Coral Reef Functioning Along a Cross‐shelf Environmental Gradient

242 Pages·2016·4.23 MB·English

1 

Coral Reef Functioning Along a Cross‐shelf Environmental Gradient:
Abiotic and Biotic Drivers of Coral Reef Growth in the Red Sea

Dissertation by
Anna Roik

In Partial Fulfillment of the Requirements
For the Degree of
Doctor of Philosophy

King Abdullah University of Science and Technology,
Thuwal, Kingdom of Saudi Arabia

June 2016
2 

EXAMINATION COMMITTEE APPROVALS FORM

The dissertation of Anna Roik is approved by the examination committee.
Committee Chairperson:
Prof. Christian R. Voolstra
Committee Members:
Prof. Burt Jones, Prof. Timothy Ravasi, Prof. Malcolm McCulloch
3 

ABSTRACT
Coral Reef Functioning Along a Cross‐shelf Environmental Gradient:
Abiotic and Biotic Drivers of Coral Reef Growth in the Red Sea
Anna Roik
Despite high temperature and salinity conditions that challenge reef growth in other
oceans, the Red Sea maintains amongst the most biodiverse and productive coral
reefs worldwide. It is therefore an important region for the exploration of coral reef
functioning, and expected to contribute valuable insights towards the understanding
of coral reefs in challenging environments.
This dissertation assessed the baseline variability of in situ abiotic conditions
(temperature, dissolved oxygen, pH, and total alkalinity, among others) in the central
Red Sea and highlights these environmental regimes in a global context. Further,
focus was directed on biotic factors (biofilm community dynamics, calcification and
bioerosion), which underlie reef growth processes and are crucial for maintaining
coral reef functioning and ecosystem services. Using full‐year data from an
environmental cross‐shelf gradient, the dynamic interplay of abiotic and biotic
factors was investigated.
In situ observations demonstrate that central Red Sea coral reefs were highly variable
on spatial, seasonal, and diel scales, and exhibited comparably high temperature, high
salinity, and low dissolved oxygen levels, which on the one hand reflect future ocean
predictions. Under these conditions epilithic bacterial and algal assemblages were
mainly driven by variables (i.e., temperature, salinity, dissolved oxygen) which are
4 

predicted to change strongly in the progression of global climate change, implying an
influential bottom up effect on reef‐building communities. On the other hand,
measured alkalinity and other carbonate chemistry value were close to the estimates
of preindustrial global ocean surface water and thus in favor of reef growth processes.
Despite this beneficial carbonate chemistry, calcification and carbonate budgets in
the reefs were not higher than in other coral reef regions. In this regard, seasonal
calcification patterns suggest that summer temperatures may be exceeding the
optima of calcifiers.
As a possible interpretation of the here observed environmental regimes, it can be
concluded that the central Red Sea may be less sensitive to ocean acidification, but is
already impacted by ocean warming. Importantly, this dissertation provides valuable
present‐day baseline data of the natural variability of relevant abiotic drivers
together with benthic community and reef growth dynamics. These data will be
important for future comparative studies and efforts to quantify the impact of future
environmental change in the region.
5 

ACKNOWLEDGEMENTS
I would like to thank my advisor C. R. Voolstra for giving me this great opportunity of
working in his lab, providing support, advice, and resources to conduct research for
my dissertation and beyond. I am grateful to the committee members, B. Jones, T.
Ravasi, and M. McCulloch for their valuable comments on this disseration. My
research would not have been possible to accomplish without the help, collaboration,
and company of my “field & research buddies” T. Röthig and M. Ziegler, who stood by
my side on the boat, in the reef, in the lab, and also when hiking volcanos, or chasing
camels, whales, and sharks. I would like to thank C. Roder for setting ground for my
first research projects and for preparing the monitoring stations together with C.
Walcher, F. Mallon, and P. Müller. Thanks to L. Smith, M. Pantalita, S. Mahmoud, D.
Pallett, H. and R. Al-Jahdali for the support with oceanographic instruments, dive
safety supervision, and logistics. A great “shukran” to the boat captains E., A., W., and
G. Al‐ Jahdali for taking me out to the reefs on regular basis. Thanks to C. Michell and
the KAUST BioScience Core Laboratory team for the sequencing of biofilm samples.
Also, I am very grateful for many scientific discussions and advices, diving support,
and lunch and coffee breaks with collegues from the Voolstra Lab and the Red Sea
Research Center. I would like to thank T. Bayer for sharing good times with me during
the years of my dissertation and for his endless patience in times when I needed to
focus on work more than on everything else. Lastly, I would like to thank my family
and friends back at home for staying in touch with me over these years. I am especially
grateful for the love, and encouragement from my mom and dad ‐ and for their
growing enthusiasm about my work and marine life.
6 

