acidification, coastal runoff and warming on marine calcifying
organisms on tropical coral reefs
Nikolas Vogel
Dissertation submitted in fulfillment of the requirements for the degree of Doctor of Natural Science
-Dr. rer.
nat.-Faculty of Biology/Chemistry University of Bremen
I, Nikolas Vogel hereby certify that I am the sole author of this thesis and any assistance received is fully acknowledged. To the best of my knowledge this thesis does not contain any material, which has been previously published or written by others. Any content of other work utilized in this thesis is cited in accordance with the standard referencing procedures.
Date:
January 2012 and January 2015. This thesis was conducted under the supervision of Dr. Sven Uthicke (AIMS) and Prof. Dr. Christian Wild (ZMT). Research for this thesis was funded by the Australian Insti-tute of Marine Science and was conducted with the support of funding from the Australian Government’s National Environmental Research Program (NERP).
First Examiner: Prof. Dr. Christian Wild
Leibniz Center for Tropical Marine Ecology, Bremen
Second Examiner: Prof. Dr. Kai Bischof University of Bremen
Additional Examiners: Prof. Dr. Claudio Richter
Alfred Wegener Institute, Bremerhaven
Dr. Mirta Teichberg
Leibniz Center for Tropical Marine Ecology, Bremen
Student Members: PhD Student Ines Stuhldreier
Leibniz Center for Tropical Marine Ecology, Bremen
Master Student Hagen Buck-Wiese University of Bremen
Many thanks to Sven Uthicke who invited me to AIMS in the first place and gave me the opportunity to set the course to conduct this thesis. His great supervision on professional and friendly basis made me come back to AIMS several times and contributed to the lovely environment that I have experienced in our working group. Thanks for giving me the opportunity to experience places that I would not have seen otherwise. It has been a great time.
Many thanks to Christian Wild, who offered to be my doctoral thesis supervisor and supported the idea to conduct this thesis as collaboration between the AIMS and the ZMT. His great supervision and impulsion considerably helped me to conduct this thesis. Thanks for inviting me to the ZMT and to the welcoming and friendly Coral Reef Ecology working group.
I am very grateful to Kai Bischof who offered to be the second examiner of this thesis. Many thanks to Claudio Richter, Mirta Teichberg, Ines Stuhldreier and Hagen Buck-Wiese to be part of the examination committee.
Thanks to Sam Noonan, who contributed with corrections to the Abstract, General Introduction and General Discussion of this thesis.
I thank the Water Quality Group at AIMS, Katharina Fabricius, Sam Noonan, Yan Ow, John Pfitzner, Britta Schaffelke, Julia Strahl, Lindsay Trott, Sven Uthicke and Irena Zagorskis, it has been a privilege working with you.
Gratitude to my co-authors Line Bay, Neal Cantin, Catherine Collier, Katharina Fabricius, Florita Flores, Paulina Kaniewska, Friedrich Meyer, Sam Noonan, Yan Ow, Julia Strahl, Sven Uthicke, Christian Wild and all my other colleagues in Australia and Germany, it has been a pleasure working with you.
Many thanks to Julia and Sam and all my other friends in Australia who made me feel like home. It has been a sensational time and I am grateful for all the fantastic things that we have done together. Many thanks also to all my friends in Germany, who reminded me on home and gave me a great time when I was visiting Germany.
Thank you Lisa for your support, motivation and understanding. I am glad that we came to the right decision in the beginning.
Last but not least, I want to thank my family, in particular my mother and father, who always supported my ideas and dreams. I love you and I am very lucky to have you.
