First Swedish discovery of Manila clam – found on Saltö
The Manila clam, previously unreported in Sweden, was discovered earlier this year on Saltö, just outside Strömstad. Youk Greeve, marine biologist and researcher, found the clam while searching for mussel and clam shells on the beach. New research shows that the clam is already widespread along the coast of Bohuslän in western Sweden.
It was in February, shortly after a winter storm had swept across northern Bohuslän, that Youk Greeve, then a PhD student at the Department of Marine Sciences, was looking for shells along one of Saltö's beaches just outside Strömstad.
”I needed something for the cover of my thesis, and after a storm there are usually lots of nice shells that have been blown up onto the beach,” he says.
Easy to confuse with cockle
Then Youk Greeve discovered a clam he had never seen before.
”It's not so easy to distinguish it from, for example, the cockle, which is common here. You need some practice,” says the researcher, whose thesis was about mussels, clams and oysters along the Swedish west coast.
It took about a day's work, but then Youk Greeve was sure of his findings; the live clam he had found was of the species Ruditapes philippinarum, a clam that had not previously been reported in Sweden and which is known in English as the Manila clam.
”I also got confirmation from others that it was indeed that particular clam.”
The closest reported occurrences are along the Wadden Sea coast, in the northern Netherlands and Germany. It originates from Asia, where it is commonly used in dishes in Korea, Japan and China, among other places.
The manila clam arrived in Europe in the 1970s, where it was introduced and then spread naturally. Here too, it is harvested commercially, from the Mediterranean to the coasts of Great Britain.
Widespread along the coast av Bohuslän
”It was really only a matter of time before it found its way here to Sweden too,” says Youk Greeve, who has written a scientific article about his discovery and the work he has done with the clam after that storm in February.
”We have now found it from Fiskebäckskil in the south to Sandefjord on the other side of the Oslo Fjord. Until now, I have found 100 living specimens,” says Youk, whose research is based at the Tjärnö marine laboratory.
The scientists do not know exactly how it arrived in Sweden. The strongest theory is that larvae have come to Sweden from the west coast of Denmark, although there are no reported observations of the clam there yet. Yet.
”That also is probably just a matter of time. It is not visible in the same way as, for example, the Pacific oyster, but burrows into the bottom sediment. And it is very easy to confuse with native species,” says Youk Greeve.
Findings show clam not entirely new
It is difficult to say how the Manila clam will affect native species. Once again, Youk Greeve draws a comparison with Pacific oysters, which have been very common along the west coast since they were first discovered in Sweden almost 20 years ago.
"At present, we cannot say that these oysters have been a problem for other species. There is certainly a theoretical possibility that this new clam could cause problems, for example by spreading parasites that could be harmful to native species. But we don't know yet.”
What happens now?
”We will continue to work with the manila clam and try to find out how far it has spread and also how it got here. We have found both small and large individuals of different ages, which indicates that it has actually been here for a while, even though no one has discovered it before,” says Youk Greeve.
Text: Mikael Andersson
- Originally native to the Indo-Pacific region, the Manila clam has been introduced globally and is now established in coastal ecosystems across Europe, North America, and beyond.
- It is the on of the most important bivalve species in global aquaculture.
- Manila clams thrive in shallow waters with sandy, muddy, or gravel substrates, often found in intertidal zones, estuaries, and even under ice.
- They can reach sexual maturity within one year, and a single female can produce up to 2.4 million eggs, especially in warmer climates.
- Widely consumed in East Asia, Manila clams are popular in dishes like soups, noodle broths, and seafood stews, prized for their sweet, briny flavour and tender texture.