UK seas are heating up, and the ocean food web may pay for it by 2050

Warming seas around the UK and the wider north-east Atlantic could knock marine food webs off balance by 2050, according to a four-year study led by the Centre for Environment, Fisheries and Aquaculture Science (Cefas). The research, published in Science Advances, projects that under a scenario of 3C of warming by 2100, the mix of species in these waters will reshuffle unevenly — with predators gaining and the tiny organisms they eat losing ground. That mismatch, the authors warn, could weaken ocean health and put food security at risk.

The numbers tell the story. By mid-century, fish and seabed invertebrate diversity could climb by about 12%, while phytoplankton diversity slips about 3% and zooplankton about 7% by 2050. Plankton sit at the base of the food chain, so losing species there matters far more than the raw percentages suggest. The team projected the effects across four key groups of marine life using long-term datasets and machine-learning techniques, extending their predictions out to 2100.

Elena Couce, a marine ecologist at Cefas and co-lead author, said the results upended the usual assumption about middle latitudes. Scientists expected species fleeing the equator to push north and south into UK waters, lifting biodiversity overall. Instead, warming didn't move diversity in one direction across the board — some groups gained species while crucial plankton groups lost them.

Lily Greig, another Cefas marine ecologist who co-led the study, put it bluntly: when predator diversity rises and prey diversity falls, the food chain can be disrupted. She said the findings show gains in some groups don't mean the ecosystem as a whole is getting more resilient. The seas around the British Isles, especially the southern North Sea, rank among 20 global marine climate hotspots that have warmed fastest over the past 50 years.

Earlier Cefas work on key fish species pointed to climate winners in north-western European waters, including anchovies, seabass and sardines, and losers such as Atlantic cod, haddock and coley. The new study covers UK waters and the wider north-east Atlantic, including Ireland and France, and involved researchers from the University of East Anglia, the Marine Biological Association, UiT the Arctic University of Norway, the Royal Netherlands Institute for Sea Research and the Technical University of Denmark.

The researchers say pinpointing where biodiversity is shifting fastest could work as an early warning system for ecosystem change. The work has already been handed to the government's review of marine protected areas, which is weighing fishery management measures. Couce's message to policymakers: climate change is already altering biodiversity, and any other management plan has to account for that first.