Seasonal variations in distribution and population structure of Microcalanus pygmaeus and Ctenocalanus citer (Copepoda: Calanoida) in the eastern Weddell Sea, Antarctica

Abstract

The abundance, vertical distribution and population structure of two important small calanoid copepod species, Microcalanus pygmaeus (G. O. Sars) and Ctenocalanus citer Heron and Bowman, were studied in the eastern Weddell Sea in summer (January/February 1985), in late winter/early spring (October/November 1986) and in autumn (April/May 1992). The population of Microcalanus pygmaeus consisted mainly of copepodite stages CII and CIII in late winter/early spring and were concentrated between 500 and 200 m depth. In summer, stage CIV was the modal stage and the bulk of the population had ascended above 300 m. In autumn the population structure was bimodal with CI and CV dominating. Most of the population was concentrated between 300 and 200 m. In all investigation periods M. pygmaeus had their maximal concentrations in the thermo-pycnocline. The developmental stages CIII to CV of Ctenocalanus citer formed the bulk of the population in late winter/early spring. In October all developmental stages had their main distribution between 500 and 200 m, except females, which were concentrated in the upper 50 m. In November most of the population occurred between 200 and 50 m. The summer population was concentrated in the upper 50 m, and numbers increased dramatically as the new cohort hatched. Copepodite stages CII and CIII dominated the population at the end of January, while CIV dominated 2 wk later. In autumn, CV was the modal stage. The majority of the population was concentrated in the upper 100 m, but there was an increase in abundance below 300 m compared to summer. Age structure changed with depth with a younger surface population and an older one in deeper water layers. The seasonal change in number of M. pygmaeus is much smaller than that of C. citer; the summer:winter:autumn ratio of the former being about one, whereas the winter: summer/autumn of the latter was about nine. Early copepodite stages and Communicated by O. Kinne, Oldendorf/Luhe

Species diversity and distributions of pelagic calanoid copepods (Crustacea) from the Southern Ocean

“…Furthermore, the Antarctic Convergence does not limit the southern boundary of the range of these three species as precisely as it limits the northern boundary of the previous fi ve epipelagic calanoids. The population structure and life histories of the three have been described (Atkinson, 1991;Schnack-Schiel and Mizdalski, 1994).…”

High summer abundances of small pelagic copepods at the Antarctic Polar Front—implications for ecosystem dynamics

“…Thus, the high abundance of C. citer seems to be a typical feature of the frontal area. Ctenocalanus citer also is a rather weak seasonal migrant (Atkinson and Sinclair, 2000), and is able to grow and reproduce before the onset of phytoplankton blooms in the water column (Schnack-Schiel and Mizdalski, 1994). Thus both species, Oithona spp.…”

“…The increasing use of finer plankton nets (55-200 mm) since the mid-1980s has provided a more realistic view of the ecological significance of small copepods such as Oithona, Oncaea, and clausocalanids (Atkinson, 1998;Chojnacki and Weglenska, 1984;Foster, 1987;Fransz, 1988;Schnack-Schiel and Mizdalski, 1994;Zmijewska, 1988). Copepod abundances of up to 8000 ind: m À3 and average zooplankton biomass of 1-2 g C m À2 have been recorded since then for the upper mixed layer of Antarctic and Subantarctic waters (Atkinson, 1996;Fransz and Gonzalez, 1997;Metz, 1995Metz, , 1996.…”

Copepod species abundance from the Southern Ocean and other regions (1980–2005) – a legacy

“…pygmaeus or Stephos longipes (e.g. Schnack-Schiel and Mizdalski, 1994;Schnack-Schiel et al, 1995;Ward et al, 1997;Schnack-Schiel, 2001). However, the stage-resolved copepod data of most species in Table 3 have not been analysed.…”