<>
European sea surface temperatures reached their highest level in at least 45 years of satellite records this summer, as prolonged marine heatwaves drove widespread ecological damage from the English Channel to the Mediterranean. Driven by greenhouse-gas emissions that trap atmospheric heat, European waters averaged 21.6 degrees Celsius (70.9 degrees Fahrenheit) between June and August, according to a Reuters analysis of satellite data dating back to 1982.
## Record Temperatures Surge Across European Waters
The extreme summer heat did not stop at the shoreline, shattering historical temperature thresholds across major marine basins. An offshore buoy near Mallorca recorded a temperature of 33.02 degrees Celsius (91.44 degrees Fahrenheit) on August 5, marking the highest reading ever registered in the Spanish port authority’s buoy network. Jean-Pierre Gattuso, senior research scientist at France’s National Centre for Scientific Research, noted the unprecedented pace of the warming. “What is surprising is the speed at which this occurs,” Gattuso said, adding that records are broken almost daily in various locations. The Bay of Biscay, situated off the Atlantic-facing coasts of France and Spain, experienced some of the most significant departures from normal conditions. Traditionally cool waters in the bay averaged 21.4 degrees Celsius (70.5 degrees Fahrenheit) over the three summer months, sitting more than 2.4 degrees Celsius above the 1991-2020 average. National Oceanic and Atmospheric Administration peaked on August 13 at 23.2 degrees Celsius (74 degrees Fahrenheit), setting a new high for the satellite era. Scientists classify a marine heatwave as a period of five or more days where water temperatures exceed an area’s historic norm. While the Bay of Biscay experienced only a handful of such heatwave days annually during the 1980s, it logged 186 heatwave days by the end of August this year, appearing on more than three out of every four days.
## Ecosystem Disruption and Kelp Forest Decline
The prolonged ocean heat is transforming marine ecosystems and threatening regional fisheries, according to a review of scientific literature and interviews with researchers and fishing industry sources. Rising temperatures subject marine life to physiological stress, reducing immune function and triggering mass mortality events. In the Bay of Biscay, the rise in temperature has devastated local underwater habitats. Jose Manuel Rico Ordas, a professor of marine ecology at the University of Oviedo in northern Spain, estimates that roughly 95% of large brown seaweed stands along the Asturias coast have vanished since 2010. Kelp forests require cold water, typically remaining below 20 degrees Celsius (68 degrees Fahrenheit), to survive. As temperatures climb, these kelp stands are disappearing, exacerbated by fish overgrazing from warm-water species such as dreamfish. “We are finding no more lobster, no more crayfish, no more sea urchins and many other species that are associated with the good status of kelp forests,” Rico Ordas said.
## Broader Impacts on Marine Life and Fisheries
The cascading effects of marine heatwaves extend across the marine food web. Rising temperatures alter migration paths for fish and marine mammals, forcing predators to search for displaced prey and disrupting spawning habitats. Reduced reproductive success during heatwaves can result in fewer young fish surviving to adulthood, ultimately shrinking future population sizes. In response to the rapid degradation of coastal habitats, conservation efforts are underway. Fishermen, scientists, and environmental activists have begun collaborating to restore kelp forests. Projects include seeding small stones with laboratory-grown kelp and manually tossing them into coastal waters, an effort supported by local fishing guilds in Galicia, such as those led by Manuel Angel Reiriz Gonzalez, president of a local fishermen’s guild in Ribeira.
Related reading