THE WHITE SEA 



205 



Abrikosov Sokolova (1948) gives a subdivision of the littoral of the Gulf of 

 Kandalaksha somewhat different from the above: 



Upper horizon 



On rocks — Littinora rudis, Mytilus edulis 



Between rocks, frequently, the flowering plant Aster trifolium 



Under rocks — pupae Insecta, Oligochaeta, Nematoda 



Middle horizon 



Balanus balanoides, Littorina rudis, Hydrobia, Rissoa, Mytilus edulis 



Lower horizon 



Littorina littorea, L. palliata, Buccinum groenlandicum, Natica clausa, 

 Margarita helicina, Asterias rubens 



Actinia equina is common on the undersides of rocks. Under the rocks 

 Gammarus spp. is found in masses. In the White Sea many of the most typical 

 littoral forms descend in considerable numbers into the sublittoral, as, for 

 instance, Mytilus edulis, Balanus balanoides, Gammarus obtusatus, the Lit- 

 torina species and others. On the other hand, as was established for the littoral 

 of the Solovetsky Islands (A. Fedorov, 1928), many sublittoral forms {Asterias 

 rubens, for instance) rise to the lower level of the littoral. But even on the very 

 littoral of the White Sea the forms that inhabit it avoid, as it were, getting into 

 the upper levels, and strain downwards, nearer the water. Sokolova has pro- 

 duced Table 89 showing the quantitative ratio of the different forms inhabiting 



Table 89 



