Influence of sestonic elemental and essential fatty acid contents in a eutrophic reservoir in Siberia on population growth of Daphnia (longispina group)

Dependence of specific integral population growth rate or specific production rate of populations with random size and age structure on elemental and essential fatty acid composition of natural seston was studied in a laboratory flow-through system using a multiple regression. Under a comparatively high content of particulate phosphorus (P), the best single predictor of the growth appeared to be content of eicosapentaenoic acid (EPA, 20:5 omega 3), as it was found earlier for somatic growth of even-aged populations of Daphnia. Regression equation with two independent variables, EPA and particulate nitrogen (N), gave a significantly better fit for the population growth as the dependent variable than the equation with EPA as the single independent variable. Interestingly, there was no significant correlation between N as the single variable and the growth. The essential omega 3 fatty acid and N appeared to be complementary indicators of the food quality, which probably limited different constituents (reproductive and somatic) of the integral population growth under the high content of particulate P.