In the neritic regions, the factors in the seasonal development of 

 phytoplankton include everything which facilitates enrichment of the 

 euphotic zone with nutrients (Heinrich, 1961a, b; Sournia, 1969; 

 Khromov, 1973). Nutrients arrive either from the deeper layers of water 

 or from the land. Therefore, the wind regime mixing the water, driving 

 it away and thereby facilitating upwelling of water, and the regime of 

 precipitation, bringing mineral salts from the land, are both important. 

 However, the seasonal changes in phytoplankton are not the same in all 

 the neritic tropical regions. Local peculiarities change the climatic 

 effects so strongly that even in closely located sections, the seasonal 

 Cycle of development of phytoplankton may be quite different (Sournia, 

 1969; Motoda, Marumo, 1963). In particular, this cycle is influenced 

 by the degree of unevenness of the shoreline, the proximity of estuaries, 

 etc. The earlier assumed (Bogorov, 1941) monocyclic development of 

 phytoplankton in the tropical drea, with a winter peak, may be character- 

 istic only of the marginal high-latitude regions. 



Peculiarities of production cycles in the main types of tropical 

 communities . Rather complete studies of production cycles of oceanic 

 communities, with observations over the course of a year or more, have 

 been conducted in the regions shown in Fig. 21. The section in the 

 Indian Ocean is located in a distant neritic region, but the composition 

 of the zooplankton during the period of the survey was typical for oceanic 

 regions. Apparently, the course of seasonal phenomena in the southern 

 portion of the section is characteristic for the central community, 

 while in the northern portion it is close to that of an equatorial community, 

 The survey in the Pacific Ocean combines equatorial oceanic and distant 

 neritic sections, which probably differ little from each other in their 

 seasonal cycles far from the coast. Unfortunately, materials have been 

 collected and processed in different regions by different methods and, 

 except for the stations in the Sargasso Sea and the section in the Indian 

 Ocean, the intervals between subsequent observations are longer than a 

 month. In the Guinea Bay, the annual cycle of plankton has been composed, 

 based on data for several years, with observations in any given year 

 lasting only two or three months. 



The similarity of a production cycle to any given type can be 

 determined directly by comparing the rates of production and consumption 

 over the course of a year, or indirectly, by keeping in mind the amplitudes 

 of fluctuation of biomass of the various trophic levels, the duration of 

 the delay of consumption, the ratio between the biomass of food organisms 

 and the organisms which feed upon them. Both methods yield only approxi- 

 mate descriptions of a cycle. 



The production cycles of oceanic tropical communities are more nearly 

 balanced than the others. For example, in the Sargasso Sea, the Indian 

 Ocean (cross section along 110°E) and in the Central Pacific, the 

 quantity of nutrients, phytoplankton and zooplankton is low and stable 

 throughout the year (Steemann Nielsen, 1958; Gushing, 1959a, b; Menzel , 

 Ryther, 1961; Tranter, 1973; King, Hida, 1957; Blackburn et al . , 1970). 



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