Zusammenfassung der Doktorarbeit . . . 1
Thesis abstract . . . 2
1 General introduction 4 1.1 Coral reef ecosystems . . . 4
1.2 Coral reefs: sociological and economic importance . . . 5
1.3 Global threats to coral reefs . . . 5
1.3.1 Ocean acidification . . . 6
1.3.2 Ocean warming . . . 9
1.4 Local threats to coral reefs . . . 10
1.4.1 Coastal runoff . . . 10
1.4.2 Other local stressors . . . 12
1.5 Combinations of global and local stressors . . . 13
1.6 Knowledge gaps & research questions . . . 13
1.7 Experimental species . . . 15
1.8 Introduction to study sites . . . 17
1.9 Publication outline . . . 18
2 Calcification and photobiology in symbiont-bearing benthic foraminifera and responses to a high CO2environment 34 Abstract . . . 35 2.1 Introduction . . . 36 2.2 Methods . . . 37 2.3 Results . . . 41 2.4 Discussion . . . 47
3 Calcareous green alga Halimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps 60 Abstract . . . 61 3.1 Introduction . . . 62 3.2 Methods . . . 64 3.3 Results . . . 69 3.4 Discussion . . . 73
Abstract . . . 87
4.1 Introduction . . . 88
4.2 Methods . . . 90
4.3 Results . . . 94
4.4 Discussion . . . 98
5 Effects of elevated dissolved inorganic carbon and nitrogen on the physiology of sclerac-tinian corals and calcareous macroalgae under ocean acidification and eutrophication con-ditions 112 Abstract . . . 113 5.1 Introduction . . . 114 5.2 Methods . . . 115 5.3 Results . . . 120 5.4 Discussion . . . 125
6 Interactive effects of ocean acidification and warming on coral reef associated epilithic algal communities under past, present and future ocean conditions 140 Abstract . . . 141 6.1 Introduction . . . 142 6.2 Methods . . . 143 6.3 Results . . . 148 6.4 Discussion . . . 153 7 General Discussion 165 7.1 Responses of coral reef organisms to ocean acidification . . . 165
7.2 Responses of coral reef organisms to combinations of ocean acidification and decreased light availability . . . 170
7.3 Responses of coral reef organisms to combinations of elevated dissolved inorganic car-bon and nitrogen . . . 171
7.4 Responses of coral reef organisms and communities to past and future OA and OW conditions . . . 172
7.5 Ecological implications . . . 173
List of tables . . . 184 List of figures . . . 187
Anthropogen verursachte Treibhausgas-Emissionen führen zu zwei wesentlichen Umweltveränderun-gen von globalem Ausmaß für Korallenriffe: Ozeanversauerung (OA) und Ozeanerwärmung (OW). Zusätzlich kann steigender terrestrischer Oberflächenabfluss, welcher Düngemittel, Abwässer, Sedi-mente und andere Verunreiniger in küstennahe Gebiete zuführt, die Wasserqualität auf lokaler Ebene verschlechtern. Folglich sind photosynthese-betreibende und kalkbildende Korallenriff-Lebewesen von OA, OW und küstennahem Oberflächenabfluss betroffen, aber interaktive Auswirkungen dieser Stress-faktoren auf Schlüssel-Lebewesen des Korallenriffs sind weitestgehend unbekannt. Das Ziel dieser Dok-torarbeit war es, zu erforschen, wie sich OA einzeln und in Kombination mit OW oder lokalen Stressfak-toren (d. h. verringerter Lichtverfügbarkeit und anorganischer Eutrophierung) auf wichtige kalkbildende Korallenriff-Lebewesen auswirkt. Eine Reihe von feld- und labor-basierten Experimenten wurde am Great Barrier Reef und an natürlichen vulkanischen Kohlendioxid-Quellen in Papua Neuguinea durchge-führt. Eine Auswahl von Reaktionsfaktoren, einschließlich Wachstum, Kalzifizierung und Photosyn-these, wurden auf der Arten- und Artengemeinschafts-Ebene untersucht. OA zeigte keine negativen Kurzzeit-Auswirkungen auf drei große benthische Foraminiferen-Arten (Kapitel 2) und Langzeit-Aus-wirkungen auf mehrere kalkbildende Grünalgen-Arten der Gattung Halimeda (Kapitel 3). OA in Ver-bindung mit verringerter Lichtverfügbarkeit führte nach kurzer Zeit zu additiven negativen Auswirkun-gen auf die Koralle Acropora millepora (Kapitel 4), während OA in Verbindung mit Eutrophierung nach kurzer Zeit keine signifikanten Auswirkungen auf die Korallen Acropora tenuis und Seriatopora hystrix, sowie auf die kalkbildende Grünalge Halimeda opuntia zeigte (Kapitel 5). Die Kombina-tion aus OA und OW führte in einem Langzeit-Experiment zu verringertem Wachstum und reduzierter Kalzifizierung von epilithischen Algen-Gemeinschaften, insbesondere von Krustenrotalgen (Kapitel 6). Die unterschiedliche Sensitivität der untersuchten Arten gegenüber globalen und lokalen Stressfaktoren deutet auf Veränderungen von Korallenriff-Gemeinschaftsstrukturen in naher Zukunft hin. Verringerte Lichtverfügbarkeit könnte die negativen Auswirkungen von OA auf Korallen verstärken und dadurch zu Verschiebungen von Korallen- zu Algen-dominierten Gemeinschaften, bei Riffen, die von küstennahem Oberflächenabfluss betroffen sind, beitragen. Die wissenschaftlichen Erkenntnisse der vorliegenden Doktorarbeit deuten darauf hin, dass OA in Verbindung mit anderen Stressfaktoren den Reichtum von kalkbildenden Lebewesen reduzieren und dadurch die Herstellung von Kalziumkarbonat der Korallen-riffe in der Zukunft verringern könnte. Dies könnte zu gemindertem Riffwachstum, erhöhter Zerbrech-lichkeit und reduzierter Erholungsfähigkeit nach akuten Störungen führen. Letztlich wird rückläufiges Riff-Habitat wahrscheinlich zu verringerter Biodiversität führen, was Auswirkungen auf die Menschen haben könnte, die auf Korallenriffe angewiesen sind, da sie ihre Lebensgrundlage bilden.
