ENERGY RESERVE LIPIDS OF ZOOPLANKTONIC CRUSTACEANS FROM ON OLIGOTROPHIC SALINE LAKE IN RELATION TO FOOD RESOURCES AND TEMPERATURE

In three zooplankton species examined over a 2-yr period in an oligotrophic saline (22 g . L-1) lake, triacylglycerols (energy reserve lipids were the most abundant lipid class followed by phospholipids and sterols. Marked seasonal differences in patterns of total and energy reserve lipid content in the herbivorous calanoid Leptodiaptomus sicilis were correlated with temporal patterns in edible algal biomass and temperature. The appearance of particular algal species, or groups of similar-sized species, occurred synchronously with changes in lipid content of both L. sicilis and Daphnia pulex. These periods of changing lipid content were used to infer nutritional suitability or inadequacy (unavailability) of specific algae for wild populations ot zooplankton. Energy transfer from phytoplankton to the carnivorous calanoid Hesperodiaptomus nevadensis through L. sicilis involved a time lag of approximately 1-2 mo; this was hypothesized to result from a feeding dependency on L. sicilis copepodites due to a gape limitation of the predator. Demographics of D. pulex in this lake were unusual because the species was consistently absent during spring. In addition, total lipids and triacylglycerols were low (< 15% and < 4.5 mug . animal-1, respectively), suggesting that D. pulex had been pushed into a subsistence niche by the rising salinity levels.