timed molts (Ikeda & Dixon 1982). As light returns in spring during the melt-back of
the ice, E. superba, particularly the larval stages and also larvae of Euphausia
crystallophorias, feed on the bloom established by meltwater stabilization, and on the
increasing epontic algae. As in the Arctic, ice surfaces, particularly frazil, support a
modestly complex community adjusted to cold and strongly varying salinity,
including forms other than krill and krill larvae. For example, Stephos longipes, a
copepod belonging to a typically epibenthic family, lives in antarctic frazil, in melt
ponds above the ice and melt layers within the ice (Schnack-Schiel et al. 2001).
(^) Adult E. superba reach a length of 10 cm, with sufficient tail muscle to make them a
desirable fishery product. Moreover, its schools constitute the largest, slightly
exploited fishery in the oceans, with an average stock estimated by Atkinson et al.
(2009) at ∼379 million metric tons (Mt). Fishing was tried in the 1970s and early
1980s, but tailed off. Special processing requirements and the great expense and
difficulty of fishing in the Antarctic have kept exploitation to a minimum.
(^) The oceanic copepods (principally larger biomass dominants Calanus propinquus,
Calanoides acutus, Rhincalanus gigas and Metridia gerlachi; small numerical
dominants Microcalanus pygmaeus, Ctenocalanus citer and Oithona similis) are the
principal grazing mesozooplankton seaward of the marginal ice zone in most of the
region south of the SAF (Atkinson 1998; Schnack-Schiel 2001). The larger species
resemble those of the Arctic (and subarctic) in that they load with lipid as a nutriment
store to see them through the winter hiatus in primary production. However, only C.
acutus and R. gigas move to mesopelagic depths during the dark season for a
prolonged copepodite diapause. In some years or for some part of the stocks of these
two, the life cycle may take two years and involve two diapause intervals. The other
species continue through the winter near the surface, living and feeding, albeit at
reduced rates. Through much of the year, the copepods feed a trophic level or two
removed from phytoplankton, since pico- and nanoplankton are the main primary
producers after the spring bloom becomes iron limited, although Phaeocystis colonies
are particularly important in this ecosystem and are significantly avoided by both
microheterotrophs and mesozooplankton grazers. Dilution experiments (Pearce et al.
2010) show control of reasonably fast phytoplankton growth by balancing grazing by
heterotrophic nanoflagellates, ciliates, and dinoflagellates.
(^) Antarctic particle-feeding copepods are preyed upon by fish, fish larvae, predatory
copepods of the family Euchaetidae, and chaetognaths, particularly Solidosagitta
marri, Parasagitta gazellae, and Eukrohnia hamata. Population outbursts of Salpa
thompsoni are also common but not related in an obvious way to habitat conditions.
Mesopelagic waters south of the SAF support mesopelagic communities similar to
those worldwide, but with many endemic species. Antarctic pelagic ecology is, of
course, much more complex than our presentation of it, and recent research has
generated massive amounts of data, thousands of papers and almost equal numbers of