254
Andrew CLARKE
fauna was later supported by analyses of asteroids and
polychaetes [see discussion by Vinogradova (1997)].
Further subdivision of the Antarctic deep-sea fauna
depends critically on the depth range considered
(Vinogradova, 1959, 1979, 1997). It has long been
recognized that species with wide bathymetric ranges
also tend to be widely distributed geographically. Thus,
whilst Zezina (1997) considered the Antarctic to form
a uniform biogeographic zone in the bathyal regions,
Vinogradova (1997) has subdivided the Antarctic deep
sea into two major subregions, namely the Antarctic–
Atlantic and the Antarctic–Pacific–Indian regions.
Finer division of the latter into Pacific and Indian
subregions is also possible.
The lower continental slopes around Antarctica
harbour a range of echinoderms, including ophiuroids,
crinoids, asteroids and echinoids. There are fewer
sponges and gorgonians than on the deep continental
shelf, but pennatulids and bryozoans are still present.
As is typical of the lower continental slope elsewhere,
there is a shift from assemblages dominated by sessile
suspension feeders to one consisting primarily of motile
forms. Biomass also decreases sharply with depth
(Menzies et al., 1973).
Sokolova (1997) has provided a detailed analysis of
the trophic structure of deep-sea faunas, emphasizing
the unusual importance of zooplankton to deepsea benthos in Antarctica. Although the connection
between high euphausiid biomass and high biomass
in the benthos beneath has long been recognized for
continental shelves (Dearborn et al., 1986), Sokolova
(1994) has emphasized the importance of zooplankton
to the abyssal fauna (a phenomenon she termed a dead
body rain). This appears to be a feature unique to
Antarctica, where high zooplankton biomass overlies
deep water.
The abyssal zone deeper than 3500 m contains large
taxa typical of deeper waters elsewhere, including the
holothurian Scotoplanes and the pennatulid Umbellula. The deepest waters contain cosmopolitan taxa
including the holothurians Psychropotes, Peniagone,
Pseudostichopus, Scotoplanes and Benthodytes, the
ophiuroid Ophiomusium, the echinoid Phormosoma,
the tunicate Culeolus and the pennatulid Umbellula.
The sparse data that exist would thus suggest that the
deep-water basins around Antarctica thus contain faunal assemblages similar in structure to those elsewhere.
The patterns of deep-water flow around Antarctica and
the history of glaciation suggest, however, that there
may also be strong affinities with the Antarctic shelf
fauna. The most detailed analyses of this have been for
isopods.
The Southern Ocean isopod fauna
Isopod crustaceans are particularly well represented in
the deep sea, and on the Antarctic continental shelf
(Table 8.3). This has led to much speculation as to
the faunal links between high southern latitudes and
the deep-sea, and isopods have been a pivotal group
in discussions of the evolution of the abyssal fauna.
Table 8.3
Number of isopod genera represented in continental shelf faunas
from different regions in the world 1
Region
Number of genera
Antarctica
55
Peru
11
Puerto Rico
19
California
23
Carolina and Georgia
25
Arctic
16
1 From Menzies et al. (1973), where original sources cited.
Kussakin (1973) advanced the view that the deepsea isopod fauna resulted from colonization by shallowwater forms, particularly those from high latitudes.
Kussakin linked this move into deeper water from
around the late Cretaceous, when high southern latitudes in particular began to cool. In contrast, Hessler
and Thistle (1975) argue that the distribution of
eyes amongst deep-sea paraselloidean families suggests
strongly a long period of evolution in situ. Present day
distributions of these isopods provide no suggestion of
a shallow-water origin.
Menzies et al. (1973) have divided the isopod
fauna of Antarctica into three groups: shelf (5–100 m),
archibenthal (deeper continental shelf, 101–800 m),
and abyssal (801–5500 m). Their analysis shows that
representatives of all three groups are found at all
depths, providing powerful evidence for complex evolutionary patterns with some taxa moving into deeper
water (evolutionary polar submergence) and other taxa
colonising the shelf from the deep-sea (evolutionary
polar emergence) (Fig. 8.8).
Brandt (1991, 1992) has undertaken a thorough
analysis of the Southern Ocean isopod fauna, including
phylogenetic analyses of families with both shelf
and deep sea representatives. She demonstrated that
Andrew CLARKE
fauna was later supported by analyses of asteroids and
polychaetes [see discussion by Vinogradova (1997)].
