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CHAPTER I Microzooplankton can be both prey and competitor for mesozooplankton. At Helgoland Roads small calanoid copepods can be regarded as direct competitors of ciliates and dinoflagellates for phytoplankton food. Their concentration ranges between 2 and 10 individuals L -1 throughout the year with highest values during the summer period (Greve et al., 2004). The mean carbon content (annual mean 2007, n = 45) of the abundant small calanoid copepod Temora longicornis (Greve et al., 2004) was 9.5 µg carbon female -1 (K. L. Schoo, unpublished) at Helgoland Roads. Assuming a maximum carbon content of 10 µg per copepod combined with the maximum concentrations given by Greve et al. (2004) would therefore result in maximum copepod carbon biomass of 100 µg L -1 (June/July). These values were surpassed by microzooplankton biomass, especially during the spring bloom. At this time the combined effects of a faster metabolism and higher productivity (Fenchel & Finlay, 1983, Montagnes & Lessard, 1999) allowed microzooplankton an undelayed direct response to an increase in prey availability (Johansson et al., 2004, Aberle et al., 2007) compared to its copepod competitors. Therefore, it is hardly surprising that recent studies have shown that microzooplankton competes not only for the same resources with copepods (Aberle et al., 2007) but may exert a stronger grazing pressure on phytoplankton than copepods (Sherr & Sherr, 2007) especially during bloom events. Our results confirm such a pivotal role of microzooplankton as phytoplankton grazers at Helgoland Roads. We found that during the summer months ciliate biomass was generally lower when compared with dinoflagellate biomass and only with their decreasing concentrations at the end of summer ciliate biomass gained the same importance as dinoflagellate biomass again. Ciliates are, however, the first microzooplankton grazers which react to enhanced food availability in spring when the concentration of small flagellated prey increases at Helgoland. Such an earlier onset of ciliate blooms can be directly linked to their higher metabolic rates and growth rates when compared to dinoflagellates (Hansen, 1992, Strom & Morello, 1998). On the other hand they are generally more restricted to the availability of particular prey types (Tillmann, 2004), especially flagellates, than dinoflagellates are (Jeong, 1999). Thus, ciliates can respond more rapidly than dinoflagellate to enhanced food concentrations but their potential for surviving starvation periods is low (Jackson & Berger, 1985) compared to dinoflagellates (Hansen, 1992, Menden-Deuer et al., 2005). This implies rapid responses to increasing food concentrations but also quick declines of ciliate concentrations as a direct response to decreasing prey concentrations. Ciliate maxima 34
CHAPTER I should therefore occur only when their appearance is coupled with the sufficient availability of adequate prey. Another factor potentially influencing abundances of both ciliates and dinoflagellates is predation, e.g., by copepods. Microzooplankton contributes substantially to copepod diets and is often positively selected by them (Nejstgaard et al., 1997, Fileman et al., 2007). The capacity of microzooplankton to synthesize highly unsaturated fatty acids and sterols makes them good quality food for copepods (Klein Breteler et al., 1999, Tang & Taal, 2005). Especially when phytoplankton prey is nutrient limited, rendering it a low quality food, microzooplankton predators are able to dampen stoichiometric constraints of their prey to a certain extent (Malzahn et al., 2010) and are therefore of better nutritional value for copepods compared to phytoplankton. We showed that microzooplankton is an important component of the food web at Helgoland Roads. Due to its temporarily high biomass concentration and occurrence at times throughout the year it can probably be regarded as the most important phytoplankton grazer group here. Microzooplankton is additionally an important food source for higher trophic levels such as copepods. As the routine plankton monitoring has a different focus it cannot resolve the diversity of microzooplankton sufficiently. Given its key role in the food web we recommend the long-term implementation of microzooplankton, especially dinoflagellates and ciliates, into the Helgoland Roads long-term sampling program. Further multivariate statistical analyses are necessary to evaluate the biotic and abiotic factors that drive microzooplankton composition and abundance patterns. The Helgoland Roads long-term series provides these important parameters and the extensive data on microzooplankton will provide an excellent background for such analyses. ACKNOWLEGEMENTS This study was part of a PhD thesis within the Food Web Project at the Alfred Wegener Institute for Polar and Marine Research and we are grateful for the funding. Furthermore, we want to thank the crew of the research vessel Aade for providing samples, Kristine Carstens for her help in the laboratory, Silvia Peters for the long-term data and Mirco Scharfe for his evaluation of the species lists. Last but not least we thank the whole team of the AWI Food Web Project for their collegiality. 35
Page 1 and 2: The role of heterotrophic dinoflage
Page 3: “What we know is a drop, what we
Page 7 and 8: INTRODUCTION INTRODUCTION Understan
Page 9 and 10: INTRODUCTION flagellates) and metaz
Page 11 and 12: INTRODUCTION The remaining species
Page 13 and 14: INTRODUCTION Figure 4: Diplopsalis
Page 15 and 16: INTRODUCTION compared to dinoflagel
Page 17: 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: CHAPTER I Figure 6: Comparison of c
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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
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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
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CHAPTER III Table 3: Temora longico
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CHAPTER III Table 4: Temora longico
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CHAPTER III The comparison of mesoc
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CHAPTER III Flagellates contributed
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CHAPTER III The effort to capture,
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CHAPTER III in words and deeds. Man
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CHAPTER III Table 2 Microzooplankto
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CHAPTER III Table 3b Temora longico
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CHAPTER III Table 4b Temora longico
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CHAPTER IV 102
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CHAPTER IV ABSTRACT The intra-speci
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CHAPTER IV Hansen, 1997). In turn,
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CHAPTER IV out in F/2 medium over 7
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CHAPTER IV the same patterns in G.
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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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