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

Chapter 8: Predators and Competitors of the Soft-Shell Clam Mya arenaria

Brian F. Beal

doi: https://doi.org/10.47886/9781934874745.ch8

Predators are key drivers regulating soft-shell clam Mya arenaria Linnaeus, 1758 populations (Mead 1900; Kellogg 1905; Belding 1916; Smith and Chin 1951; Glude 1955; Edwards and Huebner 1977; Virnstein 1977; Reise 1978; Blundon and Kennedy 1982a; Jensen and Jensen 1985; Eggleston et al. 1992; Beal and Kraus 2002; Flach 2003; Glaspie and Seitz 2018). By inducing a variety of behaviors in their soft-shell clam prey, predators can have both stabilizing and destabilizing effects on clam populations depending on habitat (Seitz et al. 2001) and other environmental conditions (Taylor and Eggleston 2000).

Clams respond to predators using numerous behaviors to help them escape predation pressure (Baker and Mann 1990). First, they may grow quickly into a refuge size with increasing sediment depth (Commito 1982a; Zaklan and Ydenberg 1997; Whitlow et al. 2003) that makes it difficult for epibenthic predators such as fish, birds, and crabs to access prey (Smith et al. 1999). The second is related to the habitat where they live. Clams are more difficult to access in coarse versus soft, unconsolidated sediments (Lipcius and Hines 1986; Thomson and Gannon 2013), or when surrounded by large, thick-shelled bivalves (Skilleter 1994). A third, partial refuge, relates to habitat-specific temperature and salinity profiles. Soft-shell clams are euryhaline and eurythermal (Matthiessen 1960; Kennedy and Mihursky 1971). This may enable them to settle and grow in habitats some predators may find physiologically inaccessible. Lastly, clam survival is a direct function of their position along the tidal gradient. Because many soft-shell clam predators are waterborne and feed in the shallow subtidal or in the intertidal during periods of tidal inundation, Mya arenaria attains a spatial refuge at/near the upper intertidal (Scapati 1984; Zaklan and Ydenberg 1997; Beal et al. 2001, 2006a).

While it was not possible to cover all types of predators, including planktonic forms (see Purcell et al. 1991), this chapter examines some of the major and minor groups of soft-shell clam predators as well as several potential competitors. Nomenclature for marine invertebrates, birds, fish, and marine mammals used in this chapter is in accordance with the World Register of Marine Species (WoRMS; https://www.marinespeceis.org) and with the Animal Diversity Web (https://animaldiversity.org) for terrestrial mammals. The sections below generally follow a taxonomic outline to facilitate finding information on various species.