THE WHITE SEA 



203 



the lowest. The biomass also increases with depth. Among all this fauna there 

 are only two species of crustaceans living in the lowest layer of the wrack, 

 which are properly marine forms — the Amphipoda Gammarus obtusatus and 

 the Copepoda Itunella mii/leri. Newly formed heaps of sea-weed are soon 



3rd Layer 



2nd Layer 



4836 g 



Fig. 88. Composition of the fauna population in the 

 debris of the White Sea sublittoral (Gurvich and 

 Matveeva). The biomass in g/m 2 is given below the 

 circles. 1 Oligochaeta; 2 Apterygota; 3 Coleoptera 

 larvae ; 4 Coleoptera imagines ; 5 Acarina ; 6 Arach- 

 noidea. 



populated by specific fauna from the bottom floor. By autumn the fauna in 

 the weed-heaps suffers a sharp impoverishment. 



Among the Oligochaeta the highest significance pertains to the Enchytraei- 

 dae family {Lumbricillus lineatus, Enchitraeus albidus and others). Among the 

 Tubificidae, Clitellio arenaria and Tubifex costatus have the greatest develop- 

 ment. These are joined also by some species of the Naididae family (Amphic- 

 teis leydigi, Paranais lit oralis and others). 



Population of the littoral. The amplitude of the tidal range in the main basin 

 of the White Sea usually reaches 1-5 to 2 m, and, as distinct from the Murman 

 coast, sand-mud beaches extend here along nearly the whole shoreline, being 

 only rarely interrupted by outcrops of cliff. Thus, although the foreshore in 

 the White Sea is not particularly broad (usually some tens and rarely some 

 hundreds of metres) yet on the whole its relative significance is much greater 

 than on the Murman Peninsula, since in the larger part of the Sea it girdles 

 the whole shore line. In the White Sea we find on the littoral all the same en- 

 vironment and biological phyla as on the Murman Peninsula, only somewhat 

 less pronounced, with a slightly smaller qualitative variety and lower quantita- 

 tive indices of flora and fauna. The whole basic selection of forms of the 

 western Murman littoral is included here almost in its entirety. Of the pre- 

 dominant forms only Nucella lapillus and Cardium edule are absent. 



