The BRI was employed by R. W. Smith etal. in 2001 in the environment of the coastal shelf of southern California that gauges the condition of a benthic assemblage, with identified thresholds for levels of environmental disturbance. A two-step process was employed in order to calculate the index, in which ordination analysis was utilized to quantify a pollution gradient within a 717-sample calibration data set taken in 10-324 m of water depth in the area located between 'point conception' and the United States-Mexico international border. The dates of sampling spanned from 1973 to 1994. Each sample was screened through 1.0 mm sieves, and identified to the lowest possible taxonomic level. The tolerance of pollution of each species was established based upon its distribution of abundance along the gradient.
This study identified four thresholds of biological response to pollution. The reference threshold, that is, the index value below which natural benthic assemblages typically take place, has been determined. The other three thresholds entailed the designation of levels of deviation from the reference condition (Table 1).
Table 1 BRI threshold values
Threshold value for loss in biodiversity
Threshold value for loss in community function
Threshold value for defaunation
Index value 25 >34
Tolerance 90% tolerance interval bound for the 25% of reference interval reference index value species lost
90% echinoderm, 75% arthropods excluded
90% of pool species excluded
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