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CHAPTER III The mesocosms were stirred by a propeller (107.5 rpm, 15 minutes on, then 15 minutes off) to ensure the continuous mixing of the water column and to avoid sedimentation of the plankton. Light was provided by computer-controlled light units (Profilux II, GHL Groß Hard- and Software Logistics, Kaiserslautern, Germany) operated via an external control computer (Programme ‘Prometheus’, GHL, modified version ‘Copacabana’). The light units were equipped with two different fluorescent tubes to obtain full light spectra (‘Solar Tropic’ and ‘Solar Nature’, JBL, Neuhofen, Germany), enabling the simulation of a daily triangular light curve (see Sommer et al. (2007) for details). The light cycle and intensity was adjusted daily to account for changes in the photoperiod during the experimental run according to the geographical position of Helgoland following the model by Brock (1981). In order to initiate the phytoplankton spring bloom after filling a light intensity of 60% of surface irradiance was chosen, simulating the intensity of light at 1.50 m water depth with a light attenuation coefficient of 0.34 (5 m Secchi depth) under in situ conditions. Calculation of the light intensity was done via equations given by Tyler (1968) and Poole and Atkins (1929). Stocking with natural inocula During early seasonal succession many plankton organisms hatch from cysts, resting eggs or other resting stages. To ensure the same successive patterns of the plankton in the enclosed mesocosms like in the field, including those organisms hatching from cysts, resting stages etc., we introduced a small inoculum of natural seawater from Helgoland Roads on a weekly basis. Five litres of 200 µm screened seawater were added to each mesocosm. An additional 15 L of filtered seawater (0.2 µm) were added to the mesocosms to compensate for evaporation and water removal due to the sampling for monitoring and experiments. Sampling the mesocosms Daily measurements Daily measurements of temperature, pH and in vivo fluorescence (chlorophyll a) (Algae Analyser, BBE Moldaenke, Kiel, Germany) were conducted between 8 and 9 am. 64
CHAPTER III Weekly monitoring In addition to the daily measurements, three litres of each mesocosm were sampled and analysed every Monday, Wednesday and Friday as well as on days with grazing experiments. Nutrients Silicate, phosphate, DIN (nitrite, nitrate and ammonia) were determined colorimetrically after filtration of at least 0.3 L of sample through 0.45 µm Nylon filters (Falcon) following the method of Grasshoff et al. (1999). Phytoplankton and microzooplankton composition For the determination of phytoplankton species 100 mL of the sample were subsampled into amber bottles and immediately fixed with neutral Lugol’s iodine solution (final conc. 0.5%) (Throndsen, 1978). For the determination of the microzooplankton 250 mL were fixed with acid Lugol’s iodine solution immediately (final conc. 2%) (Throndsen, 1978). Samples were stored cool and dark. For phytoplankton species determination 25 mL and for microzooplankton 50 mL of the sample were settled in sedimentation chambers (HYDRO-BIOS) for 24 hours and counted under a Zeiss Axiovert 135 inverted microscope using the Utermöhl method (Utermöhl, 1958). Phytoplankton (diatoms, phytoflagellates except dinoflagellates) and microzooplankton (ciliates, dinoflagellates and others) were identified where possible to genus or species level or, otherwise, pooled into size-dependent groups or “morphotypes”. It is known that most chloroplast-bearing dinoflagellates are capable of mixotrophic nutrition via phagotrophy (Du Yoo et al., 2009). Therefore, all dinoflagellate species were considered potentially heterotrophic and were assigned to the microzooplankton. For microzooplankton the whole surface of the sedimentation chamber was counted at 200-fold magnification, thus reducing counting biases against rare species. The identification of phytoplankton and dinoflagellates was primarily based on Dodge (1982), Tomas (1996), Hoppenrath et al. (2009). Ciliates were determined based on Kahl (1932), Carey (1992) and Montagnes (2003). 65
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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
Page 20 and 21: RESEARCH AIMS Apart from the pure g
Page 22 and 23: OUTLINE OF THE THESIS the two diffe
Page 25 and 26: CHAPTER I CHAPTER I Dinoflagellates
Page 27 and 28: CHAPTER I Dinoflagellates and cilia
Page 29 and 30: CHAPTER I INTRODUCTION Marine resea
Page 31 and 32: CHAPTER I counted out at 200-fold m
Page 33 and 34: CHAPTER I Dinoflagellates closely f
Page 35 and 36: CHAPTER I Figure 3: Biomass [µgC L
Page 37 and 38: CHAPTER I prevents confusion with o
Page 39 and 40: CHAPTER I Figure 6: Comparison of c
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Page 44 and 45: CHAPTER II 38
Page 46 and 47: CHAPTER II ABSTRACT Grazing experim
Page 48 and 49: CHAPTER II application, the alterna
Page 50 and 51: CHAPTER II Experiment 2 Experiment
Page 52 and 53: CHAPTER II Ciliates The three most
Page 54 and 55: CHAPTER II Experiment 2 Microzoopla
Page 56 and 57: CHAPTER II Asterisk * 1 symbolizes
Page 58 and 59: CHAPTER II DISCUSSION Transfer tech
Page 60 and 61: CHAPTER II bottles when siphoning w
Page 62 and 63: 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 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 116 and 117: CHAPTER IV the same patterns in G.
Page 118 and 119: CHAPTER IV Figure 1: General develo
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CHAPTER IV Favella ehrenbergii (Fig
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CHAPTER IV (24, 48, 72 hours of inc
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CHAPTER IV Growth response of G. do
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CHAPTER IV due to pre-conditioning
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CHAPTER IV This was also confirmed
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DISCUSSION described by competition
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DISCUSSION to know who they are. Th
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DISCUSSION Microzooplankton grazers
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DISCUSSION Figure 1: A rather simpl
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DISCUSSION 1986, Tillmann, 2004) co
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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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