Zooplankton dynamics in winter: A bottom-up analysis of a new zooplankton time series from the English Channel and the Southern Bight of the North Sea Dissertation with the aim of achieving a doctoral degree at the Faculty of Mathematics, Informatics and Natural Sciences Department of Biology of the University of Hamburg submitted by Tim Dudeck 2017 in Hamburg Evaluators Prof. Dr. Christian Möllmann Dr. Marc Hufnagl Institute for Hydrobiology and Fisheries Science University of Hamburg Olbersweg 24 22767 Hamburg Germany Certification of Written English Quality I, Rachel Harmer (born in the United Kingdom and native English speaker), hereby confirm that the thesis by Tim Dudeck entitled " Zooplankton dynamics in winter: A bottom-up analysis of a new zooplankton time series from the English Channel and the Southern Bight of the North Sea" has been prepared according to excellent written English language standards. Sincerely, “White! It serves as a beginning. White cloth may be dyed. The white page can be overwritten; and the white light can be broken.” - Saruman “And he that breaks a thing to find out what it is has left the path of wisdom.” - Gandalf Table of content 1. Summary ............................................................................................................................ 1 2. Zusammenfassung ............................................................................................................. 4 3. Outline of publications ...................................................................................................... 8 4. General introduction ......................................................................................................... 9 4.1 Climate change and bottom-up controls of ecosystems ............................................. 9 4.2 English Channel and the southern North Sea ............................................................ 10 4.3 Herring in the southern North Sea ............................................................................ 12 4.3 Plankton as lower trophic levels ................................................................................ 15 4.4 Sampling strategies and Zooplankton time series .................................................... 19 4.5 Biodiversity, Biomass and Size ................................................................................... 21 4.6 Objectives and scope of the thesis ............................................................................ 23 5. Chapter I ........................................................................................................................... 25 Winter zooplankton dynamics in the English Channel: trends and drivers from 1991 to 2013 5.1 Abstract ...................................................................................................................... 25 5.2 Introduction ............................................................................................................... 25 5.3 Material and Methods ............................................................................................... 28 5.3.1 International Herring Larvae Survey .................................................................. 28 5.3.2 Sample processing and ZooScan Analysis .......................................................... 29 5.3.3 Environmental Data............................................................................................ 30 5.3.4 General trend analyses ....................................................................................... 31 5.3.5 Generalised Additive Mixed Models .................................................................. 31 5.4 Results ........................................................................................................................ 32 5.4.1 The winter zooplankton time series ................................................................... 32 5.4.2 Spatial clustering ................................................................................................ 32 5.4.3 General trends in zooplankton dynamics .......................................................... 34 5.4.4 Drivers of change ................................................................................................ 38 5.5 Discussion .................................................................................................................. 41 6. Chapter II .......................................................................................................................... 47 Changes in herring recruitment related to bottom-up forces in winter: Evidence from 1991 to 2013 6.1 Abstract ...................................................................................................................... 47 6.2 Introduction ............................................................................................................... 47 6.3 Material and Methods ............................................................................................... 49 6.3.1 International Herring Larvae Survey .................................................................. 49 6.3.2 IBTS0 survey ....................................................................................................... 50 6.3.3 Zooplankton Analysis ......................................................................................... 50 6.3.4 Environmental Data............................................................................................ 51 6.3.5 Statistical analyses.............................................................................................. 51 6.4 Results ........................................................................................................................ 52 6.4.1 Biotic and abiotic trends and points of change .................................................. 52 6.4.2 Herring larvae and trophic relations .................................................................. 54 6.4.3 Principal components ......................................................................................... 57 6.5 Discussion .................................................................................................................. 60 7. Chapter III ......................................................................................................................... 65 Zooplankton size as an indicator for zooplankton biodiversity 7.1 Abstract ...................................................................................................................... 65 7.2 Introduction ............................................................................................................... 65 7.3 Materials and Methods ............................................................................................. 67 7.3.1 Data collection .................................................................................................... 67 7.3.2 Sample processing .............................................................................................. 68 7.3.3 Zooplankton diversity analysis ........................................................................... 69 7.4 Results ........................................................................................................................ 70 7.4.1 Zooplankton composition and annual biodiversity ........................................... 70 7.4.2 Correlation analysis ............................................................................................ 72 7.4.3 Spatially explicit diversity analysis ..................................................................... 73 7.5 Discussion .................................................................................................................. 74 7.5.1 Size diversity as potential biodiversity indicator................................................ 74 7.5.2 Reasons for the effectiveness of size diversity .................................................. 74 7.5.3 Future relevance ................................................................................................ 76 7.5.4 Potential application .......................................................................................... 76 8. General Discussion........................................................................................................... 78 8.1 Time series and methods evolved ............................................................................. 78 8.2 Climate change and its indirect effects on the trophic cascade ............................... 80 8.3 Herring recruitment and its relation to trophic cascades ......................................... 83 8.4 Size diversity and its potential as indicator for lower trophic levels ......................... 86 9. Concluding Remarks ........................................................................................................ 88 10. References..................................................................................................................... 90 11. Acknowledgements .................................................................................................... 105 12. Eidesstattliche Versicherung, Declaration on oath ................................................... 106 Summary 1. Summary Zooplankton and Phytoplankton form the basis of marine food webs worldwide. In the face of climate change and varying fish predation pressure they are the mediators of energy in ecosystems. Understanding the