Dissertation (Metadata)
Title:Trophic interactions in the pelagic
Author:Susanna Knotz
Faculty:Faculty of Mathematics and Natural Sciences
DDC:550 Earth sciences and geology
Date of thesis defense:2006-07-06
Referent:Prof. Dr. U. Sommer
second reviewer(s) :PD Dr. M. Boersma
Description: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.
Keywords:Nordsee ; Ruderfußkrebse ; Ernährung ; North Sea copepods, seston quality, digestive enzymes, C:N:P, protease isozymes, stable isotope ratios, elemental uptake, GLOBEC, grazing behaviour, Helgoland
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