The microzooplankton community during winter in NE Atlantic waters and its potential impact on condition and growth of larval Atlantic herring (Clupea harengus)

• Main Author: Bils, Franziska
• Other Authors: Peck, Myron A. (Prof. Dr.)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky 2017
• Subjects: Mikrozooplankton; Herbstlaichender Hering; Protozooplankton-Ichthyoplankton Link; Fischlarven; Nord-Ost Atlantik; microzooplankton; autumn-spawning herring; larval fish; North-East Atlantic; 570 Biowissenschaften; Biologie; 42.70 Protozoa; 42.81 Pisces; 42.90 Ökologie: Allgemeines; 42.94 Meeresbiologie; ddc:570; Atlantik; North East Atlantic; Copepods
• Online Access: http://nbn-resolving.de/urn:nbn:de:gbv:18-90034; https://ediss.sub.uni-hamburg.de/handle/ediss/7570

Microzooplankton is the planktonic size fraction between 20 and 200 μm consisting of unicellular (protozooplankton) and metazoan organisms, such as the early life stages of copepods and other invertebrate larvae. Protozooplankton (PZP) is a key player in the marine carbon cycle as part of the so-called microbial loop. Within the microbial loop, carbon is recycled through a “bacteria - small phytoplankton - PZP – loop” back into the classical food chain. During periods of low productivity, such as the winter in the NE Atlantic, more carbon is cycled via the microbial loop compared to the classical, linear food chain. While future scenarios predict more beneficial conditions for small-sized cells and, hence, a larger contribution of microbial loop dynamics, it is important to investigate trophodynamics occurring within these planktonic size fractions. For instance, PZP as well as metazoan microzooplankton, serve as a food source for early life stages of fish. Despite the recognition of the importance of microzooplankton the microzooplankton-ichthyoplankton link remains poorly studied. This thesis elucidates the autumn and winter community composition of PZP in the NE Atlantic and uses the larvae of autumn spawning Atlantic herring (Clupea harengus) as a case study to investigate the impact of the components of this small plankton size fraction on the distribution, condition and growth of overwintering ichthyoplankton. Manuscript 1 describes the findings of a broad scale field study on the winter PZP community in the North Sea. The focus was set on the taxonomic composition of the main PZP components, the hetero- and mixotrophic taxa from the phyla Ciliophora (ciliates) and Dinophyta (dinoflagellates). The dominance of small sized cells (<50 μm) in the community suggested that the microbial loop played a pronounced role in fueling the productivity of higher trophic levels. The maximum PZP carbon biomass found was approximately 50 times lower than during bloom conditions. However, highest biomass was observed in ...