Organic matter release by Red Sea cnidarians and its function as energy carrier [Elektronische Ressource] : effects of environmental variables / Wolfgang Niggl. Betreuer: Christian Wild

Wolfgang Niggl

Informations

• Publié par: ludwig-maximilians-universitat_munchen
• Publié le: 01 janvier 2010
• Nombre de lectures: 6
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Organic matter release by Red Sea
cnidarians and its function as energy
carrier – effects of environmental
variables





Dissertation zur Erlangung des Doktorgrades
der Fakultät für Geowissenschaften
der Ludwig-Maximilians-Universität München


vorgelegt von

Wolfgang Niggl
geboren in Traunstein

München, 23. September 2010
Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften der Fakultät
für Geowissenschaften der Ludwig-Maximilians-Universität München, Fachbereich
Geobiologie.

Die vorliegende Arbeit wurde in der Zeit von Juli 2007 bis September 2010 an der
Fakultät für Geowissenschaften und am GeoBio-Center der LMU in München
angefertigt.

Die mündliche Prüfung fand am 10.12.2010 statt.








Betreuer und Erstgutachter: PD Dr. Christian Wild
Zweitgutachter: Prof. Dr. Alexander Altenbach





















Table of Contents

Acknowledgements

Thesis Abstract

1 A precise and non-destructive method to calculate the surface area in living
scleractinian corals using X-ray computed tomography and 3D modelling

2 Coral surface area quantification – evaluation of established techniques by
comparison with computer tomography

3 Benthic community composition, coral-algal contact and fish distribution in
coral reefs around the urbanized area of Dahab, Northern Red Sea

4 Spatial distribution of the upside-down jellyfish Cassiopea sp. within fringing
coral reef environments of the Northern Red Sea: implications for its life cycle

5 Organic matter release by the benthic upside-down jellyfish Cassiopea sp.
fuels pelagic food webs in coral reefs

6 Carbohydrate composition of mucus released by scleractinian warm- and cold-
water reef corals

7 First evidence of coral bleaching stimulating organic matter release by reef
corals

8 Effect of water currents on organic matter release by three scleractinian corals

9 Organic matter release by Red Sea coral reef Organisms - potential effects on
microbial activity and in situ O availability 2

10 Benthic community composition affects O availability and variability in a 2
Northern Red Sea fringing reef


Curriculum Vitae














Acknowledgements

First of all, I would like to thank everyone, who helped to accomplish this PhD thesis.
My biggest thanks go to my supervisor PD Dr. Christian Wild, for giving me the
opportunity to work in the field of coral reef ecology. He provided best conditions for
preparing a PhD thesis and very enthusiastically helped wherever and whenever he could.
Without his drive this work would not have been possible.
Thanks also to Prof. Dr. Alexander Altenbach for reviewing this thesis and for general
support during the last three years. At the same time, I would like to thank the remaining
members of the thesis committee for reviewing this thesis. Among those, special thanks to
my co-supervisor PD Dr. Christian Laforsch for his commitment and enduring support.
Of course I would like to thank all members of CORE, especially Dr. Malik Naumann
and Dr. Andreas Haas for the great time on the field trips, but also Dr. Carin Jantzen, Florian
Mayer, Chris Williamson, Sandra Schöttner and all Bachelor and Master students for the
brilliant collaboration.
Thanks to Dr. Christoph Mayr, Dr. Ulrich Struck, Dr. Roland Fuß and Markus Öhlerich
for their help in sample analysis and interpretation.
Further thanks go to our cooperation partners Prof. Dr. Ronald Osinga and Dr. Miriam
Schutter at Wageningen University (The Netherlands), and to the staff of the Marine Science
Station in Aqaba (Jordan), especially to my field supervisor Dr. Riyad Manasrah.
I would also like to thank Prof. Dr. Ralph Tollrian, Mechthild Kredler, Petra Röske,
Ursula Bommhardt, Lisa Böck, Monika Brinkrolf, Christoph Haacke, and all members of the
Department of Earth and Environmental Science.
This thesis was enabled by grant Wi 2677/2-1 of the German Research Foundation
(DFG) to PD Dr. Christian Wild and a PhD stipend of University of Bavaria/Bavarian Elite
Advancement to Wolfgang Niggl. In this context, special thanks go to Anton Würfl from the
LMU-Stipendienreferat for answering all my questions.
Special thanks to my parents for their everlasting support and for their advice
whenever I needed it.
Last but not least I would like to thank Sylvie Schardt, who probably didn’t always
have an easy life with me during the last three years, but always made life easier for me.
Thanks for your loving and so important support.




























