Table 2. --Calanid genera represented above 

 and below I, 000 m. 



The species of the genus Spinocalanus also do 

 not rise above 200-500 m. and are not encoun- 

 tered in the surface layers, and therefore this 

 genus, too, should be characterized as abyssal, 

 a characterization which is confirmed by ma- 

 terial from other regions of the Pacific Ocean 

 and, particularly, from the Antarctic, Okhotsk 

 and Bering seas, Arctic Ocean, etc., where 

 species of the genus Spinocalanus are adapted 

 to great depths. As can be seen from the data 

 in table 1, out of the total number of species 

 (93) found at the station, only six are encoun- 

 tered in the upper layers, to wit, Microcalanus 

 pygnnaeus Sars, Calanus tonsus Brady, 

 Metridia pacific Brodsky, Calanus cristatus 

 Krdyer, Metridia okhotensis Brodsky, and 

 Eucalanus bungii Gsbr. /Translator's note: 

 The apparent discrepancy between this state- 

 ment and the data in table 1 is unexplained. / 

 Finally we must point out the group of surface 

 species, to which in the present case we nnust 

 assign only Pseudocalanus elongatus (Boeck) 

 and Calanus pacificus Brodsky. 



The ecological differentiation of genera and 

 species according to their vertical distribution 

 appears to be very material to an understanding 

 of the range of occurrence of Calanoida, in par- 

 ticular, in such sea basins as are isolated fronn 

 the deeps of the World Ocean by narrow straits, 

 such as the Sea of Japan, which is closed off 

 from the deeps of the Pacific, and the Arctic 

 Ocean, which, although it has a connection with 

 the Atlantic, is almost isolated from the Pacific. 

 Only that group of species which is distributed 

 vertically to the surface layers of the water can 

 penetrate into these basins by way of the sur- 

 face fauna, and in the present case these are 

 the six species indicated above. For clarifi- 

 cation of the peculiarities of the vertical 



distribution of calanids both for basins the 

 depths of which are directly linked with the 

 great depths of the World Ocean and for 

 basins which are partially isolated, we have 

 compared the numbers of species and the num- 

 bers of specimens per 1 m.-^ at various levels 

 in the northwestern part of the Pacific Ocean, 

 the Sea of Japan (Brodskii 1941), the central 

 part of the Arctic Ocean (Bogorov 1946), and 

 the Greenland Sea (Jespersen 1934) (table 3). 



In this table we have included, besides all 

 Calanoida, one species of Cyclopoida, Oithona 

 similis, as being of massive occurrence in the 

 surface waters. 



Let us consider some of the peculiarities 

 of the material which is presented in table 3 as 

 an attempt to compare the numbers of species 

 of copepods vertically in various places of the 

 World Ocean. 



The increase in the number of individuals 

 in the upper layers depends on the mass devel- 

 opment of a few surface species of copepods 

 which feed mainly on phytoplankton. It is char- 

 acteristic that such an increase in the number 

 of specimens is related to the small number of 

 species inhabiting the upper levels of the water. 

 This phenomenon can serve as a demonstration 

 of the well-known rule of the mass development 

 of a few species which have adapted themselves 

 to unfavorable conditions—', which in the upper 

 layers consist of an abundance of phytoplankton, 

 as well as relatively sharp changes in tempera- 

 ture conditions linked with seasonal changes. 



The richness in species of the deep parts 

 of the World Ocean is probably related to the 

 variety of conditions to be observed in the im- 

 mense thickness of the water mass (3-4 km.) 

 and in an important degree also to the pro- 

 longed period of tinne during which these deeps 

 have been in existence. 



The material presented in table 3 shows 

 plainly the sharp increase with depth in the 

 number of species both in the northwestern 

 Pacific Ocean and off the west coast of Green- 

 land, which is dependent on the broad con- 

 nections of these regions with the other parts of 

 the World Ocean. The small number of species 

 in the Sea of Japan increases only insignificantly 



J-' In recent times a large number of facts 

 have accumulated indicating the harmful 

 influence of mass concentrations of phytoplank- 

 ton on a number of species of calanids. 



