An evaluation of the effect of food quality on heterotrophic protists with a critical assessment of a new measuring technique (Flow CAM) [Elektronische Ressource] / vorgelegt von Florian Matthias Hantzsche

Florian Hantzsche

Sujets

• Naturwissenschaften

Informations

• Publié par: christian-albrechts-universitat_zu_kiel
• Publié le: 01 janvier 2010
• Nombre de lectures: 13
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

An evaluation of the effect of food quality
on heterotrophic protists with a critical
assessment of a new measuring technique
(Flow CAM)








Dissertation
zur Erlangung des Doktorgrades

der Mathematisch-Naturwissenschaftlichen Fakultät

der Christian-Albrechts-Universität
zu Kiel


vorgelegt von


Florian Matthias Hantzsche


Kiel 2010







































Referent: Prof. Dr. Maarten Boersma
Koreferent: Prof. Dr. Franciscus Colijn

Tag der mündlichen Prüfung: 01.10.2010
Zum Druck genehmigt: 01.10.2010 CONTENTS

CHAPTER I ............................................................................................................................... 4
General introduction............................................................................................................... 4
List of manuscripts 10

CHAPTER II............................................................................................................................ 11
Some fundamental Flow CAM measurement basics for plankton ecological surveys in the
fluorescence triggered image mode...................................................................................... 11

CHAPTER III........................................................................................................................... 34
Use of the Flow CAM for plankton abundance estimations in the field and a critical
assessment of the applied method ........................................................................................ 34

CHAPTER IV .......................................................................................................................... 62
Dietary induced responses in the phagotrophic flagellate Oxyrrhis marina........................ 62

CHAPTER V............................................................................................................................ 82
No food selection, but compensatory feeding in the phagotrophic flagellate Oxyrrhis
marina .................................................................................................................................. 82

CHAPTER VI ........................................................................................................................ 100
General Discussion............................................................................................................. 100

SUMMARY ........................................................................................................................... 112
ZUSAMMENFASSUNG....................................................................................................... 114
REFERENCES....................................................................................................................... 117
DANKSAGUNG.................................................................................................................... 128
CURRICULUM VITAE ........................................................................................................ 129
PUBLIKATIONEN................................................................................................................ 130
ERKLÄRUNG 131
CHAPTER I
CHAPTER I
General introduction

The marine pelagic food web
Marine pelagic food webs are complex and dynamic networks of many species which
are linked in manifold interactions driven by chemical and physical factors. Some of the
species interact indirectly, competing for the same resource; some of them interact directly via
consumption and predation. The human need for simplification and classification has forced
many of the interacting species into different trophic levels, consuming the levels below, and
being eaten by the level above. We also know, however, that these classifications are dynamic
in time and space, which means that a consumer might switch between food from different
trophic levels depending on prey availability, ingestibility and food quality (Sommer et al.
2002).
Phytoplankton, at the base of the pelagic food web, comprises a huge variety of
different algal species, which supply the ecosystem with energy. Light, nutrients and
inorganic carbon are the resources that regulate the quantity, distribution, and structure of the
phytoplankton community (Diehl 2002). Light serves as the primary energy source through
photosynthesis. Light and nutrients differ fundamentally, because nutrients can be recycled
and mostly do not leave the ecosystem, whereas absorbed light is transformed into energy and
only flows in one direction within the food web, ultimately disappearing again as heat. For a
long time the main consumers of the phytoplankton were thought to be the highly visible
crustacean mesozooplankters, which, in turn, are the most important food source for higher
trophic levels, such as fish (Cushing 1995). Since the 1970s it has become clear that
herbivorous and bacterivorous protists such as heterotrophic nanoflagellates (HNF),
heterotrophic/mixotrophic dinoflagellates and ciliates play a central role in the lower pelagic
food web (Pomeroy 1974; Fenchel 1982c; Azam et al. 1983; Fenchel 2008), and that the
microbial loop is of great importance in the transfer of material and energy to higher trophic
levels. It is by now well established that protistan predation can be a significant source of
mortality for suspended bacteria and phytoplankton in marine ecosystems. Protists, in turn,
can be a significant food source for metazooplankton (Fenchel 1982b; Kleppel 1993; Sherr
and Sherr 1994; Kiorboe 1998; Landry and Calbet 2004).

4 CHAPTER I
Ecological stoichiometry
Traditionally, in aquatic ecology there has been a distinction between bottom-up and
top-down control of population dynamics of species, often extended to the whole ecosystem.
It is important to realise, however, that top-down control (predation determines population
dynamics) in one trophic level is likely to lead to bottom-up control (food availability
determines population dynamics) on the next level. Therefore, comprehending the predatory
(grazing) interaction between two adjacent trophic levels is of paramount importance for our
understanding of the functioning of the ecosystem as a whole. The theory of ecological
stoichiometry has proven to be a very useful framework to advance our knowledge of trophic
interactions (Sterner and Elser 2002). Ecological stoichiometry, the study of ratios of
important nutrients in food and consumers, uses these ratios to explain the interactions
between different trophic levels and such processes as the transfer of material and energy
through the food web.

Fish
Carbon dissipation
Zooplankton
Algae, seston
0 200 400 600 800 1000
C:P ratio (molar)
Figure 1: C:P ratio of different trophic levels in an aquatic system. Redrawn from
Sterner and Elser (2002).

Previous studies have shown that a substantial difference exists in the nutrient
composition between autotrophs and heterotrophs. While the elemental composition of
autotrophs follows the availability of nutrients in the environment quite closely, heterotrophs
have a more constant body composition, i.e. are more homeostatic with respect to the ratio of
the main nutrients, carbon (C), nitrogen (N) and phosphorus (P). Obviously, this mismatch in
availability and demand between autotrophs and herbivores affects the transfer efficiency of
5 CHAPTER I
energy and organic material through the food web. As stated above, not only the quantity of
nutrients but rather the ratio of macronutrients (N, P, Si, (Fe)) for which autotrophs compete,
determines the composition of the phytoplankton community and its elemental food quality
(Tilman et al. 1982; Sommer et al. 2002). Even though heterotrophs are more homeostatic, the
different species of heterotrophs differ in their elemental composition, and species higher up
in the food chain tend to have lower amounts of carbon in their tissue relative to nitrogen and
phosphorus than those species lower in the food chain (Fig. 1). Hence, especially from a
herbivore point of view the elemental composition of its food source is highly variable
depending on the nutrient availability of the algae, their growth phase, and the availability of
light and carbon. Several mechanisms have evolved in herbivorous consumers to deal with
nutritional imbalances. Essentially, these mechanisms can be divided into two groups: pre-gut
and post-gut mechanisms. Pre-gut adaptations include selective feeding and selective transfer
of material from the gut into the body. Post-gut adaptations include differential assimilation of
different substances and respiratory and excretion processes. In most feeding processes food
is taken up as a package and not as single nutrients, and thus the ecological stoichiometry
framework mostly assumes that the majority of the processes to deal with nutritional
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