Distribution of the invasive bivalve Mya arenaria L. on intertidal flats of southcentral Alaska

The bivalve Mya arenaria L. is a common inhabitant of intertidal sediments along the southcentral Alaskan coastline. Its current distribution along the Pacific coast of the continental USA, Canada and Alaska has resulted from a series of intentional and unintentional introductions as well as larval transport between points of introduction over the previous century. Despite the apparent success of M. arenaria in intertidal habitats of coastal Alaska, no study has examined its distribution in this environment. We sampled four times over a two-year period (2001–2002) to document the distribution of M. arenaria in intertidal sedimentary habitats of the Copper River Delta and adjacent Orca Inlet (southeastern Prince William Sound), Alaska. Sampling was performed along a gradient of tidal elevations at three sites (Hartney Bay, Eyak and Pete Dahl) chosen to represent the range of physical/chemical settings of protected intertidal sand and mud flats within the study area. Among the three sampling sites, abundance of M. arenaria was lowest at sites near the outflow of the Copper River (Pete Dahl) and highest in areas of higher salinity and water clarity (Hartney Bay and low tidal elevation plots at Eyak). Within each of the two sites located on the Copper River Delta (Eyak and Pete Dahl), abundances of M. arenaria were highest at low tide plots (+ 1.1 m for Eyak, + 1.4 m for Pete Dahl), a pattern consistent with the distribution of M. arenaria within tidal flats in Europe (Wadden and White Seas). For the third site located in Orca Inlet (Hartney Bay), M. arenaria was found at all tidal elevations; however, distinct differences in the distribution of newly recruited M. arenaria (< 10 mm shell length [SL]) and older juveniles and adults (> 10 mm SL) were evident. Density and growth of M. arenaria in southcentral Alaska were most similar to values reported for the White Sea (Russia); both areas are located at similar latitude and represent the northern extreme of M. arenaria distribution.