Smithsonian at the Poles: Contributions to International Polar

150 SMITHSONIAN AT THE POLES / PARK AND FERRARI
Schnack-Schiel et al., 1995). Stephos antarcticus is known
only from its type locality, McMurdo Sound of the Ross
Sea (Wolfenden, 1908). Most species of the genus Stephos
are closely associated with the water immediately above
the seafl oor (Bradford-Grieve, 1999).
Among these eight species, the three species of Drepanopus
and the three species of Paralabidocera clearly seem
to be pelagic. The two species of Stephos appear to be
ice oriented but are considered pelagic here. All of these
inshore species are characteristically small in size, ranging
from 0.85 to 2.80 mm in body length.
EPIPELAGIC FAUNA
OF THE SOUTHERN OCEAN
The epipelagic calanoid fauna of the Southern Ocean
south of the Antarctic Convergence (Table 2) is relatively
simple in species composition. There are fi ve species, all are
very common, and their combined biomass is unsurpassed
by the epipelagic calanoid fauna of any other region of the
world’s oceans (Foxton, 1956). These fi ve epipelagic species
are, in order of abundance, Calanoides acutus, Rhincalanus
gigas, Calanus propinquus, Metridia gerlachei,
TABLE 2. Epipelagic calanoid copepods of the Southern Ocean.
CC, very common (over 100 specimens found); C, common
( between 99 and 50 specimens found).
Species name Abundance
Species endemic to Antarctic waters
Calanoides acutus CC
Calanus propinquus CC
Clausocalanus laticeps CC
Metridia gerlachei CC
Rhincalanus gigas CC
Species endemic to subantarctic waters
Calanus simillimus CC
Clausocalanus brevipes CC
Ctenocalanus citer C
Species ranging from subantarctic water to south temperate region
Calanus australis C
Neocalanus tonsus C
Subeucalanus longiceps C
Species ranging from subantarctic waters to north temperate region
Eucalanus hyalinus C
Rhincalanus nasutus C
and Clausocalanus laticeps. These are the copepods most
often associated by planktonologists with the Southern
Ocean. All were discovered during the early expeditions,
and their taxonomy and distribution have been clearly
and carefully defi ned. Although these fi ve species are more
abundant in waters south of the Antarctic Convergence,
they also may be collected north of the convergence, but
here they appear to be associated with the deeper Antarctic
Intermediate Water. Calanoides acutus and, to a lesser
extent, Rhincalanus gigas and Calanus propinquus are the
dominant herbivores south of the Antarctic Convergence,
and their role in that ecosystem is well known (Chiba et
al., 2002; Pasternak and Schnack-Schiel, 2001).
The analogous epipelagic calanoids of the subantarctic
region, between the Antarctic and Subtropical convergences,
are Calanus simillimus, Clausocalanus brevipes,
and Ctenocalanus citer. These three herbivores are very
common in the subantarctic region, but they are not as
numerous in these waters as the previous fi ve epipelagic
calanoids are south of the Antarctic Convergence. 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).
There are three additional large-sized, epipelagic herbivores
that may be collected in the subantarctic region
as well as in the south temperate midlatitudes: Calanus
australis, Neocalanus tonsus, and Subeucalanus longiceps.
Calanus australis is known to be distributed along the
southern coast of Chile, off Argentina, in New Zealand
waters, and in southeastern Australian waters (Bradford-
Grieve, 1994). Its distribution during summer has been
investigated (Sabatini et al., 2000). Neocalanus tonsus
is widely distributed in subantarctic waters but also may
be found in the deepwater of the south temperate region;
some aspects of its life history are known (Ohman et al.,
1989). Subeucalanus longiceps (Subeucalanidae) occurs
circumglobally in the subantarctic and temperate regions
of the Southern Hemisphere. These three species are important
herbivores in the subantarctic as well as the south
temperate region.
Two small-sized, epipelagic herbivores, Clausocalanus
parapergens and Ctenocalanus vanus, are found in subantarctic
waters. Clausocalanus parapergens has been reported
as far north as the subtropical convergence (Frost
and Fleminger, 1968). Specimens referred to as Ctenocalanus
vanus from the Southern Ocean by Farran (1929) and
Vervoort (1951, 1957) are Ctenocalanus citer (T. Park,