Growth and calcification of reef-building coralline algae and their response to ocean acidification

160 Pages·2016·4.12 MB·English

Growth and calcification of reef-building coralline algae and their response to ocean
acidification

Bonnie Lewis
BApp Sc (Hons)

Griffith School of Environment & Australian Rivers Institute
Griffith University, Australia

Submitted in fulfilment of the requirements
of the degree of Doctor of Philosophy

April 2016
Abstract
Coralline algae play a central role in tropical reef ecology helping to build and stabilise the
reef framework. Due to their high Mg-calcite skeleton, coralline algae are also one of the
most sensitive marine calcifying organisms to ocean acidification, and potential indicators for
assessing the impacts of climate change. However, despite their importance in reef ecology,
basic information on coralline algae, such as their growth and calcification rates, are
relatively unknown. The reason for this scarcity of information is, in part, due to the lack of
effective and efficient methods for obtaining these rates in the field, and the slow growth of
coralline algae necessitating lengthy studies. Therefore, the aims of this study were to
establish more effective methods to determine in situ growth and calcification rates of
coralline algae, to determine baseline growth and calcification rates of a key reef-building
coralline algae species on the Great Barrier Reef (GBR), and to investigate the effects future
climate change scenarios may have on these growth rates.

The first study in this project (Chapter 2) was to establish a more efficient and effective
staining method of obtaining in situ growth and calcification rates of coralline algae. To
achieve this, three calcium markers were selected from previous use on marine calcifiers in
the literature. These markers were then tested at three different concentrations and immersion
times, ranging from 1min to 24hrs, on two of the most abundant encrusting (Porolithon
onkodes) and branching (Lithophyllum pygmaeum) species of coralline algae on the GBR.
Results of this experiment found immersion time for staining coralline algae could be
reduced from the commonly used 24hr immersion time down to less than 3hrs, thus making
the staining method a far more efficient and effective technique for obtaining in situ growth
and calcification rates. In Chapter 3, I determined the seasonal growth and calcification rates
of most abundant reef-building crustose coralline alga on the GBR in a 15 month in situ
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study, and explored the effects of shaded and exposed irradiance levels on these rates.
Seasonal variation was detected in each of the metrics measured (vertical growth, marginal
growth and calcification), with maximum vertical growth and calcification observed in
spring, and marginal extension in autumn. Surprisingly the summer season did not produce
the maximum vertical or marginal rates as expected. Light treatments revealed significant
difference in growth rates between exposed and shaded treatments.

The presence of growth banding in the P. onkodes skeleton was examined in Chapter 4 to
determine if changes in mineralogy, density, cell size or reproductive cycles (conceptacle
banding) could be used to measure growth rates of coralline algae without the need for
lengthy in situ studies (such as in Chapter 3). Results from this study showed that
conceptacles viewed under UV light, and changes in skeletal density revealed in micro-CT
scans, provided easily distinguishable banding that could be used to determine growth rate of
the organism. Mineralogical mapping also revealed patterns of banding created by changes in
Mg content. The determination of this banding in the tropical CCA P. onkodes offers another
method for obtaining growth rates of coralline algae without the need for long-term in situ
studies.

The final experiment in this thesis (Chapter 5) examined the effects of future ocean
acidification conditions, coupled with increased nutrient and irradiance levels, on the growth
rates of the abundant branching coralline alga L. pygmaeum. Understanding the effects of
rising pCO and its interaction with other key photosynthetic drivers such as irradiance and
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nutrient levels is fundamental for developing accurate predictions on the response of coralline
algae to future climate change scenarios. To assess the individual and interacting effects of
these three factors on growth, a four week multi-factorial laboratory study was conducted
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incorporating three pCO levels, two irradiance and two nutrient (ammonium and phosphate)
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levels. Results from this study indicate future nutrient enrichment will decrease growth
irrespective of pCO conditions, and that these detrimental effects will be further enhanced
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when combined with low light conditions. This is very relevant to coralline algae living in
inshore GBR regions, where light levels are often reduced during flooding events.

