Abstract
Point sampling of soft sediment macrofauna was conducted across the shelf and upper slope in the northeastern Pacific Ocean off the United States Pacific Northwest coast to conduct a regional analysis of species composition and use species assemblages to define habitat types. Analyses focused on linking spatial variability in macrofauna assemblages with measured environmental parameters using nMDS plots and the LINKTREE routine in Primer. Depth was the primary structuring variable (i.e., macrofauna species assemblages first separated by depth) with sediment parameters (percent fines, grain size, and total organic carbon) secondary and nearly as statistically important. A depth break of ~90 m was the environmental variable that correlated with the greatest separation among our stations based on differences in macrofaunal assemblages, which is not a classically described depth break for shelf macrofauna. The next largest changes in assemblage composition were at 43 m and 200 m. Within each of these depth zones on the shelf, we detected significant differences in assemblages related to different sediment grain sizes. Below the 200 m break – a depth traditionally delineating the continental shelf and slope – subsequent changes in assemblage composition were detected at 221 m and 445 m depth breaks; further delineations in assemblages related to sediment parameters were not detected. Knowing how macrofaunal communities vary with grain size and depth can inform future site surveys, develop tools for mapping macrofauna habitat suitability based primarily on these physical factors, and develop hypotheses of how benthic communities might be affected by offshore projects.