TABLE OF CONTENTS

EXAMINATION COMMITTEE APPROVALS FORM ....................................................................... 2
ABSTRACT ..................................................................................................................................................... 3
ACKNOWLEDGEMENTS .......................................................................................................................... 5
TABLE OF CONTENTS .............................................................................................................................. 6
LIST OF TABLES ...................................................................................................................................... 11
LIST OF FIGURES ..................................................................................................................................... 13
LIST OF EQUATIONS .............................................................................................................................. 15
1. INTRODUCTION .............................................................................................................................. 16
1.1. Coral Reefs ............................................................................................................................... 16
1.2. Importance of reef communities in coral reef functioning ................................. 17
1.3. Importance of calcification in coral reef functioning ............................................ 18
1.4. Carbonate production states as a measure of coral reef persistence or
degradation ........................................................................................................................................... 20
1.5. Importance of the Red Sea for coral reef studies .................................................... 21
1.6. References ................................................................................................................................ 23
2. OBJECTIVES ...................................................................................................................................... 30
CHAPTER I ................................................................................................................................................. 34
3. Year‐long monitoring of physico‐chemical and biological variables provide a
comparative baseline of coral reef functioning in the central Red Sea ........................... 34
3.1. Abstract ..................................................................................................................................... 35
3.2. Introduction ............................................................................................................................ 36
3.3. Material and Methods ......................................................................................................... 40
3.3.1. Study sites and design .................................................................................................... 40
3.3.2. Currents ................................................................................................................................ 44
3.3.3. Temperature, salinity, dissolved oxygen, chlorophyll‐a, and turbidity .... 44
3.3.4. Dissolved inorganic nutrients ..................................................................................... 45
3.3.5. Sedimentation .................................................................................................................... 45
3.3.6. Univariate analyses of physico‐chemical variables ........................................... 46
3.3.7. Bacterial communities of biofilm and reef water ............................................... 47
3.3.8. Algal biofilm communities ............................................................................................ 51
7 

3.3.9. Analyses of multivariate physico‐chemical data and ‘biological‐
environmental’ matching ................................................................................................................ 52
3.4. Results ....................................................................................................................................... 52
3.4.1. Currents ................................................................................................................................ 53
3.4.2. CTD variables ..................................................................................................................... 57
3.4.2.1. Temperature .................................................................................................................. 59
3.4.2.2. Salinity .............................................................................................................................. 60
3.4.2.3. Dissolved oxygen (DO) .............................................................................................. 61
3.4.2.4. Turbidity and chlorophyll‐a .................................................................................... 62
3.4.2.5. Dissolved inorganic nutrients ................................................................................ 63
3.4.2.6. Sedimentation ............................................................................................................... 64
3.4.3. Community composition and dynamics of reef water bacteria and
bacterial biofilms ................................................................................................................................ 69
3.4.3.1. Community composition and dynamics of reef water bacteria ............... 70
3.4.3.2. Community composition and dynamics of bacterial biofilms .................. 73
3.4.3.3. Community composition and dynamics of algal biofilms ........................... 77
3.4.4. Physico‐chemical environment and drivers of biotic communities in coral
reefs 78
3.5. I. Discussion ............................................................................................................................. 82
3.5.1. Physico‐chemical baseline data of coral reefs in the central Red Sea ....... 83
3.5.1.1. Currents ........................................................................................................................... 83
3.5.1.2. Temperature and salinity ......................................................................................... 84
3.5.1.3. Dissolved oxygen (DO) .............................................................................................. 86
3.5.1.4. Chlorophyll‐a and dissolved inorganic nutrients........................................... 87
3.5.1.5. Sedimentation and Turbidity .................................................................................. 88
3.5.2. Biotic baseline data of coral reefs in the central Red Sea: reef water
bacteria and bacterial and algal biofilms ................................................................................. 90
3.5.2.1. Composition and dynamics of reef water bacteria ........................................ 90
3.5.2.2. Composition and dynamics of bacterial biofilms ........................................... 91
3.5.2.3. Composition and dynamics of algal biofilms ................................................... 93
3.5.3. Physico‐chemical drivers of biotic communities in the central Red Sea .. 94
3.5.4. Conclusions ......................................................................................................................... 96
3.6. References ................................................................................................................................ 98
8 

