Macrobenthic community structure within and beneath the oxygen minimum zone, NW Arabian Sea. (COMARGIS)

The lower OMZ boundary (0.5 ml/l) was not a zone of enhanced macrofaunal standing stock, as originally hypothesized. However, abundance maxima at 700-850 m may reflect an oxygen threshold (0.15-0.20 ml/l) above which macrofauna take advantage of organically enriched sediments. Incidence of burrowing and subsurface-deposit feeding increased below the OMZ.

Species richness (E[S100]), diversity (H’) and evenness (J’) were lower and dominance (R1D) was higher within than beneath the OMZ. Within-station (between-box core) faunal heterogeneity increased markedly below the OMZ. Surface sediment pigment concentrations and oxygen together explained 96-99% of the variance in measures of E[S100], H’ and J’ across the transect; grain size and % TOC did not yield significant regressions.

Pigments, assumed to reflect food availability and possibly oxygen effects on organic matter preservation, were negatively correlated with species richness and evenness, and positively correlated with dominance. The reverse was true for water depth. Macrobenthic patterns of calcification and lifestyle within the Oman margin OMZ (0.13-0.3 ml l~1) match the dysaerobic biofacies of paleo-environmental reconstruction models.

Total Distribution Records: 779 Total Number of Taxa: 162