Unusual find of rare sea snail in Strömstad
Six rare common limpets were found outside Strömstad in the mid-June, which is quite unusual for Sweden.
"I was very surprised. I haven't seen them since the middle of the 1960s, when I grew up," says Kerstin Johannesson, professor att Tjärnö Marine Laboratory
It was during the course "The Sea in the Classroom" that Kerstin Johannesson and her students found the unusual common limpet on Ursholmen, the westernmost of the islands in the Kosterhavet archipelago.
"But the first find was made by my husband, Bosse, who had accompanied us in the nice weather. He strolled around the beach and, sure enough, he found the first specimen. Then we all started looking, and in the end we had found six," she says.
The common limpet has a characteristic cone shape and can become up to six centimetres long, five centimetres wide, and three centimetres high. It thrives in exposed banks, needs high salinity and has no problem with tides and large temperature fluctuations. The snail rests at low water when it is dry, and feeds on algae when the tide submerges it.
Red-listend species in Sweden
The sea snail can live up to 20 years, and it used to be relatively common along the northern coast of Bohuslän, the most northern part of the Swedish west coast, albeit in limited populations according to the
"Seeing them when I grew up was no surprise. Back then, they were everywhere," says Kerstin Johannesson.
Today, the common limpet is red-listed and listed as endangered in Sweden. For a long time, scientists thought it had disappeared completely, but since the 1980s there have been a few sightings of living specimens. Otherwise, it is found along the Atlantic coast of Europe, on the British Isles and up to the Varangerfjord in Norway. It also occurs in the western Mediterranean.
The virtual disappearance of the species in Sweden may be due to eutrophication resulting in toxic algal blooms and toxic boat bottom paints. Researchers have no definite answers. Kerstin Johannesson has her own theory, which is that the snails are actually here on temporary, albeit long, visits.
"The common limpets we found were all the same size, about five centimetres long, which means they are about the same age. So they must have arrived here several years ago and then grown up on Ursholmen," she says.
Seems to be of the same age
During her research trips to the UK and elsewhere, Kerstin Johannesson has observed the species in different sizes and ages, but as she remembers from her own childhood, the common limpets in Sweden were all about the same size, like those in the new find.
"My suspicion is that they have arrived here in a year when there was a larval spread under very favourable conditions. The small individuals have managed to survive and then lived on until they died of age. And they can live to be 20 years or older," says Kerstin Johannesson.
"In addition, they are males when they are small and change sex to females when they get bigger. So there will be no new individuals locally unless news cohorts are introduced."
Are you saying that they have not really existed naturally here on the Swedish west coast?
"Yes. All species have their distribution limit somewhere, and I think there is something here on the west coast that makes it difficult for them. We don't have a tide that they thrive on, and the salinity of the water is actually too low. This may be the limit of what they can handle," says Kerstin Johannesson, who is keen to see more sightings of the greater horseshoe crab, and hopes that the public can help.
"If we've found six at Ursholmen, they're bound to be found in other places. Please report any finds of common limpet to the ," she concludes.
Text: Mikael Andersson