Photograph taken by astronauts that shows how plankton blooms change the color of the ocean as viewed from space. Nitzschia Frigida, Phytoplankton		What are phytoplankton? Phytoplankton, microscopic plant life that floats freely in the lighted surface waters, may alter the color of the water. When a great number of the microscopic plants are concentrated in an area, the color of the ocean surface will change. This is called a "bloom." This photograph shows such a change in color. It was taken by astronauts aboard the space shuttle looking down at the coast of Angola. Microscopic plant life is at the base of the marine food web and is the primary food and energy source for the ocean ecosystem. Phytoplankton convert nutrients into plant material by using sunlight with the help of the green pigment chlorophyll. The chlorophyll pigments in the plants absorb light, and the plants themselves scatter light. Together, these processes change the color of the ocean as seen by an observer looking downward into the sea. Very productive water with a lot of plankton appears blue-green. Very pure water appears deep-blue, almost black. From space, variations in ocean color can be measured with sensitive instruments. Ocean and land plants are green because of the chlorophyll in plant cells. Chlorophyll a absorbs mainly blue-violet and red and reflects green; chlorophyll b absorbs mainly blue and orange and reflects yellow-green. Satellite instruments measure the amount of reflected light of different colors. These amounts allow scientists to estimate the productivity of Earth's land masses and oceans.