The Soft-Shell Clam Mya arenaria: Biology, Fisheries, and Mariculture

Chapter 12: Vectors and Global Invasions of the Soft-Shell Clam Mya arenaria

James T. Carlton


We do not know which species was the first transoceanic exchange species, but it may be assumed that Mya arenaria was among the very earliest.
[Ivar Hessland 1946]

The North American soft-shell clam Mya arenaria represents one of the oldest recognized introductions of a marine species in the world (Ojaveer et al. 2018). First described by Linnaeus in 1758 from Europe (Figure 1), and then redescribed as a new species after being introduced to California in the 1870s (Figure 2), M. arenaria provides a superb example of a species with a complex and episodic transport history with a high probability of continued expansion. Although the nearly 800-year history of the movements of M. arenaria often obscures a fine-grained understanding of invasion trends, the overall patterns are clear of a Holocene exodus from the American Atlantic coast, first to northern and western Europe and then to the Pacific Ocean, followed by its much later arrival in Iceland, the Black Sea, and the Mediterranean.

Briefly reviewed here are (1) the known and potential human-mediated dispersal vectors that may transport M. arenaria to distant shores, (2) an overview of its history in northern and western Europe, (3) a history of its introduction and spread along the North American Pacific coast (the only region where a detailed history of its expansion is currently available), and (4) the 20th century renewal of M. arenaria’s ocean crossings. I conclude with (5) the conundrum presented by the recent recognition that the northwest Pacific Ocean Mya japonica Jay, 1857 has invaded both the northeast Pacific Ocean and Australia.