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CHAPTER III Table 4: Temora longicornis carbon specific filtration rates F c [L µgC predator -1 d -1 ] and carbon specific ingestion rates I c [µgC prey µgC predator -1 d -1 ], total filtration rates F [L d -1 ], total ingestion rates I [µgC prey L -1 d -1 ] and electivity E* [-] for different prey groups. Positive selection marked with gray background. TC = Total T. longicornis carbon biomass. P-values derived from t-tests against zero.* p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. Figure 7: (7a) Carbon specific ingestion rate I c and (7b) electivity index E* of Temora longicornis for phytoplankton and microzooplankton prey. x marks experiment with insignificant differences of I c and E* between both prey groups. Error bars correspond to one standard deviation (n = 9). 86
CHAPTER III DISCUSSION The main finding of this study is that microzooplankton was the main grazer throughout the whole period of the phytoplankton spring bloom 2009 in the North Sea at Helgoland while copepods played only a minor role, especially as the densities we used were rather high. Using a mesocosm set up and excluding mesozooplankton grazers allowed us to follow plankton spring succession focussing on top-down control mechanisms by microzooplankton solely. In fact, the close resemblance of the bloom in the mesocosms to the natural situations (where mesograzers were present) further suggested that the microzooplankton drives the spring dynamics of the phytoplankton community around Helgoland. Furthermore, the combined approach of dilution grazing experiments and T. longicornis bottle incubations allowed us to analyse microzooplankton and copepod grazing and feeding preferences in the same plankton community. Microzooplankton and T. longicornis impact on the phytoplankton bloom While microzooplankton grazed on average 120% of the potential phytoplankton production (P p ) in our experiments, average grazing impact of T. longicornis was 47%. Microzooplankton showed an almost sevenfold higher specific ingestion rate (I c ) when preying on phytoplankton in contrast to copepods. Whereas the removal of phytoplankton by T. longicornis in our experiments was slightly higher than the 10-40% given by Calbet (2001) for copepods on a global scale, the grazing impact of the microzooplankton was around twofold higher than results reported by Landry & Calbet (2004). They found an average grazing impact of 59-75% of P p by microzooplankton across a spectrum of open-ocean and coastal systems, whereas the lower border (60%) was found for estuarine systems with chlorophyll a values similar to those of our experiment. During our study the high availability of food during the bloom situation combined with a release from grazing pressure by metazoans enabled the development of a high microzooplankton grazer biomass in the mesocosms. Our results therefore should represent the maximum in microzooplankton grazing impact on phytoplankton in coastal regions. On the other hand the copepod biomass we used in our grazing experiments was at the upper level of field abundances at this time of the year (Greve et al., 2004) and therefore represents the maximal expectable grazing impact of copepods. Nevertheless, we found a much higher grazing impact by microzooplankton than by copepods. 87
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The role of heterotrophic dinoflage
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“What we know is a drop, what we
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INTRODUCTION INTRODUCTION Understan
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INTRODUCTION flagellates) and metaz
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INTRODUCTION The remaining species
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INTRODUCTION Figure 4: Diplopsalis
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INTRODUCTION compared to dinoflagel
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INTRODUCTION “seawater dilution t
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RESEARCH AIMS Apart from the pure g
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OUTLINE OF THE THESIS the two diffe
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CHAPTER I CHAPTER I Dinoflagellates
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CHAPTER I Dinoflagellates and cilia
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CHAPTER I INTRODUCTION Marine resea
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CHAPTER I counted out at 200-fold m
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CHAPTER I Dinoflagellates closely f
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CHAPTER I Figure 3: Biomass [µgC L
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CHAPTER I prevents confusion with o
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CHAPTER I Figure 6: Comparison of c
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Page 46 and 47: CHAPTER II ABSTRACT Grazing experim
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Page 54 and 55: CHAPTER II Experiment 2 Microzoopla
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Page 62 and 63: CHAPTER II ACKNOWLEDGEMENTS This st
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Page 66 and 67: CHAPTER III ABSTRACT Mesocosm exper
Page 68 and 69: CHAPTER III the prey (Cowles et al.
Page 70 and 71: CHAPTER III The mesocosms were stir
Page 72 and 73: CHAPTER III Net growth of plankton
Page 74 and 75: CHAPTER III prior to the experiment
Page 76 and 77: CHAPTER III incubation bottles with
Page 78 and 79: CHAPTER III Data analysis To monito
Page 80 and 81: CHAPTER III General development of
Page 82 and 83: CHAPTER III Ciliate community After
Page 84 and 85: CHAPTER III Other microzooplankton
Page 86 and 87: CHAPTER III Microzooplankton Experi
Page 88 and 89: CHAPTER III Figure 6: (6a) General
Page 90 and 91: CHAPTER III Table 3: Temora longico
Page 94 and 95: CHAPTER III The comparison of mesoc
Page 96 and 97: CHAPTER III Flagellates contributed
Page 98 and 99: CHAPTER III The effort to capture,
Page 100 and 101: CHAPTER III in words and deeds. Man
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Page 104 and 105: CHAPTER III Table 3b Temora longico
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Page 110 and 111: CHAPTER IV ABSTRACT The intra-speci
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Page 116 and 117: CHAPTER IV the same patterns in G.
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DISCUSSION To my knowledge similar
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DISCUSSION transported around the w
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SUMMARY by its larger competitor. T
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REFERENCES Buskey, E.J. & Stoecker,
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REFERENCES Gentsch, E., Kreibich, T
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REFERENCES Jeong, H.J., Yoo, Y.D.,
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REFERENCES Montagnes, D.J.S., 2003.
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REFERENCES Rose, J.M. & Caron, D.A.
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REFERENCES Teixeira, I.G. & Figueir
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