Interplay between energy, mineral and biochemical constraints of herbivores in the pelagic food web of Lake Constance
Final Report Abstract
Understanding trophic interactions and food web regulation and their response to anthropogenetically altered nutrient and climate conditions demands information on the food quantity and quality available for consumers. Recent studies suggest that the ratio between carbon (C, surrogate for energy) and essential nutrients, e.g. phosphorus (P) but also biochemicals such as polyunsaturated fatty acids determines the food quality of primary producers for consumers. We combined already available comprehensive long-term data on plankton abundance of the pelagic food web and environmental factors (light, temperature, mineral nutrients) of Lake Constance and combined these (1) with laboratory measurements of fatty acid and sterol contents of major algal species, which were grown under different combinations of nutrient-, light- and temperature-regimes, and (2) with measurements of C, P and fatty acid concentrations in different plankton size fractions of Lake Constance. The laboratory experiments allowed us to identify interactive effects of several environmental factors on the fatty acid and sterol composition of the phytoplankton, which were to some extent speciesspecific. The field measurements of fatty acids and environmental factors (light, temperature) combined with taxonomic species identification enabled us to establish a reliable statistical model for the prediction of fatty acid concentrations in the lake. Our results from a further experimental test clearly indicate that shifts in limitations of consumers such as daphnids have occurred during both (a) the long-term oligotrophication process and (b) the season in Lake Constance. In detail we found evidence that a simultaneous limitation by food quantity (C) and quality (by alpha-linolenic acid, ALA) in the year 1997 was replaced by a complex multiple nutrient limitation mediated by food quantity, phosphorus, ALA and eicosapentaenoic acid in the year 2008. The results help to understand the response of individual plankton groups and the entire food web to the past decades, and to predict future reactions to altered nutrient and climate conditions.
Publications
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(2010). Simultaneous effects of light intensity and phosphorus supply on the sterol content of phytoplankton. PloS one 5: e15828
Piepho, M., D. Martin-Creuzburg, and A. Wacker
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(2011). Interactions between P-limitation and different C conditions on the fatty acid composition of an extremophile microalga. Extremophiles 15: 597-609
Spijkerman, E., and A. Wacker
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(2012) Oligotrophication of a large, deep lake alters food quantity and quality constraints at the primary producer-consumer interface. Oikos 121: 1702–1712
Hartwich, M., D. Martin-Creuzburg, K. O. Rothhaupt, and A. Wacker
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(2012) Use of ciliate and phytoplankton taxonomic composition for the estimation of eicosapentaenoic acid concentration in lakes. Freshwater Biology, 57: 1385-1398
Hartwich, M., D. Straile, U. Gaedke, and A. Wacker
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(2012). Phytoplankton sterol contents vary with temperature, phosphorus and silicate supply: a study on three freshwater species. European Journal of Phycology 47: 138-145
Piepho, M., D. Martin-Creuzburg, and A. Wacker
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(2012). Species-specific variation in fatty acid concentrations of four phytoplankton species: Does phosphorus supply influence the effect of light intensity or temperature? Journal of Phycology, 48: 64-73
Piepho, M., M. T. Arts, and A. Wacker
