INTRODUCTION 



No country in the world possesses such an abundance and variety of bodies 

 of water as the u.s.s.r. Its frontiers are about 60,000 km long. Only a small 

 part of the seas of the u.s.s.r. is directly connected with the open ocean, most 

 of its shores being encirled by the accessory seas of three oceans — the Arctic, 

 the Atlantic and the Pacific. 



A comparison with other continents, which are usually almost devoid of 

 accessory seas, brings out clearly this characteristic of Eurasia. 



Twelve of the seas of the u.s.s.r. have retained their link with the open 

 oceans ; two of its greatest lake-oceans — the Caspian and Aral Seas — are at 

 present isolated from them. 



The total area of these 14 seas composes about 5 per cent of the surface of 

 the world-ocean; they astonish their investigators by the variety of their 

 physico-geographical conditions, by the abundance and variety of their flora 

 and fauna and by the complexity of their geological past, which has left its 

 ineffaceable imprint on their composition, their biological peculiarities and 

 their ranges of flora and fauna which provide huge resources of plant and 

 animal raw material. The population of the seas of the u.s.s.r. is a very rich 

 subject for scientific investigation. 



The seas of the u.s.s.r. include such pygmies as the Sea of Azov, with 

 depths no greater than 13-5 m, and such giants as the Bering Sea, with depths 

 exceeding 5 km. Some of its seas have a full marine salinity, some are brackish, 

 with a salinity of 12-10-8 parts per thousand and less. The composition of the 

 salts of some sea-lakes, such as the Caspian and the Aral Seas, has changed 

 considerably, and at present they differ greatly from that of the oceans. Some 

 details are given in Table 1. 



The Baltic and northern seas of the u.s.s.r. contain a most characteristic 

 brackish- water relict fauna, the result of a considerable and protracted loss of 

 salinity experienced during the Ice Age. Some representatives of this relict 

 fauna moved southwards, penetrated into river systems and reached the Cas- 

 pian Sea. The southern seas of the u.s.s.r. give shelter to a rich, brackish- 

 water relict fauna — a remainder of the Pontic lake-sea fauna, which has in a 

 large number of representatives penetrated into the river systems of the Black, 

 Azov and Caspian Seas. No other seas contain such rich, brackish-water 

 fauna of varied origin as those of the u.s.s.r. The penetration of representa- 

 tatives of the Mediterranean (Atlantic) fauna eastward into the Caspian and 

 even the Aral Seas is also most interesting. 



During the recent millennia the Barents Sea and the adjacent Siberian seas 

 have formed a broad route for the penetration of Atlantic fauna eastward, 

 and of Pacific fauna westward. The great depths of the central depression of the 

 Arctic basin with their original bathypelagic fauna are adjacent to the northern 

 confines of the Siberian seas. 



One of the greatest depths in the Pacific — the Kurile-Kamchatka Trench 

 — lies immediately adjacent to the eastern boundary of the u.s.s.r. 



