SEOT. 4] BIOLOGICAL SPECIES, WATER-MASSES AND CURRENTS 409 



mixing of waters in the coastal part of this area. The line of demarcation 

 between these two faunas may result in part from the width of the Continental 

 Shelf, which is narrow in the Beaufort Sea and relatively broad in the Chukchi 

 Sea as shown by the 200-m depth contour in Fig. 11. This would tend to in- 

 fluence the relative position of the neritic and of the more offshore species such 

 as Calanus hyperboreus and Metridia longa which occur in deep water but are 

 not characteristically bathypelagic species and were caught regularly in tows 

 from 100 to m depth, and also in a tow from 700 to 430 m depth. Although 

 the geographic limits shown here for these two arctic species appear to be 

 valid for the boundary of their continuous distribution, it must be mentioned 

 that both species have been reported far south of this range. Anraku (1954) 

 lumps M. longa with M. lucens from the Aleutian area; Campbell (1929) 

 reports M. longa from the Vancouver Island region; and Wilson (1942) lists 

 M. longa from both the North and South Pacific and Calanus hyperboreus from 

 the North Pacific. Some of these identifications appear to be in error. Further 

 work on deep-water plankton is needed to determine the extent of subarctic 

 penetration by these and other cold water forms into the deep cold water of the 

 Pacific. 



The truly abyssal species found in the Arctic Basin have their main connec- 

 tion with the Atlantic Ocean, since the shallow depth of the Bering Strait 

 permits transport of only the surface species and such bathypelagic forms as 

 also frequent the upper layers. 



Parts of the area here covered by the plankton surveys have also been 

 studied by Russian biologists. Their reports substantiate the conclusion that 

 Bering Sea plankton is carried northward through the Bering Strait (Stepanova, 

 1937; Brodskii, 1957). 



B. The Meroplankton 



We turn now to illustrate briefly a different aspect of plankton dispersal 

 with emphasis on the floating larval stages of bottom -living invertebrates. 



The dispersal of meroplankton has been of interest to marine biological 

 studies mainly because of its importance in the ecology, recruitment and 

 general life cycle of the animals involved. But the extent and pattern of dis- 

 persal of these forms can also contribute to the study of water currents, 

 especially on a more restricted scale, although the most widely known and 

 remarkable study ever made on the drift of marine plankton is that of Johannes 

 Schmidt (1925), dealing with the larval drift of the European eel. This eel, 

 after hatching, is carried during its two-to-three-year larval life some 3000 

 miles by currents across the Atlantic Ocean. The planktonic larval life of most 

 invertebrates is, however, usually much shorter, and their sensitivity to hydro- 

 graphic changes probably greater. Hence, they are not so likely to be carried 

 great distances away from the spawning area of adult distribution. The useful- 

 ness of these larvae as indicators lies in the fact that the spawning area of the 

 adult is often known, and the duration of the larval stage may also be known 



