European waters have just had their hottest June-to-August period in 45 years of available data.

An analysis of sea-surface temperatures found that average temperatures across European seas reached 21.6°C this summer. The heat was especially pronounced in the Bay of Biscay, where waters averaged 21.4°C, which is more than 2.4°C above the 1991-2020 average.

An offshore buoy near Mallorca also recorded 33.02°C on August 5, the highest temperature ever registered in the Spanish port authority’s buoy network.

The concern is not simply about warmer water. Marine heatwaves can change where species live, reproduce, and feed. This change can quickly affect fishermen whose livelihoods depend on relatively stable marine ecosystems.

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Too toasty

Sea surface temperatures were in excess of 5°C above normal. The extreme sea surface heat around western Europe boosted the land heat to record highs | X (@PCarterClimate)
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Sea surface temperatures were in excess of 5°C above normal. The extreme sea surface heat around western Europe boosted the land heat to record highs | X (@PCarterClimate)

A marine heatwave is generally defined as at least five days when sea temperatures remain unusually high for that location and time of year.

In the Bay of Biscay, such events were once relatively limited. By the end of August this year, the bay had recorded 186 heatwave days, Reuters found.

Scientists say the warming seas are becoming more frequent, intense, and widespread as greenhouse gas emissions raise global temperatures. The oceans absorb most of the planet’s excess heat and retain it for longer than land and the atmosphere.

Jean-Pierre Gattuso, a senior research scientist at France’s National Centre for Scientific Research, described the speed of change as particularly striking.

“What is surprising is the speed at which this occurs,” he said. “Records are broken almost every day in many places.”

A changing rhythm

A massive heat dome is making a dramatic return across Europe | X (@PCarterClimate)
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A massive heat dome is making a dramatic return across Europe | X (@PCarterClimate)

The Bay of Biscay shows what that change can mean on the ground.

Northern Spain once had extensive kelp forests that provided food, shelter, and nursery grounds for many marine species. Jose Manuel Rico Ordas, a marine ecology professor at the University of Oviedo, estimates that roughly 95% of the large brown kelp stands along parts of the Asturias coast have disappeared since 2010.

Thousands of records will be smashed in Spain, France, Germany, Switzerland, Scandinavia etc. Europe is completely rewriting its climatic history | X (@extremetemps)
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Thousands of records will be smashed in Spain, France, Germany, Switzerland, Scandinavia etc. Europe is completely rewriting its climatic history | X (@extremetemps)

He attributes the decline primarily to climate change and says kelp generally needs water below about 20°C to survive.

With the habitat disappearing, species associated with it are also becoming harder to find.

“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.

Fishermen and scientists are now trying to restore kelp by planting laboratory-grown seedlings.

New arrivals, fishermen’s worries

Life in hot water | X (@PlanktonPundit)
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Life in hot water | X (@PlanktonPundit)

At the same time, warmer waters are allowing other species to expand into places where they were once uncommon.

In the Mediterranean, researchers say more than 1,000 non-indigenous species have been recorded, many arriving from warmer regions through the Suez Canal.

Britain offers another example. Fishermen along the south coast of England reported about 2,600 metric tons of common octopus landings in 2025 and more than 3,000 tons so far this year, compared with annual landings of less than 30 tons before 2025.

One thing to remember is that an increase in one species does not necessarily mean better fishing conditions overall.

Octopuses prey on crabs, lobsters, and scallops, and some shellfishermen say their traditional catches have suffered.

The South Devon and Channel Shellfishermen’s cooperative described 2026 as an “octopus apocalypse.”

The shift is becoming harder to ignore. As some familiar species decline and others move into new waters, fishermen are being forced to adapt to a sea that is changing faster than before.

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