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CHAPTER IV out in F/2 medium over 72 hours in 73.5 mL tissue culture bottles as batch cultures with four replicates. Incubation conditions were the same as described for the predator cultures before. The total volume of each incubation bottle was fixed immediately with acid Lugol’s solution at a final concentration of 2% for the determination of cell concentrations. Samples were taken at the start and after 24, 48 and 72 hours of incubation. To avoid density-dependent differences and allow comparability between the experiments we maintained start concentrations, incubation conditions and replication of this first experiment in the following experiments if not explicitly otherwise stated. Specific interactions As we observed that G. dominans responded to the presence of the larger tintinnid predator F. ehrenbergii we focused on this species interaction with the other predator when designing the following experiments. Chemical stimulation and swimming behaviour To test whether chemical compounds excreted by F. ehrenbergii influenced the growth of G. dominans, a well fed exponentially growing F. ehrenbergii culture (15 cells mL -1 ) was filtered over 0.2 µm nylon filters (Falcon). 10 mL of filtrate, equalling a final F. ehrenbergii concentration of 2 cells mL -1 , was added to incubation bottles containing G. dominans and S. trochoidea. Controls received 10 mL of F/2 filtrate. As the enhancement of swimming speed can increase predator-prey encounter rates (Gerritsen & Strickler, 1977) and thus potentially promotes higher grazing rates, we also investigated the swimming behaviour and velocity of the prey organism S. trochoidea and the predator G. dominans in the presence and absence of compounds released by F. ehrenbergii in this experiment. After exposure to the filtrate for 24 hours, S. trochoidea and G. dominans cells were filmed under a stereo microscope (SZX16, Olympus) at 50- fold magnification for 10 seconds at a rate of 15 frames per second. Samples for cell concentrations were fixed as described above at the start and immediately after filming. Experiments on the pre-condition of the prey From the detailed observation of a freshly fed F. ehrenbergii culture we found that not every S. trochoidea cell captured by the predator was actually ingested. A certain number of cells was egested again – becoming immobile after this “manipulation” by the predator. This has led to the hypothesis that F. ehrenbergii promotes growth in G. 108
CHAPTER IV dominans by immobilizing the potential prey for the smaller species, and thus making it easier to catch. Prey immobilisation rate of Favella ehrenbergii The rate of S. trochoidea prey cells not eaten but immobilized by F. ehrenbergii was experimentally determined after 24 and 48 hours of incubation. Differentiation between mobile and immobile S. trochoidea in fixed samples is not possible, thus after the incubation immobile cells were allowed to settle in the experimental bottles for 15 minutes. This timeframe was found to be sufficient for the complete sedimentation of the immobile fraction of S. trochoidea cells. To discriminate between mobile and immobile cells, a grid was defined and ten sites of the bottom surface of each experimental bottle were filmed for 5 seconds under conditions as described above. Cells that did not change their position during the film were counted as immobile ones. The concentration of immobile cells was calculated via the extrapolation of immobile cells of the filmed area to the whole bottom plate and thereafter to bottle volume. By dividing the mean immobile S. trochoidea concentration by the mean F. ehrenbergii concentration during the time of incubation (Frost, 1972, Heinbokel, 1978a) we calculated the immobilisation rate of F. ehrenbergii per day [cells immobilized predator - 1 day -1 ]. The percentage of immobilisation of cells caught by the tintinnid was also calculated. Samples for the determination of total cell concentrations were fixed as described above immediately after filming. Growth and grazing response of Gyrodinium dominans on immobilized prey To test if G. dominans benefits from immobile prey we investigated its growth when fed with artificially immobilized S. trochoidea. The immobilisation of prey took place in an ultrasound bath via sonication of S. trochoidea in six cycles, each cycle lasting three minutes. The ratio of immobile cells was determined via films as described above. We measured growth and grazing of G. dominans as well as selectivity for mobile or immobile prey after incubation for 24 hours with sonicated S. trochoidea. Untreated prey cultures served as controls. Samples for cell counts were fixed with acid Lugol’s solution immediately before and after the time of incubation. Commensalism experiment A final experiment was designed to evaluate the results of the previous experiments. We investigated if the presence of a different newly isolated F. ehrenbergii culture led to 109
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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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CHAPTER I should therefore occur on
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CHAPTER II 38
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CHAPTER II ABSTRACT Grazing experim
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CHAPTER II application, the alterna
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CHAPTER II Experiment 2 Experiment
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CHAPTER II Ciliates The three most
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CHAPTER II Experiment 2 Microzoopla
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CHAPTER II Asterisk * 1 symbolizes
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CHAPTER II DISCUSSION Transfer tech
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CHAPTER II bottles when siphoning w
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CHAPTER II ACKNOWLEDGEMENTS This st
Page 64 and 65: CHAPTER III 58
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 92 and 93: CHAPTER III Table 4: 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
Page 102 and 103: CHAPTER III Table 2 Microzooplankto
Page 104 and 105: CHAPTER III Table 3b Temora longico
Page 106 and 107: CHAPTER III Table 4b Temora longico
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Page 110 and 111: CHAPTER IV ABSTRACT The intra-speci
Page 112 and 113: CHAPTER IV Hansen, 1997). In turn,
Page 116 and 117: CHAPTER IV the same patterns in G.
Page 118 and 119: CHAPTER IV Figure 1: General develo
Page 120 and 121: CHAPTER IV Favella ehrenbergii (Fig
Page 122 and 123: CHAPTER IV (24, 48, 72 hours of inc
Page 124 and 125: CHAPTER IV Growth response of G. do
Page 126 and 127: CHAPTER IV due to pre-conditioning
Page 128 and 129: CHAPTER IV This was also confirmed
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Page 132 and 133: DISCUSSION described by competition
Page 134 and 135: DISCUSSION to know who they are. Th
Page 136 and 137: DISCUSSION Microzooplankton grazers
Page 138 and 139: DISCUSSION Figure 1: A rather simpl
Page 140 and 141: DISCUSSION 1986, Tillmann, 2004) co
Page 142 and 143: DISCUSSION To my knowledge similar
Page 144 and 145: DISCUSSION transported around the w
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Page 148 and 149: SUMMARY by its larger competitor. T
Page 150 and 151: REFERENCES Buskey, E.J. & Stoecker,
Page 152 and 153: REFERENCES Gentsch, E., Kreibich, T
Page 154 and 155: REFERENCES Jeong, H.J., Yoo, Y.D.,
Page 156 and 157: REFERENCES Montagnes, D.J.S., 2003.
Page 158 and 159: REFERENCES Rose, J.M. & Caron, D.A.
Page 160 and 161: REFERENCES Teixeira, I.G. & Figueir
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