Local vs. site-level effects of algae on coral microbial communities

Microbes influence ecological processes, including the dynamics and health of macro-organisms and their interactions with other species.  In coral reefs, microbes mediate negative effects of algae on corals when corals are in contact with algae.  However, it is unknown whether these effects extend to larger spatial scales, such as at sites with high algal densities.  We investigated how local algal contact and site-level macroalgal cover influenced coral microbial communities in a field study at two islands in French Polynesia, Mo’orea and Mangareva.  At 5 sites at each island, we sampled prokaryotic microbial communities (microbiomes) associated with corals, macroalgae, turf algae, and water, with coral samples taken from individuals that were isolated from or in contact with turf or macroalgae.  Algal contact and macroalgal cover had antagonistic effects on coral microbiome alpha and beta diversity.  Additionally, coral microbiomes shifted and became more similar to macroalgal microbi...