The organisms inhabiting the pelagic zone are grouped
into two broad categories-plankton & nekton.
The word plankton was first of coined by Henson
,which means that which drifts.
Plankton further divided into phytoplankton &
Most phytoplankton are too small to be individually
seen with the unaided eye.
When they present in high enough numbers ,they may
appear as green discoloration of the water due to the
presence of chlorophyll within their cells.
Phytoplankton include wide variety of
photosynthetic organism like
4) Green algae
5) Blue green algae
Out of these diatoms & dinoflagellates are
The diatoms are enclosed within a box made up of
two parts or valves fitting one over another.
The box is made up of silicon dioxide & is
ornamented with species specific designs pits &
They are dominant in temperate & colder regions.
They may occur singly or may occur in chains.
The second major group of phytoplankton is
recognizable by possesssing two flagella.
They use flagella to move themselves through the
They lack the external skeleton of silicon but are
often armored with plates of the carbohydrates
They are solitary , single small organisms.
The microscopic phytoplankton float on or near the
surface of water.
As they are autotrophic components of the plankton
community they are responsible for much of the
oxygen present in earth’s atmosphere.
The population of phytoplankton in any aquatic system
is biological wealth of water for fishes & constitutes a
vital link in the food chain.
Phtyoplankton have definite role in proper growth &
maintenance of a water body.
Phytoplankton is a key food item in both Aquaculture &
mariculture .And it is utilized as food for animals being
In mariculture , the phytoplankton is naturally occuring
& is introduced into enclosures with the normal
circulation of sea water.
In aquaculture, phytoplankton must be obtained &
Phytoplankton is also used to feed many varieties of
aquacultured molluscs, including pearl oysters.
As the marine phytoplankton have declined
substantially in the world’s oceans over the past
Phytoplankton in surface waters have decreased by
about 40% since 1950 alone, at a rate of 1% per year
due to ocean warming.
Due to emission of carbon dioxide from humans it
causes increases in disturbances in marine food web
& due to this there is a percentage decline in the fish
species which feed on phytoplankton
As marine phytoplankton is declining substantially
in the world’s ocean.
There must be decrease in not only in air borne
fraction of pollutions but also in other type of
pollutions from humans.
Due to this there will be a enrichment in marine
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.