Fish tails sticking out of blue containers labelled "Sydney Fish Market" and "Get hooked on fresh fish"

Ocean heatwaves, such as the 2010–11 ‘Ningaloo Niño’ off the coast of Australia, have triggered die-offs of fish popular with human diners. Credit: Brendon Thorne/Getty

Climate change

Heatwaves take their toll on the high seas

Long hot spells have affected every ocean on Earth, and are likely to grow in severity.

As marine heatwaves become longer and more frequent, they threaten to take a huge toll on global biodiversity and the services that the world’s oceans provide to humans.

During a marine heatwave, temperatures at the ocean’s surface are substantially warmer than usual for days at a time. Globally, the number of days marked by such heatwaves rose by more than 50% during the past century, and in the past decade there were several events of record-breaking intensity.

To examine the impact of these events, Dan Smale at the Marine Biological Association of the United Kingdom in Plymouth and his colleagues combined data on biodiversity, species’ heat tolerance and human pressures such as overfishing and pollution. The scientists found that heatwaves have caused harm in all ocean basins, affecting a wide range of organisms and biological processes. Loss of seagrasses and kelp forests is disrupting nutrient cycling, robbing species of their habitats and reducing carbon burial. Local extinctions are degrading commercial fisheries.

Future climate change will make marine heatwaves still more severe, the researchers warn.