3.5.1 Taxonomic Composition 
A total of 1,482 taxa were identified region-wide, of which 1,108 were 
identified to the species level. Polychaetes were the dominant taxa, both by 
percent abundance (59% region-wide, Fig. 3.5.1) and percent taxa (44% region¬ 
wide, Fig. 3.5.2, Table 3.5.1). Crustaceans and molluscs were the second and 
third most dominant taxa respectively, both by percent abundance (17% 
crustaceans, 12% molluscs) and percent taxa (25% crustaceans, 17% molluscs). 
Collectively, these three groups represented 88% of the total faunal abundance 
and 86% of the taxa throughout the region. Crustaceans were represented 
mostly by amphipods (202 identifiable taxa, 14% of the total number of taxa) 
followed by decapods (49 taxa, 3.3% of total taxa) and cumaceans (39 taxa, 
2.6% of total taxa) (Table 3.5.1). Molluscs were composed mostly of bivalves 
(116 taxa, 7.8% of total taxa) and gastropods (112 taxa, 7.5% of total taxa). High 
proportions of polychaete and amphipod species are also characteristic of 
estuaries along the West Coast, though there are notable differences in the 
relative proportions of other taxonomic groups (Table 3.5.2). For example, 
species of larval insects represented 2.9% of total taxa in the NCA-West 
estuarine data set, but were absent in the present shelf samples. In contrast, 
ophiuroids and holothurians are more specious on the shelf than in estuaries. 
Also, while oligochaetes as a group represent only 0.2% of the total faunal 
abundance on the shelf, Nelson et al. (2005) reported them as being dominant 
(among the 10 most abundant) members of the estuarine benthos along the 
West Coast. 
Polychaetes, crustaceans, and molluscs dominated the benthic fauna 
consistently across the three states and NMS vs. non-sanctuary categories (Fig. 
3.5.1, 3.5.2). Similar to the region-wide pattern, polychaetes were the most 
dominant, by both percent abundance and species richness, consistently across 
all strata. However, while crustaceans were the second-most abundant group in 
California (similar to the region-wide pattern), molluscs were proportionally more 
abundant than crustaceans in Oregon and Washington. There were no major 
differences in the percent composition of benthic communities between NMSs 
and corresponding non-sanctuary sites. However, molluscs were proportionally 
more abundant and specious than crustaceans at non-sanctuary sites in Oregon 
and Washington than at the OCNMS. 
3.5.2 Diversity 
Species richness, expressed as the number of taxa present in a 0.1 -m 2 
grab, was relatively high in these offshore shelf assemblages. A total of 1,482 
taxa were identified region-wide from the 259 benthic grabs. Species richness 
ranged from 19 to 190 taxa/grab and averaged 79 taxa/grab (Table 3.5.3, Fig. 
3.5.3). In comparison, the NCA-West estuarine data (Nelson et al. 2004, 2005; 
U.S. EPA 2004, Hayslip et al. 2006) show an average of 26 taxa/grab in 
estuaries along the West Coast (Table 3.5.3). Only five of the 256 shelf stations, 
80 
