58
M.G. White
form of physical barrier at the shelf/slope break or mechanisms that retain
the demersal species near to the continental shelf.
The development of lee gyres at oceanic islands has been established in
the oceanographic literature for some years [21]. More recently the
importance of such features to biological processes has been recognized,
for example, Gilmartin and Revelante [22] describe the elevated
production resulting from eddy formation at Hawaii, and Heywood et al.
[23] describe the development, maintenance and the influence on
productivity of lee gyres at Aldabra in the Indian Ocean.
Evidence for lee gyres and the development of a near-shelf eddy
system at South Georgia is given by Latogursky et al. [24] during their
studies about the variations in abundance and distribution of Antarctic
Krill, Euphausia superba Dana, at South Georgia. They also showed that
the development of local eddy systems varied between years and so
inferred a mechanism for inter-annual variations in the aggregation of
krill at South Georgia. These features, though not stated by the authors
[24], will also serve to retain neritic plankton displaced off the shelf.
The presence and development of shelf-break frontal systems in the
Antarctic has thus far been inferred from the biological data such as the
ichthyoplanktonlzooplankton distribution patterns in the Weddell Sea
[17], Antarctic Peninsula [18] and at South Georgia ([9,19,25], White
and North personal observations).
Brandon and others [26] working with the most recent oceanographic
data from British Antarctic Survey research cruise JRll on "RRS James
Clark Ross" have shown strong evidence of a shelf-break front on the
northern shelf of South Georgia during January 1996. Data collected
from ca. 80 km onshore-offshore transects at right angles to the coast
demonstrated that warm low salinity water over the shelf was separated
from colder more saline off-shelf water by a well defined hydrographic
front more or less coincident with the margin of the continental shelf.
Thus there is evidence of mechanisms that would help to maintain near
passive particles over or near the shelf at South Georgia and retain fish
eggs and larvae in favourable conditions for their early development.
Indeed it is clear that this must be so if the species such as Antarctic
notothenioids; with protracted pelagic phases in their early life-history,
relative low fecundity and a dependence on shelf habitats, are to be
successful. Therefore, although the life-history strategies adopted by
Antarctic fish appear to be counter-intuitive with successful survival, we
can show that there are environmental mechanisms which permit an
extended pelagic component to be retained. The fact that a vulnerable
pelagic phase is retained suggests that it is important as a successful
adaptation to the polar environment.
M.G. White
form of physical barrier at the shelf/slope break or mechanisms that retain
the demersal species near to the continental shelf.
The development of lee gyres at oceanic islands has been established in
the oceanographic literature for some years [21]. More recently the
importance of such features to biological processes has been recognized,
for example, Gilmartin and Revelante [22] describe the elevated
production resulting from eddy formation at Hawaii, and Heywood et al.
[23] describe the development, maintenance and the influence on
productivity of lee gyres at Aldabra in the Indian Ocean.
Evidence for lee gyres and the development of a near-shelf eddy
system at South Georgia is given by Latogursky et al. [24] during their
studies about the variations in abundance and distribution of Antarctic
Krill, Euphausia superba Dana, at South Georgia. They also showed that
the development of local eddy systems varied between years and so
inferred a mechanism for inter-annual variations in the aggregation of
krill at South Georgia. These features, though not stated by the authors
[24], will also serve to retain neritic plankton displaced off the shelf.
The presence and development of shelf-break frontal systems in the
Antarctic has thus far been inferred from the biological data such as the
ichthyoplanktonlzooplankton distribution patterns in the Weddell Sea
[17], Antarctic Peninsula [18] and at South Georgia ([9,19,25], White
and North personal observations).
Brandon and others [26] working with the most recent oceanographic
data from British Antarctic Survey research cruise JRll on "RRS James
Clark Ross" have shown strong evidence of a shelf-break front on the
northern shelf of South Georgia during January 1996. Data collected
from ca. 80 km onshore-offshore transects at right angles to the coast
demonstrated that warm low salinity water over the shelf was separated
from colder more saline off-shelf water by a well defined hydrographic
front more or less coincident with the margin of the continental shelf.
Thus there is evidence of mechanisms that would help to maintain near
passive particles over or near the shelf at South Georgia and retain fish
eggs and larvae in favourable conditions for their early development.
Indeed it is clear that this must be so if the species such as Antarctic
notothenioids; with protracted pelagic phases in their early life-history,
relative low fecundity and a dependence on shelf habitats, are to be
successful. Therefore, although the life-history strategies adopted by
Antarctic fish appear to be counter-intuitive with successful survival, we
can show that there are environmental mechanisms which permit an
extended pelagic component to be retained. The fact that a vulnerable
pelagic phase is retained suggests that it is important as a successful
adaptation to the polar environment.