320 MARINE BIOTIC COMMUNITIES 



characterize terrestrial communities by showing a wide distribution of 

 some of the predominants which bind together two associations, one 

 present in the Norwegian Sea and another well represented in the 

 Gulf of Maine (cf. Hjort and Rund, 1929; Fuller and Clark, 1936). 



H erring -Calanus Community {Clupea-Calanus Association) 



This is also well represented in the Norwegian Sea; the species 

 with outstanding abundance of individuals are Calanus, Thysanoessa, 

 the mackerel, herring, and certain whales, all common to both the 

 Norwegian Sea and the Gulf of Maine. In addition, there are present 

 the sprat {Clupea sprattus) and salmon {Salmo trutta), numerous 

 copepods and other crustaceans, as well as certain pelagic Mollusca, 

 fishes, and whales that do not occur in the Gulf of Maine (Murray 

 and Hjort, 1912; Bigelow, 1924, a). 



Menhaden-Calanus Community {Brevoortia-C alanus Association) 



The association found in the Gulf of IMaine contains the mackerel 

 {Scomber scombrus) , the copepod {Calanus finmarchicus, Gun.), and 

 several other abundant species that serve to bind the two associations 

 together in one biome. Some of the other species characteristic of 

 the association are Sagitta elegans, certain euphausiid shrimps (spe- 

 cies of the genus Thysanoessa), the menhaden {Brevoortia tyrannus 

 [Latrobe]), and the North Atlantic right whale, together with many 

 others less prominent. In his exhaustive treatise on the plankton of 

 the Gulf of Maine, Bigelow (1924, a) brings out many features that 

 illustrate the character of dominance and the eoactions in pelagic com- 

 munities. Clark (1933) has discussed light relations and distribution 

 of plankton down to 114 meters. 



Nature of Dominance in the Pelagic Climaxes 



The oceanic communities present a distinct aspect because of the 

 remarkable adaptations to pelagic life exhibited by the organisms 

 characterizing the different depths. Their permanency is no doubt 

 greater than that of any of the land climaxes. Two or three impor- 

 tant questions arise with regard to the role of microscopic plants and 

 animals, and the nature of the control exercised in the habitat by the 

 organisms. The effect of organisms near the surface on the conditions 

 surrounding those deeper in the water is important and has already 

 been discussed. 



Bigelow's studies (1924, a) and those reported by other investi- 



