Search for: All records

Abstract Coral bleaching is a well-documented and increasingly widespread phenomenon in reefs across the globe, yet there has been relatively little research on the implications for reef water column microbiology and biogeochemistry. A mesocosm heating experiment and bottle incubation compared how unbleached and bleached corals alter dissolved organic matter (DOM) exudation in response to thermal stress and subsequent effects on microbial growth and community structure in the water column. Thermal stress of healthy corals tripled DOM flux relative to ambient corals. DOM exudates from stressed corals (heated and/or previously bleached) were compositionally distinct from healthy corals and significantly increased growth of bacterioplankton, enriching copiotrophs and putative pathogens. Together these results demonstrate how the impacts of both short-term thermal stress and long-term bleaching may extend into the water column, with altered coral DOM exudation driving microbial feedbacks that influence how coral reefs respond to and recover from mass bleaching events. 

ABSTRACT Subterranean estuaries (STEs) are critical ecosystems at the interface of meteoric groundwater and subsurface seawater that are threatened by sea level rise. To characterize the influence of tides and waves on the STE microbial community, we collected porewater samples from a high‐energy beach STE at Stinson Beach, California, USA, over the two‐week neap‐spring tidal transition during both a wet and dry season. The microbial community, analyzed by 16S rRNA gene (V4) amplicon sequencing, clustered according to consistent physicochemical features found within STEs. The porewater community harbored relatively abundant Proteobacteria, Verrucomicrobiota, and Bacteroidota, as well as members of the archaeal DPANN superphylum and bacterial Candidate Phyla Radiation (CPR). Tidal conditions were not associated with microbial community composition; however, a wave overtopping event significantly impacted the beach microbiome. As a baseline for environmental change, our results elucidate the unique dynamics of a STE microbiome with unprecedented temporal resolution, highlighting the transport of cellular material through beach porewater due to waves.