Species diversity and spatial distribution of pelagic amphipods in Terra Nova Bay (Ross Sea, Southern Ocean)

A greater understanding of biodiversity and the roles of various species involved in Southern Ocean pelagic food webs is needed to predict and hypothesize about responses to future scenarios in relation to climate changes. The aim of this paper was to describe for the first time the composition, relative abundance, spatial distribution and relation with water masses of pelagic amphipods in Terra Nova Bay, Ross Sea, based on stratified sampling. Zooplankton was collected by BIONESS (Bedford Institute of Oceanography Net Environmental Sampling System), during the 1987-1988 Italian Antarctic R/V Polar Queen Expedition. A total of 1331 specimens of pelagic amphipods was counted and 17 species belonging to nine families were identified. Significantly relative higher abundances were related to Modified Circumpolar Deep Water (MCDW) in the upper layer than modified Ross Sea Shelf Water (RSSW) and High Salinity Shelf Water (HSSW). Hyperiella dilatata was the most abundant species (48% of relative abundance), followed by Pseudorchomene plebs (14%), Hyperia macrocephala (8%) and Hyperiella macronyx (6%). Hyperiella dilatata was distributed widely across the study area and showed a link with Antarctic Surface Waters (AASW) and MCDW. Hyperiella macronyx and Pseudorchomene rossi were also distributed widely though were much lower in abundance. Hyperia macrocephala were high in abundance though had a narrow distribution that was linked with AASW. The vertical distributions showed variable patterns for adult and juvenile specimens. This study represents a knowledge base against which to compare more recent studies to highlight any structural changes attributable to ongoing climate change in the Terra Nova Bay and Ross Sea ecosystems.