marine ecosystem :: Plankton | Encyclopedia Britannica

Plankton

Plankton are the numerous, primarily microscopic inhabitants of the pelagic environment (see Figure 3). They are critical components of food chains in all marine environments (see Figure 1 in the article on community ecology) because they provide nutrition for the nekton (e.g., crustaceans, fish, and squid) and benthos (e.g., sea squirts and sponges). They also exert a global effect on the biosphere because the balance of components of the Earth’s atmosphere depends to a great extent on the photosynthetic activities of some plankton.

The term plankton is derived from the Greek planktos, meaning wandering or drifting, an apt description of ... (100 of 7,356 words)

Images

Figure 1: Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

diatom: cycling of silica in the marine environment

Figure 2: Cycling of silica in the marine environment. Silicon commonly occurs in nature as silicon dioxide (SiO2), also called silica. It cycles through the marine environment, entering primarily through riverine runoff. Silica is removed from the ocean by organisms such as diatoms and radiolarians that use an amorphous form of silica in their cell walls. After they die, their skeletons settle through the water column and the silica redissolves. A small number reach the ocean floor, where they either remain, forming a silaceous ooze, or dissolve and are returned to the photic zone by upwelling.

Figure 3: Representative plankton.

Figure 1: Generalized aquatic food web. Parasites, among the most diverse species in the food web, are not shown.

Galatheid crabs and shrimp grazing on the bacterial filaments that grow on the shells of the hydrothermal mussels covering the Northwest Eifuku volcano in the Mariana Arc region.

lobster: life cycle of a palinurid lobster

Figure 4: Life cycle of a palinurid lobster.

nutricline: normal and El Niño conditions off Perú

The upwelling process in the ocean along the coast of Peru. A thermocline and a nutricline separate the warm, nutrient-deficient upper layer from the cool, enriched layer below. Under normal conditions (top), these interfaces are shallow enough that coastal winds can induce upwelling of the lower-layer nutrients to the surface, where they support an abundant ecosystem. During an El Niño event (bottom), the upper layer thickens so that the upwelled water contains fewer nutrients, thus contributing to a collapse of marine productivity.

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Marine ecosystem

Plankton