Dynamics of hydrogen peroxide in a coral reef: Sources and sinks

The dynamics of hydrogen peroxide (H₂O₂) was studied in the fringing coral reef off the coast of Eilat, Red Sea. Diurnal changes in H₂O₂ concentrations in the reef lagoon were typical of photochemically produced species. During the daytime H₂O₂ accumulated in the lagoon at low tide and exceeded open water concentrations by 100-250 nM. Elevated H₂O₂ decay kinetics (termed hereafter antioxidant activity) were also recorded in the lagoon at low tide. The observed antioxidant activities were high enough to moderate H₂O ₂ accumulation in the lagoon. In pursuit of the antioxidant source, the ability of corals to release antioxidant activity to their surrounding water was examined in both natural and laboratory settings. Water collected in situ from surfaces of individual corals and next to a coral knoll contained high antioxidant activity. Incubation experiments revealed that many Red Sea corals release antioxidant activity to their external milieu. Besides serving a potential antioxidant source to the reef system, the antioxidant activity detected on coral surfaces enabled corals to lower H₂O₂ concentrations in their vicinity. The ability of corals to offset exogenous H₂O₂ was validated in incubations with Stylophora pistillata in the absence of mixing. Conversely, corals subjected to mixing in a beaker were found to release H₂O₂, implying that corals may act as both a sink and a source for H₂O₂ in the reef. This newly described ability of corals to change H₂O₂ dynamics by releasing both H₂O₂ and antioxidants may bare important implications for coral physiology and interactions with the environment. Key Points H₂O₂ dynamics in the coral reef is different from those in open seawater The reef lagoon accumulates antioxidants, probably originating from corals Antioxidant activity on coral surfaces enables corals to degrade external H2O2