Anthropogenically induced greenhouse gas emissions result in two major environmental changes on the global scale for coral reefs: ocean acidification (OA) and ocean warming (OW). Additionally, in-creasing levels of terrestrial runoff, that introduce fertilizer, sewage, sediments and other contaminants into coastal areas, can decrease water quality on the local scale. Consequently, photosynthesizing and calcifying coral reef organisms are affected by OA, OW and coastal runoff, but knowledge about the interactive effects of these stressors on key coral reef organisms is scarce. The aim of this thesis was to investigate how OA individually, and in combination with OW or local stressors (i.e. decreased light availability and inorganic eutrophication), affects important calcifying coral reef organisms. A series of field- and laboratory-based experiments were conducted on the Great Barrier Reef and at natural vol-canic carbon dioxide seeps in Papua New Guinea. A range of response parameters, including growth, calcification and photosynthesis, were investigated at the species and community level. OA showed no negative impact on three large benthic foraminiferal species in the short term (Chapter 2) and several calcifying green algae species of the genus Halimeda in the long term (Chapter 3). OA combined with decreased light availability resulted in additive negative effects on the coral Acropora millepora in the short term (Chapter 4), while OA combined with inorganic eutrophication did not exhibit any signif-icant effects on the corals Acropora tenuis and Seriatopora hystrix and on the calcifying green alga Halimeda opuntiain the short term (Chapter 5). In the long term, the combination of OA and OW resulted in decreased growth and calcification of epilithic algal communities, particularly in crustose coralline red algae (Chapter 6). The different sensitivity of the species investigated to global and local stressors, suggests that changes will occur in coral reef community structures in the near future. Re-duced light availability may amplify negative effects of OA on corals and thereby contribute to shifts from coral to algae dominated communities on reefs affected by coastal runoff. The scientific findings of the present thesis indicate that OA in combination with other stressors may reduce the abundance of calcifying organisms and thus lower the calcium carbonate production on coral reefs in the future. This may lead to reduced reef growth, increased brittleness and reduced recovery potential after acute disturbances. Ultimately, declining reef habitat will likely lead to a reduction in biodiversity and may thus have implications on the people, who are dependent on coral reefs for their livelihood.
General introduction
1.1
Coral reef ecosystems
Coral reef ecosystems are based upon living framework builders, which particularly consist of scler-actinian (stony) corals (Spalding et al. 2001). However, other calcifying organisms, such as coralline algae, mollusks and many invertebrate species, also contribute to the ‘cementation’ and structural com-plexity of coral reefs (Fagerstrom 1987; Chisholm 2000). Reef-building organisms are able to secret calcium carbonate (CaCO3). They precipitate CaCO3 as skeletons or shells and build layer upon layer of limestone and by that lay the structural foundation for coral reefs. The abiotic factors temperature, light availability and aragonite saturation determine the global distribution of coral reefs and hence are considered as ‘first-order-determinants’ (Kleypas et al. 1999). On a local scale other factors, such as wave exposure, storm frequency or biodiversity, limit coral reef development and are thus considered ‘second-order-determinants’ (Kleypas et al. 1999). The building of coral reefs is a constant and ongoing process in which reef-building as well as reef-eroding organisms are involved. Moreover, disturbances, such as storms and other extreme weather events, lead to alterations of coral reefs on a regular basis. According to the non-equilibrium hypothesis an intermediate frequency of disturbances is needed to sus-tain the high biodiversity found on coral reefs. However, as the frequency declines, or in other words if disturbances become chronic, diversity will decline (Connell 1978). Tropical coral reefs occur at water depths less than 100 m in tropical regions and many coral reef organisms rely on sunlight to conduct photosynthesis for autotrophic nutrition. With an estimated global area of 255,000 km2 (Spalding and Grenfell 1997; Spalding et al. 2001) coral reefs cover less than 0.1% of the world’s oceans and less than 1.2% of the continental shelf area (Spalding et al. 2001). At the same time, they provide habitat for about 93,000 (34%) of currently 274,000 described marine species (Reaka-Kudla et al. 1996). Thus, similar to rainforests on land coral, reefs are the ocean’s ‘biodiversity hotspots’ and are presumed to host at least 950,000 species in total with estimations ranging from 600,000 to 9 million species (Reaka-Kudla et al.
