Abstract Summary
Mass coral bleaching is increasing in frequency and severity, leading to the loss of coral abundance and diversity. However, some corals are less susceptible to bleaching than others and can provide a model for identifying the physiological and biogeochemical traits that underlie coral resilience to thermal stress. Corals from Eilat in the northern Red Sea do not bleach unless seawater temperatures are sustained at +6⁰C above their average summer maximum. This extreme thermal tolerance qualifies these as super-corals, as most corals bleach when exposed to temperatures that are only +1-2⁰C above their thermal maximum. Here, we conducted a controlled bleaching experiment (+6°C) for 37 days (equivalent to 32-degree heating weeks) on three species of corals from Eilat: Stylophora pistillata, Pocillopora damicornis, and Favia favus. While all three species appeared visibly bleached, their physiological and biogeochemical responses were species-specific. S. pistillata catabolized lipids but still maintained total energy reserves and biomass, while calcification declined. P. damicornis was the least affected by bleaching. It maintained its total energy reserves, biomass, and calcification independent of heterotrophy. Finally, F. favus suffered losses in energy reserves and biomass but still maintained photosynthesis and calcification most likely because of its high baseline heterotrophic capacity. Thus, just like their non-super-coral counterparts, maintaining energy reserves and biomass, and heterotrophic capacity appear to be traits that underlie the thermal tolerance of these super-corals from Eilat. Thus, these super-coral populations could provide viable seed stock for repopulating coral losses on other reefs.
