Scientists are warning that marine heatwaves are significantly affecting marine life in European waters, with rising sea temperatures altering ecosystems and threatening fisheries and coastal communities. Sea surface temperatures across Europe reached record highs during the summer of 2025, marking the warmest levels since satellite records began in 1982. From the English Channel to the Mediterranean Sea, temperatures have broken historical records, with an offshore buoy near Mallorca recording 33.02 degrees Celsius on 5 August—the highest temperature ever recorded by the Spanish port authority's monitoring system. Experts attribute the increasing frequency, severity, and extent of marine heatwaves to global greenhouse gas emissions. European marine waters averaged 21.6 degrees Celsius from June to August, the highest peak in 45 years of collected data. In the Bay of Biscay, which averaged 21.4 degrees Celsius over the summer, heatwave conditions persisted for 186 days by late August—over three-quarters of the period. In the Bay of Biscay, once known for its cooler waters, kelp forests have seen a dramatic decline, with about 95% of large, brown seaweed stands disappearing since 2010. Kelp requires cold water, typically below 20 degrees Celsius, to thrive, and rising temperatures have contributed to its loss. Fish overgrazing, particularly by dreamfish, has further accelerated the decline of kelp forests. The loss of kelp has had cascading effects on local ecosystems, leading to the decline of species such as lobster, crayfish, and sea urchins, which are vital to regional fisheries. In response, efforts are underway to restore kelp forests by planting seedlings grown in laboratories, in an attempt to revive these critical habitats. In other parts of Europe, invasive species are entering the Mediterranean Sea from the Red Sea and beyond, often through the Suez Canal. These non-native species are displacing local populations and disrupting established food chains. In August, a massive swarm of jellyfish clogged the cooling system of France's Gravelines nuclear power plant, forcing it to shut down temporarily. Meanwhile, fishermen in southern England are reporting a sharp increase in common octopus landings, with around 2,600 metric tons caught in 2024 and upwards of 3,000 tons so far in 2025. Octopus larvae are carried into British waters by ocean currents from breeding grounds near the Channel Islands, Brittany, and areas further south. However, the rapid growth of the octopus population has led to a decline in local shellfish stocks, with some fishermen describing the situation as an "octopus apocalypse." The Marine Biology Association estimates that the octopus bloom could result in about £10 million in lost shellfish catches, compared to about £12 million in octopus landings between January and September 2025. This shift in marine life is highlighting the complex and often unpredictable consequences of climate change on coastal economies and ecosystems. As marine heatwaves become more common, scientists and local communities are working to understand and adapt to these changing conditions.