CORAL REEF RESPONSES TO CLIMATE-INDUCED WILDFIRE DISTURBANCE

Wildfires are increasing globally in both frequency and severity, including on tropical islands adjacent to coral reefs. Burned materials from urban and rural fires, such as ash, smoke, and toxic compounds, are delivered to the atmosphere and waterways during and after wildfires. The impacts of wildfires, therefore, extend to terrestrial and aquatic ecosystems adjacent to burn zones, as well as those thousands of miles away. Within the last decade, research has shown how wildfires can impact nutrient cycling and production in the ocean. Yet the impacts of wildfires on ecologically sensitive coral reefs are largely unknown. Coral reefs foster the highest biodiversity per unit area of any aquatic ecosystem, providing $3.4B per year to the US economy alone through fisheries, tourism, and storm protection. This project expands our understanding of wildfire disturbances in tropical ecosystems by characterizing the effects of ash deposition on coral reefs and their microbial communities. This work contributes to our understanding of how wildfire and nutrient pollution affect coral reefs and will serve to inform coastal communities of fire risks to reef ecosystems. This project evaluates the functional impact of ash deposition from terrestrial wildfires on tropical coral reef ecosystems. Until the last decade, fire events in tropical latitudes were largely limited to agricultural controlled burns. Unfortunately, large scale tropical wildfire disturbances are becoming increasingly prevalent as the result of drought and more frequent and intense heatwaves. Fire acts as a nutrient transformer and ecosystem subsidy, changing the chemical composition of parent material and releasing large quantities of particles to the atmosphere (aerosols) and waterways (burned detritus), including nearshore and open-ocean ecosystems. Wildfires and the deposition of burned materials are known to have acute and long-lasting effects on nutrient dynamics and biodiversity in freshwater ecosystems. Yet little is known about the impacts of wildfires on coral reef ecosystems, alone or in combination with covarying environmental stressors, such as thermal stress. Through a series of bottle remineralization and controlled mesocosm experiments in Hawaiʻi, this research: 1) characterizes how microbial community composition and carbon metabolism is impacted by pyrogenic ash deposition; 2) evaluates the functioning of the coral holobiont in response to pyrogenic ash and increased temperature, both separately and in tandem; and 3) develops a mechanistic model to predict how scenarios of wildfire ash deposition and warming affect coral reef community composition. 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.