. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. 420 BIOLOGY OF THE SEAS OF THE The decrease in plankton numbers with depth is accompanied by its quali- tative impoverishment (Fig. 202). Below 50 m there is a considerable decrease in the amount of oxygen and in the pH value, indicating increasing amounts of free carbon dioxide. The average plankton biomass throughout the inhabited zone is 118 mg/m3 (according to Maljatzky, 100 to 130 mg/m3).. Qualitative PH —Oxygen composition Plankton biomass of zooplankton Fig. 202. Vertical distributi
. Biology of the seas of the Marine biology -- Soviet Union; Hydrology -- Soviet Union. 420 BIOLOGY OF THE SEAS OF THE The decrease in plankton numbers with depth is accompanied by its quali- tative impoverishment (Fig. 202). Below 50 m there is a considerable decrease in the amount of oxygen and in the pH value, indicating increasing amounts of free carbon dioxide. The average plankton biomass throughout the inhabited zone is 118 mg/m3 (according to Maljatzky, 100 to 130 mg/m3).. Qualitative PH —Oxygen composition Plankton biomass of zooplankton Fig. 202. Vertical distribution of oxygen, of the course of the active reaction, and of the qualitative and quantitative distri- bution of plankton in Black Sea (Nikitin). Biomass and number of plankton species of the upper horizon are taken as 100 per cent. A. Kusmorskaya (1950, 1954, 1955) has carefully studied the zooplankton of the Black Sea, chiefly as food for fish, and the life cycles of mass forms. She notes among the fish-food organisms the preponderance of the following forms: Calanus helgolandicus, Pseudocalanus elongatus, Acartia clausi, Penilla avirostris, predatory and voracious forms of Medusa, Pilemo pulmo and Amelia aurita, Pleurobrachia pileus and Sagitta setosa are usually larger in mass than food plankton, which they devour in huge amounts. Among them S. setosa only is eaten by some fish (sprat and hardtail).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Zenkevich, L. A. (Lev Aleksandrovich), 1889-1970. New York, Interscience Publishers
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