3.5.4 Biogeographical Distributions 
The 2003 probabilistic survey is one of the few regional-scale studies of 
the benthos on the continental shelf of the U.S. Pacific Coast. As such, the data 
are well suited to addressing a number of biogeographic questions. The first 
question addressed is whether the shelf fauna have restricted along-coast 
distributions or whether they have wide latitudinal distributions. To address this 
question, we utilized the Marine Ecosystems of the World (MEOW) 
biogeographic schema recently proposed by The Nature Conservancy (Spalding 
et al. 2007). The MEOW scheme is hierarchical, with 12 Realms composed of 
62 provinces, which in turn are composed of 232 ecoregions. Based on this 
scheme, we therefore evaluated the presence of species across the seven 
ecoregions of the Temperate Northern Pacific Realm that border the U.S. Pacific 
Coast (Fig. 3.5.10). These seven ecoregions include all the ecoregions of the 
Cold Temperate Northwest Pacific Province and the northernmost ecoregion in 
the Warm Temperate Northeast Pacific Province, and span from the upper half of 
the Baja Peninsula in Mexico to the Aleutian Islands in Alaska. Ecoregions within 
the Arctic Realm bordering northern Alaska are not considered, nor are the two 
other ecoregions of the Baja Peninsula that do not border the United States. 
Appendix Table 5 summarizes the biogeographic distributions, by 
ecoregion, of the 39 most abundant taxa that were identified to species (from 
Table 3.5.4). Distributional data were derived from the present study, previous 
EMAP surveys including unpublished data from Alaskan surveys (Max Hober and 
Douglas Dasher), and the Pacific Coast Ecosystem Information System (PCEIS). 
PCEIS is a database synthesizing the distributions of native and nonindigenous 
marine/estuarine species of the Pacific Coast being developed by EPA and the 
USGS (Lee and Reusser 2008). Of the 39 abundant species collected along the 
California-Oregon-Washington shelf, almost 95% of them were found in both the 
SCB and Northern California ecoregions, while 87% were found in both the 
Oregon, Washington, Vancouver Coast and Shelf ecoregion and in the Puget 
Trough/ Georgia Basin ecoregion. The percentage of species occurring off the 
coast of Canada (North American Pacific Fijordland ecoregion) and the Gulf of 
Alaska drops to about 72% and 59%, respectively. With 14 of the 39 species 
reported from the Aleutians, the percentage of the species reported declines to 
36% in the most northern ecoregion of the Temperate Northern Pacific Realm. 
These distributional patterns potentially could be confounded by 
taxonomic uncertainties. For example, seven of the species in Table 3.5.4 are 
classified as cryptogenic species, which are species of uncertain origin (Carlton 
1996). All of these cryptogenic species occur in more than one of the MEOW 
provinces and at least one possible explanation for their wide distributions is that 
they actually represent a suite of sibling species that can not be readily 
distinguished morphologically. Even for natives there can be confusion about the 
specific identity of a species. For example, the native amphipod Ampelisca 
careyi may be a variant of A. unsocalae (Chapman 2007). To reduce this source 
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