Award: OCE-1437166

Many of the major coral reef systems on our planet have seen massive bleaching events in recent years. Bleaching refers to the when the symbiotic algae that lives within the coral tissues leaves the coral under conditions of stress. Whilst some corals and reefs can recover from bleaching, in many instances it leads to coral death and the severity of bleaching events and the fact that they are occurring in successive years leaves many reefs little chance to recover, and seems likely to lead to widespread reef collapse. Scientists widely believe the principle driver of future reef collapse will be increasing ocean temperatures, as coral bleaching events are typically associated with temperature spikes in reef waters and in controlled experiments reef building corals and their algae are typically very sensitive to temperature change. However, that is not the whole picture as other factors such as diseases affecting corals and secondary effects of carbon dioxide dissolving into the oceans – termed ocean acidification – could be at play. While corals negative response to excessive heat is clear, coral response to CO2 induced ocean acidification is more complex, with widespread differences in sensitivity between species. We now have a relatively large amount of information on coral species response to environmental change including temperature and acidity, but what we lack is information on the underlying mechanisms for species-specific differences in responses. One hypothesis is that there are differences in the ability of different organisms to regulate the chemistry of the fluids that are used to form their shells and skeletons inside their tissues. By knowing the mechanisms of coral resilience or sensitivity to environmental change, we can improve conservation efforts and predictions for the future of ocean ecosystems. In this NSF-funded project, a team of scientists including international collaborators sought to explore the underlying mechanisms behind different species of corals resilience or susceptibility to ocean temperature and acidity change. The species studied included several species of warm water symbiont-bearing warm water corals, and a cold-water deep-sea dwelling coral that lacks symbionts. Using a unique combination of techniques drawn from both cell biology and geochemistry that allow us to probe the internal acidity of the fluids from which corals produce their shells and skeletons. we first confirmed the observation that diverse species of corals actively regulated the acidity of their internal fluids compared to seawater, in order to facilitate skeleton production. Secondly, we found a new relationship between symbiont activity and coral resilience to CO2 induced ocean acidification. Specifically corals grown at temperatures optimal for symbiont activity are not only resilient to high CO2 but in many cases grow faster, presumably as the symbiont utilizes the CO2 to produce energy more efficiently through photosynthesis. When corals are grown at a temperature that impaired symbiont activity, they are found to lose internal acidity control and then become more sensitive to ocean acidification. These effects were not seen in the non-symbiont bearing deep-sea coral where increasing temperature has the opposite effect, namely increasing growth. Therefore symbiont health is directly linked coral sensitivity to ocean acidification in a surprising way. In total the results confirm temperature rather than ocean acidification is the dominant risk to surface water corals. During the course of this project the project co-investigator Robert Eagle became a faculty fellow in the Center for Diverse Leadership in Science, a new entity based in the Institute of the Environment and Sustainability at UCLA. The aim of this entity is to provide multi-tier mentorship to students and researchers including those from groups underrepresented in the sciences and help individual faculty develop their skills in inclusion and become leaders in inclusive excellence. Several undergraduate students including minorities that are heavily under-represented in oceanography were recruited to do research supported by this project during the course of this grant, in line with the goals of this new center. Results were also included in undergraduate and graduate classes at UCLA taught by the PIs, including a GE class to 150 students taught for the past two years (Env Sci M10) Introduction to Environmental Science, an upper division course taught to 35 students taught for the past two years (AOS 107) Biological Oceanography, and a graduate course (AOS 235) on climate change impacts on the ocean. It was also use to create outreach activities for K-12 and community outreach, including at Central High School, an under-resourced school supporting Native American and Latinx students in downtown Los Angeles. The work was also highlighted in outreach to Latinx and African-American girls that are age 6-8 through Project Scientist. Last Modified: 02/24/2019 Submitted by: Robert Eagle