Gymnoplea decreases, while Podoplea, Ostracoda, Tunicata, Polychaeta, 

 Coelenterata and Chaetognatha increase. Thus, due to the greater relative 

 quantity of Polychaeta, Chaetognatha and Coelenterata, the significance 

 of predators increases. Furthermore, there are many more predators 

 among the Gymnoplea (Heinrich, 1951b, 1968; Timonin, 1969, 1973; Bsharah, 

 1957; Deevey, 1971; Grice, Hart, 1962; Gordeeva, Shmeleva, 1971; Greze, 

 1971). 



In tropical plankton, in contrast to boreal plankton, a single 

 function in the food chain is distributed more evenly among various 

 taxonomic groups. One good example of the composition of tropical 

 plankton is its composition in the western Pacific in the section along 

 174°W between 30°N and 30°S. The copepods average about half of the 

 biomass of zooplankton, 2/3 of them being Gymnoplea. About 20% of the 

 biomass is accounted for by the Ostracoda, about the same amount by the 

 Chaetognatha, 10°^ by the Coelenterata and Polychaeta, while the Tunicata 

 account for a small amount. 



Changes in the number, size and, therefore, biomass of the various 

 groups are found along the meridian (Heinrich, 1968). The quantities of 

 many animals (Radiolaria, Foraminifera, Coelenterata, Copepoda, Gastropoda, 

 Chaetognatha) more or less regularly increase in the equitorial region, 

 but the Ostracoda, Amphipoda and Salpidae, conversely, are more abundant 

 in the central regions. In the equatorial region, the biomass of Copepoda 

 amounts to 55-75%, in the central regions--35-50% of the total biomass 

 of zooplankton, the relative quantity of Ostracoda increasing from 10% 

 in the equatorial region to approximately 20% in the central regions. The 

 share of the Salpidae in the total biomass increases toward the periphery 

 of the tropical area. 



In the Indian Ocean, primarily within the eutrophic equatorial 

 community, the composition of plankton depends on water regime (Timonin, 

 1969, 1973). In regions with upwelling of water, Gymnoplea account for 

 70% of the biomass, in regions with stable water stratification--only 40%. 

 The Chaetognatha are relatively scarce (less than 10%) under conditions 

 of upwelling of water, more numerous (12-27%) under stable stratification 

 or with weaker upwelling of the water. The details of the trophic 

 structure also change. In regions of intensive upwelling of water with 

 high biomass of zooplankton and relatively large numbers of Copepoda, 

 filter feeders predominate (over 50% of the total biomass of zooplankton), 

 among these about 90% being coarse filter feeders. Seizing and swallowing 

 predators make up 20-25% of the total. With weak upwelling of water, the 

 filter feeders are fewer (40%), and half of them are fine filter feeders. 

 Seizing and swallowing predators amount to 30-35% of the total. When there 

 is no upwelling of water, with low zooplankton biomass, filter feeders 

 represent still less (20-30%), while the number of seizing and swallowing 

 predators increases to 45%. 



Similar results were obtained in the Bay of Guinea in a study of the 

 relationship of trophic groups among Copepoda in various seasons (Samyshev, 

 1973) and in the Sargasso Sea, where, during a short period of upwelling 

 of water, a sharp peak was observed in the abundance of the coarse 

 filter feeder Eucalanus h yalinus , while throughout the rest of the year, 

 various species of fine filter feeders predominate (Deevey, 1971; Grice, 

 Hart, 1962). 



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