estimated. A more precise estimate of the degree of balance is probably 

 impossible at present. 



The annual cycles in the relationships of herbivores and predators 

 in the tropical ocean regions are not nearly so well known. The micro- 

 nekton, including the animals caught by an Isaacs-Kidd trawl, in the 

 equatorial region of the Indian Ocean produce an annual maximum of 

 biomass after the maximum of mesoplankton. The highest correlation 

 coefficient between zooplankton and micronekton, i.e., small fishes and 

 squids, is obtained by comparison of samples collected at intervals of 

 6-12 weeks (Legand, 1969; Tranter, 1973). This is explained by the 

 longer development of the larger animals. However, in the central region, 

 and in some seasons also in the equatorial region, no such regularity is 

 observed. It is assumed that under these conditions the zooplankton 

 and micronekton are related to the mixing of waters of different origins. 

 The quantity of micronekton in these regions is more stable than the 

 quantity of zooplankton or the value of primary production. Here, 

 advection increases the stability in the interrelationships of the higher 

 levels of the trophic chain (Tranter, 1973). 



In the eastern Pacific (see Fig. 21), the amplitude of seasonal 

 fluctuations of fishes and squids is similar to that observed for algae 

 and zooplankton, but the maximum of their biomass occurs during the 

 period of the minimum of zooplankton, meaning that there is a delay of 

 four months when observations are made once each two months. The seasonal 

 changes of biomass of micronektonic crustaceans are statistically sig- 

 nificant only at the Equator; their maximum coincides with the maxima 

 of phytoplankton and zooplankton (Blackburn et al . , 1970). 



Thus, due to the longer period of development of micronekton, its 

 increase in quantity lags behind the increase in quantity of zooplankton 

 by 1.5-3 months, which introduces elements of instability to the balance 

 of production and consumption. Sometimes, the quantities equalize at 

 various times in the year due to advection, while in other cases advection, 

 probably, may lead to the opposite result. The amplitudes of fluctuations 

 of the quantity of micronektonic fishes and sauids are not great. In the 

 eastern Pacific, their quantity during the maximum is approximately 

 double that observed during the minimum, and their seasonal variability 

 in both communities of the Indian Ocean is still less (Blackburn et al . , 

 1970; Tranter, 1973). The fluctuations in the quantity of micronektonic 

 crustaceans in the eastern Pacific are quite small, with the exception of 

 the Equator, where the maximum is 15 times greater than the minimum 

 (Blackburn et al , , 1970). This has not as yet been explained. As we noted 

 earlier, this region is also distinguished by a unique composition of 

 plankton. 



Large nektonic animals (tuna, whales) in the Indian Ocean migrate to 

 the areas of seasonal concentration of micronekton, with which they are 

 connected primarily through the squids and certain fishes, immediately 

 before its maximum (Tranter, 1973). This increases the stability of the 

 trophic relationships. 



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