Missing clam found after 30 years

Published March 6, 2024 at 1 p.m.

Domestic. A mussel that was assumed to be extinct in Swedish waters has been found in Singlefjorden north of Strömstad. The finding was made in a sample from the annual environmental monitoring of soft bottoms along Sweden's coasts.

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Arne Nygren is a researcher at the Department of Marine Sciences and works with environmental monitoring of our coastal waters. Sea brush worms, snake stars, small crustaceans and other organisms brought up from the seabed are identified, measured and weighed in a lab upstairs in the Tjärnö marine laboratory.

Most of the samples are usually familiar, but the other week Arne Nygren to. He had found a mussel in the bivalve family, specifically a cross-ribbed bivalve, Cardiomya costellata.

– I immediately thought that it was something out of the ordinary. And when I saw the cross ribs it was no longer something to think about, even though this was a very small specimen, says Arne Nygren about his discovery in a press release.

The mussel has been considered extinct in Swedish waters. In the past, it has been found on suitable premises in the Koster area, but despite a series of inventories in the area during the 2000s, they have not managed to find it again until now – more than 30 years since it was last seen.

The small bivalve can grow to about one centimeter in size and has an appearance that is usually likened to a sauce snipe. It is found on current-swept soft bottoms throughout the North Atlantic, where it feeds on small crustaceans and other things that live among grains of sand and gravel.

– I found the mussel in a bottom sample from 56 meters deep in the Singlefjord, not so far from Tjärnö. It is the first time we are taking samples in the area. Here is exactly the habitat that the mussel wants, says Arne Nygren.

One explanation for why the bivalve has not been seen for a long time is that there is a lack of suitable habitats. Areas with bottom currents that keep sand and gravel free from sediment are unusual on the Swedish west coast. Eutrophication and trawling also lead to more and more seabeds getting a blanket of dead phytoplankton and other particles that fall down. Many bottom-dwelling organisms cannot stand being embedded in this way.

The cross-ribbed bivalve was found in a bottom sample taken in May last year, during the annual environmental sampling along the Swedish west coast.


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