Depth-related changes in the Arctic epibenthic megafaunal assemblages of Kangerdlugssuaq, East Greenland

The effects of depth-related differences in environmental factors (pressure, hydrography, habitat and disturbance) on the benthic megafauna at the mouth of Kangerdlugssuaq Fjord in Arctic Greenland were investigated using a towed camera platform and autonomous underwater vehicle photographs. Large reductions in faunal density (60,132 to 1881 individuals ha-1) and increases in diversity (H'=0.93-2.54), through increases in richness (ES(220)=7.6-18.8) and reductions in dominance (Berger-Parker index=0.77-0.38) were found between 270 and 720 m water depth. Assemblages were separated into distinct shallow, intermediate and deep faunas by multivariate community analysis. In the shallower sites there were high levels of iceberg disturbance, directly reducing diversity as well as creating a complex, patchy environment inhabited by high densities of mobile suspension-feeding epifauna. In the deeper areas there was small-scale disturbance from the deposition of drop stones, but at a relatively low frequency and magnitude, which allowed increased species diversity. Proportions of deposit-feeding epifaunal and infaunal taxa rose with depth, as indicated by an increase with depth in faunal traces. Decreases in faunal density probably resulted from decreased food supply with depth.