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CHAPTER IV the same patterns in G. dominans in a three-species treatment as was found in the first experiment. Bottles containing only S. trochoidea and G. dominans served as controls. We also monitored the effect of the direct presence of the larger predator on swimming behaviour and speed of S. trochoidea and G. dominans after exposure to F. ehrenbergii for 24 hours. Fixation for cell counts with acid Lugol’s solution took place before and immediately after the time of incubation and filming. Counting Samples were enumerated under a Zeiss Axiovert 135 inverted microscope using the Utermöhl method (Utermöhl, 1958). The samples were settled overnight and 4-6 circular transects of each settling chamber were counted at 200 or 400-fold magnification depending on cell concentration of S. trochoidea and G. dominans. For F. ehrenbergii the whole chamber was enumerated. Apart from the first experiment G. dominans cells containing fresh food vacuoles (indicated by the dark colour of the vacuoles) were recorded separately and food vacuoles were used as a proxy for ingestion. Calculations Growth and grazing parameters Growth rates k [d -1 ] of F. ehrenbergii, G. dominans and S. trochoidea in the experiments were calculated assuming exponential growth. Grazing rates g [d -1 ], specific filtration rates F [mL µg predator -1 d -1 ] and specific ingestion rates I [prey cells predator -1 d -1 ] of the predators were calculated according to Frost (1972) with the modification of Heinbokel (1978a) for the growth of predators. Predator biomass specific ingestion rates I b [µg prey µg predator -1 d -1 ] were calculated to allow for comparisons between the treatments by normalization of the specific ingestion rates to mean predator and prey biomass. Growth of phytoplankton is known to be density dependent. The S. trochoidea growth control in the general interaction experiment significantly exceeded the initial start concentrations after 24 and 48 hours of incubation. In contrast, the initial concentrations of S. trochoidea in the grazing treatments at these times were close to starting concentrations of the first day. We therefore always used the growth rate of S. trochoidea determined after the first day for our calculations in the general interaction experiment. 110
CHAPTER IV Selectivity and Electivity of G. dominans for mobile and immobile prey The prey selectivity index α of G. dominans preying on a population of S. trochoidea containing both mobile and immobile prey was calculated for each prey type according to Chesson (1978, 1983). We chose Chesson’s case 1 equation (prey population assumed to be constant) (Chesson, 1983) because our values of ingestion and percentage of prey in the environment were obtained by averaged prey concentrations and a strong depletion of food was not observed during our experiments. Values of α were then used to calculate the electivity index E* according to Vanderploeg and Scavia (1979a, 1979b).Values of E* cover a range from -1 to 1. E* values of 0 indicate non selective feeding, values > 0 indicate preference, values < 0 indicate discrimination against a prey type. Swimming behaviour and velocity The films of swimming behaviour were converted to single frame pictures using the freeware program “Avi4Bmp” (Bottomap Software). The first 30 pictures (equalling two seconds of each original film) were stacked with the function “overlay frames” of the freeware program “Trace” (© Heribert Cypionka, 2000-2010). These stacked images showed the path of a cell during the two-second period (Fischer & Cypionka, 2006). The length of the path of 60 cells per treatment was measured with the open source software “ImageJ”. Swimming speed [µm s -1 ] of the cells was then calculated by dividing path length by the timeframe needed for it. Changes in swimming behaviour were analysed by comparing the patterns of the swimming paths in the stacked pictures. Data analysis Statistical analyses were conducted with the software “Statistica 7.1” (StatSoft) using two-tailed t-tests and one way ANOVAs followed by Newman-Keuls post hoc tests both at significance levels of 0.05. RESULTS General patterns of interaction In the first experiment we investigated the differences in successive patterns between treatments with one predator species and treatments with two predator species preying on the same organism. Both predator species preying on Scrippsiella trochoidea displayed positive growth rates in the single predator treatments throughout the whole experiment (Figure 1a+b). 111
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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
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 114 and 115: CHAPTER IV out in F/2 medium over 7
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
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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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