In this thesis I have: 1) determined the calcium marker calcein is a more efficient and
effective staining method for use on tropical coralline algae. 2) Provided seasonal growth and
calcification rates of the key reef-building coralline alga Porolithon onkodes, and determined
seasonal variation within these rates. 3) Determined conceptacle and skeletal density banding
is present in tropical coralline algae and can be used to measure growth. 4). Demonstrated
growth of the branching coralline alga Lithophyllum pygmaeum is enhanced under elevated
pCO and light conditions, but inhibited by nutrient enrichment.
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Statement of Originality
This work has not previously been submitted for a degree or diploma in any university. To the
best of my knowledge and belief, the thesis contains no material previously published or written
by another person except where due reference is made in the thesis itself.
Bonnie Lewis
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Acknowledgements
I would like to thank my supervisor Guillermo Diaz-Pulido for his scientific and academic
support, for sharing his knowledge and enthusiasm for all things coralline algae, and for
providing me with the opportunity to work in such an amazing environment on the Great
Barrier Reef.
To my family I owe my deepest gratitude for all their support over the past four years. Thank
you for not only providing me with the financial means to go back to uni, but for taking me
on holidays, adding milo, chocolate and coco pops to your shopping lists, keeping my car
from dying, spending your weekends making fieldwork equipment, for always looking out
for me and after me, and for the million other things you’ve done to make life easier over the
course of my PhD.
To my lab group and fieldwork buddies Alex, Carlos, Cris, Emma, Lucho and Pat, thanks for
being awesome people to work with and for all your help in the field, lab, office, bar and
everywhere else in between.
Thank you to Shannon Lauchlan, Ian Banks, Victoria Stokes, Alison Hayes and all the staff at
the Heron Island Research Station for your help in the field, and to Merinda Nash, James St
John, Jo Wilkinson, Michael Turner, Frank Brink and Dorothea Bender for your help and
advice with sample preparation and data analysis.
This project was supported by Griffith School of Environment, Australian Rivers Institute,
The Great Barrier Reef Foundation and ARC grant. All fieldwork was carried out under the
Great Barrier Reef Marine Park Authority permit G13/36022.1

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List of expected publications from this thesis
 Lewis, B and Diaz-Pulido, G. Suitability of three fluorochrome markers for obtaining
in situ growth rates of coralline algae. Journal of Phycology (in review) (Chapter 2).
 Lewis, B., Kennedy, E. and Diaz-Pulido, G. Seasonal growth and calcification of the
coralline alga Porolithon onkodes on the Great Barrier Reef. Marine Ecology Progress
Series (Chapter 3).
 Lewis, B., Lough. J., Nash. M. and Diaz-Pulido, G. Presence of skeletal banding in
the tropical crustose coralline algae Porolithon onkodes on the Great Barrier Reef.
Journal of Experimental Marine Biology and Ecology (Chapter 4).
 Lewis, B., Bender, D., Dove. S. and Diaz-Pulido. Physiological responses of the
branching coralline algae Lithophyllum pygmaeum to increased levels of pCO ,
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irradiance and nutrients. Journal of Phycology. (Chapter 5).

