They range from one thousandth of a millimeter to two millimeters. A phytoplankton's growth is limited by the low light levels in the winter of the southern latitudes. In early summer, abundant nutrients and long hours of sunlight provide ideal growing conditions for these plants. Phytoplankton grow or 'bloom' very quickly and in huge quantities. These plants multiply rapidly in spring and summer as the daylight hours and temperature increase.
Diatoms are the most prevalent species of phytoplankton.
It is a member of the largest group of algae. There are more than 12,000 different species of diatoms, and about 100 species inhabit the waters around Antarctica. Diatoms are circular or oblong shaped. They are single-celled, and float helplessly in the water or attach themselves with a jellylike substance to stones or other water plants. Diatoms reproduce by cell division.