1996). This would also suggest that only ∼10% of all coral reef species have been currently described. Tropical coral reefs are among the most productive ecosystems in the world (Sorokin 1993). Gross primary productivity of coral reefs is exceptionally high compared with other marine and terrestrial ecosystems (Odum and Odum 1955; Lewis 1977). This is often considered as a paradox since trop-ical waters are oligotrophic meaning they are naturally poor in nutrients (Muscatine and Porter 1977; Crossland 1983). The high productivity can only be sustained by a complex and efficient mechanism of nutrient recycling within the coral reef ecosystem (Muscatine and Porter 1977).
1.2
Coral reefs: sociological and economic importance
Coral reefs play a critical role in human societies. Approximately 500 million people are dependent on coral reefs for food, coastal protection, building materials and income (Wilkinson 2008). This includes 30 million people, who are completely dependent on coral reefs for their livelihood (Wilkinson 2008). The physical structure of coral reefs provides habitat and protection for reef fish and pelagic fish ju-veniles as well as many invertebrate species. Thus, coral reef organisms are an important food source for people inhabiting coastal areas in tropical regions and significantly contribute to the sociological structure of island communities (Wilkinson and Buddemeier 1994). Moreover, coral reefs protect the coast line from waves and erosion, and calcifying coral reef organisms produce the reef and reef-sand which constitute the fundament of coral islands (Wilkinson and Buddemeier 1994). They also provide building material, such as sand and limestone rocks, utilized for the construction of houses. In addi-tion, many people inhabiting coastal areas in tropical regions rely on coral reefs as source of income by offering recreational activities for tourists or by exporting goods produced by the reefs (Wilkinson and Buddemeier 1994). Moreover, bioactive compounds of many of the coral reef organisms are essential for conventional medicine and many more have, yet unknown, pharmaceutical potential (Moberg and Folke 1999). The possible net benefit streams per year of coral reefs worldwide are estimated with 29.8 billion US$ in total, including 12.7 billion US$ for the Southeast Asia region and 6.3 billion US$ for Australia (Cesar et al. 2003). Not least, coral reefs have a priceless aesthetic value. All-embracing, coral reefs have a tremendous importance for humans: socially, economically as well as culturally.
1.3
Global threats to coral reefs
Worldwide coral reefs are in decline (Bellwood et al. 2004; Hughes et al. 2003). In particular, anthro-pogenically induced environmental changes on both global and local scales put pressures on coral reef ecosystems and lead to the observed declines (De’ath et al. 2012; Wilkinson 2008). Global stressors are environmental factors which affect coral reefs on a global scale. Yet, regional pollution (air pollution
in particular) is responsible for the changes happening worldwide. Global stressors are generally more difficult to manage than local stressors, since the consequences are not necessarily seen in regions where the pollution takes place, which makes it easier for polluters to disclaim responsibility. Ironically, often small island countries, which are the least responsible for the causation of these problems, suffer the most under the associated environmental changes (Wilkinson 2008).
1.3.1 Ocean acidification
Anthropogenic carbon dioxide (CO2) emissions from burning fossil fuels, cement production and fire clearance are increasing the CO2 partial pressure (pCO2) in the atmosphere. Latest projections of the Intergovernmental Panel on Climate Change (IPCC 2013) assume global mean pCO2 will rise two-or three-fold, compared to pre-industrial levels (∼280 µatm), within the present century due to an-thropogenic greenhouse gas (GHG) releases (Fig. 1.1). Four possible ‘representative concentration pathways’ (RCP2.6, RCP4.5, RCP6.0 and RCP8.5) have been suggested to estimate future atmospheric GHG concentrations (Moss et al. 2010). The different RCPs include the possibilities from immediate and drastic reduction of GHG emissions (RCP2.6) to business-as-usual GHG emissions (RCP8.5). De-pending on the RCP followed, future atmospheric CO2 concentrations are predicted to reach 420-936 µatm (RCP2.6-RCP8.5, respectively) by the year 2100 (Ciais et al. 2013).
