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Peninsula, along with recent records of anomuran lithodid crabs in the deep sea
and on the continental slope. These records raise the question of whether the
return of the crabs to the Antarctic after their extinction in the Lower Miocene
(
15million years ago) might indicate a response to global change. However,
it remains unclear when such recolonisation events actually took place and, in
the case of the Brans
eld Strait records, whether or not they involve any human
activity in the transport process or, indeed, the species (which have been recorded
only once) have actually become established. It is also plausible that periodic
(re-)colonisation of the Antarctic continental shelf by species currently limited
to the somewhat warmer adjacent slope and depths may be a more regular event
associated with systematic incursions of warmer water masses onto the shelf.
Currently, 11 species of lithodids have been reported south of the Antarctic Polar
Front, and these have probably recolonised the Antarctic via the circumpolar
deep sea.
The deep-sea benthos
Globally, the ocean depths rank amongst the least studied, visited or sampled
ecosystems on the planet, despite the fact that they cover by far the largest geographic
scale on Earth. A few decades ago it was suggested that marine biodiversity is
higher in the deep-sea benthos than on the more familiar continental shelf or slope,
and various hypotheses have been advanced to explain this. As it remains virtually
impossible to obtain animals alive and undamaged from this region, we know
virtually nothing in detail about the life histories, ecology or physiology of the
deep-sea biota.
In contrast with the Antarctic continental shelf, which serves as an
evolutionary laboratory due to its isolation and high degree of species endemism,
the deep-sea regions of the different oceans are interconnected, and their fauna is
not isolated. Vast areas surrounding the Antarctic continental shelf are deep sea.
Compared to our knowledge of the benthos of the Southern Ocean shelf,
knowledge of the deep-sea fauna remains scant, even after expeditions such as
ANDEEP, focussing on speci
c regions, and the recent publication of more than
170 scienti
c papers.
Patterns of species diversity and benthic community structure differ between
deep-sea habitats. The possible existence of latitudinal gradients in species diversity
in marine ecosystems has been hotly debated, but in truth this issue currently
remains unresolved, not least as vast areas of the deep sea, especially of the southern
hemisphere, remain unexplored. Nevertheless, data for isopod and gastropod
species richness challenge the hypothesis of latitudinal gradients in this region. High
biodiversity has been reported for some macrofaunal and megafaunal taxa in the
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