Trophic Significance of Populations

Anchovy, sprat and horse-mackerel eat plankton, so it is possible to define the role they play in the food web of the Black Sea. It is most important to find out the extent to which they use food reserves, and contribute to the transformation and cycle of matter and energy in the ecosystem. 

The close relationship between the level of lipid deposition in planktonivorous fish and the condition of their nutritive base provides indirect evidence of severe food competition, as noted in Chapter 6. 

A useful concept with which to describe the interrelations between trophic levels in an ecosystem is the efficiency of food utilization. Until now we have mostly used the coefficient but now the coefficient AT, is needed to examine 

Of especial interest is the proportion of energy used by populations for different kinds of metabolism. Active fish consume about 50% of the metabolic energy for swimming, 17-18% for feeding (food consumption and assimilation) and 13% for basal metabolism. All in all, the sum of the energy used for these different purposes exceeds considerably the energy used for construction. 

The energy budget is distributed somewhat differently in less active species. In red mullet and pickerel, which can be defined as moderately active fish, the energy from food is divided nearly equally between basal and active metabolism (30-35%) while feeding metabolism demands only 13-15%. However, the metabolic energy expenditure still exceeds that used for synthesis, although the latter is several times as great as in the most active fish. 

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