CHAPTER II .............................................................................................................................................. 111
4. Spatial and seasonal reef calcification in corals and calcareous crusts in the
central Red Sea ....................................................................................................................................... 111
4.1. Abstract ................................................................................................................................... 112
4.2. Introduction .......................................................................................................................... 113
4.3. Material and Methods ....................................................................................................... 116
4.3.1. Study sites and seasons ............................................................................................... 116
4.3.2. Benthic reef composition ............................................................................................ 118
4.3.3. Temperature profiles .................................................................................................... 120
4.3.4. Seasonal calcification rates of reef‐building corals ......................................... 121
4.3.5. Seasonal calcification rates of calcareous crusts (CC) .................................... 123
4.3.6. Statistical analyses ......................................................................................................... 125
4.3.7. Global comparison of calcification rates .............................................................. 127
4.4. Results ..................................................................................................................................... 128
4.4.1. Benthic reef composition ............................................................................................ 129
4.4.2. Temperature profile ...................................................................................................... 130
4.4.3. Seasonal calcification of reef‐building corals ..................................................... 131
4.4.4. Seasonal calcification of calcareous crusts (CC) ............................................... 133
4.4.5. Global comparison of calcification rates .............................................................. 135
4.5. Discussion .............................................................................................................................. 137
4.5.1. Spatial calcification and coral reef benthic composition............................... 137
4.5.2. Seasonal calcification and temperature dependency ..................................... 138
4.5.3. Calcification in corals vs. calcareous crusts (CC) .............................................. 140
4.5.4. Global comparison of calcification rates from the central Red Sea .......... 141
4.6. References .............................................................................................................................. 143
4.7. Supplementary Materials ................................................................................................ 148
CHAPTER III ............................................................................................................................................ 163
5. Abiotic and biotic drivers of carbonate budgets in the central Red Sea provide
insights into present‐day coral reef growth in a naturally high temperature and high
alkalinity sea ........................................................................................................................................... 163
5.1. Abstract ................................................................................................................................... 164
5.2. Introduction .......................................................................................................................... 165
5.3. Materials and Methods ..................................................................................................... 169
9 

5.3.1. Study sites and environmental monitoring ........................................................ 169
5.3.2. Abiotic parameters: continuous data .................................................................... 170
5.3.3. Abiotic parameters: seawater samples ................................................................. 171
5.3.4. Net‐accretion/erosion rates measurements using limestone blocks ...... 172
5.3.5. Reef carbonate budget estimates ............................................................................ 172
5.3.6. Statistical analyses: Abiotic parameters ............................................................... 176
5.3.7. Statistical analyses: Net‐accretion/erosion rates and carbonate budgets
177
5.3.8. Statistical analyses: Abiotic and biotic drivers .................................................. 177
5.4. Results ..................................................................................................................................... 180
5.4.1. Abiotic parameters relevant for reef growth ..................................................... 180
5.4.2. Net‐accretion/erosion rates along a cross‐shelf gradient ............................ 191
5.4.3. Carbonate budgets along a cross‐shelf gradient ............................................... 194
5.4.4. Abiotic and biotic drivers related to net‐accretion rates and carbonate
budgets 195
5.5. Discussion .............................................................................................................................. 197
5.5.1. Abiotic parameters governing reef growth in the central Red Sea ........... 198
5.5.2. Net‐accretion/erosion rates (Gnet) and carbonate budgets (Gbudgets)
along a cross‐shelf gradient ......................................................................................................... 201
5.5.3. Global and historical perspective on carbonate budgets (Gbudgets) in the
Red Sea 203
5.5.4. Abiotic drivers related to reef growth in the central Red Sea .................... 205
5.5.5. Biotic drivers related to reef growth in the central Red Sea ....................... 207
5.5.6. Conclusions ....................................................................................................................... 208
5.6. References .............................................................................................................................. 210
5.7. Supplementary Materials ................................................................................................ 219
5.7.1. References (Supplementary Materials) ................................................................ 225
6. SYNTHESIS ...................................................................................................................................... 226
6.1. References .............................................................................................................................. 238
10 

© June 2016
Anna Roik
All Rights Reserved