500 1000 1500 2000 500 1000 1500 2000 µatm RCP 2.6 RCP 4.5 RCP 6.0 RCP 8.5 Year 2100 2150 2200 2250 2300 0 5 0 2 0 0 0 2 Atmospheric CO2
Figure 1.1: Trends in atmospheric CO2 concentrations with long-term projections following RCP2.6-RCP8.5 (modified from IPCC 2013)
Atmospheric CO2 is in constant exchange with the surface ocean, and additional CO2 in the atmo-sphere leads to an increase of CO2in the ocean. By now, the world’s oceans already took up one third of the anthropogenic CO2which has been introduced to the atmosphere (Sabine et al. 2004). When CO2 diffuses into seawater the reaction of both is described in the following series of equilibria:
Equation 1.1-1.4 Equilibria in the inorganic system H2O−CO2−CaCO3, whereas g = gaseous, aq = aqueous and l = liquid
CO2(g) −−⇀↽−− CO2(aq) (1.1)
CO2(aq) + H2O(l) −−⇀↽−− H2CO3(aq) (1.2)
H2CO3(aq) −−⇀↽−− H+(aq) + HCO3−(aq) (1.3)
HCO3−
(aq) −−⇀↽−− H+(aq) + CO32−(aq) (1.4)
(Equation 1.1) Atmospheric CO2 (g) diffuses into seawater and appears as dissolved CO2 (aq) in aqueous solution. (Equation 1.2) Dissolved CO2 reacts with H2O forming carbonic acid (H2CO3). (Equation 1.3) In the following reaction, H2CO3 dissociates into hydrogen ions (H+, first ionization) plus bicarbonate ions (HCO3–). (Equation 1.4) In the next step, HCO
3– dissociates into an H+ ion (second ionization) and a carbonate ion (CO32–). Additional H+ ions decrease the pH of the seawater (since pH = −log10[H+]) making the water more acidic. This process was termed ‘ocean acidification’ (OA), and since the industrial revolution a reduction of 0.1 units has already occurred. According to projections of the IPCC (2013), future oceans will experience a further pH reduction of 0.2-0.3 units by the year 2100 (following RCP2.6-RCP8.5, respectively) (Fig. 1.2).
pH
total
Global ocean surface pH
8.20 8.00 7.80 7.60 1850 1900 1950 2000 2050 2100 historical RCP2.6 RCP4.5 RCP6.0 RCP8.5 Year
Figure 1.2: Trends in global ocean surface pH with long-term projections following RCP2.6-RCP8.5 (modified from IPCC 2013)
In turn, a decrease in pH leads to a shift of the equilibria in the seawater carbonate system to the left, from CO32– towards HCO
3– (see Equation 1.4), which reduces the CO32– ion concentration and thus leads to a reduction of the calcium carbonate saturation state (Ω, Equation 1.5). Due to a decrease in Ω many marine calcifying organisms, such as corals, mollusks, calcareous algae and foraminifera, become impaired in building up their calcium carbonate (CaCO3) skeletons (Gattuso et al. 1998; Langdon et al. 2000; Orr et al. 2005; Ries et al. 2009).
Equation 1.5 Calcium carbonate saturation state (Ω), whereas X is the metal involved in calcification (Mg or Ca) and Ks is the solubility constant of the carbonate mineral (aragonite, high Mg-, or low Mg-calcite)
Ω−−[X2+] × [CO32−] × Ks−1 (1.5)
Calcifying organisms can deposit CaCO3 in different naturally occurring polymorphs. The three main minerals of CaCO3are calcite and aragonite as well as calcite with high magnesium content (high-Mg-calcite). Calcite is the most stable, aragonite is less stable and high-Mg-calcite is the most soluble form of CaCO3. Thus, organisms depositing CaCO3 in form of aragonite and high-Mg-calcite are as-sumed to be the most vulnerable to OA (Kuffner et al. 2007).
