Nearly 40,000 shells collected from the shores of the North Sea to measure the state of marine biodiversity

“Shells are a good indicator of the state of biodiversity in the North Sea,” says a biologist from the Flemish Marine Institute.

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A volunteer collects shells in Middelkerke (Belgium), March 25, 2023. (KENZO TRIBOUILLARD / AFP)

The initiative took place on 400 kilometers of beach in France, Belgium and the Netherlands. On the shores of the North Sea, hundreds of people took part, on Saturday March 25, in the sixth great day of counting shells. Objective: take the pulse of marine biodiversity. Mussels, oysters, cockles… Armed with plastic buckets, around 800 people collected shellfish before giving them to volunteers, who carefully sorted them, then counted and recorded them by species.

The fear of invasive species

In total, some 38,000 shells were counted, roughly the same number as in 2022. “Shells are a good indicator of the state of biodiversity in the North Sea”explained biologist Jan Seys, from the Flemish Marine Institute (VLIZ), organizer of the annual event. “Last year, 15% of the shells found belonged to exotic species”, particularly watched by scientists who fear that they are invasive. “For example, we have seen American species appear on our coasts”like the American knife, continued Jan Seys.

“Organisms that normally live in warm waters have been observed to appear more and more on the coast”, added Joris Hooze, retired biologist and member of a Belgian association dedicated to the observation of marine biology. For him, “It’s a sign of climate change.”

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