Depth, m 



500 



Numbcrv sp/ltl 



1500 2000 



200 



Biomass. mg/m 

 100 200 300 400 500 



Fig. 4. 



Vertical distribution ofmesozooplankton; (a) vertical distribution of 

 numbers: and (b) vertical distribution of biomass. 



of massive development of Euphausia similis \ar. "armatu" in 

 this area. Korshenkol 1988) notedasimilarca.se for a population 

 of E. similis. The same value (35.5% of total biomass) was 

 shown by the biomass fraction of Chaetognatha at specific 

 levels of the western portion of the section. A typical portrait 

 of the structure of the mesozooplankton community of the 

 region is shown in Fig. 6. 



The general pattern of variability of the vertical structure 

 had the following characteristics: both the numbers and biomass 

 of Calanoida, Decapoda. and Appendicularia and the biomass 

 fraction of Cyclopoida and Siphonophora decreased with depth. 

 The relative content of other groups (Harpacticoida. Amphipoda. 

 Euphausiasea, Ostracoda. Chaetognatha. Salpidae. Doliolidae. 

 Siphonophora. and Polychaeta) increased with depth. 



Conclusion 



/. The qualitative composition of the mesozooplankton 

 was nonuniform in the region studied. As one moved toward 

 the equator, species diversity of the zooplankton increased. 

 The smallest number of species was recorded in the region of 

 Caroline Atoll. In the majority of cases, the number of species 

 increased with depth. It was postulated that the heterogeneitv 

 of the horizontal and vertical distributions ofmesozooplankton 

 resulted from vertical daily migrations and equatorial ascents 

 of the water masses. 



Twenty-one species ofmesozooplankton reached numbers 

 above 100 sp/m': of these groups, the group of the most diverse 

 composition was Calanoida. The number of massive species 

 increased from east to west. 



220 



