Release of hydrogen peroxide and antioxidants by the coral Stylophora pistillata to its external milieu
Hydrogen peroxide (H
2), a common reactive oxygen species, plays multiple roles in coral health and disease. Elevated H
2 production 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 H
2 and antioxidants to their external
milieu, and can influence the H
2 dynamics in the reef. Here, we present a laboratory characterization of H
2 and antioxidant activity release kinetics by intact, non-stressed
Stylophora pistillata. Experimenting with bleached and non-bleached corals and different stirring speeds, we explored the sources and modes of H
2 and antioxidant release. Since H
2 is produced and degraded simultaneously, we developed a methodology for resolving the actual H
2 concentrations released by the corals.
H 2O 2 and 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 H 2O 2 concentrations were stabilized at ~ 1 μM by 1–3 h, and then gradually declined. Solving for H 2O 2 release, corals were found to release H 2O 2 at 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 H 2O 2, possibly since the flow reduces the thickness of the diffusive boundary layer of the coral, and thus increases H 2O 2 mass 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. H 2O 2, however, was not released from bleached corals, implying that the symbiotic algae are the source of the released H 2O 2. The observed flow-induced H 2O 2 release may aid corals in removing some of the internal H 2O 2 produced by their symbiotic algae, and may possibly assist in preventing coral bleaching under conditions of elevated temperature and irradiance.