Geomicrobiology of carbonate microbialites in the Tahiti reef

Abstract

Abstract Integrated Ocean Drilling Program (IODP) Expedition 310 (Tahiti Sea Level) offered an opportunity to study the geomicrobiology of a reef framework. Offshore drilling was conducted on the coastal reefs of Tahiti (French Polynesia) at 22 sites in water depths of up to 117 m. Up to 80% of the retrieved core material comprises authigenic grey microbial carbonates with laminated or thrombolitic morphologies, which are associated with corals. Microbialites infilled the cavities during reef development and stabilized the coral reef framework. Rock-surface analyses were performed to track ongoing microbial activity in biofilms that could represent a modern counterpart of the processes at the origin of the formation of fossil microbialites. Significant concentrations of adenosine 5′-triphosphate, indicative of the presence of living microorganisms, were detected at relatively shallow depths, 0–6 m below the seafloor. Exoenzyme activities confirmed the presence of an active metabolizing microbiota forming biofilms in reef cavities. Onshore investigations of the recovered microbes and biofilms completed our picture that the rapid postglacial formation of carbonate microbialites was mediated by the activity of anaerobic microbes, such as sulphate-reducing bacteria and iron-respiring organisms, stimulated by the highly productive reef environment.