Aura-biomes are present in the water layer above coral reef benthic macro-organisms

Abstract

As coral reef habitats decline worldwide, some reefs are transitioning from coral- to algal-dominated benthos with the exact cause for this shift remaining elusive. Increases in the abundance of microbes in the water column has been correlated with an increase in coral disease and reduction in coral cover. Here we investigated how multiple reef organisms influence microbial communities in the surrounding water column. Our study consisted of a field assessment of microbial communities above replicate patches dominated by a single macro-organism. Metagenomes were constructed from 20 L of water above distinct macro-organisms, including (1) the coral <i>Mussismilia braziliensis</i>, (2) fleshy macroalgae (<i>Stypopodium</i>, <i>Dictota</i> and <i>Canistrocarpus</i>), (3) turf algae, and (4) the zoanthid <i>Palythoa caribaeorum</i> and were compared to the water microbes collected 3 m above the reef. Microbial genera and functional potential were annotated using MG-RAST and showed that the dominant benthic macro-organisms influence the taxa and functions of microbes in the water column surrounding them, developing a specific "aura-biome". The coral aura-biome reflected the open water column, and was associated with <i>Synechococcus</i> and functions suggesting oligotrophic growth, while the fleshy macroalgae aura-biome was associated with <i>Ruegeria</i>, <i>Pseudomonas,</i> and microbial functions suggesting low oxygen conditions. The turf algae aura-biome was associated with <i>Vibrio, Flavobacterium,</i> and functions suggesting pathogenic activity, while zoanthids were associated with <i>Alteromonas</i> and functions suggesting a stressful environment. Because each benthic organism has a distinct aura-biome, a change in benthic cover will change the microbial community of the water, which may lead to either the stimulation or suppression of the recruitment of benthic organisms.