Heterotrophic plasticity and resilience in bleached corals

Elevated seawater temperatures are causing widespread coral bleaching and mortality, and threaten to damage some of these important ecosystems irreversibly. Bleaching occurs when the symbiotic microalgae that normally provide corals with food are released from the host coral, which then loses its pigment and appears almost white. Some corals survive bleaching, but the mechanisms that ensure survival are poorly understood. To date, studies have focused on the microalgae: the role of coral host physiology in bleaching and recovery has been largely overlooked. A study of bleached and recovering corals from Kaneohe Bay, Hawaii now shows that the host can have a significant role in coral recovery and resilience. Increased coral feeding on zooplankton can provide an alternative food source and dramatically enhance coral survival in bleaching events. Mass coral bleaching events caused by elevated seawater temperatures1,2 have resulted in extensive coral mortality throughout the tropics over the past few decades3,4. With continued global warming, bleaching events are predicted to increase in frequency and severity, causing up to 60% coral mortality globally within the next few decades4,5,6. Although some corals are able to recover and to survive bleaching7,8, the mechanisms underlying such resilience are poorly understood. Here we show that the coral host has a significant role in recovery and resilience. Bleached and recovering Montipora capitata (branching) corals met more than 100% of their daily metabolic energy requirements by markedly increasing their feeding rates and CHAR (per cent contribution of heterotrophically acquired carbon to daily animal respiration), whereas Porites compressa (branching) and Porites lobata (mounding) corals did not. These findings suggest that coral species with high-CHAR capability during bleaching and recovery, irrespective of morphology, will be more resilient to bleaching events over the long term, could become the dominant coral species on reefs, and may help to safeguard affected reefs from potential local and global extinction.