Seasonal changes in particulate and dissolved lipids in a eutrophic prairie lake

1. Critical periods of Lipid energy transfer from phyto-to zooplankton were inferred by comparing seasonal patterns of particulate and dissolved lipid fractions in lake water with temporal changes in Lipid energy reserves of the zooplankton in a hypereutrophic lake. 2. The midsummer phytoplankton community was dominated by the bloom-forming cyanobacterium Aphanizomenon flos-aquae. The collapse of the bloom was accompanied by a 2-week period of severe nitrogen deficiency after which there was a marked increase in the concentration of lipid energy reserves in the particulate (algal) fraction. 3. Areal lipid energy reserves of the dominant herbivorous zooplankton responded positively to changes in the tri- and diacylglycerol content of the particulate fraction of lake water in a species-specific manner. 4. Bacterial numbers also peaked in September concomitant with a large increase in free fatty acids in the dissolved lipid fraction probably produced by the decay of the A. flos-aquae bloom. 5. The association between periods of nitrogen deficiency and increased energy reserve lipids in the particulate fraction supports observations made with laboratory algal cultures that periods of nutrient deficiency may intensify lipid synthesis in some algal species, thereby enhancing the rate of lipid energy transfer from phytoplankton to zooplankton.