Art and Conchlers,
 
You are right, there is not much to eat in the deep sea away from
hydrothermal vents, but that does not automatically make for low diversity.
Consider the coastal marshlands: lots of organic and mineral nutrients,
plenty of sunlight, but only a few species of plants due to the difficult
conditions. Life on the abyssal plains does have the advantage of
relatively constant conditions, no matter that the water is nearly freezing
and sunlight is absent. This means that an animal does not have to expend
effort in "insurance". No protection is needed against ultraviolet light,
exposure at low tide, or incursions of fresh water. The result is that
these animals commonly look starved or flimsy, and are often transparent.
Overfeeding would probably kill them, like overwatering a cactus.
 
As to food, like Shakespeare's mercy, it falleth as the gentle rain from
heaven. (Or sometimes, as in the case of a sinking whale or the Titanic,
it's not so gentle.) Each time food is eaten, the animals extract about ten
percent of the nutrient value, as a general rule of thumb, so the food can
support a long chain of creatures. The animals use different strategies to
collect and process food, e.g., different enzymes, different ways of
breaking it up physically. And the environment is very large, and has had
relatively stable conditions for a very long time. The organisms respond to
differences in environment that we would consider to be slight, like the
difference between ordinary sediment and the sediment around the mouth of a
crustacean's burrow. And of course the abyssal plain is only part of the
deepsea floor, but I won't get into that now.
 
So yes, the diversity of deepsea creatures turned out to be far higher in
samples than anyone expected. And people keep talking about using this
realm for waste disposal. Heck, just dumping banana peels in that
environment would probably cause major disruptions by overfeeding the
animals. It's been documented that populations of foraminifera (one-celled
protozoans with a pretty shell) have changed dramatically in deep water
offshore from areas that were newly settled and farmed, leading to greater
erosion and therefore more food delivered to the deep sea (California, Gulf
of Mexico). What has happened to the soft-bodied creatures whose bodies
leave no trace is anybody's guess.
 
Andrew K. Rindsberg
Geological Survey of Alabama