48 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



Table 20. Percentage content of zooplankton biomass in northwestern part of 



Laptev Sea (Jashnov) 



Plankton content 

 composition 



Calanus finmarchicus 



Metridia longa 

 Pareuchaeta glaeialis 

 Calanus hyperboreus 



Depth of layer, m 



0-50 50-150 150-250 250-300 300-800 



70 50 Calanus finmarchicus disappears. 



The Atlantic forms of Copepoda: 

 30 Scaphocalanus magnus, Gaigius te- 



nuispinus, Heterorhabdus norvegicus, 

 Montonilla minor and others and the 

 Polychaeta : Thvphloscolex mullerri, 

 Pelagobia longicirrata become 

 sharply preponderant 



From the above tables it can be seen that Calanus finmarchicus prepon- 

 derates in the 200 m surface layer (colder and less saline), whereas Chaeto- 

 gnatha and Coelenterata are more abundant in deeper layers. Sometimes 

 various Atlantic forms of crustaceans greatly preponderate in this deep layer 

 (200 to 800 m) which is warmer and more saline than the surface layer. 



All the data given refer, however, to sections of the Arctic basin exposed to 

 the influence of coastal waters. It may be supposed that as one penetrates 

 farther into the depths of the central part of the basin there is a significant 

 decrease of zooplankton biomass, and in this connection the collections made 

 aboard the Sadko in September 1935, northeast of Franz Joseph Land at 

 depths up to 2 km, are of great interest. Only 12 mg/m 3 of plankton biomass 

 was obtained by the first catch at a depth of up to 100 m (50 per cent of it 

 consisted of Calanus finmarchicus). In a lower layer (100 to 500 m) the biomass 

 content was found to be higher — 29mg/m 3 , but the amount of Calanus fin- 

 marchicus was limited to 20 per cent. Other Copepoda, namely Metridia longa, 

 Pareuchaeta norvegica, P. glaeialis (approximately 3 per cent), preponderate 

 here. Of the other forms Coelenterata (Aglantha digitate), Ostracoda, Amphi- 

 poda and Polychaeta are the most important. At the lowest level (500 to 

 2,350 m) most of which lies in the abyssal cold layer (below 800 m) the biomass 

 was 7 mg/m 3 . 



The Sadko data on the plankton in the central regions of the Arctic were 

 supplemented in 1937-40 during the famous drift of the G. Sedov (B. Bogorov, 

 1946) and by the researches of the drifting polar stations North Pole 2, 3 and 4 

 (K. Brodsky, 1956). In all, 73 species of zooplankton were found in this plank- 

 ton ; this includes 40 Calanoida species, 5 Amphipoda and 3 Appendicularia. 

 In direct contrast with the benthos, the majority of zooplankton species are 

 common in the Greenland Sea and northern Atlantic. The comparison be- 

 tween the number of species and the number of plankton specimens for 

 different regions of the Pacific Ocean and Arctic Seas, drawn by K. Brodsky 

 (1956), is of great interest (Fig. 8). The diversity of forms continuously dimin- 

 ishes as one moves from the Pacific Ocean to the Chukotsk Sea and only rises 



