Award: OCE-1933165

Globally coral reefs are experiencing an increase in frequency and severity of bleaching events, a phenomenon where corals lose their photosynthetic symbionts. Coral bleaching frequently leads to coral death and altered ecosystem function of coastal marine habitats. This research studied a significant bleaching event on the Island of Mo’orea, French Polynesia to quantify how bleaching impacts the local and regional water chemistry and what impacts that has on the ecology of the reef. Intellectual merit: During a bleaching event that led to partial bleaching of up to 90% of the corals on the fore-reef, we found a 37% increase in dissolved organic carbon (DOC) on the reef in contrast to decade-long averages. This comparison was facilitated by comparing our data to the Mo’orea Long Term Ecological Research (MCR-LTER) site which is situated at our study area. Further, at this site corals are known to be DOC sinks. However, corals appeared to be significant sources of carbon to the marine system as they were bleaching. We also, through empirical studies, showed that when healthy corals are exposed to this DOC it can lead to rapid tissue loss and death of the corals. This is a heretofore unrecognized feedback loop where one coral bleaching can facilitate the bleaching of adjacent corals. In addition, during the bleaching event, we quantified a disruption to the normal microbial community that inhabits the corals and an increase in viral diversity within the corals, providing a better understanding of the link between bleaching and marine homeostasis and disease. Finally, by extrapolating our quantification of DOC released during bleaching, we estimate that mass bleaching events could release giga-moles of carbon, a previously unrecognized source of carbon dioxide to our oceans and atmosphere. Broader Impacts: Coral reef health is a critical component of tropical coastal communities and thus identifying a previously unknown feedback loop of carbon stress and identifying the role of bleaching in the global carbon cycle advances our understanding of a societally-relevant concern. To communicate the impacts of this research, we collaborated with an aspiring undergraduate film student who created a short form film about this work. We also included the results into two courses that over the life of the award, communicated this research to 345 undergraduate students at Oregon State University. Further, this research was the topic of or facilitated 3 masters students’ thesis and 1 PhD student’s dissertation. Last Modified: 04/06/2023 Submitted by: Andrew R Thurber