On the Vertical Distribution of Copepods 

 in the Northwestern Pacific Ocean* 



By 



K. A. Brodskii 



In the northwestern part of the Pacific 

 Ocean southeast of Kamchatka the following 

 plankton collections were made: one vertical 

 haul from a depth of 4,000 meters, with a net 

 having an opening 100 cm. in diameter, and 

 seven horizontal hauls with a Juday net made 

 of No. 38 bolting cloth. 



The results of the analysis of the vertical 

 haul samples are presented in another paper of 

 ours in this same collection, and we will here 

 explain the results obtained from the horizontal 

 hauls. 



As we pointed out in the paper referred to 

 above, there was no information in the litera- 

 ture about the zooplankton of the northwestern 

 Pacific Ocean, neither about its composition 

 nor about its vertical distribution. Here we 

 limit ourselves only to data on the vertical dis- 

 tribution of the copepods, not bringing in any 

 materials on the specific analysis, which is 

 adequately treated in the paper referred to 

 above. 



The horizontal plankton collections were 

 made in the daytime with a Juday net, having 

 an intake opening 37 cm. in diameter, at the 

 following levels: 1,000-500, 500-200, 200-100, 

 100-50, 50-25, and 25-0 m. The processing of 

 the samples was done by counting the number of 

 organisms in acounting chamber under abinoc- 

 ular microscope and then converting the figures 

 to correspond to 1 m. ^. When the quantity of 

 specimens of a species was insignificant, the 

 transformation to 1 m. ^ was not made, and in 

 table 1, given below, the number of specimens 

 in the whole sample is given. For greater 

 quantities the figures are given for 1 m. -^ 

 (underlined figures) on the basis of a calcula- 

 tion from a counting chamber. If two figures 

 are given, the first is the result found in the 

 general examination of the whole sample, and 

 the second is the calculation from the counting 

 chamber. 



♦ From Investigations of the Far Eastern 

 Seas of the USSR. III. Deep-water Fauna of 

 the Northwestern Pacific Ocean, p. 88-94. 

 Zoological Institute, Acadenny of Sciences of 

 the USSR, 1952. 



The material in the table makes it 

 possible to divide the genera of Calanoida into 

 groups in relation to their vertical distribution, 

 that is, to separate out those which are not rep- 

 resented by a single species at depths less than 

 1, 000 meters and which are encountered only 

 below that level. To this group belong the 

 following genera: 



Bathycalanus 

 Drepanopsis 

 Aetideopsis 

 Chiridiella 



Valdiviella 



Temorites 



Xanthocalanus Augaptilus 

 Mixtocalanus Euaugaptilus 

 Cornucalanus Neoaugaptilus 

 Bathypontia 



Batheuchaeta Lophothrix 



Pseudochirella Amallothrix 



It is necessary to emphasize that the 

 vertical distribution varies depending on the 

 area. Many genera which appear only as deep- 

 water forms in the area under consideration 

 are in other regions, for example in the Arctic 

 Ocean (Temorites and Augaptilus), represented 

 by species which are encountered at slight 

 depths o r even in the surface waters. This 

 phenomenon is related to temperature conditions 

 and confirms the general rule of the ascent into 

 the surface layers in the Arctic region of the 

 abyssal species and genera of the temperate 

 and tropical parts of the World Ocean. 



To the other group we assign those genera, 

 species of which are encountered above as well 

 as below the 1, 000-m. level (table 2). 



According to the data in the table, the 

 genera Pareuchaeta, Scaphocalanus, and par- 

 ticularly Lucicutia should be regarded as pri- 

 marily abyssal genera, inasmuch as fewer 

 species of these genera are encountered above 

 1, 000 m. than in the deeper layers. 



Certainly it is very difficult to give a 

 general characterization of a genus, including, 

 in the whole, species with differing ecological 

 peculiarities, and it is probably nnore expedient 

 to distinguish within the limits of the genus indi- 

 vidual ecological groups which are differentiated 

 in terms of their vertical distribution. For ex- 

 ample, in the genus Metridia, along with three 

 typically abyssal species, there are two which 

 should be assigned to the bathypelagic group 

 (M. pacifica and M. okhotensis), while in the 

 genus Pareuchaeta only two species can be 

 counted in this group (P. japonicaand, probably, 

 P. birostrata). The genus Lucicutia is un- 

 doubtedly typically abyssal, for of seven species 

 only one appears as shallow as the 200-500-m. 

 level, while with Pareuchaeta japonica the young 

 stages are encountered in significant quantities 

 up to the shallowest level sannpled (0-25 m. ). 



