Extra High Superoxide Dismutase in Host Tissue is Associated with Improving Bleaching Resistance in "thermal Adapted" and -associating Coral

Global warming threatens reef-building corals with large-scale bleaching events; therefore, it is important to discover potential adaptive capabilities for increasing their temperature resistance before it is too late. This study presents two coral species ( and ) surviving on a reef having regular hot water influxes via a nearby nuclear power plant that exhibited completely different bleaching susceptibilities to thermal stress, even though both species shared several so-called "winner" characteristics ( containing , thick tissue, ). During acute heating treatment, algal density did not decline in corals within three days of being directly transferred from 25 to 31 °C; however, the same treatment caused . to lose < 70% of its algal symbionts within 24 h. The most distinctive feature between the two coral species was an overwhelmingly higher constitutive superoxide dismutase (ca. 10-fold) and catalase (ca. 3-fold) in over . Moreover, also contained significantly higher saturated and lower mono-unsaturated fatty acids, especially a long-chain saturated fatty acid (C22:0), than , and was consistently associated with the symbiotic bacteria , which was not found in . However, antibiotic treatment and inoculation tests did not support having a direct contribution to thermal resistance. This study highlights that, besides its association with a thermally tolerable algal symbiont, a high level of constitutive antioxidant enzymes in the coral host is crucial for coral survivorship in the more fluctuating and higher temperature environments.