WO 



zeo 



300 

 SOii 



fOO 

 200 

 300 

 ^00 

 500 



^/ ^^ ^^ 



Fig. 10. System of distribution of trophic zones on shelves of varying 

 widths and steepnesses. Shelf width not drawn to scale. 1, 

 Sestonophages; 2, Gatherers; 3, Swallowing detritophages. 



(1966, 1969, 1972) for the deep water benthos were found to be useful. 

 A eutrophic structure is formed where the pelagic community is rather 

 productive and the rate of sediment accumulation is high. These factors 

 determine the abundant supply of the surface layer of sediment with 

 organic matter and its rapid burial in a condition suitable for 

 consumption by detritophages. An oligotrophic benthos structure is 

 formed where the surface waters are more or less fully stratified, the 

 pelagic community is low in productivity, the rate of sediment 

 accumulation is very low. These factors cause the bottom sediment to be 

 supplied with little organic matter, which is buried in a condition 

 unsuitable or poorly suitable for utilization by detritophages. 



A eutrophic structure results in practically 100% occurrence of 

 representatives of the three trophic groupings and the appearance of a 

 zone of dominance of each one under the corresponding conditions of 

 dynamics of the bottom waters. With a eutrophic structure, the 

 correlation in distribution of the trophic zones with bottom relief and 

 the nature of the bottom deposits is quite clearly seen (Fig. Ua). An 

 oligotrophic structure results in low occurrence of gathering 

 detritophages, with still lower occurrence of swallowing detritophages; 

 absence of a trophic zone of swallowing detritophages and weak 

 development of a zone of gathering detritophages; universal development 

 of a zone of dominance of sestonophages, depending little on bottom 

 relief (Fig. lib). 



In the first approximation, it can be considered that the factor of 

 rate of sediment accumulation acts identically throughout the shelf; 

 therefore, in large-scale regionalization of shelves, we can abstract 

 ourselves from circumcontinental zonal ity in the mode of sediment 

 accumulation. On the shelf, only one set of three trophic zones is 

 usually found (Neyman, 1963b, 1967), so that in large-scale 



207 



