Marine heatwaves are cooking our ocean ecosystems – and will only become more common

Marine heatwaves are causing damage to ocean ecosystems and will become more common as climate change continues to warm the ocean. These heatwaves occur when the ocean remains abnormally hot for a prolonged period, killing various marine life such as coral, seagrass, and fish. While we cannot prevent these disasters, understanding them and mitigating their impacts is crucial.

Marine heatwaves result from naturally occurring patterns when hotter water near the surface doesn't mix with cooler water below, or when strong currents carry extra heat from warmer regions to colder areas. Scientists measure ocean temperatures and compare them to historical averages to identify a marine heatwave, which must last at least five consecutive days.

These heatwaves can happen anywhere, but all marine ecosystems are at risk. Mobile species like fish can swim to cooler waters, but stationary organisms like coral and sea urchins cannot. This leaves stationary marine life directly impacted by marine heatwaves, often leading to reproductive struggles and food shortages. Economically and culturally, coastal communities can suffer dearly due to lost income from fisheries, aquaculture, and tourism industries, as well as damage to culturally significant sites.

In Australia, marine heatwaves have caused widespread coral bleaching, tree deaths, and endangered cockatoo population declines. In 2026, record-high sea surface temperatures in the Mediterranean, North, and Baltic Seas threaten marine ecosystems in those regions. Climate change is making marine heatwaves more common and severe, as the ocean's thermal baseline rises, amplifying their effects.