Phytoplankton

Phytoplankton are microscopic, photosynthetic organisms that live in the water of the oceans and bodies of freshwater (the word phytoplankton is derived from the Greek for “drifting plants”). The most abundant organisms occurring within the phytoplankton are algae and blue-green bacteria, but this group also includes certain kinds of protists (especially protozoans) that contain symbiotic algae or bacteria (algae or bacteria that co-exist with the protists, to the benefit of both).

Phytoplankton are the key food source in the food chain in the ocean. Marine phytoplankton range in size from extremely small blue-green bacteria, to larger (but still microscopic) unicellular and colonial algae. Oceanic phytoplankton are grazed by tiny animals known as zooplankton (most of which are crustaceans). These are eaten in turn by larger zooplankton and small fish, which are fed upon by larger fish and baleen whales. Large predators such as bluefin tuna, sharks, squid, and toothed whales are at the top of the marine food web. Marine phytoplankton are much more productive near the shores of continents, and particularly in zones where there are persistent upwellings of deeper water. These areas have a much better nutrient supply, and this stimulates a much greater productivity of phytoplankton than occurs in the open ocean. In turn, these relatively fertile regions support a higher productivity of animals. This is why the world’s most important marine fisheries are supported by the continental shelves (such as the Grand Banks and other shallow waters of northeastern North America, near-shore waters of western North and South America, and the Gulf of Mexico) and regions with persistent upwellings (such as those off the coast of Peru and elsewhere off western South America, and extensive regions of the Antarctic Ocean).

Some inland waterbodies occur in inherently fertile watersheds, and are naturally eutrophic, meaning they have a high productivity and biomass of phytoplankton (in shallow waters, larger aquatic plants may also be highly productive). So-called cultural eutrophication is a kind of pollution caused by nutrient inputs associated with human activities, such as the dumping of sewage waste and the runoff of fertilizer from agricultural land. Both fresh and marine waters can become eutrophic through increases in their nutrient supply, although the problem is more usually severe in freshwaters. The most conspicuous symptom of eutrophication is a large increase in the biomass of phytoplankton, which in extreme cases is known as an algal bloom. In the ocean, algal blooms have been occurring with greater frequency since the 1980s. As of 2006, the prevailing view is that the warming atmosphere and changing chemistry of some portions of the ocean (particularly with respect to pH) may be creating conditions more favorable for the explosive growth of alage that occurs during a bloom.

Phytoplankton

Phytoplankton are microscopic, photosynthetic organisms that float in the water of the oceans and bodies of freshwater (the word phytoplankton is derived from the Greek for "drifting plants"). The most abundant organisms occurring within the phytoplankton are algae and blue-green bacteria , but this group also includes certain kinds of protists (especially protozoans) that contain symbiotic algae or bacteria.

Phytoplankton are responsible for virtually all of the primary production occurring in the oceans. Marine phytoplankton range in size from extremely small blue-green bacteria, to larger (but still microscopic) unicellular and colonial algae. Oceanic phytoplankton are grazed by tiny animals known as zooplankton (most of which are crustaceans). These are eaten in turn by larger zoo-plankton and small fish , which are fed upon by larger fish and baleen whales. Large predators such as bluefin tuna , sharks , squid , and toothed whales are at the top of the marine food web. Marine phytoplankton are much more productive near the shores of continents, and particularly in zones where there are persistent upwellings of deeper water. These areas have a much better nutrient supply, and this stimulates a much greater productivity of phytoplankton than occurs in the open ocean . In turn, these relatively fertile regions support a higher productivity of animals. This is why the world's most important marine fisheries are supported by the continental shelves (such as the Grand Banks and other shallow waters of northeastern North America , near-shore waters of western North and South America , and the Gulf of Mexico) and regions with persistent upwellings (such as those off the coast of Peru and elsewhere off western South America, and extensive regions of the Antarctic Ocean).

Some inland waterbodies occur in inherently fertile watersheds, and are naturally eutrophic, meaning they have a high productivity and biomass of phytoplankton (in shallow waters, larger aquatic plants may also be highly productive). So-called cultural eutrophication is a kind of pollution caused by nutrient inputs associated with human activities, such as the dumping of sewage waste and the runoff of fertilizer from agricultural land. Both fresh and marine waters can become eutrophic through increases in their nutrient supply, although the problem is more usually severe in freshwaters. The most conspicuous symptom of eutrophication is a large increase in the biomass of phytoplankton, which in extreme cases is known as an algal bloom.

Phytoplankton

Photosynthetic plankton , including microalgae, blue-green bacteria, and some true bacteria. These organisms are produced in surface waters of aquatic ecosystems, to depths where light is able to penetrate. Sunlight is necessary since, like terrestrial plants, phytoplankton use solar radiation to convert carbon dioxide and water into organic molecules such as glucose. Phytoplankton form the base of nearly all aquatic food chain/webs, directly or indirectly supplying the energy needed by most aquatic protozoans and animals. Temperature, nutrient levels, light intensity, and consumers (grazers) are among the factors that influence phytoplankton community structure.

phytoplankton The photosynthesizing plankton, consisting chiefly of microscopic algae, such as diatoms, and dinoflagellates. Near the surface of the sea there may be many millions of such organisms per cubic metre. Members of the phytoplankton are of great importance as they form the basis of food for all other forms of aquatic life, being the primary producers. Compare zooplankton.

phytoplankton The plant plankton and primary producers of aquatic ecosystems, comprising mainly diatoms in cool waters with dinoflagellates being more important in warmer waters.