Figure 2. --Distribution of the biomass of the seston in the 

 0-100 m. layer in May-June 1953 (composed by L. A. 

 Ponomareva). 1 - less than 500 mg. /nn. ; 2. - 500 to 

 1, 000 mg. /m.^; 3 - more than 1, 000 mg. /m.^. 



many representatives of warm-water neritic 

 plankton. The latter makes possible the rich 

 development of life in the warm waters lying 

 from 3&^N. latitude to the Lesser Kuriles chain. 



The transition from the boreal region to the 

 warm waters of the Kuroshio is characterized 

 by a sharp drop in the plankton biomass. In the 

 waters of the Kuroshio it is everywhere less 

 than 100 (and usually 50) mg. /m.^. 



With the comparatively snnall nets (0. 1 and 

 0.5 m. ) adopted by us for the collection of 

 plankton it was not possible to capture adequate- 

 ly the rapidly moving forms of the macroplank- 

 ton (large amphipods, euphausiids); therefore 

 we cannot adduce reliable quantitative data on 

 their distribution. We point out only the pre- 

 dominance in the boreal zone of, among the 

 euphausiids, Euphausia pacifica, which forms, 

 according to a communication from M.M. 

 Sleptsov (1955), colossal aggregations (at the 

 very surface of the water), Thisanoessa inermis, 

 T_. longipes , and in the coastal area T. rashii; 

 among the amphipods Parathemisto japonica 

 and, in the deeper layers, Cyphocaris challengeri. 

 In the Kurile Islands and at the southern tip of 

 Kamchatka, in the zones of exit of the cold 

 waters, large Parathemisto libeUula are en- 

 countered. The distribution of the large Cope- 

 poda which compose the overwhelming mass of 

 the plankton in the waters of the boreal zone ac- 

 tually forms the same picture of the distribution 



of the plankton biomass that we looked at above. 

 The greatest quantity of large Copepoda is 

 spread in a broad band running along the Kurile 

 Islands at a distance from the coast of 40-50 

 miles o r somewhat nearer. Farther out the 

 quantity dinninishes, but in some sections which 

 are under the action of waters from the Bering 

 Sea it may again increase. 



As an example let us look at the distribution 

 of one of the leading species of the boreal plank- 

 ton, Calanus cristatus. In waters with a cold 

 intermediate layer, so characteristic of the 

 Okhotsk and Bering seas and the waters of the 

 Kurile-Kamchatka Trench, C. cristatus is 

 present in the greatest quantity in the 25-50 m. 

 layer, and is scarcer at 50-100 m. In the cold 

 intermediate layer the quantity of the crustacean 

 diminishes sharply, and often it is entirely 

 absent. From a depth of 200 m. the quantity of 

 C. cristatus again increases. 



South of the moderate region, where there 

 is no cold intermediate layer and the water 

 temperature decreases evenly with depth, the 

 vertical distribution of C. cristatus has a dif- 

 ferent character: this organism is completely 

 absent in the warmed surface waters to a depth 

 of 25-50 m. , but below 50 m. , and especially 

 below 100 m. , it inhabits the whole layer of 

 water, and its biomass is never minimal in the 

 100-200 m. layer. 



10 



