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CHAPTER IV Favella ehrenbergii (Figure 1b) generally grew faster (t = 6.27, df = 22, p < 0.001, twotailed t-test) in the single predator treatment when compared to G. dominans (Figure 2b). Mean growth rates of the tintinnid increased constantly from 0.54 to 0.98 d -1 and were on average 0.77 d -1 . Specific ingestion rates dropped from 165 to 86 cells predator -1 d -1 and averaged 64 cells predator -1 d -1 during the course of the experiment. As found for G. dominans the grazing rates of F. ehrenbergii hardly exceeded the growth rates of S. trochoidea for the first two days (0.43 and 0.51 d -1 ). However, during the last day of the experiment as a result of the increasing predator population the grazing rate amounted 2.55 d -1 leading to a sharp decline in the prey population. Predator specific filtration rates recorded for F. ehrenbergii were not different (t = 0.05 , df = 22, p = 0.96, two-tailed t-test) from those recorded for G. dominans and ranged between 0.31 and 0.64 mL µg predator -1 d -1 (mean value 0.49 mL µg predator -1 d -1 ). In treatments with G. dominans as sole prey for F. ehrenbergii (Figure 1c), the larger predator displayed a mean grazing rate of 0.20 d -1 . Although prey was always available at high concentrations, grazing rates decreased from higher values (0.21 and 0.34 d -1 ) to a value of 0.04 d -1 on the last day of the experiment. This was also reflected by the specific ingestion: The ciliate initially ingested 115 and 111 cells predator -1 d -1 on the second day but then ingestion dropped to a value of 6 cells predator -1 d -1 (mean 70 cells predator -1 d -1 ). Even if F. ehrenbergii ingested high numbers of prey cells it was not able to increase growth rates as with the prey S. trochoidea. Growth rates amounted to 0.32 d -1 on average and dropped from 0.50 to 0.08 d -1 during the experiment. While both predators in the single predator treatments roughly only consumed the daily production of S. trochoidea until day three of the experiment, a completely different picture emerged in the two predator treatments (Figure 1d, 3). Although the initial predator and prey biomass were the same as in the single predator treatments, S. trochoidea biomass already decreased after 24 hours and was completely grazed down at the end of the experiment. Consequently, grazing rates in the two predator treatments were consistently higher (0.60 and 1.89 d -1 ) than those measured in the single predator treatments on the first two days of the experiment (after 24 hours: t = 5.91, df = 10, p < 0.001, after 48 hours: t = 16.50, df = 10, p < 0.001, two-tailed t-tests: pooled g of single predator treatments against g in the two predator treatment). After 72 hours this effect was only measurable in one replicate due to the extinction of the prey (Figure 3). 114
CHAPTER IV Figure 3: Grazing rates [d -1 ] of Gyrodinium dominans and Favella ehrenbergii on Scrippsiella trochoidea in single predator treatments and two predator treatments after 24, 48 and 72 hours of incubation; calculated for 24 hour intervals. Error bars correspond to one standard deviation, n = 4. Significant differences between single predator treatments and two predator treatment are marked by asterisk (twotailed t-tests). x: No comparison possible as grazing was measurable only in one replicate of the two predator treatment while the prey population was grazed down totally in the others. Despite higher grazing rates, biomass specific ingestion rates I b were not different between the single predators nor between single predator treatments and two predator treatment (G. dominans: mean 0.98 µg µg -1 d -1 , F. ehrenbergii: mean 0.85 µg µg -1 d -1 , two-predator treatment: mean 0.97 µg µg -1 d -1 , F 2,9 = 1.18, p = 0.35, ANOVA) after the first 24 hours of the experiment. Keeping in mind that the start concentrations of cells were the same, this indicates that the higher grazing rates in the two predator treatments were due to the faster growth of predator biomass only. After 48 hours I b differed between all treatments (G. dominans: mean 0.92 µg µg -1 d -1 , F. ehrenbergii: mean 0.52 µg µg -1 d -1 , two-predator treatment: mean 0.80 µg µg -1 d -1 , F 2,9 = 100.95, p < 0.001, ANOVA). No difference was found between both predators at the end of the experiment (G. dominans: mean 0.48 µg µg -1 d -1 , F. ehrenbergii: mean 0.44 µg µg -1 d -1 , t = 1.45, df = 6, p = 0.20, two-tailed t-test) whereas a comparison of I b with the two predator treatment was not possible due to the extinction of prey. We observed no difference in the growth rates of F. ehrenbergii between the single and two predator treatments when looking at the single sampling days (Figure 2b) 115
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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
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CHAPTER III 58
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CHAPTER III ABSTRACT Mesocosm exper
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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
Page 108 and 109: CHAPTER IV 102
Page 110 and 111: CHAPTER IV ABSTRACT The intra-speci
Page 112 and 113: CHAPTER IV Hansen, 1997). In turn,
Page 114 and 115: CHAPTER IV out in F/2 medium over 7
Page 116 and 117: CHAPTER IV the same patterns in G.
Page 118 and 119: CHAPTER IV Figure 1: General develo
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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School of Engineering and Science - Jacobs University

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