Decline in plankton across North East Atlantic sends warning for ocean health

A study based on more than six decades of data suggests plankton abundance has declined across large areas of the North East Atlantic, covering waters from Portugal to Norway, including the North Sea.

Phytoplankton produce around half of the Earth’s oxygen, while plankton support marine food webs, fisheries, carbon cycling and wider ocean ecosystems.

The study combined data from 23 plankton datasets provided by 13 research institutions with satellite observations to produce what the researchers describe as the first quantitative, integrated assessment of whether the pelagic habitats of western Europe meet Good Environmental Status under the EU and UK Marine Strategy Framework Directive.

Pelagic habitats are open-water environments where plankton are the dominant organisms. Previous policy assessments have described changes in plankton populations but have not integrated those findings into a regional environmental status assessment. In this study, researchers combined monitoring data from assessment units and fixed-point stations before integrating multiple plankton indicators and habitat types to assess regional environmental status.

The assessment found that none of the pelagic habitats examined across the North East Atlantic achieve Good Environmental Status. Six habitat-region combinations are classified as Not Good Environmental Status, three as Uncertain and one as Not Assessed because of insufficient data.

At a regional level, the Celtic Seas and the Bay of Biscay and Iberian Coast are classified as Not Good Environmental Status, while the Greater North Sea is classified as Uncertain. The weakest results are generally recorded in shelf habitats, where changes in plankton communities and declines in phytoplankton biomass and zooplankton abundance are most evident.

The study also identifies rising sea surface temperatures, changing nutrient conditions, declining pH and altered ocean mixing among the factors associated with changes in plankton and their habitats.

Reducing emissions best way to slow decline

The researchers say reducing greenhouse gas emissions is the most significant action to help protect pelagic habitats. They also identify reducing nutrient pollution, particularly nitrogen, and maintaining investment in long-term plankton monitoring as priorities. Several long-term plankton monitoring programmes within the OSPAR assessment area have already been paused or face uncertainty because of reduced resources.

The study was led by researchers at the University of Plymouth and involved universities, scientific organisations and environmental agencies across Europe.

Lead author Abigail McQuatters-Gollop, professor of marine conservation at the University of Plymouth, says: “I’ve been studying plankton for more than two decades, but for the most part they are totally underappreciated. The majority of people don’t even know what they are, which is crazy when you think they are responsible for half of the breaths we take, form the diet of species such as blue whales and basking sharks, and are key to cycling carbon and removing it from our atmosphere.

“Our study is the first to provide a quantitative assessment of the state of plankton across key regions such as the Celtic Sea, the Bay of Biscay and the North Sea. It has shown there is an urgent need to improve the health of these waters and to reduce the harm we are causing to the ocean, at both a local and a global level.

“It has also shown we need to establish new ways that science and policymakers can work together to generate more data and figure out how we transition to good status in the future.

“The warning is clear: plankton are changing across some of Europe’s most important seas, and those changes matter far beyond the plankton themselves. They affect food webs, fisheries, carbon cycling and the wider benefits people receive from the ocean. The challenge now is to use this evidence to drive practical action, from climate mitigation to better nutrient management and long-term monitoring.”

The research drew on contributions from around 40 plankton experts working through OSPAR, the Regional Seas Convention for the Northeast Atlantic. It also builds on the OSPAR Quality Status Report 2023, which assesses the condition of the Northeast Atlantic marine ecosystem.

The assessment is based on 23 phytoplankton and zooplankton abundance datasets covering the Greater North Sea, the Bay of Biscay and the Celtic Sea. Researchers compared measurements including water depth, sea temperature, salinity, plankton biomass and species diversity to assess the environmental status of pelagic habitats against criteria developed through OSPAR.

Each region and habitat was assigned one of four classifications: Good Environmental Status, Not Good Environmental Status, Uncertain status or Not Assessed, depending on the integrated assessment and the availability of data.

The full study – McQuatters-Gollop et al: Integrating plankton indicators to assess the state of pelagic habitats in the Northeast Atlantic – is published in Ecological Indicators.