Linking phytoplankton biodiversity and food quality effects in herbivore zooplankton

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The objective of the submitted project is to integrate biodiversity effects into food quality research in order to understand responses of aquatic consumers to changing environmental conditions and accompanied changes in species richness. We aim to reveal beneficial or detrimental effects of phytoplankton diversity on life history traits of aquatic consumers by considering morphological, elemental and biochemical properties of the phytoplankton prey, using the freshwater keystone herbivore Daphnia as model organism. This includes the need of a better understanding of (A) how heterogeneity in food quality (morphology and bio/chemical composition) is linked to prey diversity, and (B) how heterogeneity in food quality is generated by interactions among phytoplankton species growing in differently diverse communities. We approach this by unraveling (I) the behavioural and physiological response of Daphnia (i.e., ingestion, digestion, assimilation, respiration, excretion, production, and reproduction) to different prey species richness levels, and (II) the role of morphological, elemental and biochemical properties of phytoplankton, which originates from a more diverse community composition, in triggering possible effects of higher prey diversity on Daphnia performance. This demands knowledge of the variation and species-specific adjustments in morphological, elemental and biochemical properties of phytoplankton interacting in differently diverse communities. Furthermore, we focus on changes in environmental factors such as light and nutrient availability that may affect the phytoplankton diversity. We address our aims by using laboratory experiments. Studying the above described mechanisms will lead to a better mechanistic understanding of the consequences associated with chances in phytoplankton diversity for the performance of aquatic consumers. We will gain insights on the origin of heterogeneity in the phytoplankton (primary producers) community and will enhance our knowledge on processes involved in changes in the bioavailability of essential bio/chemicals. The results will improve our ability to understand responses of important aquatic consumers to changing environmental conditions and accompanied changes in species richness. Further it will help to enable the establishment of predictive frameworks for biochemical limitations induced by deficiencies in fatty acids and sterols. These frameworks will specifically consider the biochemical heterogeneity in trophic interactions between primary producers and consumers.