Development, Dispersal and Recruitment: A Paradox for Survival Among Antarctic Fish
55
circulation patterns have been observed but the temporal and spatial
persistence of these has yet to be described in detail.
The flow of a strong current past a sea-mount or island will cause the
development of gyres and eddies, An island such as South Georgia with a
shelf that is heavily dissected by glacial canyons will also be expected to
have eddies associated with these features. Such topographically generated
eddies should act as retention zones for the local zooplankton
communities.
The Paradox
The fish populations are dependent upon the continental shelf as nursery
grounds for juveniles and habitat for adults. These shelf environments
particularly those of islands are subject to the strong current systems.
Benthic Antarctic invertebrates have usually been strongly selected for
species that have reduced or eliminated the pelagic larval phase [15].
Demersal fish, on the other hand, have maintained an extended pelagic
larval phase - even though most species have low relative fecundity and
are dependent on shelf habitats as adults. The strong C\.lrrent systems
should advect the eggs and larval stages away and cause substantial losses.
Therefore the maintenance of a protracted pelagic early life-history
among the dominant groups of Antarctic fish in a strongly advective
oceanic system appears to be inconsistent with a successful survival
strategy.
Is There Evidence for Dispersal or Retention of Pelagic
Stages?
The early juvenile stages of some demersal fish species are found widely
dispersed away from the shelf habitats over which they were spawned [6],
but these are the exception because the eggs and larvae of the majority of
species are usually found concentrated in neritic waters over the
continental shelf [5]. Examples of the distribution patterns of the larvae of
demersal shelf species at South Georgia, South Shetland Islands,
Kerguelen and the Weddell Sea [11,16-19] show that their distribution is
largely over the continental shelf and adjacent waters - with a relatively
well defined junction between shelf and oceanic species at the shelf/slope
junction.
For example, Fig. 1 shows the distribution patterns for eggs and larvae
of common demersal nototheniids, a channichthyid, a muraenolepidid as
well as an oceanic paralepidid, Notolepis coatsi Dollo collected during a
55
circulation patterns have been observed but the temporal and spatial
persistence of these has yet to be described in detail.
The flow of a strong current past a sea-mount or island will cause the
development of gyres and eddies, An island such as South Georgia with a
shelf that is heavily dissected by glacial canyons will also be expected to
have eddies associated with these features. Such topographically generated
eddies should act as retention zones for the local zooplankton
communities.
The Paradox
The fish populations are dependent upon the continental shelf as nursery
grounds for juveniles and habitat for adults. These shelf environments
particularly those of islands are subject to the strong current systems.
Benthic Antarctic invertebrates have usually been strongly selected for
species that have reduced or eliminated the pelagic larval phase [15].
Demersal fish, on the other hand, have maintained an extended pelagic
larval phase - even though most species have low relative fecundity and
are dependent on shelf habitats as adults. The strong C\.lrrent systems
should advect the eggs and larval stages away and cause substantial losses.
Therefore the maintenance of a protracted pelagic early life-history
among the dominant groups of Antarctic fish in a strongly advective
oceanic system appears to be inconsistent with a successful survival
strategy.
Is There Evidence for Dispersal or Retention of Pelagic
Stages?
The early juvenile stages of some demersal fish species are found widely
dispersed away from the shelf habitats over which they were spawned [6],
but these are the exception because the eggs and larvae of the majority of
species are usually found concentrated in neritic waters over the
continental shelf [5]. Examples of the distribution patterns of the larvae of
demersal shelf species at South Georgia, South Shetland Islands,
Kerguelen and the Weddell Sea [11,16-19] show that their distribution is
largely over the continental shelf and adjacent waters - with a relatively
well defined junction between shelf and oceanic species at the shelf/slope
junction.
For example, Fig. 1 shows the distribution patterns for eggs and larvae
of common demersal nototheniids, a channichthyid, a muraenolepidid as
well as an oceanic paralepidid, Notolepis coatsi Dollo collected during a