red tide image Furthermore, 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 Vegetation (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, bacterial 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.

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