UK Seas Shift as Marine Heatwaves Reshape Wildlife
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- Sunfish sightings have surged off British shores this summer, with Brighton charter skipper Kurt Lander spotting them mid-Channel — a shift scientists attribute to ongoing marine heatwaves after the Met Office labelled last year "exceptional," with heatwave conditions persisting in some British waters for three-quarters of the year.
- Cod catches along the southern coast have collapsed from "at least a couple of hundred a year" to one or two per summer for Lander, as cold-water species shift their range to cooler Scottish seas and warm-water fish such as bass, comber and triggerfish replace them.
- Common octopuses have arrived in force in Devon and Cornwall since January last year, with 2026 catches soaring and some boats pivoting from crab fishing — though the octopuses are eating crabs straight out of pots in the process.
- Kelp and seagrass meadows have suffered devastating losses, with the UK estimated to have lost roughly 92% of seagrass since the 1930s and Sussex potentially down more than 96% of its kelp — a collapse that, project founder Chris Williams notes, plays out hidden beneath the surface unlike a burning woodland.
- Warm-water newcomers are turning up on UK beaches and in UK waters, including smalltooth sand tiger sharks, hair curler sea slugs normally found in the Caribbean and Mediterranean (first recorded in 2025), and a new sea squirt called Didemnum pseudovexillum now under close scientific watch.
- Dr Zoe Jacobs of the National Oceanography Centre in Southampton warned that cod and mackerel fisheries in southern waters may be "done," that beach-closure infrastructure for harmful algal blooms is not yet in place in the UK, and that cold-water species that moved north may never come back.
Why it matters: British fisheries face a generational restructuring: cod and mackerel may not return to southern waters even after heatwaves end, while Scottish boats gain from cold-water species shifting north and southern fleets pivot to triggerfish and octopus. The collapse of kelp and seagrass — vital carbon stores and coastal defenses — is a slower-burning cost UK policy and infrastructure are not yet set up to handle.
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