Project: Epidemiology and spatial ecology of a tropical coralline fungal disease in the face of ocean warming and acidification

Coral reefs worldwide have suffered catastrophic losses of calcifying (reef-building) organisms such as corals and crustose coralline algae (CCA). These calcifiers construct and cement the reef together, providing a complex three-dimensional structure for a diverse array of reef-associated species. On many reefs, these calcifiers have been replaced by non-calcifying, "fleshy" species such as seaweeds and other invertebrates. Such drastic shifts in ecosystem structure and function, documented since the 1980s, are driven by complex interactions between anthropogenically induced changes to the marine environment (i.e., eutrophication, sedimentation, or over-fishing), climate-related change (increase frequency and severity of storms, global warming, and ocean acidification), outbreaks of predators, and the spread of disease. Traditionally, investigations have largely focused on one stressor at a time, and rarely explore the complexity introduced when combinations of stressors impact a marine ecosystem, a reality most coral reefs face. This project examines an important, yet difficult to study, interaction between climate driven physical parameters (seawater temperature and pH) and the disease ecology of a coralline fungal infection, recently identified by investigators on this project, for an understudied but critical component of reef ecosystems. The primary scientific and societal broader impacts of this project will be advancing our ability to predict the future effects of climate change on disease outbreaks that negatively affect carbonate accretion and primary production of key taxa in coral reef ecosystems. This project supports the education and training of undergraduate students and a postdoctoral scholar in an international arena, engages the governor's Coral Reef Advisory Group in American Samoa, and informs the general public through in-person discussions online (Google Hangout) and at a Café Scientifique.

Many tropical species of CCA are particularly sensitive to slight changes in temperature and pH in an experimental setting and the central hypothesis is that climate induced change will hasten the spread and severity of the coralline fungal disease (CFD). The exact mechanisms of how and why a previously healthy CCA host becomes infected by the endolithic fungi are unclear. Thus the two major goals of the proposed research include: 1) a description of the CFD dynamics (incidence, prevalence, and mechanism of transmission across, and progression within, various coralline host species), and 2) an exploration of how climate-driven global change (i.e., rising SST and seawater acidity) will affect these dynamics using lab experiments and field observations. A combination of high-resolution, large-scale benthic imagery and novel sensor technology arrayed across reef habitats on Palmyra Atoll will be used to relate the spatial distribution of infected or resistant host CCA species, fungal colony-forming units, and environmental conditions over time in a natural setting at a reef-scale. High frequency time series of seawater pH, pCO2, salinity, and temperature data, calibrated and complemented by discrete sampling for additional carbonate parameters (total alkalinity and dissolved inorganic carbon), will be related with biological data (disease prevalence, incidence, and host physiology). In addition, these field measurements will inform laboratory experiments performed at an organismal scale and designed to test alternative hypotheses about agents of disease progression within a calcareous host.