Postdoctoral Fellowship: EAR-PF: Tracing Coral-Algal Symbiosis Across Geologic Time Using Nitrogen Isotopes

Coral reefs support marine biodiversity, protect coastlines from storms, and sustain fisheries, tourism, and other livelihoods. These benefits depend on a partnership between corals and algae that live inside coral tissues. When ocean temperatures or nutrient conditions change, this partnership can fail, leading to coral bleaching, mortality, and reef declines. Because algae are rarely preserved as fossils, scientists have few ways to determine whether ancient corals hosted algal partners or how that partnership changed through Earth's history. This project will examine how past changes in coral-algal symbiosis were linked to the persistence, transformation, or decline of coral reefs under past environmental conditions comparable to those affecting reefs today. The project serves the national interest by improving knowledge relevant to coastal protection and resource management while enhancing the science and technology workforce through undergraduate and high school research opportunities. This project will calibrate and apply coral skeleton-bound nitrogen isotopes as a proxy for reconstructing coral-algal symbiosis through geologic time. The project builds on evidence that symbiotic corals have distinct nitrogen isotopic composition compared to symbiont free corals because algal symbionts recycle ammonium within the coral assemblage. The main research effort will analyze well-preserved fossil and sub-recent coral collections spanning the Miocene through the Anthropocene and include multiple coral species from each interval, allowing comparisons among taxa, reef communities, and regions. Skeleton-bound organic nitrogen will be extracted and analyzed for nitrogen isotopic composition. Targeted laboratory experiments under reef-relevant nutrient and temperature conditions will help interpret the fossil skeleton-bound nitrogen isotopic composition. By linking coral-algal symbiosis and reef paleoecology to past environmental change, the project will improve understanding of coral reef resilience and help society anticipate changes in reefs that support biodiversity, coastal protection, and livelihoods. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.