The Vertical Distribution of Zooplankton in Relation to Habitat Zones in the Area of the Atlantis II Deep, Central Red Sea

Abstract

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.

Are taxonomic details of relevance to ecologists? An example from oncaeid microcopepods of the Red Sea

“…Also, the newly recorded Epicalymma type in the Red Sea was monotypic and occurred at shallower depth than in the adjacent Arabian Sea, where this genus displays a great species diversity in the meso-and bathypelagic zones (Bo¨ttger-Schnack 1996, as species group 1). The lack of a special deep-sea fauna in Red Sea Oncaeidae corresponds to observations on various other zooplankton taxa (Weikert 1982(Weikert , 1987 and has been explained by the extremely limited downward transport of organic matter to the bathypelagic zone caused by the unusually high deep-sea temperatures and correspondingly high remineralization (Wishner 1980;Weikert 1982). …”

“…Weikert 1982Weikert , 1987Beckmann 1984Beckmann , 1996Bo¨ttger 1987;Bo¨ttger-Schnack 1994) and function (e.g. Lenz et al 1988; of the pelagic communities.…”

Vertical changes in abundance, biomass and community structure of copepods down to 3000m in the southern Bering Sea

“…Mauchline, 1998). Vertical distribution of copepod community structure down to greater depths has been studied in the Arctic Ocean (Auel and Hagen, 2002;Darnis et al, 2008), Arabian Sea (Koppelmann and Weikert, 2005), Greenland Sea (Richter, 1994), western subarctic Pacific (Yamaguchi et al, 2002), Red Sea (Weikert, 1982) and Mediterranean Sea (Weikert and Trinkaus, 1990). To evaluate accurate copepod community structure the mesh sizes of the nets are important.…”

Vertical distribution and population structure of Macrosetella gracilis (Copepoda: Harpacticoida) in the Red Sea in relation to the occurrence of Oscillatoria (Trichodesmium) spp. (Cyanobacteria)

“…The occurrence of later copepodids and adults is not restricted to the surface. They have been found in the Atlantic Ocean to a depth of 1750 m (Grice 1963, Owre & Foyo 1964 and Weikert (1982) has also reported its occurrence in deep waters of the Red Sea. It is still unknown whether a relationship exists between surface populations and deep water specimens of Macrosetella gracilis and if so what the nature of relationship may be.…”

“…Such resting stocks are known from a variety of calanoid copepod species, which are undergoing a 'diapause' (Alldredge et al 1984). In the Red Sea, a deep population of Rhincalanus nasutus, dwelling in the oxygen minimum zone at 450 to 600 m, is also considered to b e such a resting stock (Weikert 1980, 1982, Beckmann 1984. For marine harpacticoid copepod species, similar phenomena have not previously been reported.…”