Photosynthesis and respiration of organisms play a crucial role in calcification (Equation 1.6-1.8). By taking up CO2during photosynthesis, the consequential increase in Ω alters the carbonate chemistry of the intra- and extracellular environment and thus facilitates the deposition of CaCO3. Vice versa, dur-ing darkness respiratory CO2release reduces Ω and thus alters the organisms’ environment to conditions unfavorable for calcification.
Equation 1.6-1.8 Chemical reaction of photosynthesis, respiration and calcification
CO2+ H2O −−→ CH2O + O2 (1.6)
CH2O + O2−−→CO2+ H2O (1.7)
Ca2++ 2 HCO3−−−→CaCO3+ CO2+ H2O (1.8)
Besides effects on growth and calcification rates, OA can have negative impacts on other physiologi-cal parameters. For instance, OA can have impacts on responses of fish towards olfactory cues impairing their predator and habitat recognition and thus reducing their chance of survival in future environments (Munday et al. 2009; Dixson et al. 2010). In addition, coral recruitment can be implicated as a conse-quence of disrupted larval-algal interactions due to OA (Doropoulos et al. 2012). Moreover, OA can have negative impacts on egg fertilization and early development of marine invertebrates (Kurihara and Shirayama 2004; Havenhand et al. 2008; Uthicke et al. 2013).
Nevertheless, there are also studies that observed several calcifying species are not impacted, but show resilience (Comeau et al. 2014) or even benefit under future OA conditions (Fabricius et al. 2011). One common example is seagrass which is assumed to be limited in dissolved inorganic carbon (DIC) concentrations under ambient pCO2 conditions. Seagrass will likely overcome this limitation under
future OA (i.e. elevated DIC) environments by increasing photosynthetic capacity and performance in comparison with calcareous epiphytes (Fabricius et al. 2011). Thus, the emerging paradigm of OA being harmful for marine life should be considered with caution, and impacts of OA should be evaluated at the species level.
1.3.2 Ocean warming
Next to OA, greenhouse gas emissions have another major impact on many marine organisms on the global scale. Due to the greenhouse effect, the mean global surface temperature is predicted to rise be-tween 1.0 and 3.7 °C depending on the RCP followed (RCP2.6 and RCP8.5, respectively) by the year 2100 (Collins et al. 2013). Part of this heat energy is absorbed by the oceans, which consequently leads to an increase in sea surface temperatures with highest warming in tropical and subtropical regions. Pro-jections estimate an ocean warming (OW) in the top one hundred meters of about 0.6-2.0 °C (RCP2.6-RCP8.5, respectively) (Collins et al. 2013). Seasonal fluctuations in water temperature are natural, and organisms generally benefit from warmer summer months by increasing their metabolic- and growth rates (Pörtner 2001). However, many tropical and subtropical species today already live close to their thermal limits and an additional increase of 2 °C above summer maxima may have deleterious effects on marine life (Hoegh-Guldberg 1999). With higher frequencies of temperature anomalies bleaching of corals living in symbiosis with zooxanthellae will become more common (Hoegh-Guldberg 1999; Hallock et al. 2006). A rise in temperatures of only 1-2 °C disrupts the coral-zooxanthellae symbiosis and leads to an expulsion of the endolithic algae by the host, or to the loss of pigments by endolithic algae (Buddemeier and Fautin 1993), leaving the corals bleached and colorless. Similar mechanisms have been reported in other organisms living in symbiosis with algae such as soft corals, anemones, giant clams and foraminifera (Buddemeier and Fautin 1993; Hallock et al. 2006; Schmidt et al. 2011). Bleaching in corals depends on the zooxanthellae type, the coral species and is region specific. Some species show higher sensitivity towards temperature stress than others, and corals from some regions show less tolerance than the same species in other regions (Berkelmans and Willis 1999; Baker et al. 2004). Moreover, recovery is possible after minor bleaching events, but without these vital symbionts and their photosynthetically derived carbon source the host organisms may starve (Hoegh-Guldberg 1999; Harriott 1985). Subsequently, mass bleaching events can lead to complete loss of live corals in entire regions and indicate substantial alterations to coral reefs in future (Hoegh-Guldberg 1999).
