404 JOHNSON AND BRINTON [CHAP. 1 



changes or from gradual flow into higher or lower latitudes where the effects of 

 temperature or evaporation alter the distinguishing features. 



It is often of interest to follow the course of these moving, changing masses, 

 which have now lost part or all of their chemical-physical identities, and 

 exist as modified extensions in the form of currents, tongues or wedges, into 

 other geographic positions. Assuming that the planktonic fauna characterizing 

 the water-mass is well known, it is here that further application of an "in- 

 dicator species" can serve to corroborate physical-chemical studies, or even 

 provide a clue not otherwise obtainable as to the water's origin or circulation. 



Many planktonic species, although dependent on certain waters for reproduc- 

 tion and development, may be swept from these endemic areas and survive for 

 some time as expatriates. Some reproduction may take place at first, but 

 eventually only adults and submature specimens will be found and these, too, 

 finally succumb to changing environmental conditions. 



A. Transport from the Bering Sea into the Arctic Ocean 



Beginning in 1934 and continuing in the next two decades, considerable 

 oceanographic study, both physical and biological, has been concerned with 

 determining the extent and character of flow of North Pacific and Bering Sea 

 water and its floating life through the Bering Strait into the Arctic Ocean. 

 Parts of these studies will provide some idea of the application of plankton 

 species in following the movement of water-masses, and, conversely, of the kind 

 of dispersal pressure that planktonic species must be subject to under the 

 influence of a current system sweeping them relentlessly downstream into 

 more and more unfavorable living conditions. In this instance, the contrast 

 between the endemic area and the area involuntarily invaded is probably so 

 great that it militates against the evolution and establishment of epiplanktonic 

 species or forms adapted to the more severe environment of the Arctic. How- 

 ever, it has become increasingly evident that some planktonic species hitherto 

 considered common to widely separate areas, such as the North Pacific and the 

 Arctic and boreal waters of the Atlantic, may be distinct species or varieties 

 that have evolved in the Arctic. Outstanding among these is Calanus glacialis, 

 established by Jaschnov (1955) as a new species. Although relatively larger 

 than Calanus finmarchicus Gunnerus, it was previously identified with that 

 species. Also, Brodskii (1950, 1957) has named a surprising number of new 

 copepod species, some of which are closely allied to common Atlantic or arctic 

 forms. Taxonomically, this affects the present analysis only in that Metridia 

 lucens and Calanus tonsus as previously recognized by authors for the Pacific 

 form are probably Brodskii's Metridia pacifica and Marakawa's Calanus 

 plumchrus, both of which are North Pacific and Bering Sea species. 



Parts of the arctic areas that we shall be here concerned with were widely 

 surveyed during the short arctic summers by the U.S. Coast Guard cutter 

 Chelan, the U.S.S. Nereus and H.M.S. Cedarwood in the Bering Sea and parts 

 of the Chukchi Sea in 1934, 1947 and 1949 respectively, and by the U.S. ice 



