representing about 2% of the shelf area, had < 26 taxa/grab (Fig. 3.5.4). This 
greater species richness was reflected over large areas of the shelf. For 
example, approximately 50% of the area of the shelf had species richness > 67 
taxa/grab and 10% of the shelf had >110 taxa/grab (Fig. 3.5.4, Table 3.5.3). In 
comparison, the corresponding CDF 50 th percentile value for estuaries was 49 
taxa/grab and the 10 th percentile value was 90 taxa/grab (Table 3.5.3). Species 
richness along the shelf was highest off California (mean of 94 taxa/grab) and 
nearly equally lower in Oregon and Washington (means of 55 and 56 taxa/grab, 
respectively). Estuarine means by state were much lower for California (24 
taxa/grab) and Oregon (11 taxa/grab) though similar for Washington (48 
taxa/grab) (Table 3.5.3). Average species richness was very similar between 
sanctuary vs. non-sanctuary stations for both the California and 
Oregon/Washington regions (Fig. 3.5.3). 
A more detailed examination of species richness, using quartile ranges, 
further confirmed a pattern of increasing species richness along the shelf with 
decreasing latitude (Figs. 3.5.3, 3.5.5). There were 61 stations with values in the 
upper quartile of all stations (i.e., values > 100 taxa/grab). All but one of these 
sites (WA03-0015) were in California, most were in the SCB. A correlation 
analysis (SAS 2003) revealed a highly significant negative association between 
numbers of species and latitude (Pearson’s correlation coefficient r = -0.61, p 
<0.0001). This is different from the pattern observed in estuaries. For example, 
the NCA-West 1999-2000 database for estuaries shows that the highest species 
richness among the three states was in Washington, especially in Puget Sound 
(Table 3.5.3; also see Partridge 2007). In fact, all estuarine stations with > 100 
taxa/grab were in Washington. The high species richness reported here for shelf 
waters, particularly those off the California coast, is consistent with an earlier 
study by Hyland et al. (1991) for offshore waters of the Santa Maria Basin, which 
showed numbers of species (> 0.5-mm size) averaging about 100 to 150/grab 
(0.1 m 2 ) at comparable outer shelf/upper slope depths under 200 m. 
The high species richness, as well as a relatively even distribution of 
species abundances within samples, also resulted in fairly high values of the 
diversity index H' (log base 2) for many stations across the region. Values 
ranged from 2.04 to 6.63/grab and averaged 5.01/grab region-wide (Table 3.5.3, 
Fig. 3.5.6). Approximately 50% of the shelf area had H' values > 4.82, and 10% 
of the area had H' values > 5.80 (Fig. 3.5.7). In comparison, mean diversity and 
the CDF 50 th percentile point for estuarine habitat along the West Coast 
correspond to lower H' values of 2.41 and 3.84, respectively (Table 3.5.3). Mean 
H' in the present shelf survey was highest in California (5.36) and lowest in 
Washington (4.27) (Fig. 3.5.7, Table 3.5.3). There were no major differences in 
mean H' between sanctuary vs. non-sanctuary stations for both the California 
and Oregon/Washington regions. 
81 
