This summer, European coastal waters experienced record-breaking heat, setting new records since satellite measurements began in 1982. According to an analysis of surface temperature data, sea temperatures soared across regions from the English Channel to the Mediterranean, with an offshore buoy near Mallorca registering a peak of 33.02°C on August 5, the highest recorded in Spain’s port authority network. Experts attribute these unprecedented marine heatwaves to the broader impact of rising global temperatures driven by greenhouse gas emissions, noting that oceans absorb and retain much of the excess heat, reshaping marine ecosystems and threatening fisheries.

Between June and August, European seas averaged 21.6°C, marking the warmest summer in 45 years. The Bay of Biscay, spanning the Atlantic coastlines of France and Spain, experienced particularly severe warming. Water temperatures there averaged 21.4°C during the same period, exceeding the 1991-2020 average by more than 2.4 degrees. On August 13, surface readings peaked at 23.2°C—the highest ever recorded by satellite in the area. Scientists define a marine heatwave as five or more consecutive days of water temperature significantly above historical averages. While the Bay of Biscay previously saw only a few such days annually in the 1980s, this year it recorded 186 days—more than three out of every four days.

The rapid and sustained warming has led to the near disappearance of kelp forests along the Asturias coast in northern Spain, once abundant underwater ecosystems critical for regional fisheries. Marine ecologist Jose Manuel Rico Ordas reported that about 95% of the large brown seaweed has vanished since 2010, largely due to higher water temperatures exceeding kelp’s preferred threshold of 20°C. Overgrazing by species such as the warm-water dramfish has compounded the loss. The decline in kelp has had cascading effects on marine life, including the disappearance of lobsters, crayfish, and sea urchins, all integral to local fisheries.

Fishermen in Galicia have collaborated with scientists and activists to attempt restoration efforts by planting laboratory-grown kelp seedlings. Manuel Angel Reiriz Gonzalez, president of a fishermen’s guild in the area, highlighted the threat climate change poses to traditional livelihoods. His family, which has harvested sea urchins and clams for generations, has seen the influx of invasive species like Portuguese man o’ war and trigger fish, further disrupting local ecosystems. While some recovery has been achieved through clam reseeding programs, concerns remain that ongoing habitat loss may jeopardize the fishermen’s future.

Elsewhere in Europe, the Mediterranean is witnessing a rise in non-native species entering through the Suez Canal, with over 1,000 alien species reported by a recent regional scientific survey. These newcomers are altering food webs and competitive dynamics in the basin’s fisheries.

In the English Channel and along the south coast of England, warming waters have allowed species like the common octopus to flourish. Annual octopus catches have surged from less than 30 metric tons before 2025 to over 3,000 tons this year, according to the UK Marine Management Organisation. Researchers from the Marine Biological Association attribute this expansion to prolonged marine heatwaves that have persisted for roughly half the year since 2022, enabling octopuses to breed locally rather than relying solely on larvae transported from more southerly breeding grounds.

This octopus population boom has generated mixed economic impacts. For some, like Devon-based fishmonger Ian Perkes, the rise offers new commercial opportunities, especially in southern European markets where demand is high and no quotas limit harvests. However, members of the South Devon and Channel Shellfishermen’s cooperative describe the situation as an “octopus apocalypse,” reporting drastic declines in catches of crabs, lobsters, and scallops due to predation by octopuses. The cooperative’s executive officer, Beshlie Pool, noted that four vessels have ceased operations in the past year amid these challenges.

Scientists warn that the unpredictable nature of these ecosystem changes complicates adaptation efforts. If octopuses overconsume local shellfish populations and subsequently experience die-offs, fishermen could face further uncertainty about future stocks and livelihoods. The current marine heatwaves and their cascading effects underscore the growing vulnerability of European fisheries in the face of climate change.