The bottom of the sea is very interesting there, because it is densely populated but the abundant species are very different from other seas and more similar to what can be found in other places only at much higher depths.
Instead of abundant crabs and other crustaceans and mollusks, "Under Antarctica" the most abundant big animals on the bottom are echinoderms, sea spiders and nemertean worms.
It is not known for sure, but the most plausible explanation is that during the last Ice Ages the crabs and most fish have disappeared from there due to low temperatures.
The disappearance of these predators has allowed other animal groups to flourish, while in other places those groups are restricted to higher depths, where such predators are also absent.
Are you sure that's it? Sea water doesn't get any colder than a couple degrees below 0C, so the whole antarctic and arctic seas are all very similar temperatures no matter what part or what depth you're at. The crabs and fish have antifreeze protein in their blood too.
A massive effort is currently underway by undersea mining companies to dredge the life out of huge swaths of largely unexplored seabed, including Antarctic and Polar regions.
It's the same insanity that allows industrial fishing fleets to drag kilometers-long nets through the sea scooping up megatons of bycatch -- although, this time we are likely to obliterate seabed ecosystems before anyone even has a chance to see them.
Some brilliant reads on these and surrounding topics:
We really are the most invasive species.. reading about the abundance of octopuses makes me sad that 1 monkey-derived species got smart enough to invent tools and is now on its way to killing its host...
