@PhdThesis{diss_mods_00001922, author = {Knotz, Susanna}, title = {Trophic interactions in the pelagic}, year = {2007}, publisher = {Christian-Albrechts-Universit{\"a}t zu Kiel}, address = {Kiel}, keywords = {Nordsee; Ruderfu{\ss}krebse; Ern{\"a}hrung; North Sea copepods; seston quality; digestive enzymes; C:N:P; protease isozymes; stable isotope ratios; elemental uptake; GLOBEC; grazing behaviour; Helgoland}, abstract = {Physiological and nutritional factors that influence the population dynamics of North Sea copepods were identified. Five digestive enzymes were measured in individual copepods. Short-term starvation elicited complex enzyme reactions. Protease isozyme patterns did not change. Seston C:N and POP:TPP correlated with reproductive success. Grazing behaviour and digestive system mediated the effect. Copepods took up N:P in ratios matching their body ratios. C:N and POP ingestion followed the seston pattern. Compensatory feeding was observed. Food quality and stable isotope signatures changed over time (Helgoland, 2004-2005) and between GLOBEC-stations (southern North Sea). Seston d15N and d13C revealed major composition shifts in spring and a strong heterotroph component in summer. A. clausi and T. longicornis utilised different carbon sources despite similar high trophic levels. A low seston d13C (spring) was favourable. Chitobiase activity indicated C assimilation, the other enzymes N assimilation. A low body d13C may denote high turnover rates. Combining methods explains zooplankton- phytoplankton interactions better than only one approach.}, url = {https://macau.uni-kiel.de/receive/diss_mods_00001922}, file = {:https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00001922/d1922.pdf:PDF}, language = {en} }