T he history of life has shown
that climate has never
been stable, and the evolution
of the Southern Ocean
fish fauna over the past 55 million
years has taken place as the temperature
of their sea-water habitat
has undergone an overall reduction
from about 20°C to the polar
extremes we see today (-1.86’C)
(Box 1). Throughout evolutionary
history the general response of
organisms to a slow climatic shift
has been a parallel shift in geographic
range, tracking the movement
of climatic zones. For a fauna
of essentially shallow-water fish
isolated by large expanses of deep
water, such a shift in distribution
is, however, geographically constrained.
Following the isolation of
Antarctica, the existing shallowwater
fauna was forced to adapt to
the changing climate or become
extinct.