more pronounced in nitrogen poor water and can easily be seen when blooms form, trapping large Trichodesmium colonies at the surface. As a diazotroph, Trichodesmium contributes a large portion of the marine ecosystem’s new nitrogen, estimated to produce between 60 and 80 Tg of nitrogen per year. Nitrogen fixed by Trichodesmium can either be used directly by the cell, enter the food chain through grazers, be released into dissolved pools, or get exported to the deep sea. Compared to eukaryotic phytoplankton, Trichodesmium has a slow growth rate, which has been hypothesized to be an adaptation to survival in high energy but low nutrient conditions of oligotrophic waters. Growth rate is limited by iron and phosphate concentrations in the water. In order to obtain these limiting nutrients, Trichodesmium is able to regulate buoyancy using its gas vacuole and move vertically throughout the water column, harvesting nutrients. Colonies Various species of Trichodesmium have been described based on morphology and structure of colonies formed. Colonies may consist of aggregates of several to several hundred trichomes and form fusiform (called "Tufts") colonies when aligned in parallel, or spherical (called "Puffs") colonies when aligned radially. Trichodesmium colonies have been shown to have large degree of associations with other organisms, including bacteria, fungi, diatoms, copepods, tunicates, hydrozoans, and protozoans among other groups. These colonies may provide a source of shelter, buoyancy, and possibly food in the surface waters. Most of these associations appear to be commensal, with the Trichodesmium providing substrate and nutrition while deriving no obvious benefit from the organisms dwelling within the colonies. Blooms Trichodesmium forms large, visible blooms in the surface waters. Blooms have been described in the Baltic Sea, the Red Sea, the Caribbean Sea, the Indian Ocean, the North and South Atlantic and the North Pacific, and off the coast of Australia. One of the earliest blooms was described by E. Dupont in the Red Sea, noticed for turning the surface of the water a reddish color. This bloom was said to extend about 256 nautical miles. Most blooms are several kilometers long and last one to several months. Blooms can form in coastal or oceanic waters, most frequently when the water has been still for some time and surface temperatures exceed 27 °C. Trichodesmium blooms release carbon, nitrogen and other nutrients into the environment. Some species of Trichodesmium have been shown to release toxins which cause mortalities in some copepods,