Phytoplankton:
Plants of the Sea
by Prentice
K. Stout
P637
To the casual
observer, the oceans and bays are vast trackless bodies of water.
Beneath their surfaces are countless fish. But more numerous by
far are the tiny microscopic animals and plants collectively called
plankton, a word derived from the Greek meaning wandering.
The plant portion
of this complex oceanic soup is called phytoplankton. The term
phyto comes from the Latin phyton meaning tree or plant.
This large grouping is composed mostly of single-celled algae and bacteria.
It is known
that green plants liberate oxygen and produce carbohydrates, a basic
link in the food chain of plants to animals to people. Collectively,
this chemical process is referred to as photosynthesis (photo
= light, synthesis = to make). In these tiny food factories, there
is a chemical compound called chlorophyll that, in combination with
sunlight, converts carbon dioxide, water, and minerals into edible carbohydrates,
proteins, and fats. Thus, these phytoplankton are the basis for
the oceanic food chain. Animals cannot perform this biological
food-making process. Two-thirds of all the photosynthesis that
takes place on this earth occurs in the oceans that yearly create 80
to 160 billion tons of carbohydrates. So numerous are these tiny
plant forms that they often turn the water green, brown, or reddish.
Among the most
abundant phytoplankton are the diatoms. Some 20,000 species make
up this plant group. They consist of a tiny blob of protoplasm
enclosed in a transparent pill-box structure made of silica. This
silica, the main ingredient of glass, is extracted from the surrounding
seawater. Minute holes or pores in their shells permit nutrient
absorption and an exchange of carbon dioxide and oxygen to take place
with the surrounding seawater. Under favorable conditions, a single
diatom can reproduce 100 million offspring in a month. Clearly,
such reproductive capacity creates vast numbers - as many as a billion
of them in a gallon of seawater. Those that are not eaten die
and their virtually indestructible shells settle to the bottom of the
ocean. In some areas of the sea, their skeletal remains form layers
up to 700-feet thick. This diatomaceous earth has been
used as a fine abrasive in toothpaste and automobile polish. A
drop of oil within the protoplasm in the shell may have created the
earth's petroleum supply. This oil in the diatom is eaten by a
number of small fish; one is called the capelin, which, in turn,
are eaten by codfish. From the codfish bodies come cod liver oil
detested by some, but rich in vitamins A and D.
While diatoms
are essentially cool water inhabitants, their counterparts in tropical
waters are called dinoflagellates. Equipped with whip-like projections,
they propel themselves about in a jerky motion.
Dr. C.P. Idyll,
noted oceanographer, states, "The various species of dinoflagellates
resemble chinese hats, carnival masks, children's tops, urns, pots,
and vessels of many kinds, the spiky knobs of medieval war clubs, balloons
on strings, hand grenades or lances."
Flagellates,
like diatoms, are proficient in their ability to reproduce. By
splitting in half, a dinoflagellate can reproduce thirty-three million
offspring in only twenty-five divisions. One species of dinoflagellate,
Gonyaulax, whose excessive reproductive ability can create havoc,
produces the "red tide." In the seventh chapter of the
Book of Exodus, the people of Egypt were plagued with what could have
been an outbreak of the red tide. Charles Darwin, on his around
the world voyage on the Beagle, wrote one of the first scientific
accounts of a dinoflagellate outbreak that discolored the waters off
Chile.
Another interesting
dinoflagellate, if disturbed, emits light in the form of bioluminescence.
Called Noctiluca, this small organism combines two chemicals,
luciferin and luciferase (Latin: lucifer = "bearer
of light"). This is the same combination of chemicals that
gives our familiar firefly its ability to blink during warm summer evenings.
A simple tool
can be used to study these plant forms. One needs a coat hanger
that has been worked into a circle. Then over this frame stretch
a pair of discarded pantyhose. Cut off the legs of these stockings
just below the knee and place a small plastic pill jar in the openings.
Tightly wind some thread around the fabric and the mouth of the
jars and then tow it through the water. The fine mesh stocking
of the pantyhose will capture may of these small plant forms as well
as their animal counterparts. (See fact sheet on zooplankton.)
A hand lens or microscope will assist in the viewing of these fascinating
organisms.
References
Buschbaum, Ralph
and Milne, Lorus J. 1960. The Lower Animals, Doubleday
and Co. New York.
Silverberg,
Robert. 1972. The World Beneath the Ocean Wave. Weybright
and Talley, New York.
Links
Dinoflagellates
Fun
with Phytoplankton
