The distribution of marine organisms depends on the chemical and physical properties of seawater (temperature, salinity, and dissolved nutrients), on ocean currents (which carry oxygen to subsurface waters and disperse nutrients, wastes, spores, eggs, larvae, and plankton), and on penetration of light. Photosynthetic organisms (plants, algae, and cyanobacteria), the primary sources of food, exist only in the photic, or euphotic, zone (to a depth of about 300 ft/90 m), where light is sufficient for photosynthesis . Since only about 2% of the ocean floor lies in the photic zone, photosynthetic organisms in the benthos are far less abundant than photosynthetic plankton (phytoplankton), which is distributed near the surface oceanwide. Very abundant phytoplankton include the diatoms and dinoflagellates (see Dinoflagellata ). Heterotrophic plankton (zooplankton) include such protozoans as the foraminiferans they are found at all depths but are more numerous near the surface. Bacteria are abundant in upper waters and in bottom deposits.
The scientific study of marine biology dates from the early 19th cent. and now includes laboratory study of organisms for their usefulness to humans and the effects of human activity on marine environments. Important marine biological laboratories include those at Naples, Italy at Plymouth and Millport in England and at Woods Hole, Mass., La Jolla, Calif., and Coral Gables, Fla. Research has been furthered by unmanned and manned craft, such as the submersible Alvin.
See also oceanography .
See R. Carson, The Sea Around Us (rev. ed. 1961) R. Ballard, Exploring Our Living Planet (1983) M. Banks, Ocean Wildlife (1989) W. J. Broad, The Universe Below (1997).
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