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

Chapter 4: Population Genetics of the Soft-Shell Clam Mya arenaria

Joseph I. Hoffman and David L. J. Vendrami


The soft-shell clam Mya arenaria is a benthic marine bivalve found in coastal habitats across the northern hemisphere. Population genetic studies of this species began in the 1970s and have been motivated over the years by a variety of questions. Due to the ability of the soft-shell clam to persist over a wide range of water temperatures and salinities, this species was soon recognized as a good candidate for investigating how environmental heterogeneity can shape genetic variation. This, together with its abundance for sampling, led to M. arenaria being described as “an excellent organism for the study of selection, migration and genetic differentiation” (Morgan et al. 1978). The soft-shell clam is also commercially important in several regions of North America (Kennedy 2023, this volume) where it has been subject to stocking operations aimed at counteracting declines in landings caused by overfishing (Beal 2023, this volume), habitat degradation, and predation by invasive species (Strasser and Barber 2009). This has promoted an interest in characterizing patterns of population genetic structure and local adaptation (see Glossary in Appendix 1 for specialized terms indicated in italics), which can inform effective management. Finally, M. arenaria is believed to have gone extinct in the eastern Atlantic during the Pleistocene (Hessland 1945) and to have subsequently recolonized European shores as a consequence of repeated anthropogenic introductions from North America dating back to the 13th century (Petersen et al. 1992; Beets et al. 2003; Behrends et al. 2005). Eastern Atlantic populations of M. arenaria therefore provide a unique system for investigating how anthropogenic translocations followed by natural dispersal can affect patterns of population structure and genetic diversity in marine organisms.

This chapter will provide a concise overview of studies that have used genetic markers to investigate the population genetics of Mya arenaria. We will not cover the genetic basis of disease (see Seitz et al. 2023, this volume), including the well-documented role of the retroelement, Steamer, in transmissible neoplasia (Arriagada et al. 2014). We will describe how methodological developments over the past few decades have advanced our understanding of three major topics: genetic diversity, population structure, and historical demography. We will identify areas of consensus in the literature as well as key outstanding questions. Finally, we will conclude with the outlook for future studies of the population genetics of soft-shell clams.