playing a substantial role in the warm-water 

 plankton. 



In waters with temperatures above IS C. 

 the plankton no longer has anything in common 

 with the plankton of colder waters, either in its 

 species composition or in the relationships and 

 significance of the different taxonomic groups. 

 The diversity of species increases sharply. 

 Especially noticeable is the appearance of var- 

 ious Pteropoda (Euclio, Peraclis, Cavolinia, 

 and others), Heteropoda (Pterotrachea, 

 Carinaria, Atlanta), hypereid Curvicornia 

 (Lycaeidae, Brachyselidae, Oxycerhalidae, 

 Rhabdosomidae, and others), Sergestidae 

 (Lucifer), the genera Sapphirina, Copilia, and 

 Corycaeus among the copepods, salps (Salpa, 

 Cyclosalpa, Doliolum), siphonophores, 

 Halobates bugs, and other groups characteris- 

 tic of tropical plankton. 



The plankton of these areas is quantitatively 

 very poor despite the great diversity of species. 



With further movement to the south and a 

 raising of the temperature to 20°-26°C. a num- 

 ber of new species appear, but the general as- 

 pect of the plankton remains almost unchanged. 



The sharp change in the specific composi- 

 tion of the plankton, accompanied by a decrease 

 in its bionnass, observed in crossing from the 

 moderately cold waters of the northern part of 

 the Pacific Ocean to the warm waters of the 

 Kuroshio permits us t o consider the zone of 

 contact of these waters as the boundary between 

 different zoogeographical regions. An analo- 

 gous conclusion was reached by K. A. Brodskii 

 (1955). 



Judging by our data, in August-Sej tember 

 this boundary is at 40°-iZ°N. latitude, and only 

 towards Japan, under the influence of the cold 

 current running along the Kurile chain, does it 

 drop farther south. Its location changes de- 

 pending on the changes in the northern limit of 

 the waters of the Kuroshio. 



The material collected by M. M. Sleptsov 

 in August 1954 and worked up by us shows that 

 separate tongues of Kuroshio water, inhabited 

 by warm -water plankton, jenetrate to 

 43°-44°N. latitude. 



In all of the areas investigated, excepting 

 those directly adjacent to Japan and under the 

 action of the current issuing througl-. tlie Tsugaru 

 Strait from the Japan Sea, this boundary coin- 

 cides with the I8°C. surface isotherm (fig. 1). 

 In 1951-52 (Anraku 1954) the zone of sharp 



change in the fauna was at approximately the 

 same latitude (38°-42°N. ). 



Besides their faunistic composition, the 

 boreal waters also strongly differ from the 

 Kuroshio waters in the total biomass of their 

 zooplankton. The boreal surface waters are 

 everywhere abundantly populated by plankton. 

 The biomass of plankton in the upper 100-meter 

 layer varies from 200 to 1, 000 mg. /m. , while 

 in the same layer of the Kuroshio waters it is 

 usually 10-20 times less. 



A comparison of the prinnary production of 

 the plankton (by photosynthetic action using the 

 "flask nnethod") showed that the diurnal produc- 

 tion of carbon in the warin waters of the Kuro- 

 shio is 10-20 times less than in the boreal 

 region (Bogorov and Beklemishev 1955). Thus, 

 in the waters of the Kuroshio the plankton is a 

 great deal poorer than in the boreal waters. 

 This impoverishment is expressed in the fact 

 that there is very little forage plankton in the 

 surface layer of the warm waters--the great 

 accumulations of calanids and other large cope- 

 pods, euphausiids, and amphipods are absent. 

 Therefore the feeding conditions for large con- 

 c entrations of plankton-eating fishes and whales 

 are unfavorable here. 



Distribution of the Plankton Biomass 



The boreal waters in the area of investiga- 

 tion can be subdivided into several zones 

 according to the distribution of the.biomass of 

 the plankton. The first zone includes the 

 waters in the immediate vicinity of the Kurile 

 Islands, the second the waters over the Kurile- 

 Kamchatka Trench; the third occupies the 

 southern part of the area of the boreal waters. 

 The waters lying 20-30 miles from Hokkaido 

 must be set off separately. 



The waters in the immediate vicinity of the 

 Kurile Islands are somewhat impoverished. In 

 May- June 195 3 the plankton biomassJ-' in the 

 0-100 n-i. layer near the Kuriles did not exceed 

 500 mg. /m. ; in August-September 1 ^^ 5 4 it 

 varied from 250 to 500 mg. /m.^ in this region. 

 The breadth of this "belt" is relatively small, 

 from several to 50 miles from the coast (figs. 

 2 and 3). 



J./ Data on the biomass of plankton in May- 

 June are cited on the basis of the report of 

 L. A. Ponomareva, who was in charge of plank- 

 ton collecting in 1953 aboard the researcli ship 

 Vitiaz . 



