Coral thermotolerance retained following year-long exposure to a novel environment

Coral reefs are facing significant declines worldwide, prompting the need for active management to help support reef resilience under a changing climate. Active restoration strategies targeting the use of corals with naturally elevated heat tolerance are gaining popularity for their potential to enhance reef resistance. While extreme systems such as mangrove lagoons have been documented as housing such stress-tolerant corals, assessing the ability of corals to maintain tolerance when moved to a novel, often more benign, habitat is a critical first step to determining the suitability of this approach for reef conservation. Here, we compared the thermal thresholds (via Fv/Fm photophsyiological performance-based ED50s in response to acute heat stress) of Pocillopora acuta colonies from a mangrove lagoon known to experience higher temperature maxima and variability to colonies from an adjacent reef site with more benign conditions. Following one-year translocation of mangrove and reef colonies to a reef environment, colonies were re-assessed to determine if their observed thermal tolerance was retained following long-term exposure to a novel habitat. We demonstrate that mangrove colonies had a higher standardised thermal tolerance than reef corals in both years (year one: 37.3 ºC vs 36.7 ºC, respectively; year two: 37.9 ºC vs 36.8 ºC, respectively), and critically, that mangrove corals exhibited no difference in thermal tolerance following one-year translocation to a less variable and extreme habitat (year one: 37.3 ºC, year two: 37.6 ºC). Upregulation of genes associated with DNA repair, metabolism, and homeostasis suggest the importance of these pathways in helping mangrove corals mitigate bleaching stress, while measured epigenetic modifications of DNA methylation appeared to have a lesser effect. Our findings suggest the use of heat tolerant corals from extreme systems could hold great promise as part of active intervention strategies aiming to increase reef resistance to a warming climate