ENSO-Driven Ocean Extremes and Their Ecosystem Impacts

El Niño–Southern Oscillation (ENSO) events can cause extremes in the ocean environment that have substantial impacts on marine ecosystems. In the shallow-water/coastal marine environment, ENSO-related extremes in sea level and seawater temperature have been found to impact coral, kelp, seagrass, and mangrove ecosystems. Coastal impacts from sea level extremes include exposure of shallow-water ecosystems and inundation in low-lying areas. Ocean temperature extremes, including marine heatwaves, cause coral bleaching and can impact kelp and seagrass density. This chapter reviews knowledge and understanding of ENSO’s role in sea level extremes and ocean temperature extremes, and their impacts on these key shallow-water/coastal marine ecosystems.