How to Distinguish from Similar Species: Butter clams Saxidomus gigantea have only concentric sculpture. Native littleneck clams Protothaca staminea are as high as they are long, their ridges are less prominent, their siphons are fused all the way to the tips, and the inner ventral margin of the shell is finely serrated. These other species do not have purple markings inside the shell. Another introduced species, Nuttallia obscurata, has purple markings inside the shell but the light brown periostracum is smooth and shiny.
Geographical Range: Asia, Central BC to southern CA.
Depth Range: High intertidal
Habitat: Sand, mud, or gravel in the high intertidal zone. May occasionally be attached to a stone by a byssus.
Biology/Natural History: The siphon of this clam is not long (even though it has a well-developed pallial notch) and the clam buries only to 10 cm depth. This clam is introduced from Asia. It was first accidentally introduced into British Columbia in 1936 along with Pacific Oyster spat. It has now become well established and is one of the main species of clam harvested along the coast of Washington and British Columbia. Moon snails Polinices lewisii don't often attack this species because the species lives so high in the intertidal. Breeds in the summer. May contain pea crab symbionts Pinnixia faba or P. littoralis. Tolarates salinity as low as 1/3 seawater. May live 14 years. May contain red tide toxins.
et al. (2005) found that the common local cancer crabs Metacarcinus
magister (Dungeness crab) and Cancer
productus (red rock crab) preferred the
varnish clam Nuttallia
obscurata to the thicker-shelled clams Leukoma
staminea and Venerupis philippinarum
if access to all was
equally easy. However, Nuttallia
obscurata typically lives deeper in the sediment
than do Leukoma
staminea or Venerupis philippinarum.
If they had to
dig for them, Metacarcinus
magister still ate more Nuttallia
obscurata than it did of the other clam species,
productus' preference switched to Leukoma
staminea and Venerupis philippinarum.
Fitch, 1953 (as Tapes demidecussata)
Kozloff 1987, 1996 [as Tapes (Ruditapes) philippinarum]
Ruesink, Jennifer L., B.E. Feist, C.J. Harvey, J.S. Hong, A.C. Trimble, and L.M. Wisehart, 2006. Changes in productivity associated with four introduced species: ecosystem transformation of a 'pristine' estuary. Marine Ecology Progress Series 311: pp 203-215. doi 10.3354/meps311203
General Notes and Observations: Locations, abundances, unusual behaviors:
Authors and Editors of Page:
Dave Cowles (2006): Created original page