THE BARENTS SEA 91 



Thus the accumulation of organic matter in the bed depends on the abund- 

 ance of plankton and benthos life, which is its source, and on the conditions 

 favouring its deposition on the sea-floor; the two factors, however, may act 

 in the reverse direction. 



The C/N ratio for the Barents Sea, close to 7, characteristic for plankto- 

 genetic organic substance, indicates a sufficient aeration of the whole water 

 column and the very limited role of the littoral vegetation on the genesis of 

 organic matter. From this point of view the data of T. Gorshkova (1939) on 

 the Motovsky Gulf are most interesting. Although the shores are close to each 

 other the ratio of C/N is here also about 7. There is no increase of organic 

 carbon which remains constant at 0-15 to 2-76 per cent, so that even near the 

 shores the littoral vegetation does not affect the amount and nature of the 

 organic matter in the sea-bed. The closeness of the shores affects only the 

 chlorophyll content, which is higher here than in regions farther removed 

 from a shore. 



III. FLORA AND FAUNA: GENERAL CHARACTERISTICS 



The fauna of the Barents Sea, in spite of a complete or partial absence of a 

 number of groups which are characteristic of warmer seas (radiolarians, 

 Siphonophorae, corals, cephalopod molluscs, crabs, salpes, pyrosomes and 

 some others), is both varied and abundant and consists mainly of bivalves 

 and gastropods, polychaetes, echinoderms, lower and higher crustaceans, 

 Porifera, hydroids, bryozoans, ascidians and Foraminifera (Fig. 31). 



The number of animal species living in the Barents Sea is, probably, not 

 less than 2,500. At present, however, owing to an insufficiently systematic 

 study of many groups of the Barents Sea population, only an approximate 

 estimate of the number of its species is possible. 



Plankton 



The composition ofphytoplankton. The Barents Sea phytoplankton has not yet 

 been adequately investigated, especially as regards its productivity. Accord- 

 ing to I. Kisselev (1937) the plankton of the Barents Sea includes: 

 Green algae 9 forms 



Diatomaceous algae 92 forms 



Peridinean algae 69 forms 



Flagellatean algae 7 forms 



Others 2 forms 



Total 179 forms 



The actual number of phytoplankton forms is probably above 200. 



However, in this fairly rich stock only a few are of importance, among 

 the diatoms the following : Chaetoceras diadema, Coscinodiscus subbul liens, 

 Corethron criophilum, Sceletonema costatum, and two species of Rhizoselenia- 

 R. styliformis and R. semispina. Of the green algae only Halosphaera viridis is 

 very widely distributed ; of the peridineans Peridinium depressum, P. ovatum, 

 P. pallidum ; and the three species of Ceratium— C. longipes, C. arcticum and 

 С fusum, that is 13 forms in all. 



