54
M.G. White
Incubation from spawning to hatching is often protracted (>100 days)
[6,7]. Once hatched, the larvae are usually large (> 12 rom) and develop
pelagically over several months before recruiting to the demersal juvenile
population [8,9]. Some species have a specialist neustonic juvenile phase
or have a juvenile morphology adapteQ for a pelagic habit, such as the
post-larval and juvenile stages of many channiclithyids.
Affinities
Despite the apparent potential for extensive dispersal because of the
opportunities for distribution of the pelagic life-history stages on ocean
currents, endemism is high and each peri-Antarctic island group has a
discrete species composition and therefore constraints over dispersal must
prevail. Biogeographical studies on Antarctic fish clearly divide the
Southern Ocean ichthyofauna into geographically separated regions [1,10].
There is evidence for the influence of the West Wind Drift to disperse
species eastwards (cf. [3,10]). Commonly, the closest affinities are
between neighbouring island groups.
Physical Environment
The Southern Ocean is well known for low ambient temperatures and
seasonal sea-ice development; however, the most striking feature is the
oceanographic current system that is dominated by the circum-continental
West Wind Drift, that influences most of the peri-Antarctic islands, and its
complementary counter current adjacent to the Continent. Major gyres are
well known, particularly those in the Weddell and Ross Seas, and these are
strongly implicated in the life-history of euphausiids [11] and some high
Antarctic fish e.g. Pleuragramma antarcticum [12].
The largely circum-polar East Wind Drift and the near continuous shelf
habitats around the Antarctic continent offer few barriers to pelagic
dispersal and juvenile recruitment among high-Antarctic species. Here,
high-Antarctic species exhibit circum-continental distribution patterns
with little regionalization. By contrast, the peri-Antarctic island groups are
separated by deep ocean and great distances and these result in
considerable barriers to colonization. All are strongly influenced by the
West Wind Drift.
South Georgia is a typical example. The Discovery Expedition [13]
demonstrated that strong currents approach South Georgia from the south
east and south west, flow around the shelf and leave the island on the
northern side. Studies undertaken more recently [14] support the major
features of the large- and meso-scale circulation patterns. The fine-scale
M.G. White
Incubation from spawning to hatching is often protracted (>100 days)
[6,7]. Once hatched, the larvae are usually large (> 12 rom) and develop
pelagically over several months before recruiting to the demersal juvenile
population [8,9]. Some species have a specialist neustonic juvenile phase
or have a juvenile morphology adapteQ for a pelagic habit, such as the
post-larval and juvenile stages of many channiclithyids.
Affinities
Despite the apparent potential for extensive dispersal because of the
opportunities for distribution of the pelagic life-history stages on ocean
currents, endemism is high and each peri-Antarctic island group has a
discrete species composition and therefore constraints over dispersal must
prevail. Biogeographical studies on Antarctic fish clearly divide the
Southern Ocean ichthyofauna into geographically separated regions [1,10].
There is evidence for the influence of the West Wind Drift to disperse
species eastwards (cf. [3,10]). Commonly, the closest affinities are
between neighbouring island groups.
Physical Environment
The Southern Ocean is well known for low ambient temperatures and
seasonal sea-ice development; however, the most striking feature is the
oceanographic current system that is dominated by the circum-continental
West Wind Drift, that influences most of the peri-Antarctic islands, and its
complementary counter current adjacent to the Continent. Major gyres are
well known, particularly those in the Weddell and Ross Seas, and these are
strongly implicated in the life-history of euphausiids [11] and some high
Antarctic fish e.g. Pleuragramma antarcticum [12].
The largely circum-polar East Wind Drift and the near continuous shelf
habitats around the Antarctic continent offer few barriers to pelagic
dispersal and juvenile recruitment among high-Antarctic species. Here,
high-Antarctic species exhibit circum-continental distribution patterns
with little regionalization. By contrast, the peri-Antarctic island groups are
separated by deep ocean and great distances and these result in
considerable barriers to colonization. All are strongly influenced by the
West Wind Drift.
South Georgia is a typical example. The Discovery Expedition [13]
demonstrated that strong currents approach South Georgia from the south
east and south west, flow around the shelf and leave the island on the
northern side. Studies undertaken more recently [14] support the major
features of the large- and meso-scale circulation patterns. The fine-scale