SELECTING HEAT TOLERANT CORALS FOR RESILIENT REEF RESTORATION

Abstract

As coral reefs face increasing threats from warming oceans, there is burgeoning interest in reef restoration as an intervention to retain living coral cover. Given that thermal stress is inevitable in the near term, selecting putatively resilient coral stocks for restoration projects may improve efficiency and success. Understanding the level and range of heat tolerance available in coral populations is critical to determining their viability and for choosing corals for outplanting. Whether breeding to produce novel genotypes or asexually propagating fragments, determining if selection criteria translate into long-term success is critical. In this study, we sampled a model population of a dominant reef-building coral (Montipora capitata), subjected fragments to an artificial heat-stress, and subsequently revisited and assessed source colonies at the height of a moderate natural bleaching event. We also exposed asexually propagated fragments of known bleaching phenotypes and sexually derived juvenile samples selected via acute heat exposure to realistic long-term temperature profiles simulating past, contemporary, and future climate conditions. We measured a range of performance outcomes including survival, growth, and bleaching performance. Selection criteria broadly translated to improved subsequent performance across experiments. There was substantial response variation in the population during exposure to increasingly detrimental future temperature conditions suggesting extant adaptive potential. These results align with the view of heat tolerance as a complex, heritable trait. While the only tenable solution to the cascading problems of warming oceans is drastic reduction in fossil fuel emissions, utilizing corals picked for thermal resilience might help reef restoration projects buy time for climate change mitigation to occur.