The world's oceans are filled with microscopic plants, called phytoplankton. The phytoplankton themselves are at the bottom of the food chain, serving as nutrition for a wide range of fish that humans catch and eat.
Phytoplankton contain chlorophyll which allows them to convert sunlight into energy. In the process known as photosynthesis, they combine the sunlight with water and carbon dioxide to create carbohydrates which they use as nutrients.
Along with sunlight, water and carbon dioxide, phytoplankton require a variety of other nutrients from the water including nitrogen, phosphorous and iron. The most important are nitrogen and phosphorous which are essential to survival and reproduction. Nitrogen is in short supply in some areas but in other areas, phosphorous is limited. Phytoplankton cannot continue to grow when one or the other has been used up.
The nutrients phytoplankton require are created in nature when rocks weather and from atmospheric conditions that convert nitrogen gas into a usable form. In addition, humans introduce phosphorous and nitrogen to the water as runoff from such things as detergents, sewage and fertilizers.
The fact that phytoplankton are common, live in all the Earth's oceans and rely on basic environmental conditions found in seawater and sunlight makes them a good source of study on changes in the environment and climate. Scientists can study their abundance or chemistry, viewing them as early warning signals of changes in the earth's climate, seawater or other environmental conditions.
Although miniscule in size, phytoplankton have a large effect on our world. Their abundance in the oceans, with their process of photosynthesis and use of carbon dioxide, helps ensure a balance in the carbon that is transferred along the food chain. The more phytoplankton pulls carbon dioxide from the environment, the lower the amount of this gas. Some theorize that by using carbon dioxide in the nutritional process, phytoplankton populations help lesson carbon dioxide levels that are attributed to global warming.
Phytoplankton are on the bottom of the food chain so their nourishment and population growth are essential to other creatures from the small fish that eat them, to larger fish and eventually, humans.If phytoplankton cannot survive, they cannot support the other fish that eat the phytoplankton and they too die.
In 2008 the Massachussets Institute of Technology, supported by the National Science Foundation, created a detailed study of the food-finding ability of phytoplankton. The study's design considered the "foraging abilities and behavior of marine microbes" based on the belief that the environmental factors influencing phytoplankton was essential in understanding environmental fluctuations.