Nearly one in ten shells on our coast are exotic, according to the results of the Big Shell Count Day

During the edition of Saturday, March 23, 2024, more than 2,000 participants went out to sea. According to established protocol, they counted and identified 114,093 shells and snails from a total of 77 different species. The absolute top spots were semi-cut beach clam (30%), clam (27%), and nun (8%). The fact that these first three shells repeat themselves over and over again, sometimes in a slightly different order, is no coincidence, says Jan Sies (VLIZ): “About half of the shells found have been on our beaches for a long time and will remain there for a while. To stay.” This is particularly on semi-cut beach snails and shells, the main part of which is sub-fossil. This means that they date back as much as eight thousand years ago. So they go back to a time when our coast looked very different and these species were having a good time This is why these species still dominate the shell fauna found on our beaches today. The other half of the shells died off recently and gives us an idea of ​​what is happening on and around the sea floor today.

Clear differences between the Netherlands, Flanders and northern France

Oysters and semi-harvested inshore cockles rank in the top five in each of the three countries. In Belgium and the Netherlands, they rank first and second. On the two beaches of northern France, the common carpet shell is the most numerous. It is striking that this species only reaches the top 10 in Belgium on the west coast, that is, near the border with France. In other places the number is much lower. There are other striking differences: mussels are counted much less in the Netherlands than on other coasts, and only mussels made it into the top three in Belgium.

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Exotic species are increasing towards the channel

Throughout this edition, special attention has been paid to non-native shells, foreign species that ended up here with the help of humans. Of the total 77 species collected, nine percent appear to have come from another continent. Expressed in specimens, the total number of exotic species was eight percent of all beach shells and snails found. This group includes some rare species, but also includes ubiquitous non-native shellfish such as the American swordfish. Slippers, American digger mussels, Japanese oysters, and Philippine carpet shells are also well-established values. The share of non-native shells (expressed as a percentage of collected specimens) increases towards the Channel: from five percent in the Netherlands, more than nine percent in Belgium to nearly one in five in northern France.

The “LifeWatch” large shell counting day is now an established value in Europe. The Flemish Marine Institute (VLIZ) has been coordinating this citizen science initiative since 2018, receiving full support from Eos Science, the Province of West Flanders, Natuurpunt, the Beach and Coastal Heritage Action Group and the ten coastal municipalities. In addition, there is the crucial assistance of nearly a hundred guides and serendipity experts. Since 2022, the Netherlands (led by Naturalis) has joined the initiative, and since last year also northern France (coordinated by CPIE Flandre Maritime).

Megan Vasquez

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