of uncertainty, the analysis was repeated excluding 14 problematic species 
(Appendix Table 5). Removal of these problematic species reduces the 
percentage species overlap in all the ecoregions but did not substantially alter 
the general biogeographic pattern. Southern and Northern California ecoregions 
still had the highest percentage of species, with 92% and 88% of the species, 
respectively. As with the full set of species, a high percentage (> 75%) of the 
species were found in Puget Sound and along the coasts of Oregon and 
Washington, with a reduction northward up into the Gulf of Alaska and then a 
further reduction in the Aleutian ecoregion. 
Another source of uncertainty in defining biogeographic ranges is the 
different levels of sampling along the coast. The SCB ecoregion has been 
intensively sampled (see SCAMIT 2001), as has Puget Sound. Northern 
California, Oregon, and Washington shelves have not been sampled as 
intensively, although the fauna of this section of the coast is reasonably well 
known (e.g., Carlton 2007). The data for northern Canada (N. American Pacific 
Fijordland ecoregion) were derived primarily from the dataset for the Haida Gwaii 
archipelago 
(http://gcmd.nasa. gov/KeywordSearch/Metadata.do?Portal=caobis&MetadataTyp 
e=0&KeywordPath=&MetadataView=Full&Entryld=OBIS.GwaiiJnv). While 
limited in spatial extent, this dataset includes information on more than 2,500 
taxa. The Gulf of Alaska distributions were derived primarily from the EMAP 
2002 survey in South-central Alaska (Saupe et al. 2005), unpublished data from 
the 2004 Southeast Alaska EMAP survey, and pre- and post-Exxon Valdez oil 
spill surveys of Prince William Sound (Hines and Ruiz 2000, Hoberg and Feder 
2002). These various sources should be adequate to detect the occurrence of 
abundant species in most cases. In comparison, the sources for the Aleutians 
were more sparse and included unpublished data from the 2006-7 EMAP 
surveys in the Aleutians, reports on Alaskan and Canadian bivalves (Bernard 
1967, Macpherson 1971, Baxter 1987), and the Global Biodiversity Information 
Facility (GBIF; http://data.qbif.org/ ). It is possible that the absence of some 
species from Aleutian ecoregion is result of the more limited sampling in this 
region. 
Even with these sources of uncertainty, it can be concluded that the 
majority of the abundant benthic species on the California-Oregon-Washington 
shelf have wide latitudinal distributions along the Pacific Coast of the United 
States. All three of the abundant bivalves, the pinnixid crab Pinnixa occidentalis, 
six polychaetes, and possibly the amphipod A. careyi extend from Southern 
California into the Aleutians. Another eight species have been reported from 
Southern California to the Gulf of Alaska. Conversely, only the sabellid 
polychaete Pseudofabriciola californica was limited to a single ecoregion, while 
the amphipod Rhepoxynius boreovariatus and the polychaetes Myriochele 
striolata and possibly Monticellina cryptica have been reported from only two of 
the ecoregions. 
100 