Besides implications on symbioses, OW also affects other physiological responses in a range of marine organisms. Calcifying organisms show a linear increase in calcification rates with warming sea-water temperatures (Lough and Barnes 2000; De’ath et al. 2009). However, studies also show non-linear responses, leading to declined calcification rates at high temperatures (Cooper et al. 2008; Marshall and
Clode 2004; Cantin et al. 2010). Thus, interim benefits for calcifiers from OW will be removed under heat stress and temperature anomalies. In addition, heat stress can have negative implications on pho-tophysiology (Jones et al. 1998; Middlebrook et al. 2010; Schmidt et al. 2011) and metabolism (Pört-ner 2001) of coral reef organisms. In turn, physiological stresses compromise host resistance towards pathogens. Consequently, warmer water promotes the dispersal of diseases and pathogens in marine biota, leading to increased mortality of coral reef organisms (Harvell et al. 2002; Harvell et al. 1999).
1.4
Local threats to coral reefs
Local stressors affect coral reef ecosystems on a smaller spatial scale and in contrast to global stressors only occur in confined areas. Often, local stressors occur seasonally or over short temporal scales, but in some cases they can become chronic, too. Local stressors are generally easier to manage than global stressors since environmental action plans can be implemented in particular regions in order to improve the local water quality. Several of these local stressors are interconnected and global environmental changes may have an influence on local stressors, as well. For instance, OW may lead to an increasing frequency and destructiveness of tropical cyclones in the future (Knutson et al. 2010; Emanuel 2005) which affect coral reefs locally. In addition, warming oceans are predicted to increase mean precipitation and promote heavy precipitation events, particularly in tropical regions, with associated increases in future coastal runoff (IPCC 2013).
1.4.1 Coastal runoff
The term runoff incorporates a range of land derived substances which get transported into the ocean by freshwater from precipitation and thereby decrease the water quality on a local scale. In tropical regions, particularly during the summer months, enhanced precipitation leads to increased land- and riverine runoff with related implications on near-shore reef communities. For one thing, freshwater from precipitation acts as a ‘means of transport’ by carrying nutrients, sediments and other contaminants into the ocean. For another thing, freshwater on its own can alter the seawater quality by reducing salinity. Rapid decreases in salinity have been shown to cause coral death (Hoegh-Guldberg and Smith 1989) and extensive mortality after flood events (Goreau 1964; Egana and DiSalvo 1982). Steadily declining water quality along the populated coast next to the Great Barrier Reef (GBR), since the European settlement, has been well documented (Wooldridge et al. 2006; Devlin and Brodie 2005; Furnas and Mitchell 2001). The main impacts of coastal runoff on water quality are seen in elevated dissolved inorganic nutrients (DIN), increased suspended particulate organic matter (POM), reduced light availability from turbidity and increased sedimentation (Fabricius 2005).
Agricultural land-use requires fertilizer; mostly nitrogen and phosphorous. The production and use of fertilizers have steadily increased in the past decades and are predicted to rise in the future (IPCC 2013; Galloway et al. 2008). But only a fraction of the dispensed fertilizer gets taken up by the plants, while the residuals get carried into the ocean leading to increased DIN concentrations at locations af-fected by coastal runoff. In combination with organic nutrients, mostly derived from sewage in populated areas, the seawater gets artificially enriched with nutrients, a term named eutrophication. As outlined earlier, coral reef organisms are adapted to oligotrophic conditions, and artificially increased DIN con-centrations have been shown to affect coral reef ecosystems on the local scale. While corals respond with an increase in photosynthesis and zooxanthellae numbers (Fabricius 2005), macroalgae are relieved from nutrient limitation by enhancing their productivity and growth rates under elevated DIN conditions (Ped-ersen and Borum 1997; Larned 1998; Schaffelke 1999; Schaffelke et al. 2005). Ultimately, prolonged or repeated exposure to increased DIN may lead to a shift in the community composition from coral to macroalgae dominated reefs (Bell 1992; Fabricius et al. 2005; Schaffelke et al. 2005; Lapointe 1997). In addition, elevated DIN concentrations lead to increased chlorophyll in the water column, enhanced growth of phytoplankton and are responsible for algae blooms in eutrophic areas (Fabricius 2005; La-pointe 1997; Beman et al. 2005). In turn, the latter alterations lead to increased turbidity and decreased light availability accompanied by negative implications for photosynthesizing coral reef organisms.
