Coral mucus release and following particle trapping contribute to rapid nutrient recycling in a Northern Red Sea fringing reef

Abstract

Mucus released by corals can function as an important energy carrier and particle trap in reef ecosystems with strong tidal currents. In fringing reefs with calm conditions, these processes may occur on smaller spatial scales. Observations of coral mucus dynamics in the Northern Red Sea revealed highly particle-enriched and negatively buoyant mucus strings attached to ∼27% of coral colonies for up to 79 min. Mucus strings of the scleractinian coral genus Acropora exhibited three orders of magnitude higher particulate organic carbon and nitrogen concentrations when compared with freshly released coral mucus, which confirms efficient particle trapping. After detachment from the coral surface, more than 95% of mucus strings rapidly descended to the reef sea floor within less than 1 m. Such mucus-induced transport may account for 21–25% of the total sedimentary particulate organic matter supply. In situ and laboratory analyses of planktonic and benthic microbial degradation of mucus strings showed high rates of up to 16 and 26% particulate organic carbon h^–1, respectively. These findings suggest a newly discovered, tight sediment–water coupling mechanism via coral mucus that may contribute to rapid nutrient recycling in oligotrophic fringing coral reefs.