that Bermuda’s marine populations are panmictic and self-seeding. Population connections with upstream reef systems have been inferred genetically for some but not all of the few species investigated. For Bermuda, population connectivity characteristics are so diverse, even among species with apparently similar reproductive and dispersal patterns, that best practices for management and conservation should be developed on a species by species basis.