Stoichiometric constraints in primary producers affect secondary consumers

• Main Author: Schoo, Katherina
• Format: Thesis
• Language: English
• Published: 2010
• Subjects: European lobster; Homarus gammarus; Copepods
• Online Access: https://oceanrep.geomar.de/id/eprint/10555/; https://oceanrep.geomar.de/id/eprint/10555/1/Schoo_KL_Dissertation.pdf; https://macau.uni-kiel.de/receive/diss_mods_00005178

This thesis investigates the effects of nutrient limitation in primary producers on higher trophic levels. To this aim the nutrient conditions and their effect on primary consumers in the North Sea were examined. Furthermore experiments were carried out to test the effect of nutrient limitations on tri-trophic food chains in controlled laboratory conditions. Despite the prevailing assumption that the herbivorous primary producers maintain strict homeostasis, thus buffering any nutrient imbalances at the base of the food web and providing their consumers with food of a high and constant quality, their nutrient stoichiometry and fitness was affected by the nutrient content of their food. The nutrient deficiency of the primary producers can thus be passed on through the food web and affect higher trophic levels. In a set of laboratory based experiments the nutrient contents of primary producers was manipulated to change their C:nutrient ratio and thereby their food quality. Primary consumers were reared on these producers and in turn were the food source for a higher consumer. The ctenophore Pleurobrachia pileus was exposed to copepods with manipulated C:P ratios along a gradient. The reaction of the ctenophore to food with a high C:P ratio, generally considered to be food of lower quality, was unexpected. P. pileus was negatively affected by nutrient replete food with a low C:P ratio and displayed higher levels of fitness when feeding on food with a high carbon:P ratio. This ctenophore is therefore more likely to be energy limited than nutrient limited. A possible explanation for this is the high body C:P ratio observed in P.pileus. The results are discussed in light of possible future scenarios in the aquatic environment. Freshly hatched larvae are very vulnerable and the mortality during this stage is particularly high. Therefore the effect of food with different C:N:P ratios was tested on larvae of the European lobster Homarus gammarus. Larvae were exposed to food with varying nutrient content either throughout ...