II. Challenges of Deep-Sea Living
My focus today, as Bruce said, is going to be on adaptations to
the deep sea. What types of changes in organisms, particularly in their
physiological, biochemical and molecular systems, enable them to live in
an environment that is very "hostile". It's dark. It's very cold,
although you'll see that near the hydrothermal vents it can get very warm.
And, throughout it's a high pressure world. What I would like to do then
is to walk you through some of the studies that we and others have done
to figure out basically how organisms thrive in this extreme environment.
Let us review a few of the most salient features about the deep sea that make
life rough for organisms. As was mentioned before, the average depth of
the ocean is nearly 4 kilometers. The deepest trenches are around 11 kilometers.
What that spells is an environment that's going to be very high in pressure.
Hydrostatic pressures go up by one atmosphere each 10 meter increase in
depth as one moves down through the marine water column. So in the deepest
parts of the ocean, pressures are over 1,000 atmospheres. Those are crushing
pressures that certainly no shallow water organism could withstand. Yet
even in these deepest trenches, as some of the early explorers of the deep
sea learned, we find organisms. In most of the deep sea, the temperatures
are very low. They are only a few degrees above zero degrees celsius. One
reason for this, of course, is that a lot of the deep sea water forms at
high latitudes. For example, around the Antarctic continent, sea water gets
very cold and dense, and it sinks and spreads along the sea floor towards
the equator. So deep sea organisms are not only living in a very high pressure
environment, but they're living in water near its freezing point. We can
intuit that high pressure and chilling temperatures are two very severe
stresses that organisms are likely to have had to adapt to at all levels
of their biological organization.
Now, most of the deep sea, probably 99.999% of it is cold. A very small
fraction, but a very interesting fraction, of the deep sea water is very
warm. Jim Childress was going to talk about the hydrothermal vent communities.
I'll try and do justice to part of what he would cover, emphasizing something
about the way in which organisms at these deep sea vents cope with extremely
high temperatures and extremely wide ranges of temperatures. Over a distance
of perhaps one meter at the vents, there is a 400 degree celsius thermal
gradient. One question I will address is, Where do organisms partition themselves
within this extraordinarily steep thermal gradient?"
Another characteristic of the deep sea, again one that you're familiar with,
is its darkness. As you go below roughly 150-250 meters, depending on the
clarity of the water, there is no longer any photosynthetic activity. It's
a dark environment where except at the vents and cold seeps, there is no
primary production. An additional stress in some deep-sea areas is low oxygen.
In certain areas of the oceans that are called the oxygen minimum layers,
the sea is very low in oxygen--suffocatingly low levels of oxygen as far
as shallow living organisms are concerned. Yet, despite all of these things,
life goes on in the deep sea. I will try and tell you some of the ways in
which evolutionary adaptation has this is made possible.
|
|
|
Narrative Index
BioForum Index
