Benthic community composition affects O2 availability and variability in a Northern Red Sea fringing reef

Many coral reef ecosystems experience shifts in benthic community composition from scleractinian corals to algae. However, consequences of such phase shifts on O-2 availability, important for many reef organisms, are unresolved. This study therefore comparatively investigated potential in situ effects of different benthic cover by reef macroalgae and scleractinian corals on water column O-2 concentrations in a Northern Red Sea fringing reef. Findings revealed that mean daily O-2 concentrations at algae-dominated sites were significantly lower compared to coral-dominated sites. Minimum O-2 concentrations were significantly negatively correlated, while diurnal variability in O-2 concentration was significantly positively correlated, with increasing benthic cover by algae. In contrast, no correlation with coral cover was found. These results indicate that shifts from corals to benthic algae may likely affect both in situ O-2 availability and variability. This may be particularly pronounced in reef systems with low water exchange (e.g. closed lagoons) or under calm weather conditions and suggests potential O-2-mediated effects on reef organisms.