A new report has revealed the scale of climate-driven change already reshaping plankton communities across UK seas, with consequences that reach from the ocean floor to the food on our dinner tables.

Published by the Marine Climate Change Impacts Partnership (MCCIP) and led by researchers at the University of Plymouth, the assessment draws on a review of more than 500 scientific studies to document shifts already underway at the very base of the marine food web, and to project what those shifts mean for the health of UK waters in the decades ahead.

Long-term monitoring shows declines in both large phyto- and zooplankton in oceanic waters beyond the continental shelf, while smaller plankton and microbial species are increasingly dominating in warmer, stratified shelf waters. 

The problem with that substitution – the report notes –  is efficiency. Smaller species transfer energy less effectively up the food chain, reducing the food available to the fish, seabirds, and marine mammals that depend on them. The timing of the spring plankton bloom – a critical event that triggers feeding and spawning across the entire ecosystem – has already advanced in many parts of the North Sea, creating the risk of dangerous mismatches with fish spawning cycles that have evolved over millennia.

Warming seas are driving warm-water species northward while others contract their southern ranges or disappear from them altogether. Jellyfish are increasing in some regions. Marine heatwaves are imposing new and still poorly understood stresses on plankton communities. And all of it is being amplified by human activity which includes eutrophication, agricultural runoff, coastal darkening caused by land-based sediment, commercial fishing pressure, and the development of offshore energy infrastructure.

“Plankton form the foundation of marine food webs, supporting fisheries and playing a fundamental role in carbon cycling, yet they often receive far less attention than more visible parts of the marine environment,” said Dr Matthew Holland, Research Fellow at the University of Plymouth’s Centre for Marine Biology and Conservation Science and lead author of the report. 

“By summarising the latest evidence, I hope this report provides policymakers, managers, and the wider public with a better understanding of how climate change is already affecting UK seas, and what future changes could mean for the benefits that our shared marine ecosystem provides to society.”

Future warming is expected to further intensify water-column stratification, depleting the levels of nutrients towards the surface of the ocean and reduce overall primary productivity. Smaller phytoplankton species -better adapted to nutrient-poor conditions – are expected to become more dominant, weakening the transfer of carbon to the seafloor that UK seas currently provide, and reducing the ocean’s capacity to draw down atmospheric carbon. 

Fish larvae, meanwhile, will likely need more prey to survive as warmer water increases their metabolic demands – a pressure that arrives precisely as the food web producing that prey becomes less productive.

The report, which updates a previous MCCIP assessment published in 2020, was coordinated by Dr Holland alongside 17 co-authors drawn from institutions including the Marine Biological Association, Plymouth Marine Laboratory, the Environment Agency, Cefas, the Scottish Government, and the Scottish Association for Marine Science. Its authors note significant gaps in monitoring across parts of the coastal and marine environment, leading to uncertainty in some regional trends – a gap they argue must itself become a policy priority.

Professor Abigail McQuatters-Gollop, Professor of Marine Conservation at the University of Plymouth and a co-author of the report, has spent decades tracking exactly these changes. “We have been saying for decades that plankton communities are changing as a result of shifts in the global climate and human activities, and more comprehensive evidence is the only way we can bring that to greater attention,” she said. 

“This report, and the robust scientific evidence it is based on, can hopefully be another piece of the jigsaw that ultimately leads to joined-up action for marine biodiversity management at a regional and global scale.”

Plankton are rarely the subject of public concern in the way that whales, coral reefs, or seabirds are, remaining invisible to most people while the crisis they face unfolds in waters far from the public eye. However, the authors are quick to note that the food on our plates, the fish in the sea, and the carbon in the atmosphere are all – in the end – plankton problems. 

This report – they suggest – is one more piece of the puzzle to give us a clear picture of the health of the global ocean.

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