Abstract
Abstract. Hydrogen peroxide (H2O2), a common reactive oxygen species, plays multiple roles in coral health and disease. Elevated H2O2 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 H2O2 and antioxidants to their external milieu, and can influence the H2O2 dynamics in the reef. Here, we present a laboratory characterization of H2O2 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 H2O2 and antioxidant release. Since H2O2 is produced and degraded simultaneously, we developed a methodology for resolving the actual H2O2 concentrations released by the corals. H2O2 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 H2O2 concentrations were stabilized at ~ 1 μM by 1–3 h, and then gradually declined. Solving for H2O2 release, corals were found to release H2O2 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 H2O2, possibly since the flow reduces the thickness of the diffusive boundary layer of the coral, and thus increases H2O2 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. H2O2, however, was not released from bleached corals, implying that the symbiotic algae are the source of the released H2O2. The observed flow-induced H2O2 release may aid corals in removing some of the internal H2O2 produced by their symbiotic algae, and may possibly assist in preventing coral bleaching under conditions of elevated temperature and irradiance.
Highlights
Hydrogen peroxide (H2O2) is a commonly occurring reactive oxygen species (ROS) of great biological importance
We found that the coral Stylophora pistillata produces and releases superoxide (O−2 ) and enzymes, degrading superoxide to its surrounding water (Saragosti et al, 2010)
Release of antioxidants and H2O2 from Stylophora pistillata to the surrounding water was observed in all experiments, when the coral fragments were subjected to stirring
Summary
Hydrogen peroxide (H2O2) is a commonly occurring reactive oxygen species (ROS) of great biological importance. H2O2 is generated during photosynthesis, respiration and numerous other pathways, and its concentrations can reach tens of micromolars (Halliwell et al, 2000; Apel and Hirt, 2004). H2O2 and other ROS serve as important signaling molecules (Bartosz, 2009). ROS production and accumulation beyond the capacity of an organism to quench them efficiently or to repair the resulting damage, a state known as oxidative stress, results in extensive damage to cellular components, including proteins, lipids, and DNA, all of which may eventually lead to cell demise (Apel and Hirt, 2004; Gechev and Hille, 2005). Whether ROS will act as a damaging or signaling molecule depends on the delicate equilibrium between ROS production and degradation (Sharma et al, 2012)
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