Release of hydrogen peroxide and antioxidants by the coral Stylophora pistillat to its external milieu

Abstract

Hydrogen peroxide (H2O2), a common reactive oxygen species, plays multiple roles in coral health and disease. Elevated H2O2production by the symbiotic algae during stress may result in symbiosis breakdown and bleaching of the coral. We have recently reported that various Red Sea corals release H2O2and antioxidants to their external milieu and can influence the H2O2dynamics in the reef. Here, we present a laboratory characterization of H2O2and antioxidant activity release kinetics by intact, non-stressed Stylophora pistillat. Experimenting with bleached and non-bleached corals and different stirring speeds, we explored the sources and modes of H2O2and antioxidant release. Since H2O2is produced and degraded simultaneously, we developed a methodology for resolving the actual H2O2concentrations released by the corals. H2O2and antioxidant activity steadily increased in the water surrounding the coral over short periods of 1-2 h. Over longer periods of 5-7 h, the antioxidant activity kept increasing with time, while H2O2concentrations were stabilized at ∼ 1 μm by 1-3 h, and then gradually declined. Solving for H2O2release, corals were found to release H2O2at increasing rates over 2-4 h, and then to slow down and stop by 5-7 h. Stirring was shown to induce the release of H2O2, possibly since the flow reduces the thickness of the diffusive boundary layer of the coral, and thus increases H2O2mass flux. Antioxidant activity was released at similar rates by bleached and non-bleached corals, suggesting that the antioxidants did not originate from the symbiotic algae. H2O2, however, was not released from bleached corals, implying that the symbiotic algae are the source of the released H2O2. The observed flow-induced H2O2release may aid corals in removing some of the internal H2O2produced by their symbiotic algae, and may possibly assist in preventing coral bleaching under conditions of elevated temperature and irradiance.