4: Phytoplankton - All things great and small


Now that we understand the basic principle behind ocean color remote sensing (that wasn't too hard now, was it?), it is very important to realize that phytoplankton do a great deal more for us than just give the ocean a nice green color. There are at least five main points about phytoplankton that we need to understand:

red tide image However, not all phytoplankton are green. They come in a variety of shapes and colors and while most of them are harmless, some can bloom in such large numbers and produce toxins that can be quite harmful to marine life and in some cases, to humans as well. When phytoplankton growth is stimulated by an overabundance of nutrients from sources such as sewage discharge or runoff of agricultural fertilizers used on land, the consequences can be quite serious. Dense blooms of phytoplankton can essentially block sunlight from reaching the bottom in shallow areas of bays or estuaries and can cause the massive decline in the Submerged Aquatic Vegetaion (SAV) that has been taking place in places like Chesapeake Bay. These grasses are vital nursery grounds for many species of fish and invertebrates and their loss can have dire ecological results. In addition, when these blooms die and the plankton sink to the bottom, bactierial decomposition of all this organic matter essentially strips the water of oxygen. Fish, shellfish and most other living things require oxygen to survive and decaying phytoplankton blooms have been the cause of many massive fish kills over the years. Of the phytoplankton that can be directly harmful on their own, the most commonly known form of these, dinoflagellates, are the source of red tides.

More Information:

  1. What are Phytoplankton- an article from the Earth Observatory
  2. Diatom Home Page - Indiana University
  3. ALGAE - Smithsonian Institution
  4. Diatom Collection - California Academy of Sciences


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gene carl feldman (gene@seawifs.gsfc.nasa.gov) (301) 286-9428