School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

DISCUSSION To my knowledge similar results have not been published for the marine system up to now. These novel results show that extrapolating laboratory results of single species experiments to the field can be extremely difficult, as this strategy strongly neglects food web interactions. My findings show furthermore that we are just starting to understand marine food web interactions. Especially the impact of such interactive relationships between members of the microzooplankton needs further research. Mathematical models can provide deeper insights into the effect of such inter-specific interactions within the microzooplankton and will be applied in future studies. Microzooplankton in a “climate change” environment We know now that microzooplankton can play a crucial role in the marine food web, especially as phytoplankton grazer. Understanding its role in a changing environment caused by the anthropogenic increase of CO 2 will be one of our future challenges. Current climate scenarios predict a further rise in air and water temperature (IPCC, 2007). Indeed a strong warming trend has already been observed for the North Sea, where the mean annual temperature rose by 1.7°C since 1962 (Wiltshire et al., 2010). As growth and grazing rates of heterotrophic organisms like microzooplankton species are linked to temperature (Müller & Geller, 1993, Montagnes & Lessard, 1999) it can be assumed that these rates will also increase with increasing ambient temperatures. Similarly, a study on maximal growth rates of algal grazers showed that these decrease much more rapidly with decreasing temperature than those of their algal prey. This fact partly explains the phenomenon of distinct blooms in temperate and arctic oceans at times when coldest temperatures co-occur with conditions that favor increased phytoplankton growth and also the absence of such blooms in warmer regions (Rose & Caron, 2007). In the temperate North Sea the seasonal succession of plankton is initiated by the spring bloom of phytoplankton which is predominantly triggered by the combined effects of increasing light and nutrient availability (Sommer, 1996). The spring bloom is almost a start from zero, because only few phytoplankters will have survived the winter (Sommer et al., 2007). Warmer water temperatures especially during the colder period of the year might be expected to induce a higher metabolic rate in microzooplankton and consequently higher grazing rates. These higher grazing rates potentially lead to shifts in seasonal patterns of phytoplankton density: Even less phytoplankton survives winter time due to grazing by the more active microzooplankton species. This has already been 136
DISCUSSION reported for the North Sea around Helgoland where an increase in water temperature has led to a later onset of the spring bloom (Wiltshire & Manly, 2004). Furthermore, higher water temperatures also led to an increase in average cell size of the phytoplankton (Wiltshire et al., 2008), which could also be a result of selective grazing of microzooplankton on smaller phytoplankton fractions (compare Chapter III). A temperature-dependent shift in the size spectrum of phytoplankton has also been reported for the Baltic Sea (Sommer et al., 2007) where an increase in temperature also resulted in altered microzooplankton community structures and enhanced grazing rates (Aberle et al., 2007). With growth rates in the same range as those of its prey (Müller & Geller, 1993, Montagnes & Lessard, 1999), unicellular microzooplankton can respond faster to increasing phytoplankton availability (Johansson et al., 2004, Aberle et al., 2007), when compared to mesozooplankton, i.e. copepods. Copepods are at a disadvantage in that they need to develop from egg and larval stages and have overall lower growth rates (Rose & Caron, 2007). Although increased water temperatures favor all zooplankton to some extent (Rose & Caron, 2007) microzooplankton grazers will be favored even more by higher temperature than their mesozooplankton competitors. This could lead to a more pronounced recycling and retention of energy in the microzooplankton fraction and less energy being transferred directly from phytoplankton to the classic herbivorous food chain with copepods as important grazers. In addition, the recruitment success of higher trophic levels such as copepods is highly dependent on synchronization with phytoplankton blooms (Edwards & Richardson, 2004) especially in temperate environments like the North Sea. Shifts in bloom timing, as mentioned above, can therefore lead to classic mismatch situations. Consequences are not assessable yet but have potentially severe implications for trophic interactions, food web structures and also for higher trophic levels of human interest such as fish stocks. On the other hand there is evidence that the reproductive success of copepods can be enhanced directly by a microzooplankton diet (Tang & Taal, 2005) and higher copepod densities could consequently support higher fish stocks (Castonguay et al., 2008). Another aspect that has also to be taken into account when dealing with climate change are alterations in plankton biodiversity (Beaugrand et al., 2009, Goberville et al., 2010) which can also concern the microzooplankton. Warmer waters could promote warmadapted species (Wiltshire et al., 2010) and thus also support the invasion of new species from warmer regions. With ships’ ballast water planktonic species are 137
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 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 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?