PELAGIC COMMUNITIES 



317 



habitant of shore vegetation, had a value of 25 (Shelf ord, 1918, a). 

 Based on sulphur dioxide, the pelagic herring was rated at 10, the 

 perch at 21, and the bottom flounder at 1100. 



Pelagic Communities of the North Atlantic 



The only modern consideration of pelagic communities in which 

 the larger organisms and plankton are treated together as a unit is 

 that represented by Murray and Hjort (1912:101-108; 617-704). 



M 



150 



500 



1000 

 2000 

 3000 

 4000 

 5000 



• Myctophum - Salpa Biome 



^Scomber - Calanus^ 

 / Biome } 



Arevropelecus - Cauliodus Blome 



C. signata - A. purpurea 

 Association 



'iw '^<}^ C. microdon - A multispina 



^ '%, Association 



40 50 60 



Degrees - Latitude North 



80 



Fig. 73. — Diagrammatical vertical section of the North Atlantic with the several 

 communities described by Murray and Hjort indicated, arranged so as to follow 

 the practice in terrestrial communities. The depths to which the communities 

 occur probably decrease from the equator to 60° N., owing to the difference in the 

 penetration of solar radiation, but this is not indicated. 



These writers describe various communities of the pelagic waters of 

 the North Atlantic which may perhaps be interpreted as biomes as 

 suggested below. Furthermore, each appears divisible into two or 

 more associations based upon the abundance of certain fishes and 

 other larger animals that may be regarded as making the nearest ap- 

 proach to dominants. The boundaries are apparently less definite 

 than those between major land communities, but this is by no means 

 certain, as the facts are much more difficult to ascertain. The ar- 

 rangement of these (following IMurray and Hjort) is suggested in 

 Fig. 73. While the small amount of observation renders the classifi- 

 cation more or less hypothetical, it serves to illustrate probable 



