and the like of organisms and organism interactions in the marine environment. These top-down active and passive imaging technologies are increasingly powerful but still probe only a small range of the key processes and locations. Figure 5-6 shows satellite imaging of biological dead zones in the Gulf of Mexico. These zones are the result of an overabundance of nutrients from fertilizer run-off, followed by hypoxia, the condition in which bottom water oxygen concentrations are less than 2 mg/L, causing what is known as eutrophication.

Researchers have many tools and techniques at their disposal with which to study biological systems. These tools allow for the study of cells, organisms, and



Satellite Imagery of Eutrophication along the U.S. Gulf Coast

Summertime satellite observations of ocean color from MODIS/Aqua show very turbid waters, which may include large blooms of phytoplankton extending from the mouth of the Mississippi River all the way to the Texas coast. When these blooms die and sink to the bottom, bacterial decomposition strips oxygen from the surrounding water, creating an environment in which it is very difficult for marine life to survive. Reds and oranges represent high concentrations of phytoplankton and river sediment. Image taken by NASA and provided courtesy of the NASA Mississippi Dead Zone Web site. Available at

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