322 MARINE BIOTIC COMMUNITIES 



posed. Such species of fishes as constitute the genera Cyclothone, 

 Storaias, Chauliodus, and Argyropelecus appear to be voracious feed- 

 ers in the oceanic communities south of the British Isles, while squids 

 and the better-known pelagic fishes operate in a similar manner in 

 the Norwegian Sea. Dominance in pelagic communities appears to de- 

 pend upon superior fecundity and numbers, as well as greater ability 

 to hunt or strain out and devour other animals, as well as plants. The 

 principal larger dominants appear to be partially non-competitive in 

 their food relation, which suggests a much finer adjustment of the 

 constituents to one another than is found in terrestrial communities. 



ECOTONE BETWEEN PeLAGIC AND BOTTOM COMMUNITIES 



A goodly number of bottom animals swim about, entering the pe- 

 lagic conditions just as the species independent of the bottom and 

 shore do, in a manner comparable to that of birds, bats, insects, etc., 

 in land communities. Some of these motile forms roam over two or 

 more major communities (biomes), using one for breeding, and another 

 for feeding and other activities of a non-breeding portion of the year. 

 The fishes have a mobility of about the same magnitude with refer- 

 ence to major communities as do birds and a few of the largest mam- 

 mals, while bottom crustaceans, mollusks, echinoderms, etc., have a 

 power of movement roughly equal to that of the smaller animals (cf. 

 Hutchinson, 1928; Hutchinson, Lucas, and McPhail, 1929; F. S. Rus- 

 sell, 1928-1932). 



The ecotone between the benthic communities of the continental 

 shelf and the pelagic ones is also quite evident. It is characterized by 

 fishes and crustaceans dividing their time between the bottom and 

 the water above, though primarily dependent upon the bottom. Fur- 

 thermore, the pelagic community, as the enclosed waters are ap- 

 proached, presents a series of communities characterized by the loss 

 of oceanic species and the addition of larval stages of benthic animals 

 and adult and post-larval fishes of the continental shelf. 



COMMUNITIES OF THE SEA BOTTOM 



Sea-bottom communities include both sessile and motile animals, 

 together with plants. Unfortunately, like pelagic communities, these 

 three groups have been considered separately and the community 

 unity and many of the coactions have been passed over or treated in 

 an isolated manner. The sessile, sedentary, and slow-moving inverte- 

 brates of bottom communities have commonly been roughly subdi- 

 vided into three life-habit and life-form groups. The most conspicu- 