Thesis Abstract

Release of organic matter into the ambient seawater is a phenomenon described for a
variety of marine plants, algae and animals and is particularly important for the oligotrophic
coral reef ecosystems. Present coral reefs are affected by changing environmental
conditions caused by both local and global anthropogenic impacts. However, investigations
on potential influence of environmental factors on the release of organic matter by coral reef
organisms are rare. In addition, the Red Sea represents a largely under-investigated area of
the world ocean. The main objective of the present PhD thesis therefore was to investigate
the impacts of environmental factors on organic matter release by dominant Northern Red
Sea coral reef cnidarians and to trace the pathway of released organic matter as a trophic
vector in a series of interconnected field and laboratory studies.
The reasons for extracellular release of organic matter are manifold, but include active
disposal of excess carbon, passive permeation through the cell membrane, protection,
feeding or locomotion. Once released to the water column, the organic matter can fulfil
important roles for coral reef ecosystem functioning. The adhesive, insoluble organic
compounds released by corals efficiently trap particles from the water column increasing
their initial organic carbon and nitrogen content by orders of magnitude before they rapidly
settle. Coral-derived particulate organic matter (POM) thereby supports benthic life and
reduces loss of energy and nutrients from the reef ecosystem. Additionally, organic exudates
are directly taken up by a variety of reef organisms thus serve as a source of food and
thereby initiate metabolic communication. While the particulate fraction of released organic
matter can be consumed directly by e.g. fishes, crabs or worms, the dissolved fraction is
primarily accessible for microbes, but become accessible for higher trophic levels via the
microbial loop.
Due to its importance for reef ecosystem functioning, organic matter release by scleractinian
corals has been quantified recently by several studies. Most of these studies thereby chose
the corals surface area as reference parameter. Hence, the accuracy of the applied surface
area quantification is crucial to guarantee reliable results. The complex and delicate 3-D
structures of many coral species pose a big challenge and require sophisticated approaches.
Given, that coral tissue is only a thin layer covering the coral skeleton in scleractinian corals,
the skeleton itself has been widely used to assess the surface area of coral colonies. A
frequently used method is the foil wrap technique which is based on surface area to mass
correlation. An alternative approach for estimating the surface area is to coat corals by
dipping them into liquids such as dye or melted paraffin wax and subsequently correlating the
amount of the adhering liquid to the surface of the coral skeleton. However, techniques
described above are all harmful or destructive, thus generally not recommendable and
additionally not applicable for long-term studies requiring repeated measurements. Non-
destructive techniques such as 2D planar projection of 3D structures or simplifying 3D structures to geometric forms have also been applied but depending on the colonies growth
form may rather represent inaccurate approximations.
For these reasons, as part of this thesis, a novel, non-invasive and completely harmless
technique was developed to quantify the coral skeleton’s surface area at a yet nonpareil
accuracy (see Chapter 1). Conventional high-resolution medical computed tomography (CT)
was used to scan living coral colonies. The resulting ‘X-ray slices’ were than processed
using 3D modelling software, providing realistic 3D coral skeleton surface reconstructions
enabling high accuracy surface area measurements. This technique however is restricted to
the availability of CT, thus usually not applicable in the field.
Therefore, in a second study the surface area estimates obtained from the state-of-the-