Unit I (Ecology) - Day 7- Complex Aquatic Ecosystems
Why Big, Fierce Animals Are Rare
, Chapters 8 and 9
Explain why the sea is blue. Give the physical and biological reason.
The sea is blue because there are not enough plants to make it green.
Light, however, passes
through perfectly clear water and is absorbed bit by bit.
The low energy wavelengths, such as
red, are absorbed first, followed by the progressively longer wavelengths.
Only blue light
reaches a few hundred feet down, and it follows that any reflected light that has made a double
journey from the surface to the depths and back is blue.
This is why the sea is blue.
Explain why there are so few plants in the sea.
Most of the sea is not fertile; instead, it is a chemical desert.
Potassium, phosphorus, silicon,
iron, nitrates, and the rest are always present in seawater, but in very low concentrations.
plants of the water are tiny.
In chemically rich areas, like polluted estuaries, the tiny plants
multiply and multiply until the water is pea-green, but in oceans that are chemically-poor,
plants stay few, thus the light penetrates the depths of the sea and blue light shines through,
making the ocean seem blue.
Explain why there are so few nutrients near the ocean's surface.
Because there is, more frictions in the top layers of ocean water than there are at the bottom.
The sea is constantly moving and churning, and there is no source of nutrients in upwellings like
that from the run-off of pollutants from the land.
Explain why the plants that live in the sea are so small.
Plants that live in the sea are so small because the surface area is larger in terms of being small
than mass and weight.
Small entities, however, use their nutrients efficiently.
There must thus
be an disadvantage to being big in the ocean.
This disadvantage comes at a floating cost.
plants would float and usually drift away from where they want to be, or to stay.
have an advantage that if, and when, they are taken away, they allow themselves to sink and
return by a returning current.
Large plants cannot survive because of the ever-moving water
that would sweep them away and never return them.
Explain why there are big plants only in the Sargasso Sea.
The Sargasso Sea is like an oceanic whirlpool that spins and collects material in the center, and
then by some luck, sends it back where it came from.
Sargassum species of algae had adapted
enough so that its whole life cycle can be carried out as it floats.
We do not find these kinds of
plants all over the ocean because the ocean does not stay still.
Natural selection thus forces
extreme smallness on the plants that are there, for the tiny ones are the best ones to be able to
disperse about the seas.