Abstract
DNA barcoding, as it is currently employed, enhances use of marine benthic macrofauna as environmental condition indicators by improving the speed and accuracy of the underlying taxonomic identifications. The next generation of barcoding applications, processing bulk environmental samples, will likely only provide presence information. However, macrofauna indices presently used to interpret these data are based on species abundances. To assess the importance of this difference, we evaluated the performance of the Southern California Benthic Response Index (BRI) and the AZTI Marine Biotic Index (AMBI) when species abundance data were removed from their calculation. Presence only versions of these two indices were created by eliminating abundance weighting while preserving species identity. Associations between the presence and abundance BRI, and the presence and abundance AMBI were highly significant, with correlation coefficients of 0.99 and 0.81, respectively. The presence versions validated almost equally to the abundance-based indices when applied to the spatial and the temporal monitoring data used to validate the original indices. Simulations in which taxa were systematically removed from calculation of the indices were also conducted to assess how large the barcode library must be for the indices to be effective. Correlation between the BRI-P and BRI remained above 0.9 with only 370 species in the library and reducing the number of species to 450 had almost no effect on correlation between the presence and abundance versions of the AMBI.
Highlights
Marine benthic macrofauna are frequently used as indicators of environmental condition because they reside in sediments where contaminants accumulate and their immobility allows them to integrate exposure at a site [1,2,3]
The ERM quotient measures the ratio of the observed concentration to the value at which biological effects are likely, and the mean ERM quotient for the eight metals is an integrated measure of the likelihood of contaminant effects
Application of the Benthic Response Index (BRI)-P assessment thresholds calculated by applying the equation from the calibration linear regression analysis (Table 1) resulted in 92% of the 493 calibration samples assigned to the same assessment category by both indices
Summary
Marine benthic macrofauna are frequently used as indicators of environmental condition because they reside in sediments where contaminants accumulate and their immobility allows them to integrate exposure at a site [1,2,3]. Benthic community composition is typically summarized using benthic indices that allow easy communication of complex biological information as a single number that ranks sites on a scale from good to bad. These index values allow managers to prioritize impacted sites, track trends over time, or correlate biological responses with stressor data. Every captured organism must be identified, typically to species, which requires highly skilled taxonomists that provide expertise over the range of different taxonomic groups This adds substantial cost and is subject to error, when the specimens are damaged or immature life stages are present
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