Diversity and distribution of coral-associated bacteria

Abstract

Coral reefs are the most biodiverse of all marine ecosystems; however, very little is known about prokaryotic diversity in these systems. To address this issue, we sequenced over 1000 bacterial 16S rDNAs from 3 massive coral species (Montastraea franksi, Diploria strigosa, and Porites astreoides) in Panama and Bermuda. Analysis of only 14 coral samples yielded 430 distinct bacterial ribotypes. Statistical analyses suggest that additional sequencing would have resulted in a total of 6000 bacterial ribotypes. Half of the sequences shared <93% identity to previously published 16S sequences, and therefore probably represent novel bacterial genera and species; this degree of novelty was substantially higher than that observed for other marine samples. Samples from the Panama corals were more diverse than those from Bermuda, paralleling diversity gradients seen in metazoans. The coral-bacteria associations were non-random. Different coral species had distinct bacterial communities, even when physically adjacent, while bacterial communities from the same coral species separated by time (~1 yr) or space (3000 km) were similar. Analysis of the branching coral Porites furcata showed that bacterial ribotypes can also be structured spatially within colonies. Therefore, corals and reefs represent landscapes of diverse, ecologically structured prokaryotic communities.