THE BALTIC SEA 303 



Dictyosiphon foeniculaceus, Gobia baltica, Strichtyosiphon tort His, Ceramium 

 diaphanum and Asterocystis ramosa ; moreover, here they are greatly reduced 

 in size. 



There are no tides in the Baltic Sea ; however, considerable changes in the 

 level of the Sea have been observed under the effect of the wind and of differ- 

 ences in pressure. These fluctuations are at times as large as 1 to 1-3 m. This 



Fig. 144b. Correlation between salinity and the distribution of flowering marine 



plants (Gessner). 



is reflected in the zonal distribution of the coastal vegetation and can be 

 expressed in the following pattern (M. Waern, 1952; F. Du Rietz, 1950): 



(7) The geolittoral or geo-amphibiotic belt. Covered with water either when 

 the sea-level rises, or by waves and the swell. The upper limit of summer 

 growth of algae. 



(2) The hydrolittoral or hydro-amphibiotic belt. Exposed at a low level of 

 water, thickly covered by threadlike sea-weeds {Cladophora glomerata). 

 The lower limit of summer growth of algae. 



(3) Sublittoral. Always covered with water. 



Zoobenthos 



Qualitative composition. One of the three main components of Baltic Sea fauna 

 is the greatly impoverished North Sea fauna (Atlantic fauna), which pene- 

 trates into the body of water through the straits and undergoes, with the fall 

 in salinity, a marked loss in the number of species (Fig. 145), and the degenera- 

 tion of individuals. K. Brandt was the first to estimate the Atlantic fauna in 

 the Baltic Sea (1897). Ekman revised Brandt's data in 1935 from data 

 published in the series Die Tierwelt der Nord- und Ostsee. We give below 



