Key points are not available for this paper at this time.
The vertical distribution of mesozooplankton has been studied in the central Red Sea to determine its relationship to discrete habitat zones defined according to density, oxygen and nutrient concentrations, seston, and phytoplankton profiles. A disproportionately large amount of the 300 pm net plankton occurs both day and night in the epipelagic zone, which occupies the upper water layer above the abrupt thermohalocline at about lOOm In contrast, in the lower bathypelagic zone, a layer between 1,050 and 2 1,850 m, the numerical abundance and biomass of the zooplankton (0.2 specimens and 5 0 . 0 5 m g wet weight m-3) correspond to values encountered in other oligotrophic regions in tropical oceans below a depth of 4,000 to 6,000 m. The subsurface zooplankton maximum is situated in the core of the oxygen minimum layer, which is located in the mesopelagic zone (100 to 750m). Minimum oxygen values at ca. 400 m delimit the upper and lower interzonal (mesopelagic) assemblages. The unusual plankton distribution, the predominance of a few species and the ontogenetic segregation of the interzonal species are related to the abnormally high temperature (2 21.5") and salinity ( 2 4 0 . 5 % S) in the subsurface waters, coupled with a depleted oxygen content in the mesopelagic zone and lack of food in the bathypelagic zone. Vertical transport of organic matter is achieved by the 'ladder of migrations', involving a few interzonal species that descend into the upper bathypelagic zone but remain above ca 1,100m. Transport of organic debris below this depth by sinking is ineffective because its decay is too rapid.
Horst Weikert (Fri,) studied this question.