Describe the causes and effects of eutrophication. What will be an ideal response?

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Some dissolved organic substances act as nutrients or fertilizers that speed the growth of
marine autotrophs, causing eutrophication. Eutrophication is a set of physical, chemical, and
biological changes that take place when excessive nutrients are released into the water. Too
much fertility can be as destructive as too little. Eutrophication stimulates the growth of some
species to the detriment of others, destroying the natural biological balance of an ocean area.
The extra nutrients come from wastewater treatment plants, factory effluent, accelerated soil
erosion, or fertilizers spread on land. They usually enter the ocean from river runoff and are
particularly prevalent in estuaries. Eutrophication occurs at the mouths of almost all the
world’s rivers.The most visible manifestations of eutrophication are the red tides, yellow
foams, and thick green slimes of vigorous plankton blooms. These blooms typically consist
of one dominant phytoplanktonic species that grows explosively and overwhelms other
organisms. Huge numbers of algal cells can choke the gills of some animals, and (at night,
when sunlight is unavailable for photosynthetic oxygen production) deplete the free oxygen
content of surface water, a condition known as hypoxia. In nearshore waters, hypoxia is now
thought to cause more mass fish deaths than any other single agent, including oil spills. It is
the leading threat to commercial shellfisheries.