Dietary effects on reproductive traits, development, and fatty acids in cladocerans and calanoid copepods

Herbivorous zooplankton play an important role in pelagic systems as grazers of phytoplankton and as a food source for higher trophic levels. In freshwater lakes, cladocerans and calanoid copepods are the most important pelagic herbivores, both in terms of numbers and grazing impact. Although much has been learned over the past two decades about the dietary requirements of freshwater zooplankton in terms of quantity and qualitative composition, recent comparative studies of zooplankton and their diets have yielded contrasting results in terms of dietary dependence, demonstrating that the often-repeated principle "you are what you eat" seems to apply only in part. Here we used a fatty acid approach to investigate different diets and their effects on reproductive and life-history responses in both Daphnia longispina and Eudiaptomus graciloides. Dietary fatty acid composition was generally reflected in consumer tissues in both grazers, and the nutritional quality of the diet affected zooplankton fitness and reproductive success differently depending on grazer feeding mode. However, a differential accumulation of PUFAs was observed between cladocerans and calanoid copepods, and mismatches in some fatty acids suggested a possible enzymatic modification of dietary fatty acids adopted to cope biochemical deficiencies of the diets. As the ability of freshwater zooplankton to synthesise and/or biochemically convert FAs is still unresolved and highly controversial, the integration of different approaches and zooplankton dietary information is needed to improve our understanding of the feeding ecology of freshwater zooplankton and how this affects trophic interactions and plankton dynamics under changing environmental conditions and resource availability