• A study by Ifremer reveals that the composition of plankton has been permanently affected by human pollution since World War II.

  • The analyzes were carried out in the harbor of Brest where the presence of heavy metals following the bombardments was observed.

  • The waters of the harbor are also contaminated by intensive agriculture.

It is not good to be a plankton in the harbor of Brest. A study published on Monday by Ifremer thus shows that the composition of these microorganisms has been irreversibly affected by pollution caused by the Second World War and intensive agriculture. To achieve this result, researchers at the institute took sediment cores several meters in length in the harbor and then analyzed the DNA preserved in these sediments to determine which organisms it belongs to.

Scientists have thus been able to trace the plankton species present in the water for around 1,400 years.

The most radical variations appear from the Second World War.

And starting in the 1980s, researchers saw an increase in the abundance of toxic microalgae, such as the dinoflagellate Alexandrium minutum which produces paralyzing toxins.

The presence of heavy metals due to the bombardments

“We expected to find a change in microalgae communities over the past decades, but not necessarily such a drastic change going back to World War II,” explains Raffaele Siano, biologist at Ifremer.

The presence of pollutants such as heavy metals or PCB would be at the origin of this change.

“The Brest harbor was marked by extreme pollution events during the Second World War, notably with Allied bombing, we found traces of it with high levels of heavy metals in the layers of sediments of the time. », Adds Raffaele Siano.

"Since then, the harbor has been the receptacle of chronic pollution with contaminants resulting in particular from intensive agriculture, which is what we find in the more recent sediments of the 1980s and 1990s", he continues.

Plankton play a key role in marine ecosystems

Over time, the plankton did not regain the composition it had in the Middle Ages, which “demonstrates the irreversibility of the changes observed after the cumulative effect of pollution from war and agriculture”, according to the study published in the American scientific journal

Current Biology

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Changes in the composition of plankton, which plays a key role in marine ecosystems, could also have "cascading effects on other biological components of the ecosystem, affecting the entire marine food web", believe the authors of the study.

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  • Ifremer

  • Pollution

  • Brest

  • Environment

  • Sea

  • Planet