Spain: Researchers at the Scientific Research Council (CSIC) have confirmed that the Manila clams (Ruditapes philippinarum) present in Europe are of North American origin, a finding they hope will help improve the management of natural banks and industrial rearing of this species.
Until now it was believed that this clam, the world's most important bivalve in aquaculture after the oyster, came to Europe in the 1970s from specimens belonging to breeding grounds in Canada. On the other hand, it is believed that North American stocks were introduced accidentally during the importation of oysters from Japan in the 1930s.
To verify this historical sequence, and to exclude further introductions from other geographical areas, CSIC scientists have studied the DNA of populations in China, Japan, the United States and Europe. Among the populations studied there are some from the most important clam production areas in Spain, such as Arousa and Vigo estuaries or the Ebro delta.
"Our results confirm that European clams would have their closest relatives in North America," says CSIC researcher Carlos Saavedra, who works at the Torre de la Sal Aquaculture Institute in Castellon.
"Besides, their most remote relatives would be in Japan, not in mainland Asia, since there is no genetic trace of countries such as China. This is important because the clams in mainland Asia are genetically very different from those in Japan and may have different farming characteristics that we might be ignoring," adds the scientist.
Researchers have also found that European populations of Manila clams have less genetic variability than those of North American populations from which they come, "probably," says CSIC researcher David Cordero, "because of the use of few broodstock for breeding the species."
The results of this study, published in the journal Scientific Report, are a first step to improve the management of natural banks and industrial breeding, given that "it is of great interest to know whether all the populations currently living on the European coasts come from the original introduction or if there have been additional introductions," Saavedra explained.