THE WHITE SEA 

 IV. FLORA AND FAUNA 



193 



Plankton 



Qualitative composition. The plankton of the White Sea has up to now been 

 very insufficiently studied. Its qualitative composition is given in Table 82. 



Table 82 



The composition of phytoplankton according to P. Usachev. 



In connection with the fact that the surface layers of the White Sea are 

 warmed more in summer than those of the Barents Sea, and the deeper ones 

 are warmed less, the thermophilic forms are concentrated in the surface layers 

 and the cold-living forms in the deeper layers. 



Of the former one should distinguish the ciliates Amphorella subulata, the 

 peridineans Ceratiumfusus, Peridinium conicum, the copepods Calanus finmar- 

 chicus, Oithora similis, Microsetella atlantica, Centropages hamatus and Temora 

 longicornis, the Cladocera Evadne nordmanni, the appendicularian Fritillaria 

 borealis and some others. Correspondingly considerable predominance in 

 the deep layers pertains to, for instance, the cold-water crustaceans Metridia 

 longa, and the ciliates Tintinnopsis campanula and T. ventricosa. Finally, the 

 third group of forms is distributed evenly throughout the whole column. To 

 these should be related the medusa Aglantha digitalis, the rotifer Anuraea 

 cruciformis and the crustacean Pseudocalanus elongatus. In the plankton the 

 predominant forms are the Arctic and Arctic-boreal, but also in the plankton 

 there are true boreal elements which are partly relict already. Thus the Cado- 

 cera Oothrix bidentata, for instance, which is encountered in the northern 

 part of the Atlantic Ocean, is absent from the Barents Sea, but has been estab- 

 lished in the White Sea. The ciliate Tintinnopsis campanula, which is known 

 from the Mediterranean, Black and North Seas and from the Gulf of Fin- 

 land, has likewise been discovered in the White Sea. It has not been found in 

 the Barents Sea. In the parts of the Barents Sea adjacent to the White Sea 

 many plankton forms are not encountered which are common in the White 

 Sea. Of these one may name the ciliate Amphorella subulata, the crustaceans 



N 



