Testing depth-related multivariate patterns of macrofauna on the Indian continental shelf using reduced taxonomic resolution and data transformation

Although taxonomic sufficiency (TS) was developed for rapid environmental assessments, it has recently been adopted to study the spatial patterns of macrobenthos in relation to natural environmental gradients. To accept TS as a routine approach in wider benthic studies, it needs to be valid for various taxa and geographically different water masses. This study examined the effects of taxonomic resolution on depth-related multivariate patterns of macrobenthic polychaetes on the western Indian continental shelf. An extensive data set based on samples collected from a wide geographical area (7°-22°N latitudes) covering a large depth gradient (30-200 m) has been analysed. Species level polychaete community data had shown a significant variation between shallow and deeper waters. Our results indicated that generic and family level data also can detect community shifts along a depth gradient in a similar way to species level data. The entire western continental margin (200 m depth) is lying in the oxygen minimum zone (dissolved oxygen <0.5 ml l^-1). This study indicated that family level results were sufficient to document the correlations of low oxygen on macrobenthic polychaetes. This study also tested the effects of transformations on depth-related patterns of polychaetes. In multivariate analyses, transformations play a role in defining the balance between contributions from common and rare species in the measure of similarity of two samples. Our results showed that the type of transformations did not make any prominent differences in the multivariate analyses.