THE BALTIC SEA 



271 



The Swedish zoologist S. Loven (1864) laid the foundation of the study of 

 the fauna of the western part of the Baltic Sea. 



A number of comprehensive works on the fauna of the Baltic Sea appeared 

 in the second half of the last century, among which the following should be 

 noted: the researches of K. Mobius (1873) on invertebrates and, in colla- 

 boration with Fr. Heinke (1883), on fish; the work of K. Brandt on Kiel 

 Bay fauna (1897), and that of O. Nordquist on the fauna of the invertebrates 

 of the north of the Baltic Sea and of the Gulf of Bothnia. In the 'nineties 

 Danish and Finnish scientists began their study of the Baltic Sea. From 1913 

 onwards a whole series of papers was published by the Swedish zoologist 

 Sv. Ekman. 



The first quantitative survey of this fauna was carried out by the Dane, 

 С G. Joh. Petersen (1913, 1914, etc.) and by the Swede, G. Thulin (1922). 



The extensive series Die Tierwelt der Nord- und Ost-see, which first appeared 

 in 1927 is the most comprehensive summary of work on fauna of the Baltic 

 Sea. A number of significant studies have been carried out by K. Demel, 

 A. Remane, K. Shliper, Sv. Sagerstrale, I. Valinkangas and others during 

 recent decades. 



III. PHYSICAL GEOGRAPHY, HYDROLOGY, HYDRO- 

 CHEMISTRY AND GEOLOGY 



Size and subdivisions 



A characteristic feature of the orography of the Baltic Sea is its considerable 

 extent from south to north (more than 1 ,200 km) ; from Copenhagen to the 

 end of the Gulf of Bothnia is about 1,500 km. This causes great climatic 

 differences between the southern and northern parts of the Sea. 



In Spethmann's opinion (1912) the area of the Baltic Sea is equal to 385,000 

 km 2 (Sagerstrale suggests that it is 420,000 km 2 ), while its volume is 21,700 

 km 3 . The greatest width of the Sea is approximately 300 km. 



The annual inflow of fresh water is 630 km 3 , or 1/34 of the total volume of 

 the Sea. Four hundred and sixty-five km 3 of water is brought into the Baltic 

 Sea by the 250 rivers which flow into it. 



The Baltic Sea, with its large number of islands and bays and its somewhat 

 varied bottom topography, is subdivided into several natural areas. The system 

 of subdivision accepted by Sv. Ekman (1931) is set out below, although other 

 investigators prefer other subdivisions : 



A. Belts (transitional area) 



B. Oresund (transitional area) 



C. Baltic Sea proper 



D. Gulf of Riga (marginal area) 



E. Gulf of Finland (marginal area) 



Called also West 

 Baltic Sea 



I. South Swedish- 

 Pomeranian Baltic 



II. Central part of 

 Baltic Sea 



1. Danish belt 



2. German belt 



3. Arcona or Rugen 

 region 



4. Bornholm region 



5. West Baltic central 

 part 



6. East Baltic central 

 part 



