Plankton Dynamics and Distribution in the Eastern Mediterranean Sea Dissertation zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Christian-Albrechts-Universität zu Kiel vorgelegt von Georgia Assimakopoulou Kiel 2011 Referent: Prof. Dr. Franciscus Colijn Korreferent: Prof. Dr. Ulrich Sommer Tag der mündlichen Prüfung, 18 Oktober 2011 Zum Druck genehmigt Kiel, 10 Dezember 2011 Der Dekan Δίνει ο μαΐςτροσ το πανί Στη θάλαςςα Τα χάδια των μαλλιών Στην ξεγνοιαςιά του ονείρου του Δροςιά- The northwest wind bestows the sail To the sea The hair’s caress In the insouciance of its dream Dew – cool – From Orientations (1940) By Odysseus Elytis Table of Contents Chapter 1: General introduction ...................................... 11 1.1. Theoretical background ...................................... ....11 1.2. Phytoplankton ............................................ .... 12 1.3. Fronts ...... ......................................... ..... 14 1.4. Role of autotrophic picoplankton ......................... .......... 16 1.5. Study areas-General ................................... 18 1.5.1. North Aegean Sea ........................................ 20 1.5.2. Saronikos Gulf .................... ....................... 22 1.6. Thesis Objectives .................................... .......... 24 1.6.1. Chapter 3 .................... ............... ........... 24 1.6.2. Chapter 4 .................... ............... ........... 24 1.6.3. Chapter 5 .................... ............... ........... 24 Chapter 2: Material and Methods ..................................... 27 2.1. Sampling and Hydrography ...................................... 27 2.2. Nutrients ....................... ........................ ..... 27 2.3. Total and size fractionated chlorophyll α .......................... ... 28 2.4. Total and size fractionated primary production .................. ....... 29 2.5. Qualitative and quantitative analysis of phytoplankton ................ ... 30 2.6. Flow cytometric analysis - Autotrophic picoeukaryotes ................. .. 31 2.7. Population and biomass estimations ............................. ... 34 2.8. Biomass-specific primary productivity (P/B) ......................... .. 34 2.9. Growth rate ................................................ .. 35 2.10. Data analysis ................................................ 36 2.10.1. Statistical analysis ................................. ...... 37 2.10.2. Multivariate analysis ................................ ..... 38 Chapter 3: Seasonal differences in chlorophyll distribution and phytoplankton composition in a frontal region of the oligotrophic North Aegean Sea (Eastern Mediterranean) . ..... 41 Abstract ............................. ............................ ... 41 3.1. Introduction ............................................... ... 42 3.2. Material and methods ....................................... .... 43 3.2.1. Study area and sampling ............................... .... 43 3.2.2. Nutrients .................... ..................... ......44 3.2.3. Phytoplankton chlorophyll α ............................ .....45 3.2.4. Phytoplankton populations ................................. 45 3.2.5. Integrated values calculations ................................45 3.2.6. Statistical analysis ....................................... 46 3.3. Results .................................. .................... 47 3.3.1. Physical, chemical and biological characteristics ......... ...... ... 47 3.3.2. Nutrient and phytoplanktonic biomass distribution ................ 49 3.3.3. Nutrient ratios ................................. .......... 49 3.3.4. Phytoplanktonic biomass ......................... .......... 50 3.3.5. Phytoplankton community structure ................. .......... 52 3.4. Discussion ........................................... ........ 55 3.4.1. Hydrology ..................................... ......... 55 3.4.2. Nutrient distribution .............................. ........ 55 3.4.3. Phytoplankton biomass distribution in relation to the frontal structure . 56 Chapter 4: Dynamics of autotrophic picoplankton in the N. Aegean Sea ............................... ...... 75 Abstract .................................................... ........ 75 4.1. Introduction .............................................. .... 76 4.1.1. Study periods ................................ ........... 79 4.2. Material and methods .................................... ....... 79 4.2.1. Study area ................................... ........... 79 4.2.2. Field sampling ................................. .......... 79 4.2.3. Total and size fractionated chlorophyll α ............... ........ 81 4.2.4. Total and size fractionated primary production ............. ...... 