Heatwaves happen in the ocean as well as in the atmosphere. Marine heatwaves  are extended periods of unusually warm ocean temperatures relative to the typical temperatures for that location and time of year. Due to climate change, the number of days with MHWs has increased by 54% over the past century. These MHWs cause mortalities in a wide variety of marine species, from corals to kelp to seagrasses to fish to seabirds, and have consequent effects on ecosystems and industries like aquaculture and fisheries.
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report