The distribution and abundance of krill faecal material and oval pellets in the Scotia and Weddell Seas (Antarctica) and their role in particle flux

Summary

The abundance and depth distribution of zooplankton faeces in spring to early summer were investigated along meridional transects (47°W and 49°W) that extended from the Scotia Sea (57°S) across the Weddell-Scotia Confluence and into the Weddell Gyre (62°S). The sea ice edge retreated from 59°30′S to 61°S during the study. Faeces were sampled with nets, Niskin bottles and sediment traps and subsequently analysed by light and electron (SEM) microscopy. Krill faecal strings and oval faecal pellets of unknown origin were by far the most important zooplankton faeces and highest concentrations were always found in the Confluence often close to the ice border. Krill faeces were usually more abundant in the uppermost layer (0–50m) where they contributed an average of 130 μg dry weight m⁻³. There was an exponential decrease with depth, with a minimum of 0.6 μg dry weight m⁻³ in the 500–1000 m stratum. Oval pellets were more evenly distributed in the upper 1000 m of the water column, with an average of 9 μg dry weight m ⁻³, although there was a small peak (20 μg dry weight m⁻³) in the subsurface layer (50–150 m depth). Consecutive collections (day-night) of krill faeces using drifting sediment traps showed that only the larger strings sank from 50 to 150 m depth. Peritrophic membranes appeared to deteriorate during sinking. Diatoms (in particular Nitzschia and Thalassiosira spp.) contributed by far the bulk of material in krill and oval faeces. In samples collected near or under the pack ice, remains of crustaceans in both krill- and oval faeces were also found.