Along a stony, or particularly rock-cliff intertidal zone, in 

 areas where the shoreline is quite broken, the population is varied. A 

 single rock or column may manifest differences in the quantity, composition 

 and vertical position of the band-forming communities on different sides, 

 with different exposures to the waves. On cliffs extending out into 

 the open sea, the communities are quite different from those on cliffs 

 protected from the surf, and in sections of rock projections located 

 near sandy beaches, the composition of the population is altered in 

 comparison to clean rocks. In areas where fresh water runs down the 

 rocks, the quantity of brown and red algae decreases sharply, the green 

 or blue-green forms becoming dominant. In clefts in the rock, in 

 grottoes or beneath overhangs, communities similar to sublittoral 

 communities develop in abundance, or sponges, Actinea , Ascidia , etc., 

 may be encountered in abundance in these areas alone. On flat reefs 

 with many breaks, large numbers of pools, puddles and depressions are 

 left at low tide. The banded distribution is completely disrupted in 

 these areas, since the pools and depressions have their own communities 

 (sometimes several communities in each pooll), depending on the position 

 of the pool, its depth, the nature of the bottom, etc. Since one or 

 two, less frequently three, species predominate clearly over the others 

 in rocky littoral communities, the appearance of each community can be 

 easily distinguished from the others. Therefore, the variety of the 

 communities is easily seen. In one rocky high boreal intertidal zone 

 in open Kronotskiy Bay, not distinguished either by variety of bionomic 

 types or by richness of species of fauna and flora, in 1970 we found no 

 less than 27 band-forming groups, clearly different as to dominant 

 species. 



Thus, for an intertidal zone great changes in communities in the 

 vertical direction and great variability of communities under the influence 

 of local factors are both characteristic. Considering the great local 

 variability, we assume that the littoral biota is almost infinitely 

 variable. Nevertheless, the intertidal zone in almost all regions of 

 the earth, under bionomically similar conditions, supports communities 

 which dre of the same type or quite similar, with a limited selection of 

 the very same, either variant or morphologically similar species. As a 

 result, the great variety of littoral communities, upon careful examination, 

 is found to consist of a small number of regularly repeating series 

 of similar communities. Following the lead of botanists (Feldmann, 

 1951) and certain hydrobiologists (e.g., Dellow, 1950), these series 

 should be called formations. 



R. Bolin (1949) believes that the linear distribution of littoral 

 organisms, where almost each individual is peripheral, greatly increases 

 the chances for survival of mutants and gives the organisms high evolu- 

 tionary potential. This, in his opinion, is one important reason for 

 the tremendous richness of species in the intertidal zone. However, if 

 we exclude the large number of 1 i ttoraloxene species, which dre atypical 

 for the intertidal zone, the number of littoral species is relatively 

 low. On the average, the number of species of animals in an intertidal 

 zone is 1/2-1/4 the number in the upper sublittoral, although the environ- 

 ment there is generally less variable. Apparently, this results from the 

 fact that only the most eurybiotic species can exist in the intertidal 

 zone and supra! ittoral zones. These species, which have great ecologic 



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