wetted by spray from the surf, and in friable soils, by capillary rise 

 of sea water. In this area, the forms of terrestrial origin predominate 

 as to number of species (insects, arachnids, flowering plants, etc.), 

 although in the quantitative aspect, specialized forms of marine origin 

 may dominate (Talitridae Amphipoda, in the tropics--crabs, etc.). 



1 .1 Zonal ity of the Intertidal Zone 



The Question of the principles of vertical subdivision of the 

 intertidal zone into systems of coordinated units of lower rank has been 

 discussed approximately since the middle of the last century. The expe- 

 diency of this type of subdivision is beyond doubt, since the vertical 

 stratification of organisms and their complexes is particularly clearly 

 manifested in the intertidal zone, and frequently, particularly if the 

 shoreline is not broken, groups of flora and fauna (communities) may 

 extend almost without interruption for hundreds of kilometers, forming 

 clear stripes but a few decimeters or even centimeters in width. However, 

 the question of the principles upon which the subdivision of the inter- 

 tidal zone should be based remains in dispute. 



It would seem most simple to accept the biotic principle, i.e., to 

 divide the intertidal zone in accordance with the communities or types 

 of communities--formations forming the strips along the shoreline, which 

 we observe in nature, particularly since they are not distinguished by 

 great variety. The overwhelming majority of schemes of this type, 

 however, have reflected the specifics of only a limited sector of the 

 shoreline and are therefore only of historic interest. The greatest of 

 the schemes of this type is the universal scheme of zonal ity suggested 

 by T. A. and E. Stephenson (Stephenson, Stephenson, 1949) for a rocky 

 intertidal zone. The Stephensons subdivide the intertidal zone into 

 three "zones," each with its own typical inhabitants, usually relating 

 to the same life forms, but with different species or genera in the 

 different regions: the supral ittoral edge, or the littorine zone; the 

 middle littoral zone or the barnacle zone; the sublittoral, or infra- 

 littoral edge. Later, an attempt was made (Dahl, 1953) to provide a 

 similar system for an intertidal zone with friable sediment. One signifi- 

 cant shortcoming of such a system, like others based only on the distribu- 

 tion of organisms, is the failure to give proper weight to the significance 

 of tidal variations in sea level as the primary factor defining the 

 vertical distribution of the organisms and their communities in the 

 intertidal zone. Furthermore, harder sediments, sand and mud do not 

 have common communities; therefore, the systems developed for different 

 sediments are different and difficult to compare and, finally, the 

 leading groups of any sediment, if they are cosmopolitan, may be located 

 at Quite different levels, due to differences in temperature and salinity 

 of the water, insolation, surf power, etc. Furthermore, even under 

 similar conditions, the vertical distribution of indicator species is 

 not always constant. For example, in the British Isles, the upper 

 boundary of the middle intertidal zone, defined according to the upper 

 boundary of massive accumulation of barnacles, is significantly higher 

 where Chthamalus s tellatus predominates than where Balanus b alanoides , 

 which lives at a lower level, dominates. Thus, systems based on indicator 

 organisms and their communities cannot yield universal vertical boundaries 

 for subdivision of the intertidal zone. 



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