Comparison of the specific composition and biomass of the 

 macrobenthos of the communities of brown algae Fucus distichus . 

 characteristic for the middle littoral of the boreal zone in the North 

 Pacific--the lower boreal (southern Kurile) and higher boreal (eastern 

 Kamchatka) zones--shows that, in spite of the fact that eastern 

 Kamchatka and the southern Kurile belong to different biogeographic 

 subareas, the specific composition of the communities of _F. evanescens 

 is quite similar--54 species are common, something less than 2/3 of the 

 number of species in each of the regions compared, their biomass making 

 of the total biomass of the macrobenthos in the community 

 A quite different picture is observed as we compare the 

 of the vicariant communities of _F. distichus and £. evanescens 



biomass (84-86.5% of total biomass) is 



up 94-98% 

 (Table 1) 

 structure 

 (Table 2) 

 accounted 

 than half 



Here, most of the 

 for by the vicariant species, although they represent less 

 of the total number of species present in the community. The 

 common species present is not great, the degree of similarity, 



number of . . 



as defined by Jnccard, is only 11.8%, increasing somewhat (to 14.6%) if 



we compare the communities of the higher boreal regions alone. 



Table 1. Changes in the composition of the community Fucus evanescens in various 

 biogeographic provinces. 



Eastern Kamchatka, higher Southern Kurile, lower 

 boreal littoral. Total boreal littoral. Total 

 biomass 4534 g/m^ biomass 4879 g/m^ 



Categories of 

 Species 



No. of % of total Biomass No. of % of total Biomass 

 Species No. of % of Species No. of % of 

 Species total Species total 



Species common 



Undefined species 

 Total species 



62 



18 



20 



98(35)' 



1 

 0.1 



54 



18 



16 



61 

 21 



18 



87 



94 



(9)* 



1 

 5 

 5 



♦Parentheses show biomass excluding dominant species F. evanescens . 



3. Convergent or isomorphic communities. Groups of organisms occupying 

 similar biotopes, the dominant species of which are not closely related forms, 

 but belong to the same life forms. For example, in the upper intertidal zone 

 of the tropics, Littorinidae hv^i. frequently replaced by Neritidae, while 



the middle intertidal zone, the prosobranchial mollusks (of the families 



in 



144 



