Coral reef fish biomass and nutrient availability losses from thermal stress

Thermal stress driven by climate change is a major threat to tropical coral reef ecosystems1, with marine heatwaves expected to increase in frequency and intensity throughout the century. While corals are most often the focus of impacts2,3, thermal associated changes on reef fishes may lead to important flow-on effects for the nutrients available for people dependent on reef fisheries for food4. Here, we examine the cumulative impacts of thermal stress on reef fish assemblages between 1996 and 2020 to project the potential impacts of different climate change scenarios on reef fish biomass and associated nutrients available to human populations. We show that reefs that have experienced greater thermal stress in the past tend to have less reef fish biomass across all trophic guilds, and reduced nutrient availability across all nutrients. Applying such association to future thermal stress projections implies a continued decline in reef fish biomass and nutrient provision throughout the century. However, spatial variability in thermal stress projections pinpoints the locations and reef-based food systems that could (i) suffer the largest biomass and nutrient availability losses, and (ii) benefit the most from implementen climate mitigation strategies. Overall, our study provides empirical evidence that both climate change mitigation and adaptation are needed to bolster reef fish assemblages and associated tropical nutrition security.