3. Nontrophic Regulatory Interactions of Marine Invertebrates . 

 (E. A. Zel ickman) 



3.1 Metabolic Regulation 



Chemical communication is the most ancient of all systems of exchange 

 of information between organisms and, correspondingly, of regulation of 

 intrapolation and intraspeci fie relationships. The chemical substances 

 excreted by plants and animals into the water are elements which communi- 

 cate and regulate the activity of the community, modifying the numbers of 

 individuals of the species. They may be attractants, repellents, may 

 facilitate the development of certain species and suppress others, etc. 

 These allelopathic relationships are well known in continental phytocenoses , 

 vertebrates and insects as well. The species-specificity of metabolic 

 signals in certain cases has been experimentally proven. Lukas (1954) 

 referred to this type of relationship as nonpredatory ecologic connection. 

 These connections are achieved by chemical agents with a broad spectrum of 

 action which, after they are liberated into the water, become an environ- 

 mental factor for the organisms in the community. Exocrines may be products 

 of excretion or of decomposition of organisms. 



Some marine bacteria excrete metabolites which are toxic for algae, thus 

 changing the population of the latter (Berland et al . , 1972), In water rich 

 in diatoms, the population of blue-green algae will not be great (Marumo, 

 Asaoka, 1974). The excreted metabolites can be considered for neighboring 

 organisms a method of adaptation to the interrelationships in the community. 

 This type of metabolic interaction relates the population of the diatom 

 Skeletonema costatum and the flagellate 1 isthodiscus luteus (Pratt, 1966). 

 In a medium favorable for both species, they cannot achieve simultaneous 

 abundance. The advantage will go to that species, the cells of which begin 

 intensive division with larger numbers or at a younger phase of the 

 population. The substance excreted by the flagellates simulates cell 

 division of the Skeletonema in a rarefied culture of diatoms, and depresses 

 cell division in a compact culture. In a community, these species have 

 different survival strategies, which can be interpreted as behavior in 

 the broadest sense: The diatom must "try" to begin its first division 

 with a large number of cells; the flagellate conducts "chemical warfare" 

 with it. The Skeletonema may suppress (or stimulate) the growth of 

 bacterial cells as well (Be et al . , 1974). 



Suppression of a competing species by means of "chemical weapons" is 

 a common occurrence in the sea. When the hydroids Hydractinia e chinata 

 and P odocoryne carnea are simultaneously cultivated, their stolons never 

 interweave, and after a certain period of time, P odocoryne completely 

 suppresses the growth of Hydractinia (Gallien, Govaere, 1974). The same 

 type of interaction, but intraspecific, may regulate the number of individ- 

 uals in clusters of the hydromedusa Tiaropsis multicirrata (Zelickman, 1969; 

 Zel ickman et al., 1969). 



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