Zooplankton dynamics, fish zonation and trophic interactions at two seamounts in contrasting regimes of the Eastern Atlantic Dissertation zur Erlangung des Doktorgrades an der Fakultät für Mathematik, Informatik und Naturwissenschaften der Universität Hamburg vorgelegt von Anneke Denda Hamburg 2015 Tag der Disputation: 06. November 2015 Folgende Gutachter empfehlen die Annahme der Dissertation: Prof. Dr. C. Möllmann Prof. Dr. F. Buchholz __________________________________________________________________________________ Table of Content 1 Summary ...........................................................................................................................................1 2 Zusammenfassung............................................................................................................................3 3 General Introduction .......................................................................................................................7 3.1 Seamount ecosystems ..................................................................................................................7 3.2 Microzooplankton vs. mesozooplankton ...................................................................................10 3.3 Respiratory carbon demand .......................................................................................................10 3.4 Stable isotopes in trophic analyses ............................................................................................11 3.5 Objectives of the study ..............................................................................................................12 3.6 References..................................................................................................................................15 4 Manuscript 1: Zooplankton distribution patterns at two seamounts in the subtropical and tropical NE Atlantic 4.1 Abstract......................................................................................................................................21 4.2 Introduction................................................................................................................................22 4.2.1 Study sites .........................................................................................................................24 4.2.1.1 Ampère Seamount....................................................................................................24 4.2.1.2 Senghor Seamount ...................................................................................................24 4.3 Material and Methods................................................................................................................25 4.3.1 Zooplankton sampling......................................................................................................25 4.3.2 Biomass analyses .............................................................................................................27 4.3.3 Statistical analyses ...........................................................................................................27 4.3.4 Calculation of respiratory carbon demand .......................................................................27 4.3.5 Taxonomic analyses.........................................................................................................28 4.4 Results .......................................................................................................................................28 4.4.1 Hydrography ....................................................................................................................28 4.4.2 Zooplankton composition.................................................................................................29 4.4.3 Distribution of standing stocks and size classes...............................................................30 4.4.4 Small-scale distribution of standing stocks in the upper 100 m: orthogonal transects ....32 4.4.5 Biomass concentrations and size class distribution from horizontal surveys ..................33 4.4.6 Vertical distribution patterns of biomass concentrations .................................................37 4.4.7 Carbon demand ................................................................................................................38 4.5 Discussion..................................................................................................................................39 4.5.1 Latitudinal and seasonal variability of zooplankton biomass ..........................................39 4.5.1.1 Ampère Seamount and the sphere of the subtropical gyre.......................................40 4.5.1.2 Senghor Seamount and the sphere of the tropical gyre............................................41 4.5.2 Latitudinal differences in zooplankton composition........................................................42 __________________________________________________________________________________ 4.5.3 Small-scale spatial variability and size distribution patterns of zooplankton biomass ....42 4.5.3.1 Sphere of Ampère Seamount ...................................................................................43 4.5.3.2 Sphere of Senghor Seamount...................................................................................44 4.5.4 Latitudinal and vertical variability of zooplankton respiratory carbon demand ..............45 4.6 Conclusions................................................................................................................................47 4.7 Acknowledgements....................................................................................................................47 4.8 References..................................................................................................................................48 5 Manuscript 2: Microzooplankton and the dispersal of meroplanktonic larvae at two seamounts in the subtropical and tropical NE Atlantic 5.1 Abstract......................................................................................................................................53 5.2 Introduction................................................................................................................................54 5.3 Materials and Methods ..............................................................................................................55 5.3.1 Study sites ........................................................................................................................55 5.3.1.1 Ampère Seamount....................................................................................................55 5.3.1.2 Senghor Seamount ...................................................................................................56 5.3.2 Hydrographic data collection ...........................................................................................57 5.3.3 Zooplankton sampling......................................................................................................57 5.3.4 Biomass analyses and carbon demand .............................................................................59 5.3.5 Taxonomic analyses.........................................................................................................60 5.3.6 Data analyses....................................................................................................................61 5.4 Results .......................................................................................................................................62 5.4.1 Hydrography ....................................................................................................................62 5.4.2 Abundance and composition............................................................................................66 5.4.2.1 Total Zooplankton....................................................................................................66 5.4.2.2 Associations between zooplankton and location......................................................70 5.4.2.3 Meroplanktonic larvae .............................................................................................71 5.4.3 Spatial distribution of biomass standing stocks ..............................................................74 5.4.4 Vertical biomass distribution ...........................................................................................76 5.4.5 Carbon demand ................................................................................................................79 5.5 Discussion..................................................................................................................................80 5.5.1 The influence of the large-scale current regime and the local flow field on biomass and abundance..................................................................................................................................81 5.5.2 The influence of oxygen concentration and food supply on the vertical distribution......82 5.5.3 The composition of the zooplankton community.............................................................83 5.5.4 The distribution of meroplanktonic larvae.......................................................................85 5.5.5 The variability of zooplankton respiratory carbon demand .............................................87 5.6 Conclusions................................................................................................................................88