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Table of Contents

Abstract ...................................................................................................................................... ii
Statement of Originality ............................................................................................................. v
Acknowledgements ................................................................................................................... vi
List of expected publications from this thesis.......................................................................... vii
Table of Contents ................................................................................................................... viii
Table of Figures ........................................................................................................................ xi
List of Tables .......................................................................................................................... xvi
Chapter 1: General introduction................................................................................................. 1
Coralline algae importance..................................................................................................... 1
Threats to coralline algae on the Great Barrier Reef .............................................................. 1
Growth and calcification ........................................................................................................ 4
Current methods of obtaining growth and calcification rates ................................................ 5
Study Site ............................................................................................................................... 9
Thesis aims ........................................................................................................................... 10
Thesis outline ....................................................................................................................... 11
Chapter 2: Suitability of three fluorochromes markers for obtaining in situ growth rates of
coralline algae .......................................................................................................................... 13
Introduction .......................................................................................................................... 13
Materials and Methods ......................................................................................................... 16
Sample collection & staining ............................................................................................ 16
Detection of marker using Fluorescence Microscopy and Vertical Growth Measurements
.......................................................................................................................................... 19
Statistical analyses ............................................................................................................ 20
Results .................................................................................................................................. 21
Effects on Growth ............................................................................................................. 21
Visibility ........................................................................................................................... 29
Relationship between Growth & Visibility ...................................................................... 34
Discussion ............................................................................................................................ 34
Effects of toxicity on growth ............................................................................................ 34
Visibility ........................................................................................................................... 36
Average growth and visibility .......................................................................................... 37
Advantages and disadvantages of the markers ................................................................. 38
Efficiency .......................................................................................................................... 40
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Conclusion ............................................................................................................................ 41
Chapter 3: Seasonal growth and calcification rates of the coralline alga Porolithon onkodes
on the Great Barrier Reef ......................................................................................................... 42
Introduction .......................................................................................................................... 42
Materials and Methods ......................................................................................................... 46
Sample collection & staining ............................................................................................ 46
Growth measurements ...................................................................................................... 49
Calcification measurements .............................................................................................. 51
Statistical Analysis ........................................................................................................... 52
Results .................................................................................................................................. 52
Vertical growth measurements ......................................................................................... 52
Marginal growth measurements ....................................................................................... 55
Calcification rate ............................................................................................................... 55
Discussion ............................................................................................................................ 58
Comparison between metrics ............................................................................................ 66
Conclusion ............................................................................................................................ 67
Chapter 4: Presence of skeletal banding in the tropical crustose coralline algae Porolithon
onkodes on the Great Barrier Reef ........................................................................................... 68
Introduction .......................................................................................................................... 68
Materials and Methods ......................................................................................................... 77
Sample collection & staining ............................................................................................ 77
UV images to examine conceptacle banding .................................................................... 79
X-ray imaging and micro-CT scans to examine density banding .................................... 80
SEM to examine cell size and density banding ................................................................ 82
X-ray Diffraction (XRD) to determine seasonal mineralogy ........................................... 82
Results .................................................................................................................................. 83
UV images to examine conceptacle banding .................................................................... 83
Micro-CT scans to examine density banding ................................................................... 84
Mineralogy mapping to determine Mg-calcite banding ................................................... 87
SEM to examine CaCO carbonate and cell size banding ................................................ 89
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X-ray Diffraction (XRD) to determine seasonal mineralogy ........................................... 91
Discussion ............................................................................................................................ 92
UV images to examine conceptacle banding .................................................................... 92
Density and cell size banding ........................................................................................... 94
Mineralogy mapping to determine Mg-calcite banding. .................................................. 96
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X-ray Diffraction (XRD) to determine seasonal mineralogy ........................................... 97
Conclusions .......................................................................................................................... 99
Chapter 5: Physiological responses of the branching coralline algae Lithophyllum pygmaeum
to increased levels of pCO , irradiance and nutrients. ........................................................... 101
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Introduction ........................................................................................................................ 101
Materials and Methods ....................................................................................................... 105
Experimental set-up and sample collection .................................................................... 105
Experimental set-up, treatments and monitoring ............................................................ 106
Water quality parameters ................................................................................................ 109
Water parameters ............................................................................................................ 111
Response Variables – Growth, Respiration and Photosynthetic parameters .................. 112
Statistical Analysis ......................................................................................................... 113
Results ................................................................................................................................ 114
Vertical Growth .............................................................................................................. 114
Net Productivity, Respiration and LEDR ....................................................................... 115
Photosynthetic parameters .............................................................................................. 119
Relationships between response variables ...................................................................... 120
Discussion .......................................................................................................................... 121
Effects of pCO ............................................................................................................... 121
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Effects of Irradiance ....................................................................................................... 123
Effects of nutrients .......................................................................................................... 124
Relationship between response variables ....................................................................... 125
Conclusion .......................................................................................................................... 126
Chapter 6. General Discussion ............................................................................................... 128
Effective calcium markers to determine coralline growth ................................................. 128
Baseline growth and calcification rates .............................................................................. 129
Skeletal banding in tropical crustose coralline algae ......................................................... 131
Climate change and coralline algae growth ....................................................................... 131
Major findings .................................................................................................................... 133
References .............................................................................................................................. 134

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