War, urbanization, pesticides, plastics... How have human activities disrupted the ecosystems of Eu-rope's coasts?

All pollution generated by human activities eventually reaches the ocean, with coastal ecosystems in the front line. In 2023, Ifremer has embarked on a vast European survey, taking 124 sediment cores from 15 coastal sites in 9 countries. The aim: to find out if and how major historical events of the Anthropocene, such as the Second World War, Chernobyl or the rise of certain practices ranging from pesticide use to port construction, have upset the fragile health of ecosystems.

Did you know that human history is also archived in marine sediments? This is what Raffaele Siano, a researcher in the molecular ecology of micro-organisms at Ifremer, revealed in 2021 in the journal Current Biology, when he demonstrated, thanks to traces of ancient DNA preserved in sediments, a clear correlation between drastic and irreversible changes in the planktonic communities of the Brest roadstead and major human impacts, notably the Second World War and the rise of intensive agriculture.

These locally-demonstrated discoveries were the first step towards a larger project called Paleocore, which is part of two other European programs:

• The TREC (Traversing European Coastlines) project, conceived by the EMBL - European Molecular Biology Laboratory, in collaboration with the Tara Océan consortium, the Tara Océan Foundation, the EMBRC and over 90 scientific institutions, includingIfremer. Its aim is to explore the biodiversity and adaptability of microbial communities and a selection of key organisms along European coasts from Finland to Greece. Over an 18-month period, the scientific teams involved collected 70,000 samples of water, soil, sediment and air from 115 sampling sites on land and at sea.
• The BIOcean5D project, jointly led by EMBL and CNRS, involves more than 20 institutes in Europe, including Ifremer. It shares a common goal of exploring marine life and its evolution in relation to space, time and the impact of mankind.

Going back in time to better understand current and future developments

Unlike other studies organized as part of TREC or BIOcean5D, Ifremer's scientists have not sought to study the current diversity of plankton and organisms by taking live samples.

“The whole point of the Paleocore project lies in this 'paleo' prefix,” insists Raffaele Siano, a researcher in the molecular ecology of micro-organisms at Ifremer. Just as paleontologists used traces of metals and fossils found in geological layers to link the disappearance of the dinosaurs to intense volcanic activity and a meteorite fall in the Cretaceous, we're looking to link changes in plankton communities to major historical human impacts by tracking traces of pollutants and DNA of different plankton species in ancient marine sediments”.

Over 10,000 samples collected in 9 European countries

Of the 124 cores measuring between 50 and 120 cm that were taken in 2023 and 2024 at 15 sites in Europe, Ifremer teams, in collaboration with local partners and EMBL, extracted 10,0000 samples. These cores will make it possible to go back to the end of the ^20th century or the beginning of the ^21st century, and even beyond for some which cover longer periods beyond the 18th century. All will enable us to link changes in biodiversity to the history of the impact of human activities in Europe, from war in 1945 to microplastics from the 1990s onwards, via pesticides in the 1980s and Chernobyl in 1986, or to major local events, whether natural or man-made.

“Depending on the location, we target certain peaks of human activity or major historical events," explains Raffaele Siano. In Naples, for example, the core samples we take enable us to go back to 1816 and track down all the changes potentially linked to the use of pesticides in agriculture, urbanization, the boom in tourism and also the eruption of Mount Vesuvius (1944). Sediments from Lorient, Gdansk (Poland) and Rostock (Germany), on the other hand, are likely to have retained memories of the effects of port development and the Second World War. Samples taken at La Tremblade and Etang de Thau in France, and at Turku in Finland, respectively, focus on the effects of oyster and salmon farming.

A complete examination to reveal the history of each core

Once repatriated to Ifremer, each sediment core begins a long process of analysis. All have been dated in collaboration with the EPOC unit in Bordeaux. They will now be examined from every angle by 5 Ifremer teams: from the granulometry of the sediments, the study of chemical contaminants present, the genetic analysis of DNA traces left by the species then present, to the identification of any small organisms less than a millimetre in size still nesting in the sediments (meiofauna) and phytoplankton cysts. The first results will be available by the end of 2025. They will provide a new reading of the ecological history of our coasts in relation to human history. They will also enable us to assess the resilience of an ecosystem in the face of such impacts. All of these new elements are essential for European-level reflection on the management of chemical contamination in the marine environment and the protection of biodiversity.

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