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



above 1 ,000 m (Candacia columbiae, Racovitzanus antarcticus, Heterorhabdus 

 tonneri, Pareuchaeta japonica and others) and those adapted to greater depths 

 (from 2,000 to 3,000 m) (Pleuromamma scutulata, Scolecithricella ovata and 

 others). The species of the second group do not migrate and do not rise into 

 the upper layer {Halaptilus, pseudooxycephalus, Scaphocalanus magnus, 

 Pseudociphella spinifera and others). 



The plankton of the Sea of Okhotsk is specially noted for its radiolarians ; 

 81 species have been recorded there. 



Benthos (Fig. 396) 



The coastal flora of the Sea of Okhotsk comprises about 162 species of sea- 

 weeds. The Kuril Islands flora is considerably richer {Table 317). 



Table 317. Number of macrophyte species in the Sea of Okhotsk and Kuril Islands 



The great wealth of species of the sea-weeds of the Kuril Islands is due to 

 the penetration of a series of oceanic and mainly warm-water forms. The 

 Kuril ridge may be divided, according to its coastal sea-weeds, into two 

 regions — a northeastern one embracing all the main ridge, and the southern 

 Islands of Urup, Iturup, Kunashir and all the islands of the small Kuril 

 ridge. Laminaria, Thalassiophyllum, Cymathere, Fucus evanescens, Mono- 

 stroma groenlandica, M. grevillei are predominant in the northern region, and 

 Pelvetia, Kjelmaniella, Cystoseira, Leathesia, Colpomenia, Chondrus and 

 Neodilsea in the southern. The range of the tides in the Okhotsk Sea is very 

 great : on southern Sakhalin and the Kuril Islands the range is no more than 

 50 cm, while in the Penzhinskaya Inlet it attains more than 13 m. Moreover, 

 the tides belong mostly to the mixed type — irregular semi-diurnal and irre- 

 gular diurnal (R. Ushakov, 1951). Most of the shore of the Sea of Okhotsk 

 is exposed to a strong swell, where the littoral fauna and flora are mostly 

 poorly developed ; a rich littoral population is concentrated in those coastal 

 sectors protected from the swell, in the inlets and bays of the northern coast of 

 the Sea of Okhotsk. 



The littoral fauna of the Sea of Okhotsk, like that of the Barents and White 

 Seas, is typically boreal. It has much in common with the faunas of these Seas, 

 in the species it contains, in its general bionomic structure and in the structure 

 of its individual biocoenoses. The phenomena of amphi-boreal resemblance 

 is reflected in the littoral fauna, most of all in the mass development of its 

 representative species: Littorina rudis, L. sitchana, L. littores, L. squalida, 

 Arenicola marina, A. claparedii, Nucella lapillus, Thais lima and others. The 



