aphotic zone

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aphotic zone:

see oceanocean,
interconnected mass of saltwater covering 70.78% of the surface of the earth, often called the world ocean. It is subdivided into four (or five) major units that are separated from each other in most cases by the continental masses. See also oceanography.
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aphotic zone

[a′fäd·ik ‚zōn]
(oceanography)
The deeper part of the ocean where sunlight is absent.
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TABLE 1 Minimum, averages [+ or -] Standard Deviation, and maximum values of abiotic variables, trophic state indices, and total biomass at the three collection points in the euphotic (*) and aphotic (**) zones of the Argemiro de Figueiredo reservoir (Brazil) from August/2007 to July/2009 Confluence of the tributaries rivers (PC) Min Mean [+ or -] SD Max Secchi disk (m) 0.
Organismal transparency (rather than simply ocular) is extremely rare on land, rare in the aquatic benthos, uncommon in aphotic regions, somewhat more common in dysphotic and neustonic habitats, and ubiquitous at euphotic depths in clear water.
As mentioned above, transparent species are rare at aphotic depths, generally being replaced by species with whole-body red or black pigmentation (Hardy, 1956; Herring and Roe, 1988; McFall-Ngai, 1990).
The salinity of the aphotic layer is remarkably uniform, but its temperature first declines rapidly with depth (the permanent thermocline, down to the first 3,281 ft [1,000 m]) and then maintains an almost constant thermal condition, with cold temperatures between 39 and 28[degrees]F (4 and -2[degrees]C); moreover it does not undergo the seasonal changes experienced at the surface.
The precise bathymetric limits given to the different subzones of the aphotic zone suggests they may well be artificial.
Seasonal /1985 and sampling June-July 1999-2000; /1987 monthly sampling 2001-2006 Depths 2; 5; 10; 2; 5; 10; 100; 15; 1% 15; 20; 15; 20; 25; of incident 25; 30 m 30 m light and aphotic zone (Secchi) Total-P -- -- Mackereth et al.
This is perhaps most easily seen if one recognizes the fact that the formulation is mathematically equivalent to the steady-state description of an idealized two-layer model of the ocean with a perfectly mixed photic zone, no sedimentary loss, and all mineral nutrients from organisms transported into the aphotic zone by turbulent diffusion being immediately remineralized.
aphotic zones, and under isolated and grouped conditions.
Comparison of gametogenesis and gonadal index between populations found in the photic and in the aphotic zones
We studied the gametogenic development and gonadal index in two populations of sea cucumbers, one found in the photic zone (10 m depth, a depth at which light penetrates all year long) and the other in the aphotic zone (110 m, a depth at which no light penetrates all year long; Babin et al.
Comparison of gametogenesis and gonadal index between populations in the photic and aphotic zones
Gametogenesis in photic and aphotic natural habitats