Physiology of Winter Coral Bleaching in Temperate Zone

Abstract

With high-temperature stress due to climate change threatening corals in the tropics, cooler high latitudes may become a potential refuge. Already established high latitudes coral communities experience severe cold stress during winter, stress that would be fatal to most of the tropical coral species. Here we studied the physiological response of two high latitude coral species in Japan: Alveopora japonica and Porites heronensis, through field transplantation and in situ incubations. The specimens experienced 243 days at a temperature under 18 °C, which is the limit for the development of reefs and, and 110 days under 15 °C. While bleaching was observed for both species, none of the specimens died, highlighting the high resilience of temperate coral species to cold stress. The survival strategies to the cold temperature seem to differ among the species. P. heronensis exhibited decreased Fv/Fm and highly decreased metabolism (photosynthesis, calcification, respiration, ETSA) suggesting that this species could survive the winter by decreasing its basal metabolism. It also shows a mitotic index of more than 30% during the warmer period that could a prompt recovery from the stress experienced during winter. A. japonica, which showed several bleaching for around three months, also showed decreased metabolism but to a lesser extent suggesting that it was able to use an alternative source of energy. These kinds of adaptations to cold stress may not be widespread among tropical coral species, highlighting the need for better conservation of this future reservoir of biodiversity that represents marginal high latitude coral communities.