Functional diversity of microbial communities associated to the mucus of scleractinians around Moorea (French Polynesia)

Abstract

Mucus production by scleractinians appears as an antifouling mechanism which prevents settlement of other organisms and accumulation of sediments on their surface. This Surface Muccopolysaccharide Layer (SML) harbours dense populations of bacteria which play a paramount role in scleractinians nutrition, metabolism and good health maintenance. However, environmental disturbances can alter these microbiocenoses. Characterization of bacterial communities was carried out using a set of simple techniques that enable us to describe the state and functions of whole microbial communities associated with different hard coral species. Multi-comparisons have been performed on bacterial communities from open water, interstitial water, sedimentary interface and macro algae as well as between healthy and bleached colonies, and patches associated or not with Pomacentridae fishes. The functional study included measurements of bacterial biomass, respiration, oxydative and hydrolytic metabolisms. Non-Fungiidae corals and sedimentary interface have a quite similar bacterial biomass but open water, interstitial water and macro-algae are characterized by higher bacterial biomass. Bacterial respiration potential is similar on corals and at the sedimentary interface, but it is higher in interstitial water and lower in open water and for bacterial community associated with macro-algae. Hydrolytic activities are highest in SML. Bleached corals and patches associated with Pomacentridae fishes show more abundant bacteria, with higher respiration rate and higher hydrolytic activity than corals without fishes and healthy ones. In addition, bacteria of bleached corals display a higher division percentage, a higher growth rate and a lower turn-over time We confirmed that bleaching events or the presence of sedentary fishes modify the bacterial communities structure and affect relationships between coral, endosymbiotic algae, SML-associated microbial community and associated organisms. Such results highlight that SML-bacterial communities are modified by bleaching and raise the question of a potential protection of fishes against pathogens