IDENTIFYING OPPORTUNITIES FOR RESILIENCE IN REEF-BUILDING CORALS AS OCEAN WARMING CONTINUES

Abstract

Identifying and harnessing processes that promote coral recovery and resilience is crucial. The declining status of coral-reef ecosystems has led to proposed interventions to selectively propagate thermally resistant corals, aiming to increase coral resilience under ocean warming and intensified bleaching events. Using a combination of field and laboratory studies, this research assesses fundamental biological traits, with an emphasis on reproduction, of Porites astreoides along the Florida Keys Reef Tract (FRT) and Montipora capitata within Kāneʻohe Bay, Hawaiʻi during and after the 2015 global coral bleaching event. By assessing two coral species considered ecological “winners” in U.S. coral reef ecosystems, I highlight limitations and potential challenges associated with coral restoration efforts considering “exceptional” reef selection, selective breeding, and thermal conditioning. First, I compared seasonal and spatial patterns in the biological function of P. astreoides at sites located along the FRT to determine trade-offs during and after bleaching. Second, I assessed the impacts of differential bleaching susceptibility (bleached and recovered vs. nonbleached) of Montipora capitata on sexual reproduction and selectively bred offspring in subsequent spawning seasons. Third, I examined the parental effects of M. capitata associated with bleaching history and thermal conditioning on sexual reproduction and offspring performance. My results demonstrate that despite a severe bleaching event, (i) there is an exceptional site in the FRT where corals are not limited by trade-offs but the environmental and biological drivers remain unknown, (ii) sexual reproduction in Hawaiʻi appears to be robust regardless of bleaching response; however, there were delayed beneficial maternal effects in bleaching resistant colonies on offspring survivorship, and (iii) high thermal conditioning reduces reproductive output regardless of parental bleaching susceptibility and parental effects did not elicit lasting thermal resistance. Further research is required to determine the risks, benefits, efficacy, and scalability of human interventions to preserve resilient reefs in conjunction with action to reduce the use of fossil fuels that significantly contribute to ocean warming.