been created. The first model, widely used in planktonology, is based on 

 the trophodynamic aspect of an ecosystem ("the Lindeman approach"). It 

 looks upon a community as a system of organisms at various trophic levels, 

 related primarily by predator-prey relationships, i.e., "strong relation- 

 ships"--by analogy with physical phenomena in the microcosm (MacArthur, 

 1972). This aspect of a community is the basis of many models of eco- 

 systems, beginning with the classic approach of Lotka and Volterra and 

 extending to quite modern works. 



The second model, more widespread among researchers studying benthic 

 fauna, concentrates attention on the organisms of a single trophic level 

 and their interactions. For simplicity, it is assumed that migrating 

 organisms are not included in the biocenosis (Thorson, 1957; and others). 

 This means that predators which enter a given biocenosis only to feed are 

 practically not studied. If we consider that most of the floor of the 

 seas and oceans lies below the zone of habitation of producers, it can 

 be stated that a typical benthic biocenosis is populated primarily by 

 consumers of detritus. 



The interrelationship of species in both models, naturally, is 

 studied on the basis of the same primary postulates of ecologic science-- 

 Elton's theory of the ecologic niche and the law of competitive exclusion 

 of Volterra and Gause. The stability of the "vertical" model requires 

 maximization and stabilization of relationships between species, since 

 these species are of different trophic levels, while stability of the 

 "horizontal" model requires minimization of species relationships, i.e., 

 the greatest possible separation of niches. 



The most important processes in marine biology in recent years have 

 been related to reconsideration of these traditional models of ecosystems. 

 In planktonology, works have been extensively developed on the study of 

 "nonpredatory" ecologic relationships, primarily the interrelationships 

 between organisms mediated by external metabolites (Johnston, 1955; Lucas, 

 1955, 1965; Provasoli, 1958; and many others), developing in the study of 

 the ecologic metabolism of the sea (Khaylov, 1971). It has become clear 

 that exocrines and dissolved organic matter bind the producers, consumers, 

 predators and reducers into a single network, which corresponds more 

 closely to the actual picture of a conmunity than a network based only 

 on trophic relationships. The role of external metabolites is varied: They 

 act as food (dissolved organic matter), sources of indispensable substances 

 (vitamins, particularly Bi2» trace elements, vital amino acids), as sub- 

 stances which suppress the growth of competing organisms, as signalling 

 substances, etc. Consideration of this type of relationships between 

 species can answer many curious questions in the ecology of marine communi- 

 ties. For example, the differing demand for external metabolites such as 

 growth substances and vitamins, the capability of a species to grow with a 

 lower concentration of these substances, may be one of the factors involved 

 in specialization of species of phytoplankton and one explanation of the 

 "plankton paradox" (Hutchinson, 1961)--the coexistence of phytoplankton 

 species with similar demands for the primary biogenes, which should, 

 therefore, be in acute competition. Furthermore, if any organism requires 



