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Figure 6.17
Sea urchins caught with the sediment pro
le camera in the central Powell Basin at
1955 m. Urchins of 5 cm in diameter sit on a silty clay with some coarse-sand sediment, which
was disturbed when the camera entered the sediment. (Credit: Robert Diaz)
As early as 1936, Gunnar Thorson proposed that polar environmental conditions,
whose in
uence on
sensitive early life-history stages and favoured brooding. In general, biogeographic
patterns of taxa may be linked to larval ecology. Groups such as the isopods,
ostracods and nematodes have poor dispersal capabilities and hence reduced gene
uence has been felt since the Cretaceous, had a particular in
cult to prove.
In contrast, other groups such as polychaete worms appear to be able to cross the
barrier between the Southern Ocean and adjacent oceans and have a much wider
zoogeographic and bathymetric distribution. Brooding is thought to be much less
common amongst polychaetes, making dispersal via their free-swimming
trochophore larvae more common. Polychaetes may also have particularly high
physiological
flow, making restricted species distributions more plausible, albeit dif
flexibility in coping with temperature and pressure changes.
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