Cooperative Fish and Wildlife Research Units Program: Washington
Education, Research and Technical Assistance for Managing Our Natural Resources

In Washington State, commercial culture of geoduck clams (Panopea generosa) involves large-scale out-planting of juveniles to intertidal habitats and installation of PVC tubes and netting to exclude predators and increase early survival. Here we examine whether structures associated with this nascent aquaculture method affect patterns of use by resident and transient macrofauna. We summarize results of regular surveys of aquaculture operations and reference beaches in 2009-2011 at three sites during three phases of culture: 1) pre-gear [- geoducks, -structure]; 2) gear-present [+geoducks, +structures]; and 3) post-gear [+geoducks, -structures]. Resident macroinvertebrates (infauna and epifauna) were sampled monthly (in most cases) using coring methods at low tide during all three phases. Differences in community composition between culture plots and reference areas were examined with Permutational Analysis of Variance (PerMANOVA) and homogeneity of Multivariate Dispersion (HMD) tests. SCUBA and shoreline transect surveys were used to examine habitat use by transient fish and macroinvertebrates. Analysis of Similarity (ANOSIM) and complementary non-metric Multidimensional Scaling (NMDS) were used to compare differences between species functional groups and habitat type at different aquaculture phases. Results suggest that resident and transient macrofauna respond differently to structures associated with geoduck aquaculture. No consistent differences in the community of resident macrofauna were observed at culture plots or reference areas at the three sites during any year. Conversely, total abundance of transient fish and macroinvertebrates were more than two times higher at culture plots than reference areas when aquaculture structures were in place. Community composition differed (ANOSIM) between culture and reference plots during the gear-present phase, but did not persist to the next farming stage (post-gear). Habitat complexity associated with shellfish aquaculture may attract some structure-associated transient species observed infrequently on reference beaches, while displacing other species that typically occur in areas lacking epibenthic structure. This study provides the first look at the effects of multiple phases of geoduck farming on macrofauna and has important implications for management of a rapidly expanding sector of the aquaculture industry.