. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. THE ARAL SEA 659 the open Sea, according to G. V. Nikolsky (1940), is 3-23 cm3 per 1 m3. Diaptomus salinus, Cladocera and Dreissena larvae make daily vertical migra- tions ; in daytime they keep mainly at a depth of 10 to 20 m (Fig. 311). 'These daily plankton migrations', says A. Behning,' have real significance in the life of the Sea. They enable the plankton animals to use all layers of water in their search for food; masses of diatoms are found by them in day- time in the depths—Actinocyclus, C
. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. THE ARAL SEA 659 the open Sea, according to G. V. Nikolsky (1940), is 3-23 cm3 per 1 m3. Diaptomus salinus, Cladocera and Dreissena larvae make daily vertical migra- tions ; in daytime they keep mainly at a depth of 10 to 20 m (Fig. 311). 'These daily plankton migrations', says A. Behning,' have real significance in the life of the Sea. They enable the plankton animals to use all layers of water in their search for food; masses of diatoms are found by them in day- time in the depths—Actinocyclus, Campylodiscus, Pleurosigma—and by night in the upper layer they find flagellates and other species of phyto- plankton.' In bays and inlets, which usually have a somehat higher salinity and are subject to greater temperature and salinity fluctuations, the most common forms among the plankton, accord- ing to A. Behning, are the algae Chroococcus turgidus, Oscillatoria tenuis, Lyngbya aestuarii, two species of peridinians Cyclotella and Melosira Borreri, among the animals the Rotifera Brachionus bakeri, B. mulleri, and Colurella adriatica, and among the Crustacea Halicyclops aequoreus, Cyclops viridis and Alona rectangula. The mean plankton biomass is here about 2-75 mg/m3. Near the mouth of the rivers Amu- and Sur-Daria,. SEA AREA LITTORAL AREA ?? ESTUARINE AREA Fig. 310. The region of the north- western part of the Aral Sea according to plankton composition (Behning). ens Fig. 311. Vertical migrations of plankton in the Aral Sea in August 1933 according to the number of specimens (Behning). within the areas of the lower surface salinity, the plankton composition changes, many forms of the saline Aral waters are not found, and there is a considerable admixture of fresh-water forms. The most characteristic are the following: Microcystis aeruginosa, Dinobryon sertularia, Ceratium hirundinella, Eudorina elegans, Fragilaria crotonensis, Keratella aculeata and Diaphanosoma brachyur
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