[en] Terrestrial runoff and sedimentation are common environmental disturbances on tropical coral reefs, often exacerbated by precipitations, coastal development and unmanaged land use. A variety of effects of these stressors on corals have been reported, both at the level of the coral host and its zooxanthellae symbionts, with known effects ranging from local tissue necrosis to broad scale ecological changes. While terrestrial runoff and sedimentation have frequently been suggested as a potential disturbance to coral associated microbial communities, such effects have as yet not been thoroughly investigated.
Coral microbial communities play important roles in coral health and disease resistance, primarily through niche occupation and the production of antimicrobial compounds. However their composition and function are known to shift in response to a variety of environmental disturbances including changes in temperature, pH and nutrients. While such stressors influence coral holobionts indirectly through modifications of the surrounding environment, terrestrial runoff and sedimentation may affect corals both indirectly (e.g. water quality degradation, eutrophication) and directly through consistent particulate deposition on the coral surface resulting in modifications of the surface microenvironment. Such alterations could cause a shift in coral-associated microbial communities and thereby influence the coral holobiont as a whole, for example resulting in the development of opportunistic infections.
To explore these effects, we assessed the responses of Montipora patula and Pocillopora damicornis microbial communities to ecologically relevant levels of short term (24h) and prolonged (two weeks; P. damicornis only) sediment stress. Taxonomic profiles were obtained through v4-v5 16S-targeted high throughput assays (Roche 454 and Illumina MiSeq) and compared between sediment-stressed and control colonies. Preliminary results suggest that coral microbial communities might resist perturbation resulting from short-term sediment deposition. Prolonged exposure may however exceed the threshold for sediment stress resistance resulting in significant changes in coral microbial populations.
