Size distribution of the amphipod Paramoera walkeri (Stebbing) along a depth gradient in Antarctica

Body weight distributions of the amphipod Paramoera walkeri colonizing litter-bags at different depths (2, 5, and 10 m) in Terra Nova Bay were compared. This species dominated the vagile benthic community and was found nearly alone at the shallow sites. At the deepest site it co-occurred with two smaller benthic species (the gastropod Laevilitorina antarctica and the isopod Munna antarctica) but still accounted for most of the animal biomass (80.2%). The frequency size-class distributions of the three dominant species were sharply distinct in a condition of stable coexistence. The total biomass was inversely related to the abundance of animals and diminished with increasing depth. Both species and size-class diversities were higher in deep water which offered a more diversified and favourable habitat than shallow water. At the shallow sites only the large size classes of P. walkeri were present. Differences in the mean individual ash content between samples support the hypothesis that different size individuals of P. walkeri segregated along the depth gradient on the basis of their metabolic requirements and the related ability to exploit sub-optimal environments.