Further subdivision of the Antarctic deep-sea fauna
depends critically on the depth range considered
(Vinogradova, 1959, 1979, 1997). It has long been
recognized that species with wide bathymetric ranges
also tend to be widely distributed geographically. Thus,
whilst Zezina (1997) considered the Antarctic to form
a uniform biogeographic zone in the bathyal regions,
Vinogradova (1997) has subdivided the Antarctic deep
sea into two major subregions, namely the Antarctic–
Atlantic and the Antarctic–Pacific–Indian regions.
Finer division of the latter into Pacific and Indian
subregions is also possible.
The lower continental slopes around Antarctica
harbour a range of echinoderms, including ophiuroids,
crinoids, asteroids and echinoids. There are fewer
sponges and gorgonians than on the deep continental
shelf, but pennatulids and bryozoans are still present.
As is typical of the lower continental slope elsewhere,
there is a shift from assemblages dominated by sessile
suspension feeders to one consisting primarily of motile
forms. Biomass also decreases sharply with depth
(Menzies et al., 1973).
Sokolova (1997) has provided a detailed analysis of
the trophic structure of deep-sea faunas, emphasizing
the unusual importance of zooplankton to deepsea benthos in Antarctica. Although the connection
between high euphausiid biomass and high biomass
in the benthos beneath has long been recognized for
continental shelves (Dearborn et al., 1986), Sokolova
(1994) has emphasized the importance of zooplankton
to the abyssal fauna (a phenomenon she termed a dead
body rain). This appears to be a feature unique to
Antarctica, where high zooplankton biomass overlies
deep water.
The abyssal zone deeper than 3500 m contains large
taxa typical of deeper waters elsewhere, including the
holothurian Scotoplanes and the pennatulid Umbellula. The deepest waters contain cosmopolitan taxa
including the holothurians Psychropotes, Peniagone,
Pseudostichopus, Scotoplanes and Benthodytes, the
ophiuroid Ophiomusium, the echinoid Phormosoma,
the tunicate Culeolus and the pennatulid Umbellula.
The sparse data that exist would thus suggest that the
deep-water basins around Antarctica thus contain faunal assemblages similar in structure to those elsewhere.
The patterns of deep-water flow around Antarctica and
the history of glaciation suggest, however, that there
may also be strong affinities with the Antarctic shelf
fauna. The most detailed analyses of this have been for
isopods.
The Southern Ocean isopod fauna
Isopod crustaceans are particularly well represented in
the deep sea, and on the Antarctic continental shelf
(Table 8.3). This has led to much speculation as to
the faunal links between high southern latitudes and
the deep-sea, and isopods have been a pivotal group
in discussions of the evolution of the abyssal fauna.
Table 8.3
Number of isopod genera represented in continental shelf faunas
from different regions in the world 1
Region
Number of genera
Antarctica
55
Peru
11
Puerto Rico
19
California
23
Carolina and Georgia
25
Arctic
16
1 From Menzies et al. (1973), where original sources cited.
Kussakin (1973) advanced the view that the deepsea isopod fauna resulted from colonization by shallowwater forms, particularly those from high latitudes.
Kussakin linked this move into deeper water from
around the late Cretaceous, when high southern latitudes in particular began to cool. In contrast, Hessler
and Thistle (1975) argue that the distribution of
eyes amongst deep-sea paraselloidean families suggests
strongly a long period of evolution in situ. Present day
distributions of these isopods provide no suggestion of
a shallow-water origin.
Menzies et al. (1973) have divided the isopod
fauna of Antarctica into three groups: shelf (5–100 m),
archibenthal (deeper continental shelf, 101–800 m),
and abyssal (801–5500 m). Their analysis shows that
representatives of all three groups are found at all
depths, providing powerful evidence for complex evolutionary patterns with some taxa moving into deeper
water (evolutionary polar submergence) and other taxa
colonising the shelf from the deep-sea (evolutionary
polar emergence) (Fig. 8.8).
Brandt (1991, 1992) has undertaken a thorough
analysis of the Southern Ocean isopod fauna, including
phylogenetic analyses of families with both shelf
and deep sea representatives. She demonstrated that