Antarctic Polar Biome
473
were correlated with chlorophyll, dilution experiments performed at three seasons all
suggested very low rates of phytoplankton cell removal. Massive blooms observed here in
extremely cold water are perhaps due to the low activity of microbial herbivores under
such conditions (Caron et al., 2000).
However, this is a very diverse region and a quite different balance between production and consumption also occurs (e.g., Brandini, 1993): in some coastal bays, such
as Admiralty Bay in the South Shetlands, nanosized diatoms (Nitzschia) dominate the
phytoplankton during open-water and stable conditions, and these are held at relatively
low concentration by very intense grazing by ciliates that dominate the protistan herbivores. Production during the brief summer season is maintained entirely by regenerated
nitrogen and micronutrients, and larger cells are very scarce, occurring deeper in the
chlorophyll profile.
The benthos of the continental shelf responds both to the general constraints of a
very cold environment, and to the special conditions imposed everywhere by topography
and sediment type. The fauna of the sea floor below permanent ice shelves is sufficiently
attenuated as to be effectively absent in some regions, but elsewhere it may be very dense
though rapidly rarified with depth. Obviously, where the water depth is such as to permit
scouring by drifting ice, the benthic community is sparse and is retained permanently
in the early stages of recolonization of the substrate. As in the high arctic, the fauna is
attenuated in the sense that some groups, abundant in the benthos of temperate shelves,
are absent; the ecology of those organisms that are abundant on the Antarctic shelf is
characterized by relatively slow growth compared with similar kinds of organisms in
similar habitats in warmer seas, despite the effect of cold-adapted metabolism. Note
that the seasonal temperature variation here is as small as anywhere and decreases with
increasing latitude. There is also a characteristic avoidance of the planktonic larval stage
in the life history in favor of brooding of eggs and larvae (as Thorson would have
predicted), this preference leading to the relative dominance of groups that habitually
brood, even in lower latitudes: thus, among the crustacea, amphipods and isopods are
abundant, but decapods and cirripedes are not. Incubation duration is an excellent key to
the consequences of cold temperatures on the physiology of benthic invertebrates: four
species of Antarctic amphipods brood for 5–7 months, seven temperate species brood
for only 8–49 days in summer. There seems no reason to quarrel with the long-accepted
explanation for this peculiarity: although high-latitude seasonality is, in general, very
predictable, what occurs in any year at any place is highly variable and, further, larval
transformation for most species could not be completed within one season.
A thick ground cover of suspension- and particle-feeding sponges, bryozoa, brachiopods and coelenterates, together with asteroids and nudibranchs, may dominate the
benthic communities on sand, gravel, and cobbles. These matlike communities appear to
be restricted to water depths exceeding 50–60 m; presumably, in shallow water, ice scour
would prevent the formation of this biotope. Otherwise, diverse bottom types support
diverse benthic communities in a manner not very different from that in lower latitudes,
the benthic community structure responding in the anticipated manner to the presence
of rock, sand, mud, macroalgae, and tidal scour. Muddy sediments do not, of course,
support mats of suspension-feeding organisms but rather a fauna typical of such a habitat:
annelids, mollusks, nematodes, and so on. Fish are dominated by notothenids, a group
that is rather poor in species: Sakurai et al. found only five: one generalist, two on rocky
bottoms, and two species among kelp.
Of course, it was the large animals of the austral regions that first drew scientific
attention to the Antarctic: various estimates, all very large, have been made of the pristine
numbers and biomass of whales, seals and birds. Of 36 species in all seas, the crabeater
seal (Lobodon) of the Antarctic comprised at one time half of the total world stock
of pinnipeds (Laws, 1984). In this province, close to the continent, crabeaters, Ross’s
473
were correlated with chlorophyll, dilution experiments performed at three seasons all
suggested very low rates of phytoplankton cell removal. Massive blooms observed here in
extremely cold water are perhaps due to the low activity of microbial herbivores under
such conditions (Caron et al., 2000).
However, this is a very diverse region and a quite different balance between production and consumption also occurs (e.g., Brandini, 1993): in some coastal bays, such
as Admiralty Bay in the South Shetlands, nanosized diatoms (Nitzschia) dominate the
phytoplankton during open-water and stable conditions, and these are held at relatively
low concentration by very intense grazing by ciliates that dominate the protistan herbivores. Production during the brief summer season is maintained entirely by regenerated
nitrogen and micronutrients, and larger cells are very scarce, occurring deeper in the
chlorophyll profile.
The benthos of the continental shelf responds both to the general constraints of a
very cold environment, and to the special conditions imposed everywhere by topography
and sediment type. The fauna of the sea floor below permanent ice shelves is sufficiently
attenuated as to be effectively absent in some regions, but elsewhere it may be very dense
though rapidly rarified with depth. Obviously, where the water depth is such as to permit
scouring by drifting ice, the benthic community is sparse and is retained permanently
in the early stages of recolonization of the substrate. As in the high arctic, the fauna is
attenuated in the sense that some groups, abundant in the benthos of temperate shelves,
are absent; the ecology of those organisms that are abundant on the Antarctic shelf is
characterized by relatively slow growth compared with similar kinds of organisms in
similar habitats in warmer seas, despite the effect of cold-adapted metabolism. Note
that the seasonal temperature variation here is as small as anywhere and decreases with
increasing latitude. There is also a characteristic avoidance of the planktonic larval stage
in the life history in favor of brooding of eggs and larvae (as Thorson would have
predicted), this preference leading to the relative dominance of groups that habitually
brood, even in lower latitudes: thus, among the crustacea, amphipods and isopods are
abundant, but decapods and cirripedes are not. Incubation duration is an excellent key to
the consequences of cold temperatures on the physiology of benthic invertebrates: four
species of Antarctic amphipods brood for 5–7 months, seven temperate species brood
for only 8–49 days in summer. There seems no reason to quarrel with the long-accepted
explanation for this peculiarity: although high-latitude seasonality is, in general, very
predictable, what occurs in any year at any place is highly variable and, further, larval
transformation for most species could not be completed within one season.
A thick ground cover of suspension- and particle-feeding sponges, bryozoa, brachiopods and coelenterates, together with asteroids and nudibranchs, may dominate the
benthic communities on sand, gravel, and cobbles. These matlike communities appear to
be restricted to water depths exceeding 50–60 m; presumably, in shallow water, ice scour
would prevent the formation of this biotope. Otherwise, diverse bottom types support
diverse benthic communities in a manner not very different from that in lower latitudes,
the benthic community structure responding in the anticipated manner to the presence
of rock, sand, mud, macroalgae, and tidal scour. Muddy sediments do not, of course,
support mats of suspension-feeding organisms but rather a fauna typical of such a habitat:
annelids, mollusks, nematodes, and so on. Fish are dominated by notothenids, a group
that is rather poor in species: Sakurai et al. found only five: one generalist, two on rocky
bottoms, and two species among kelp.
Of course, it was the large animals of the austral regions that first drew scientific
attention to the Antarctic: various estimates, all very large, have been made of the pristine
numbers and biomass of whales, seals and birds. Of 36 species in all seas, the crabeater
seal (Lobodon) of the Antarctic comprised at one time half of the total world stock
of pinnipeds (Laws, 1984). In this province, close to the continent, crabeaters, Ross’s