CAREER: Characterizing the mechanisms linking bleaching recovery to pathogen susceptibility in a model cnidarian system

Coral reefs are an example of fragile symbioses and have been declining in health in recent years. Coral reefs support global marine ecosystems and have been undergoing a destructive breakdown of the symbiotic relationships with their microbes, resulting in bleaching and decimation of fish and millions of other organisms that depend on stable coral reefs for survival. This project will use a coral model system called a brown anemone to investigate how breakdown and re-establishment of symbioses affect host immunity and pathogen susceptibility. The results of this work will have conservation implications. Specifically, by advancing our understanding of coral symbioses and coral resiliency, the results of this project may be able to enhance the survival and recovery of reef-building corals and the rebuilding of damaged coral reefs. These reefs support the marine fisheries and coastal tourism economy of the United States, making this research essential for advancing the bioeconomy. This research will also contribute to the education of Americans by providing undergraduate students with the opportunity to participate in project-based research through hands-on research opportunities in the summer and course-based research experiences during the academic year. Symbiotic associations between microbes and their animal hosts have significant impacts on host fitness including host immune responses. However, little is known regarding the impact of dynamic changes in symbioses on host immunity. This project leverages the cnidarian model system Exaiptasia diaphina to characterize how environmentally-induced breakdown and recovery of symbiosis affects host immunity and pathogen susceptibility. The central hypothesis is that dynamic changes in both energetic reserves and photosymbiont density affect host immunity during bleaching recovery, with effect sizes varying through time. Specifically, the project will: 1) characterize mechanisms linking heat-induced symbiosis breakdown and recovery to increased pathogen susceptibility, and 2) compare these mechanisms linking symbiosis breakdown/re-establishment to increased pathogen susceptibility across environmental triggers (heat, cold, light). Exaiptasia diaphana will be exposed to various environmental triggers of symbiosis breakdown and tracked through 4 weeks of recovery using a combination of physiological sampling and periodic pathogen challenges to characterize mechanisms linking bleaching and increased pathogen susceptibility. The results of these three objectives will be synthesized to create a robust conceptual model describing the effects of dynamic changes in symbioses on host immunity. This model will provide an important conceptual framework which can be applied to and evaluated in the context of diverse symbiotic systems. As a result, the outputs will directly inform improved understanding of symbioses in the context of multiple stressors. 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.