tropical neritic communities, particularly in regions with strong upwelling 

 water, is the presence of common commercial fish, feeding on the phyto- 

 plankton (Heinrich, 1970; Rojas de Mendiola, 1969). Off the coast of 

 California, both in the distant neritic and in the neritic region, the 

 most important herbivore is the pelagic stage of the Decapoda Pleuroncodes 

 planipes (Longhurst, 1967). In the oceanic regions, there are no 

 herbivorous fish, and the food chains are long (Heinrich, 1962; Parin, 

 1968). 



5.2 Production Cycles 



The production cycles of communities are seen here as the relation- 

 ship between the seasonal cycles of the phytoplankton and mesozooplankton 

 and, as possibly, the higher trophic levels. Yu. I. Sorokin (see IV. 2) 

 assigns an extremely important role to bacteria, although his conclusions 

 are not universally accepted (Steemann Nielsen, 1972; Banse, 1974; 

 Skopintsev, 1972). Due to the lack of year-round observations of 

 bacteria and protozoa in the open ocean, their participation in the 

 production cycle will not be discussed in this book. 



Two extreme types of production cycles are theoretically possible: 

 balanced and unbalanced (Cushing, 1959a). In a balanced cycle, throughout 

 the year the daily grazing of live algae is equal to their net production. 

 Regulation is achieved through the relation of production and consumption 

 of algae, the rate of breeding and growth of herbivores and regeneration 

 of nutrients with an extremely short delay period between the beginning 

 of an increase in the quantity of algae and an increase in their con- 

 sumption. Similar dependencies occur at the higher trophic levels as 

 well, but the regulation of trophic relationships in nekton animals occurs 

 not so much through breeding as through migration. Stability of abiotic 

 conditions helps to maintain this type of cycle. In contrast to this, 

 with an unbalanced production cycle, the production of algae fluctuates 

 widely due to the effect of unstable abiotic conditions, herbivores 

 develop slowly. There is a long delay period, during which grazing 

 increases to match the increased production of algae; in some cases, 

 this occurs only after the algae reach their maximum quantity which is 

 possible given the reserve of nutrients available. The algae are under- 

 utilized for a long period of time. Cushing considered that these cycles 

 do not exist in nature in clear form, but that the tropical communities 

 located outside the regions of strong upwelling of water are closest to 

 the balanced cycles, while the cycles of communities in the temperate 

 and polar waters are closest to the unbalanced cycles. 



Factors in the seasonal development of plankton . The physical 

 factors which create instability in the production cycles of tropical 

 communities are primarily those which facilitate the seasonal develop- 

 ment of phytoplankton. 



In the high-latitude edges of central communities, they are close 

 to those in the boreal area. Thus, in the Sargasso Sea (see Fig. 21), 

 the peak of phytoplankton is formed in the spring, soon after stability 



116 



