macroplanl<ton--20, considering macroplankton, approximately 8-10. In other 

 words, animals living at lower than 200-1000 m receive approximately 5-10 

 times less energy per unit of biomass than animals in the surface layers. 

 If we compare the energy balance of the surface animals and the animals 

 living below 1000 m, the difference will be still greater. 



It should be kept in mind that interzonal migrating species feeding 

 in the surface layers represent a significant fraction of the plankton 

 only down to depths of 500-1000 m. At greater depths, particularly in 

 the tropical regions, their significance decreases rapidly and the 

 unique food relationships of the oligotrophic bathypelagic zone are 

 clearly seen. 



In the food-rich surface layers, even significant energy losses, 

 related to the active movement of the animals, can be comparatively easily 

 compensated for by increasing the intensity of feeding. In the poorer 

 deep waters, this is not always possible. It is believed (J0rgensen, 

 1966) that the energy expenditures of plankton filter feeders are expedient 

 only if the quantity of organic detritus which can be assimilated from the 

 water is over 25 mg/liter. Actually, the quantity of organic detritus 

 in the deep waters is 0-32 mg/liter as protein equivalent, or 0-70 mg/liter 

 as organic matter. 



Adaptation to existence under conditions of extremely scarce food 

 resources in groups having different types of nutrition may be manifested 

 differently and to a different extent. However, the tendency to reduce 

 the expenditure of energy is inherent in the entire population of the 

 depths. The upper and interzonal animals, which spend only a part of 

 their life cycle in the deep waters, decrease their metabolic level 

 sharply at this time. For example, Calanus hyperboreus , which descends 

 in the winter to a depth of 500-2000 m, decreases its energy expenditure 

 for respiration by a factor of 3. This change in the intensity of 

 respiration is purely adaptive and is independent of temperature. Calanus , 

 remaining in the deeper layers for the winter, is in a unique state of 

 anabiosis (Conover, 1962). 



As the depth increases and the food resources decrease, the mean 

 dimensions of animals change. They increase significantly for predators and 

 certain other forms in the bathypelagic zone. In the abyssopelagic zone, 

 the role of predators, as we have stated, is gradually reduced to nothing 

 and, therefore, the mean size of zooplankters decreases (Vinogradov, 1968). 

 The increase in the dimensions of carnivorous forms results not only from 

 predominance of representatives of larger genera of animals, but also from 

 deep-water gigantism. The essence of this phenomenon is an increase in 

 the dimensions of animals of the same genus or similar genera with increasing 

 depth. For example, in various species of the genus Serges tes , the mean 

 dimensions increase from 27 mm (S. vigilax- -habitat 110-6b0 m) to 94 mm 

 (§-• lobustus^-- habitat 550-800 mmT; for Taaningichthys , the corresponding 

 figures are from 65 mm (T. minimus --mean depth of habitation 475 m) 

 to 95 mm (T. paurolychnus- -mean depth 900 m); for euphausiids of the genus 

 Stylocheiron- -from 6 mm (S. suhmi --mean depth 25 m) to 30 mm (S^. maximum- - 

 mean depth 550 m). Attempts have been made to explain this phenomenon by 

 the effects of various abiotic factors, primarily pressure and temperature 



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