81 4.2.5. Microplankton stock measurements ....................... .... 82 4.2.6. Biomass-specific primary productivity (P/B) .......... ............ 82 4.2.7. Growth rate calculations .................... ............... 82 4.2.8. Flow cytometry ............................ .............. 83 4.2.9. Plankton conversion to biomass ................. ............. 83 4.2.10. Statistical analysis ........................ ............... 83 4.3. Results ........................................ .............. 84 4.3.1. Hydrography ............................ ................ 84 4.3.2. Nutrients .................... ............ ...............86 4.3.3. Size-fractionated chlorophyll α ............................... 87 4.3.4. Size-fractionated primary production .............. ........... 89 4.3.5. Picoplankton abundances .......................... .........91 4.3.6. Phytoplankton community composition based on light microscopy . ... 93 4.3.7. Autotrophic carbon biomass ..................... ............94 4.3.8. Total and size fractionated C:Chlα –ratios ............ ........... 94 4.3.9. Phytoplankton growth rates ..................... ........... 95 4.3.10. Carbon standing-stocks and production of autotrophic picophytoplankton ...................................... 96 4.4. Discussion ........................................ ........... 96 4.4.1. Seasonal variability of Chl α concentration ...................... 96 Chapter 5: Seasonal variability of autotrophic picoplankton in the Saronikos ........................................ 123 Abstract ........................................................... 123 5.1. Introduction ................................................. 123 5.2. Material and methods .......................................... 126 5.2.1. Study area ............................................. 126 5.2.2. Field sampling .......................................... 128 5.2.3. Total and size fractionated chlorophyll α .................... ... 128 5.2.4. Flow cytometry ......................................... 129 5.2.5. Plankton conversion to biomass ............................. 129 5.2.6. Statistical analysis ....................................... 130 5.3. Results ..................................................... 130 5.3.1. Hydrography ........................................... 130 5.3.2. Nutrients .................... .......................... 132 5.3.3. Size-fractionated chlorophyll α ........................ 132 5.3.4. Picoplankton abundances .................................. 133 5.3.5. Biomass distribution over size classes ......................... 136 5.4. Discussion .................................................. 137 Chapter 6: Conclusions ............................................. 157 Chapter 7: References .............................................. 161 CHAPTER 8: Zusammenfassung ...................................... 177 CURRICULUM VITAE ..................... .......................... 181 ACKNOWLEDGEMENTS ............................................. 185 ERKLÄRUNG .................... ..................... .............. 187 CHAPTER 1: General introduction CHAPTER 1: General introduction 1.1 Theoretical background Biological activity is closely linked to dynamical processes, which regulate the vertical supply of nutrients, and the movements of phytoplanktonic cells in the euphotic layer. Thus far the study of marine plankton has largely focused on growth rates of ecosystem components and how they affect biogeochemical cycles. In the ocean, intense primary production is usually coupled to hydrodynamic features that favour the replenishment of nutrients in the photic layer. For example, phytoplankton biomass often develops and accumulates in density fronts where nutrient enrichment of the surface layer may result either from tidal mixing (tidal fronts) or from the interaction between wind stress and internal tides (shelf-break fronts) (see reviews by Holligan 1981, Loder & Platt 1984, Lefévre 1986, Legendre et al., 1986). The breaking of large eddies can also inject nutrients from the mixed to the stratified side of these fronts (Bowman & Iverson 1978, Loder & Platt 1984, Lefévre 1986). Analysis of the functioning of ocean ecosystems requires an understanding of how the structure of the ecosystem is determined by interactions between physical, chemical and biological processes. Such analysis needs to consider the interactions across a wide range of spatial (approx. 10m–10000km) and temporal (minutes to centuries) scales, and across all trophic levels (primary producers to top predators; Murphy et al., 1988; Angel, 1994). There are, however, few areas of the global ocean where there is sufficient knowledge to achieve such an integrated analysis (de Young et al., 2004). Circulation