which coincides most closely with the horizons and stages distinguished 

 on the basis of tidal levels. This type includes many bays, the interiors 

 of certain gulfs, as well as areas of open but broken coastlines pro- 

 tected from strong surf. 



Second bionomic type (open sea shore). Characterized by fourth or 

 fifth degree surf. Salinity approximates normal oceanic; conditions of 

 aeration good, water frequently supersaturated with oxygen. The harmful 

 mechanical effect of the surf predominates over the useful effect. The 

 bands of plants and animals are shifted upward, and many of the bands 

 characteristic for areas with weaker surf are absent. 



Third bionomic type (open ocean coast). Characterized by maximum 

 Surf, strong and constant wetting of entire intertidal zone by spray, 

 even during lowest tide; the harmful effect of the surf is so great that 

 the population is greatly impoverished, but the most enduring forms, 

 having no competition, extend almost throughout the intertidal zone. 

 There is often practically no precise vertical stratification. The 

 communities of the sublittoral edge are shifted upward and occupy 

 almost all or even all of the intertidal zone, while the littoral 

 communities themselves are usually located in the supral ittoral zone, 

 which is constantly wet by the surf and spray. 



Fourth bionomic type (lagoons). Characterized by total absence 

 of surf (first degree surf) and extensive development of mud and sandy 

 sediments. Salinity usually depressed to some extent, but elevated in 

 countries with arid climate. 



Fifth bionomic type (estuaries). Surf usually absent, less frequently 

 second or third degree. Salinity greatly reduced, and usually changes 

 with the phases of the tide. An estuarine intertidal zone is an area in 

 which the continental, marine and fresh-water biota come together. 



Sixth bionomic type (pools). We include here all depressions and 

 large indentations in rock, as well as the pools left between rocks and 

 on beaches at low water. This type is characterized by absence of surf 

 or a reduction in the harmful influence of the surf, while retaining its 

 aerating influence, remains quite wet even during the lowest tides, 

 and has a complex hydrologic mode. The temperature and salinity of the 

 water frequently change greatly. One specific feature of pools is that 

 water is constantly present, even if they are located in the supral ittoral . 

 This means that the conditions of existence in pools are similar to those 

 of the sublittoral, except that the variations in hydrologic factors are 

 significantly greater than in the sublittoral zone. The main factors 

 determining the composition of the population of pools are their position 

 above the zero depth level, the nature of the sediment, the size and 

 particularly the depth, the effects of wind and surf, the peculiarities 

 of their connection with the sea during low tide (if there is any such 

 connection), the degree of influence of continental runoff, steepness 

 of the walls, nature of change of hydrologic factors and illumination. 



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