School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

DISCUSSION Microzooplankton grazers at the base of the North Sea food web “Classic” food chain theories stress the role of primary production of photosynthetic phytoplankton grazed by crustacean mesozooplankters (> 200 µm) and those consumed by larger predators such as fish. Towards the end of the last century scientific findings emphasized the role of the microbial loop (Azam et al., 1983) as a major biological force in the ocean (Azam, 1998) and the significant importance of microzooplankters (< 200 µm) for the consumption of primary production. The aim of this thesis was to contribute in elucidating their role as phytoplankton grazers in the planktonic food web of the North Sea (Figure 1). Heterotrophic dinoflagellates and ciliates are the most important groups within the microzooplankton (Capriulo et al., 1991) especially in water of higher productivity (Calbet, 2008) and from a biomass perspective this was also confirmed in this study. The monitoring program conducted as an important basis for this thesis (Chapter I) verified the importance of heterotrophic dinoflagellates and ciliates. Summarized they showed carbon concentrations (652 µgC L -1 ) comparable to results from other studies (Riegman et al., 1993, Brussaard et al., 1995). During a phytoplankton spring bloom situation (Chapter III) the biomass of heterotrophic dinoflagellates and ciliates made up around 70-96% of the biomass of the microzooplankton and other studies confirm such an importance of both groups in the North Sea (Brussaard et al., 1995, Stelfox- Widdicombe et al., 2004). Whereas in my experiment (Chapter III) the phytoplankton showed a maximum carbon biomass concentration of 269 µgC L -1 , the microzooplankton reached concentrations of up to 126 µgC L -1 . At its maximum, microzooplankton contributed more than 50% to the available carbon of the plankton size fraction > 5µm. Especially during bloom situations, unicellular microzooplankton can respond quickly to increased phytoplankton food availability (Johansson et al., 2004, Aberle et al., 2007). This pattern has also been observed during a mesocosm spring bloom situation (Chapter III) where the phytoplankton peak (24.03.09) was followed by a microzooplankton maximum with less than one week delay (30.03.09). A meta-analysis by Calbet & Landry (2004) showed that microzooplankton grazing accounts on average for 60% of the mortality of the daily phytoplankton production in estuarine and coastal environments with chlorophyll a concentrations (3-13 µg L -1 ) comparable to those at Helgoland Roads (0.05-28 µg L -1 , Chapter I). The results for the grazing impact of microzooplankton obtained during a typical North Sea spring bloom 130
DISCUSSION (average 120%, Chapter III) even surpassed this range and showed the big potential and importance of this grazer group in waters around Helgoland. Copepods have long been considered the main herbivorous force in the plankton. However, taking into account the grazing impact of copepods during the spring bloom experiment (average 47%, Chapter IV) I showed that throughout the bloom phase the microzooplankton was the more important phytoplankton grazer group, even though it was always present in lower biomass concentrations (30-94 µg L -1 ) compared to copepods (103 µg L -1 ). In addition, our findings (Chapter I) suggest that in the field copepods biomass only plays a minor role when compared to microzooplankton. The combination of those two facts stresses the importance of microzooplankton grazers in the North Sea. Furthermore, my findings support results reported in other studies (Calbet, 2001, Calbet & Landry, 2004, Putland & Iverson, 2007, Sherr & Sherr, 2007). Irigoien (2005) proposed that microzooplankton grazing is of such importance that only phytoplankton species which can escape control by microzooplankton are able to bloom. Supporting this view, I showed in Chapter III that microzooplankton selective grazing can also have a stabilizing function on the blooming phytoplankton assemblage, leading to constant shares of the bloom-forming taxa. In my study the high grazing impact of ciliates prevented small flagellates from blooming, whereas the selective feeding of dinoflagellates led to a diatom bloom consisting of only three genera (Rhizosolenia, Thalassiosira, Chaetoceros). Microzooplankton is not only in direct competition with herbivorous mesozooplankters, such as copepods (Hansen, 1992, Aberle et al., 2007, Sherr & Sherr, 2007), but it is also an important food source for higher trophic levels (Kleppel, 1993). Thus, microzooplankters play a fundamental role as trophic intermediaries. They link small planktonic size fractions, unavailable to most metazoan consumers (Gifford, 1991), to mesozooplankton (Klein Breteler et al., 1999). Grazing experiments with copepods during the spring bloom experiments conducted in this thesis (Chapter III) showed that microzooplankton was always an important food source for them. Several other studies support this finding (Nejstgaard et al., 1997, Calbet & Saiz, 2005, Fileman et al., 2007, Figueiredo et al., 2009, De Laender et al., 2010). Nutritionally “poor” food can have negative effects on copepods (Schoo, 2010) and if they have the choice they obviously actively choose food according to their nutritional needs (Cowles et al., 1988, Kleppel, 1993). 131
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 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
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 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 120 and 121: CHAPTER IV Favella ehrenbergii (Fig
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
Page 130 and 131: 124
Page 132 and 133: DISCUSSION described by competition
Page 134 and 135: DISCUSSION to know who they are. Th
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
Page 146 and 147: 140
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
Page 162 and 163: 156
Page 164 and 165: 158
show all

School of Engineering and Science - Jacobs University

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?