Marine heatwaves are reshaping the ecosystem of British seas, with shifting water temperatures causing significant changes in fish populations and marine biodiversity. Traditionally cold-water species such as cod have become increasingly rare off the southern coast, with fishers reporting dramatic declines in catches. Meanwhile, warm-water species including bass, comber, triggerfish, sardines and anchovies are becoming more abundant in these same areas.
The warming waters are also facilitating the arrival and proliferation of species not typically found in British coastal regions. Small-spotted catsharks, which prefer temperatures around 16-17C, have become scarce as summer waters reach approximately 20C. In contrast, common octopuses, native to the UK but rarely seen, have arrived in significant numbers since January of the previous year, creating challenges for crab and lobster fishers while simultaneously providing a food source for marine predators. Risso’s dolphins and various jellyfish species, including potentially problematic mauve stingers from the Mediterranean, have also been observed with greater frequency.
Other species making rare or unprecedented appearances include smalltooth sand tiger sharks and hair curler sea slugs, typically found in warmer regions. Scientists are monitoring newly arrived sea squirt species to determine whether they may cause ecological damage similar to invasive carpet sea squirts.
The warming poses serious threats to critical marine habitats. Kelp forests and seagrass meadows, which provide essential shelter for marine animals and protect shorelines from erosion, are under particular stress. The UK has lost approximately 92% of its seagrass meadows since the 1930s, with some regions experiencing kelp losses exceeding 96%. Researchers are working on conservation efforts, including cultivating kelp varieties adapted to warmer temperatures and restoration projects aimed at recovering 15% of UK seagrass meadows by 2030.
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