Meeting Abstract

P1.45  Monday, Jan. 4  The effect of sediment type of the distribution of the invasive purple varnish clam and associated native kleptoparasitic pea crabs on Pacific Northwest beaches SHISHIDO, C. M.*; BURNAFORD, J.L.; HENDERSON, S.Y.; University of Puget Sound; CSU Fullerton; CSU Fullerton cshishido@pugetsound.edu

Nuttallia obscurata (the purple varnish clam) is an invasive species that inhabits sandy and muddy beaches in the Pacific Northwest. This invasive clam is associated with at least 3 species of native kleptoparasitic pea crabs, and the distribution of clams and pea crabs varies from site to site. We investigated potential causes of variation in infection rates between sites by focusing on two locations, Jackson Beach and Argyle Beach on San Juan Island, WA. These beaches are separated by less than 150m. We used field surveys to quantify the sediment characters and distribution of clams and crabs at each site. At Jackson Beach, where the sediment was sandy, Nuttallia were found deep in the sediment and pea crab infection rates were high (28.7% of clams infected). At Argyle Beach, where the sediment was muddy and rocky, Nuttallia were shallow and pea crab infection rates were low (15.6 % of clams infected). We used laboratory manipulations to determine whether these differences in sediment characteristics affected the clam/crab association. Nuttallia burial depths were different in sediment from the two sites, but sediment type had only a weak effect on crab movement. Long term comparisons of clam growth rates at the two sites indicate the possibility of physiological differences in clam populations which may affect the clam/crab association. These data increase our understanding of this close association between native species and an abundant invader of Pacific Northwest beaches