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CHAPTER I ABSTRACT A monitoring program for microzooplankton was started at the long-term sampling station “Kabeltonne” at Helgoland Roads (54°11.3’N; 7°54.0’E) in January 2007 in order to provide more detailed knowledge on microzooplankton occurrence, composition and seasonality patterns at this site. Ciliate and dinoflagellate cell concentration and biomass were recorded on a weekly basis. Heterotrophic dinoflagellates were considerably more important in terms of biomass than ciliates, especially during the summer months. However, in early spring ciliates were the major grazers as they responded more quickly to food availability. Mixotrophic dinoflagellates played a secondary role in terms of biomass when compared to heterotrophic species, nevertheless, they made up the intense late summer plankton bloom in 2007. The photosynthetic ciliate Myrionecta rubra bloomed at the end of the sampling period. Due to its high biomass when compared to crustacean plankton especially during the spring bloom, microzooplankton can be regarded as the more important phytoplankton grazer group at Helgoland Roads. Based on these results, analyses of biotic and abiotic factors driving microzooplankton composition and abundance are necessary for a full understanding of this important group. Keywords: dinoflagellates, ciliates, North Sea, monitoring, Helgoland Roads, seasonality 22
CHAPTER I INTRODUCTION Marine research has a long tradition on Helgoland. Water temperature has been measured at the Helgoland Roads long-term station “Kabeltonne” (54°11.3’N; 7°54.0’E) since 1873 (Wiltshire & Manly, 2004) and biological, chemical and physical parameters have been recorded continuously on a work-daily basis since 1962 (Franke et al., 2004). This makes the Helgoland long-term data series one of the longest and most detailed aquatic data sets in history. Unique in this data set are the phytoplankton species numbers counted work-daily to species level wherever possible (Wiltshire & Dürselen, 2004). Augmenting this: Since 1975 the time-series also includes meso- and macrozooplankton determined to species level three times per week (Greve et al., 2004). Thus the time-series provides an excellent basis for analyses of long term trends including changes evinced in the North Sea pelagic system over the recent decades (Schlüter et al., 2008, Wiltshire et al., 2008). Furthermore, it is a very important basis for the parameterisation and validation of mathematical ecosystem models and is invaluable in biodiversity and global change considerations (Wirtz & Wiltshire, 2005). However, one important group of planktonic organisms is underrepresented in the long term series so far - the microzooplankton. Although data on heterotrophic dinoflagellates exist in the long-term series, they were recorded with varying degrees of accuracy (Wiltshire & Dürselen, 2004) and did not always mirror the diversity in species composition (Hoppenrath, 2004). Long-term data on ciliates, another crucial microzooplankton group, are completely lacking at Helgoland Roads. The term microzooplankton refers to the size fraction of heterotrophic planktonic organisms between 20 and 200 µm. Consisting of a diverse array of protozoa and metazoa its numerically most important components are heterotrophic dinoflagellates and ciliates (Capriulo et al., 1991). Recent research demonstrated the fundamentally important role of microzooplankton as phytoplankton grazers showing that grazing by microzooplankton can be as high as 60-75% of the daily phytoplankton production (Landry & Calbet, 2004). Furthermore, results indicate that microzooplankton tends to surpass mesozooplankton as primary consumers (Sherr & Sherr, 2007). A meta-analysis of Calbet & Landry (2004) revealed that microzooplankton grazing can be responsible for 60% of phytoplankton mortality in coastal and estuarine environments comparable to Helgoland Roads in terms of chlorophyll a concentration. We realized that microzooplankton could also potentially be the most important grazer group in waters around Helgoland. Therefore, the aim of this study was to supplement the regular plankton monitoring series at Helgoland with an intensive monitoring of the 23
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: CHAPTER I Dinoflagellates and cilia
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
Page 41: CHAPTER I should therefore occur on
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
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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
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CHAPTER III Data analysis To monito
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CHAPTER III General development of
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CHAPTER III Ciliate community After
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CHAPTER III Other microzooplankton
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CHAPTER III Microzooplankton Experi
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CHAPTER III Figure 6: (6a) General
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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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