Phytoplanktons are photosynthetic hence they live within about 200 meters of the ocean surface, because phytoplankton require light to survive.
Phytoplanktons are primary producers. They are organisms that require light from the sun to produce their own food via photosynthesis.
Photosynthesis is the process by which green plants produce food in the presence of sunlight and carbon dioxide.
Since they require light, phytoplanktons they live within about 200 meters of the ocean surface.
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