Award: DEB-1416889

Coral reefs inject billions of dollars annually into the US economy and are estimated to provide more than $375 billion of annual economic value globally. They protect coastal communities from damaging storms, feed more than half a billion people, and contain among the highest biodiversity of any habitat on the planet. Despite their major economic, societal, and biological importance, coral reefs have been severely damaged over the last few decades from the combined impacts of coastal development, pollution, overfishing and climate change. Recent studies report that nearly half of the corals across the planet have already died due to human stressors, and based on current trends, there is deep concern that the other half may collapse over the next 30-50 years in response to climate change. Coral reefs are complex ecosystems that contain a huge number of interacting species. Not all species show the same vulnerabilities to climate change, but the responses of entire reef ecosystems under future ocean conditions remains difficult to predict. The purpose of this study was to examine the responses of biologically diverse reef communities to ocean acidification and warming (the most serious threats posed to reefs by climate change), and to test whether experimental coral reef ecosystems collapse or persist under warmer, more acidic conditions like they will experience over coming decades. Results of this study confirm that ocean acidification and warming pose grave threats to coral reef ecosystems, and hence to the people and the economies that reefs support. Nonetheless, this study finds that coral reef ecosystems also show greater capacity than was previously thought possible to change in response to these stressors and persist. When exposed to acidification and warming simulating mid- to late-century conditions, reef communities experienced serious damage due to the death of some corals and other reef organisms, yet these species were replaced by others and the overall communities persisted and did not collapse as feared. Similarly, the corals showed greater ability to respond to ocean acidification and warming over coming decades than previously assumed. Even a modest amount of adaptation alters projections of reef futures substantially, demonstrating the importance of this study for predicting possible future outcomes of coral reefs under climate change. Unmitigated climate change, along with other stressors such as coastal development, overfishing and pollution, will undoubtedly result in catastrophic damage to coral reefs. Our results suggest that coral reef ecosystems freed from other anthropogenic impacts are likely to persist in an altered state. The technologies and knowledge base needed to mitigate many of these additional anthropogenic impacts already exist, underscoring the importance of societal decisions to maintain the valuable benefits that coral reefs provide. Our results demonstrate that effective mitigation of local and global stressors offers a viable pathway to preserve these iconic ecosystems as well as the economies and the people that they support for generations to come. Overall, the mesocosm array developed for this project formed the basis for 3 completed PhD dissertations and 4 on-going PhD dissertations. The cumulative training provided from this award included 7 post-doctoral fellows, 10 graduate students, 24 undergraduates, and 12 high school students, in addition to 8 international exchange students (61 cumulative personnel), of which 2/3 were women and more than 1/4 of them were from groups under-represented in STEM fields (the most common of which were Pacific Islanders). In sum, we expect more than 30 publications resulting in whole or in part from this award. Last Modified: 10/20/2020 Submitted by: Robert J Toonen