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♤ Phytoplanktons are limited to the uppermost layers of the ocean where light intensity is sufficient for
photosynthesis to take place.
♤ The photosynthetic rate varies with light intensity.
Nutrients
♤ The major inorganic nutrients required by phytoplankton for growth and reproduction are nitrogen and phosphorus.
♤ Diatoms and silicoflagellates also require silicate (SiO2) in significant amounts.
♤ Some phytoplankton can fix nitrogen and can grow in areas where nitrate concentrations are low.
♤ They also require trace amounts of iron which limits phytoplankton growth in large areas of the ocean because iron concentrations are very low.