The photic zone is the region of water that is penetrated by light and is therefore characterized by the presence of plant life, notably phytoplankton and larger attached algae.
The depth to which the photic zone extends is determined largely by the density of suspended matter in the water, which in turn depends on weather conditions and substrate stability. Light penetration is described fairly well by dI/dt = −kI, where I is incident light, t is depth, and k is the extinction coefficient.
Even very clear water (k = .03) absorbs 50% of the light in the first meter and 90% in the upper 20 m. Open oceanic water may have a k of .1 and coastal seawater, a k of .3 and upward (Krebs, 1972).
The component wavelengths of sunlight are differentially absorbed by water and dissolved compounds, and penetrate to greatly varying depths (Fig. 1). This characteristic, together with the total drop in intensity with increasing depth, leads to biotic zonation in the photic region. Because different...
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Reference
Krebs, C. J., 1972. Ecology: The Experimental Analysis of Distribution and Abundance. New York: Harper and Row, 694p.
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© 1982 Hutchinson Ross Publishing Company
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Sheppard, C.R.C. (1982). Photic zone . In: Beaches and Coastal Geology. Encyclopedia of Earth Sciences Series. Springer, New York, NY. https://doi.org/10.1007/0-387-30843-1_325
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DOI: https://doi.org/10.1007/0-387-30843-1_325
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