Marine heatwaves threaten European coasts and marine ecosystems

Marine heatwaves are prolonged periods of unusually high sea‑surface temperatures that can last from days to months, affecting surface waters and even depths beyond one kilometre. They are driven by sustained hot, sunny, low‑wind conditions that limit mixing of warm surface water with cooler deeper layers, by overall climate‑change‑induced ocean warming, and by large‑scale phenomena such as El Niño.

The impacts are wide‑ranging: coral bleaching, the spread of heat‑loving species and mortality of vulnerable organisms, including shellfish, can disrupt fisheries, aquaculture and tourism. Stressed marine life may release stored carbon, amplifying greenhouse‑gas effects. Warmer oceans also increase evaporation, adding moisture to the atmosphere and potentially intensifying rainfall and flood risk on land, while reducing the cooling breezes that normally moderate coastal temperatures.

These changes are being observed across parts of the Mediterranean, with experts in Greece and Cyprus highlighting the need for further research and monitoring.