Phytoplankton are tiny, microscopic plants that form the base of the food web in marine ecosystems; they are consumed by zooplankton, or microscopic animals, which in turn are eaten by variety of fish, whales, and birds. A large population or bloom was occurring in the Black Sea (the body of water in the upper right corner of the image) when this image was acquired on January 29, 2006. Often blooms such as this one are fed by the upwelling of nutrients, which can occur when currents beneath the surface reach the coastline and are forced to the surface, carrying minerals towards the surface. Phytoplankton are poised to rapidly exploit this temporary resource, growing very rapidly under such conditions. However, as nutrients are depleted, the blooms die and decay. The decay process involves their ingestion by oxygen-consuming bacteria, creating hypoxic (low oxygen) and anoxic (no oxygen) conditions, which in turn can lead to “fishkills”. According to the World Wildlife Fund, there are 77 species (and subspecies) of fish living in the Black Sea. The region suffers from numerous environmental issues, including overfishing, urbanization along the coastline, industrial pollution, and the construction of hydroelectric projects that restrict movement and disrupt habitat. Images such as this one can be used to assess water quality by using the ratio of reflectance from the blue and red channels. High amounts of blue light reflecting off of the surface of water and low amount of red indicates good water quality, while bodies with poor water quality tend to reflect less blue and more red light.
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