GENERAL CHARACTERISTICS OF FAR EASTERN SEAS 749 



recent spread into the new habitat. It can, in general, be considered as an 

 immense experiment in acclimatization by Nature herself — a conquest of vast 

 new habitats, often more spacious than the original ones. This experiment is a 

 good illustration of the actual and potential habitats (L. Zenkevitch, 1940); a 

 comparison of these two concepts should be kept in mind when plans are 

 worked out and measures for trans-oceanic acclimatization are put into effect. 

 A. P. Andriashev ( 1 944) gives 50 cases of amphi-boreal distribution among fish 

 including cod, navaga, herring, several species of flatfish, halibut and others. 



Amphi-boreal forms are even more frequent among the invertebrates 

 (crustaceans, polychaetes, echinoderms, molluscs). Among them the follow- 

 ing commonly known mass forms may be mentioned : prawn {Pandalus 

 borealis), crab (Lithodes), barnacle {Balanus balanoides), starfish {Asterias 

 rubens), brittle stars (Ophiura robusta), holothurians {Cucumaria frondosa), 

 molluscs (Modiola modiolus), Enteropneusta {Balanoglossus mereschkowskii) 

 and many others — more than 100 species in all. It is characteristic that many 

 amphi-boreal organisms, predominant in one ocean, play only a modest 

 role in the other. Thus, for example, the forms dominant in the Bering Sea 

 benthos such as the echinoderms Ctenodiscus crispatus and Strongylocentrotus 

 droebachiensis; the worms Phascolosotna margaritaceum, Spiochaetopterus 

 typicus and Maldane sarsi; the molluscs Cardium ciliatum and many others, 

 become of secondary importance in the Pacific Ocean. Calanus finmarchicus, 

 markedly predominant in the plankton of North America, is intensively 

 developed in only a few areas of the Far Eastern Seas. Andriashev is in- 

 clined to refer the formation of the amphi-boreal community mainly to 

 the pre-glacial period, when, apparently, the Bering Strait was deeper 

 and wider and the temperature of its waters was (judging by its fossil mol- 

 luscs) 5° to 10° higher than it is now, and when the whole Arctic basin was 

 considerably warmer. The exchange of faunas could also have taken place, 

 but apparently in a much more restricted form, within the warm inter- 

 glacial periods and the post-glacial Littorina era. 



Whereas the appearance of disconnected habitats along the latitude is 

 linked with the periods of rise of temperature, the bipolar distribution is the 

 result of periods of colder climate, when the organisms of moderate latitudes 

 could penetrate through the somewhat cooled equatorial belt. 



The phenomenon of bipolarity is just as marked in the Pacific Ocean as in 

 the Atlantic. Laminariales among sea-weeds and sardines among fish may 

 serve as excellent examples of it. Along the Asian coast Laminaria have only 

 reached the Yellow Sea. They disappear farther south, appearing on the 

 western coast of the ocean only in 30° S latitude. On the eastern side, however, 

 they reach the Galapagos Islands. Their spread so far north along the coast 

 of South America is the result of the cooling effect of the Humboldt current. 

 Laminaria and penguins move with this current to the equator and the Gala- 

 pagos Islands. The order Laminaria includes only 30 genera and 130 species. 

 In the northern part of the Pacific Ocean 27 genera (90 per cent) and 84 

 species (65 per cent) of them are found, and in the southern hemisphere only 

 6 genera (20 per cent) and 22 species (17 per cent). Four species only are 

 recorded for the Yellow Sea. 



