7. Trophic Structure of the Deep-Water Benthos . 

 (M. N. Sokolova) ~ 



The various size-groups of the deep-water bottom population react 

 differently to changes in feeding conditions. Therefore, we should 

 analyze separately the structure of the macrobenthos and meiobenthos. 

 By meiobenthos, we mean invertebrates measuring 0.5-5 mm. (The minimum 

 dimension is determined by the size of the apertures in a No. 140 

 screen, through which the samples are usually washed, while the maximum 

 is selected arbitrarily.) We consider all organisms larger than 5 mm to 

 be macrobenthos. The meiobenthos makes up the main portion of the 

 samples taken by bottom grabs; the macrobenthos, the main portion of the 

 catch of deep-water trawls. The deep-water macrobenthos is usually 

 absent in the bottom-grab samples (area 0.25 m^), due to its scarcity, 

 while the meiobenthos is only partially retained in trawl samples. 



The majority of the entire deep-water macrobenthos, and 

 particularly of the meiobenthos, falls in the deposit- feeding group (see 

 3.5), i.e., it feeds on the organic matter contained in the sediment. 

 The invertebrate suspension-feeders consuming suspended (living or dead) 

 organic matter represent a significant portion of the deep-water 

 macrobenthos, but are rare in the meiobenthos. The carnivorous 

 invertebrates, utilizing both living prey and dead animals, are in the 

 minority in the deep-water free-ranging and sessile macrobenthos but, 

 apparently, represent the absolute majority of the nektobenthos. They 

 are in the minority in the meiobenthos. 



The trophic structure of the deep-water benthic population, i.e., 

 the quantitative ratio (in our studies--by weight) of invertebrates with 

 various types of feeding experiences significant alterations in the 

 World Ocean in connection with the changes in feeding conditions for the 

 dominant trophic group, i.e., for macrobenthic deposit-feeders. The 

 body sizes of the invertebrate macro- and meiobenthos differ by an 

 average of a factor of 10, which results from the variation in thickness 

 of the sediment layer necessary for maintaining of deposit-feeders of 

 these two size-groups. The requirements of the smaller organisms can be 

 satisfied with a smaller quantity of food, and therefore they can exist 

 in a thinner layer of sediment than can the larger organisms. 



On the scale of the World Ocean, the greatest changes in thickness 

 of the surface layer of sediment suitable for feeding of deep-water 

 deposit-feeders are found at the boundaries of the global zones of 

 oceanic sedimentogenesis--in connection with the climatic and circum- 

 continental zonal ity of sediment formation (Bezrukov, 1962; Lisitsyn, 

 1974). 



In general, in the arid zones only the surface film of sediment is 

 available for the nutrition of deposit-feeders, while in the humid and 

 equatorial zone--a layer of several centimeters is available, and in 



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