Late winter abundance and distribution of phaeodarian radiolarians, other large protozooplankton and copepod nauplii in the Weddell Sea, Antarctica

Abstract

Large (>64 µm) protozooplankton (radiolarians, thecate dinoflagellates, foraminiferans, and tintinnid ciliates) and copepod nauplii were sampled at six stations located in sea-ice-covered waters, using a multinet at five depth intervals between the surface and 1000 m depth during a late winter expedition of R.V. ‘Polarstern’ on a west-east transect across the Weddell Sea in 1989. Large (>400 µm) phaeodarian radiolarians contributed more than 98% of the carbon in the large protozooplankton fraction; large protozooplankton represented ca. 38% of the total protozooplankton carbon during late winter under the close pack ice in the upper 250 m. Large protozooplankton may therefore be an important food source for small particle-feeding zooplankton in the upper 250 m, and a modest food source down to 1000 m. Phaeodarian species distributions showed a distinct vertical pattern. Except for spumellarian and nassellarian radiolarians all other protozooplankton (foraminiferans, thecate dinoflagellates, tintinnids) were most abundant in the upper 250 m. The horizontal variation showed a western, central and eastern pattern most probably due to the differing regional hydrography. Feeding ecology of the dominant species of phaeodarians was examined using transmission electron microscopy of contents of feeding vacuoles. The 58 specimens were trophic generalists. The predominance of silica fragments and amorphous material in vacuoles and the similarity of vacuole contents of specimens from three depth zones suggest that phaeodarians in late winter may have fed on organic aggregates.