Marine scientists warn that continued warming of South Hams waters is likely to cause major changes to plankton, the tiny drifting plants and animals that form the foundation of marine food webs and feed the fish that end up on our plates.

A new study from the Marine Climate Change Impacts Partnership (MCCIP) reveals that climate change is making the UK’s marine food web less efficient. As plankton communities change, less energy is passed up the food chain to fish, raising concerns about the future productivity of UK fisheries and the long-term security of seafood supplies.

Findings from the review, Impacts of Climate Change on plankton and pelagic habitats in UK waters around the UK and Ireland, show that as sea temperatures rise, the annual spring plankton bloom is expected to start earlier and last longer in some areas, while many plankton species’ populations are likely to shift further north, following a latitudinal shift in suitable conditions. Fish and other marine wildlife are expected to follow these shifts.

Pelagic habitats, and the plankton they support, form the foundation of marine ecosystems in UK waters, underpinning fisheries, food webs, biodiversity, and climate regulation.

Plankton are sensitive to environmental change, making them useful early warning indicators of climate impacts.

The rolling review is led by Dr Matthew Holland from the Centre for Marine Biology and Conservation Science (CMACS) at the University of Plymouth and co-authored by scientists including David Johns and Dr Clare Ostle at the Marine Biological Association, Plymouth Marine Laboratory, Environment Agency, Cefas, the Marine Directorate of the Scottish Government and the UK Scottish Association for Marine Science.

They worked from a range of data sources that bring together the latest evidence on how climate change is affecting UK seas, including impacts on habitats, species, fisheries and coastal communities.

A key source of data was the Marine Biological Association’s Continuous Plankton Recorder (CPR) Survey, one of the world’s longest-running and most geographically extensive marine ecological surveys.

Its near-century record of plankton observations is crucial evidence as it allows scientists to distinguish long-term climate-driven changes from natural variability, track shifts in plankton abundance, timing and distribution, and to assess what those changes mean for food webs, fisheries and ocean health.

The scientists predict that warmer seas will become more ‘layered’, making it harder for nutrients from deeper waters to reach the ocean surface.

This could reduce the amount of plankton produced overall and favour the smaller species that can survive in nutrient-poor waters.

David Johns explains: “This new MCCIP report shows that warming seas are driving major changes in plankton communities around the UK and Northeast Atlantic.

Spring blooms are occurring earlier, warm-water species are shifting northwards, and smaller plankton and microbial species are increasingly replacing larger, more nutritious plankton.”

These changes matter because plankton support virtually all marine life, from commercially important fish to seabirds and marine mammals. Changes could make marine food webs less productive and less efficient, potentially affecting fish populations and reducing catches in some fisheries.

Fish most likely to be affected by these changes include herring, mackerel, sprat, and sandeel (an important prey for seabirds, larger fish and marine mammals).