links in the chain--fish, cephalopods, and aquatic mammals, which are of 

 the greatest interest from the standpoint of their utilization. 



Let us analyze some other approaches to the construction of 

 simulation models of pelagic ecosystems. 



1.3. Model Considering the Distribution of Elements by Area 



The modelling of changes in the pelagic ecosystem not in depth, as 

 was done in the previous section, but rather over the area of a body of 

 water, can serve as another approximation of reality. This approach is 

 particularly important for water areas with a complex system of surface 

 currents and various faunistic groups in the plankton. 



The prototype for the creation of a model considering the 

 distribution of elements over a water area (Menshutkin et al . , 1974) was 

 the Sea of Japan, in which, due to the sparsity of shallow zones, we can 

 separate the open part of the sea as an independent pelagic ecosystem. 

 The strong but inconstant flow of water through Tsushima Strait creates 

 significant horizontal heterogeneities, justifying the model type 

 selected. In addition to the passive transfer of hydrobionts with the 

 current, nektonic animals actively migrate through Tsushima Strait-- 

 squid and fish--entering the Sea of Japan in the spring and summer and 

 leaving it in the winter. 



To make the model more concrete, ecologic-faunistic characteristics 

 of the plankton of the Sea of Japan and data on the trophic 

 relationships among the primary groups of its population, obtained 

 during the 52nd cruise of the VITYAZ' and a number of shoreline 

 expeditions, were used (Pasternak, Sushkina, 1973; Sushkina, 1972). 



In constructing the model, the entire water area of the sea was 

 divided into squares 150 km on a side. Each square corresponds to an 

 elementary cell of the ecosystem, in which the volume of water down to a 

 depth of 200 m is studied. Within each cell, the heterogeneities of 

 horizontal distribution of abiotic and biotic elements are assumed to be 

 insignificant. 



The transfer of dissolved matter or suspended particles of 

 detritus, phytoplankton and zooplankton from one cell into another 

 results from the currents. A diagram of the currents presented by I. V. 

 Sizova (1961) was accepted, with the loss of detail resulting from the 

 size of the cells. Seasonal changes in the speed of the Tsushima 

 Current, following S. Nishimura (1969), were considered sinusoidal with 

 a maximum in September. The effective temperature (mean water 

 temperature at which the population of a given species finds itself in a 

 given cell) was assumed to be a function of time and the coordinates of 

 the cell, while the temperature field was taken from S. Nishimura 

 (1969). 



Each cell of the model of the ecosystem contained twelve elements 

 (Fig. 6). The group of inanimate elements was represented by the 

 concentrations of nutrients (n) and detritus (d). Plankton was divided 



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