The Oceans are full of life with all sorts of fish, whales, dolphins, squid, seals and turtles. Of them the most abundant form of life is the plankton, the uncountable tiny creatures that swim only feebly or float passively with the currents in the surface layers of the sea.
Planktons include both plants and animals. Most of them are microscopic in size like diatoms (algae existing as colony). Others include slightly bigger animals that feed on plants, on smaller animals and on each other. Among the many other creatures of the plankton are miniature shrimplike animals called copepods (most of them smaller than a grain of rice) and other transparent little animals that are almost invisible but for their tiny dot of their eyes.
Life in sea is nourished by planktonic plants. Though microscopic in size, these superabundant algae form the basis of ocean food chains. When we talk about the food chain, planktons are the fundamental source of food. Copepods for example, feed mainly on diatoms and other algae. They are in turn eaten by small fish. At the top of the food chain are the biggest carnivores, such as killer whales, sharks, and giant tunas, on which few or no other animals prey. Also few species of these big animals also feed on planktons. Thus they rely indirectly on the energy produced by the microscopic planktonic plants.
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