Cut trough shell and Common cockle stand firm in the Big Annual Seashell Survey | Lifewatch regional portal

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Cut trough shell and Common cockle stand firm in the Big Annual Seashell Survey

Added on 2023-03-29 15:32:32 by Tavernier, Annelies
Two thousand volunteers counted 82,444 shells, from a total of 66 species during the sixth edition of the Big Annual Seashell Survey last Saturday. Cut trough shell and Common cockle made it into the top five in Belgium, the Netherlands and France. But there were also interesting regional differences. Less than 1% of the checked shells had a 'drill hole' due to predation by snails.
Growing into mega-event

The Big Annual Seashell Survey, with shells collected across more than 400 kilometres of beaches, has become one of the largest citizen science initiatives on Europe's coasts. This annual 'LifeWatch' initiative started in Belgium in 2018, driven by the Flanders Marine Institute (VLIZ) and in close cooperation with EOS Science, the Province of West Flanders, Natuurpunt, the Strandwerkgroep, Kusterfgoed and the ten coastal municipalities. In 2022, at the fifth edition, the Dutch participated for the first time on a trial basis. And during last Saturday's edition on 25 March, our northern neighbours counted their entire coast, and staff from CPIE Flandre Maritime in Zuydcoote (northern France) experimented with a first participation.

Toppers and regional differences

In total, the estimated 2,000 participants picked 82,444 shells (B: 40,770 ex.; NL: 34,689 ex.; F: 6,985 ex) from the beach. In the three countries combined, volunteers encountered 66 different species (B: 51; NL: 55; F: 35). The two best represented shells remain Cut trough shell and Common cockle. They make the top five in each of the three countries. There are also clear regional differences. Belgium again saw its 'traditional' trio score highest, with Cut trough shell (23%), Baltic tellin (23%) and Common cockle (21%). In the Netherlands too, the Cut trough shell was the most numerous shell (32%), but here followed by Common cockle (18%) and Elliptical trough shell (17%). The Baltic tellin made it into the top five only in Zeeland. The Zuydcoote counting station in France then again saw a top-3 formed by Common cockle (24%), Pullet carpet shell (21%) and Blue mussel (17%). There, Cut trough shell stranded only at position five. And Atlantic razor shell finished fourth in each of the countries.
Project initiator Jan Seys analyses the figures: "Over the entire length of the counted stretch, Cut trough shell and Common cockle are omnipresent. Most of these shells are old, as you can derive from the low number of double shells (<4%), and you find them everywhere. On top of that, you can clearly see local differences, with typically many Baltic tellin on the Belgian east and middle coasts and on the Zeeland coast, and for instance a striking number of recent Pullet carpet shell and Grooved razor shell towards the French border. The Netherlands, in turn, has more fossil Elliptical trough shell. To see those patterns, you need a Big Annual Seashell Survey.

There were also striking differences among individual species. For instance, the Netherlands counted only 1188 Blue mussel in total, while France collected 1200 specimens at barely one station (and Belgium: 3398 ex. At all ten stations). Soft-shelled clam, on the other hand, was only found in the Netherlands, and in decent numbers (total: 436 ex.).

In the three countries combined, the participants found 6 exotic species or 9% of the shell species. Expressed in number of specimens, the occurrence of exotics appears to increase proportionally towards the Channel. The abundance there of Atlantic razor clam, supplemented by Dwarf surf clam and Japanese carpet shell makes the difference (F: 14.8%; B: 13.2%; NL: 7.7%). Other important exotic species are American piddock, Pacific oyster and Slipper mullet.

'Murder holes'

Finally, this year, attention also went to the occurrence of round holes in shells. They testify to the silent death of shells by the action of predatory snails, such as necklace shells and Dogwhelk. These bore through the calcareous shells with their grating tongue, only to suck up the soft flesh with their proboscis. In any case, the snails themselves were relatively rare (Dogwhelk: 14 ex.; Spotted necklace shell: 106 ex.; Common necklace shell: 147 ex.). And their killing behaviour was not too bad either. Based on almost three hundred checked samples from the Belgian coast, less than 1% of all shells showed bore holes. Half of these occurred on the Cut trough shell; other important prey were Banded wedge-shell, Elliptical trough shell, Thick trough shell and Baltic tellin. Incidentally, many of the affected specimens were (sub)fossil ones.

Everyone welcome!

This year – more than ever – the Big Annual Seashell Survey was for everyone. In Ostend, two reception classes for foreign-speaking newcomers (OKAN) actively participated in the shell count, with 14-18-year-old participants from Pakistan, Romania, Ukraine, Somalia and Saudi Arabia, among others. And in Ghent, Ekoli vzw, working diligently for inclusive science, went to work with the 5th-grade students of VBS Sancta Maria Gentbrugge.

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Photo: VLIZ | Annelies Tavernier


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