A widespread decline in summer abundance of the most nutritious plankton types across the north-east Atlantic continental shelf is affecting animals higher up the food web such as fish, marine mammals, and seabirds, says a new study published today in the journal Global Change Biology.

A change from cloudy, wetter summers to hotter, drought conditions leads to earlier onset and increased stability of the warm surface layer in shelf waters. These conditions lead to persistent sub-optimal conditions for larger omega-3 rich phytoplankton, and favour smaller, less nutritious picophytoplankton, especially the cyanobacterium Synechococcus. This change negatively impacts the success of the copepod community, and propagates throughout the food web. This trend has been observed over the last 60 years.

A new study published today in the journal Global Change Biology says that "Extended periods of water column stratification, droughts and heat waves … across the NE Atlantic … will increasingly benefit the advance of Synechococcus into shelf areas."

The study was led by scientists at the University of Plymouth, working with colleagues from Plymouth Marine Laboratory, the Marine Biological Association, and the University of Southampton. It brought together experts from a range of fields including trace metal analysis, plankton taxonomy, and satellite data.

Lead author Dr Katrin Schmidt, a plankton ecologist in the University of Plymouth’s School of Geography, Earth and Environmental Sciences, said: “Zooplankton such as copepods are considered beacons of climate change, and the ~50% decline in their abundance over the last six decades is worrying. Our study is the first to provide a mechanism for such a wide-spread decline, and this understanding is essential to project future responses to climate change. We also need to explore the wider impacts and whether the changing nutrient supply could, for example, lead to reductions in omega-3 within the entire food chain.”

Co-author, David Johns, Head of the Continuous Plankton Recorder Survey, added: “While the CPR Survey samples the larger plankton community, declines in some key groups over past decades can be linked to changes in the smallest plankton that are driven by climate change. We have previously witnessed direct climate impacts on the plankton community, from seasonality (temporal) to large scale movements (spatial), via changes in temperature. This study demonstrates a knock-on effect through the food web, and it is only by continuing our monitoring that we will identify multiple stressors acting on our marine environment, and hopefully sustain and protect our productive oceans.

Read the University of Plymouth press release.

Find out more about the Continuous Plankton Recorder Survey (CPR Survey)

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Jun 8, 2020 By guba