Many coral reef organisms rely on sunlight to conduct photosynthesis for autotrophic energy acquisi-tion. Decreased light availability from turbidity reduces their productivity, calcification and subsequently growth rates (Rogers 1979; Telesnicki and Goldberg 1995; Anthony and Hoegh-Guldberg 2003). Light requirements are species specific with some being able to sustain positive growth rates in low light con-ditions, while others are not (Fabricius 2005). Intermediate light availability has been shown to support the highest species richness by balancing the abundance between fast- and slow-growing species (Cor-nell and Karlson 2000). Moreover, in the short term organisms are able to acclimatize to reduced light availability by increasing the size and the amount of chloroplasts (Fabricius 2005). However, eventually reef development is limited as a function of light availability from > 40 m in clear water to < 4 m in turbid conditions (Birkeland 1987; Yentsch et al. 2002).
Another component affecting near-shore reef communities on the local scale is sedimentation. Sed-iments from land erosion get carried into the ocean mainly by rivers. While larger grain sizes are deposited within the first few kilometers of river catchments, smaller particles can travel over longer distances (Fabricius 2005). Direct impacts of sedimentation can be seen in reduced photosynthetic ef-ficiency of organisms (Philipp and Fabricius 2003) and increased metabolic costs for the removal of particles (Telesnicki and Goldberg 1995). Heavy sedimentation can have severe effects on coral reefs, leading to the death of reef building corals and the subsequent collapse of the reef framework (Risk and
Edinger 2011; Rogers 1990). Next to these direct effects, sedimentation also affects coral reefs indi-rectly by increasing turbidity and reducing the light availability with the associated negative impacts as outlined above.
The limited data available on the effects of POM on coral reef organisms suggests some organisms may benefit from increased POM availability, while others do not (Fabricius 2005). Recent experiments indicate calcareous algae experience reduced productivity, while corals showed increased growth under elevated POM (Meyer et al. pers. comm.). This may further contribute to changes in community compositions.
1.4.2 Other local stressors
Besides coastal runoff, other disturbances can have severe impacts on coral reef ecosystems on the local scale. For instance, in the past 27 years the GBR has lost half of its coral cover, and tropical cyclones accounted for 48% of the observed decline (De’ath et al. 2012). Keeping in mind that the frequency and intensity of tropical cyclones are predicted to rise with climatic change (Knutson et al. 2010; Emanuel 2005), coral reefs are facing increased structural damage and less time to recover in the future.
The coral eating ‘crown of thorns seastar’ Acanthaster planci accounted for 42% of the coral losses observed over the past few decades (De’ath et al. 2012). In small numbers, crown of thorns seastars (COTS) are part of the natural disturbance cycle and contribute to the high biodiversity found on coral reefs (Sebens 1994). However, large population outbreaks are increasing in frequency with destructive effects on coral reefs worldwide (Fabricius et al. 2010; Wilkinson 2008). Outbreaks of COTS have been linked to increasing eutrophication of inshore waters promoting phytoplankton growth which is the preferred natural food of COTS larvae (Bell 1992; Fabricius et al. 2010).
Industrial developments, such as dredging of shipping channels as well as dredging and blasting for port development increase sedimentation on coral reefs with associated negative impacts (Risk and Edinger 2011; Fabricius 2005; Nelson 2009). Recent studies also linked sedimentation from dredging activity to increased coral disease (Pollock et al. 2014).
Unsustainable tourism, particularly structural damage from anchoring and destructive fishing tech-niques, such as trawling and dynamite fishing, put additional pressures on local coral reefs (Wilkin-son 2008). Furthermore, overfishing can change the ecological communities by decreasing herbivore abundance and thus facilitating proliferation of algae, causing widespread changes in reef ecosystems (Anthony et al. 2011; Hughes et al. 2003; Jackson et al. 2001).
1.5
Combinations of global and local stressors
In the coming decades, coral reef ecosystems will be increasingly affected by global and local stressors. Yet, coral reefs are not only facing one stressor in isolation, but combinations of global and/or local stressors which may have additive, synergistic or antagonistic effects. While additive effects are char-acterized by the sum of the individual stressors, synergistic effects result in larger effect sizes than the sum of individual stressors combined and antagonistic effects result in smaller effects than the sum of individual stressors (Dunne 2010). The exposure to one stressor may make coral reef organisms more susceptible to other stressors, leading to synergistic effects.
With increasing atmospheric carbon, tropical coral reef organisms are facing the inevitable combi-nation of both OA and OW, regardless of the presence of local stressors. Studies indicate interactive effects of OA and OW on calcification, growth, or photophysiology of a vast range of marine organisms such as scleractinian corals (Edmunds and Moriarty 2012; Reynaud et al. 2003), crustose coralline algae (Johnson and Carpenter 2012; Anthony et al. 2008; Martin and Gattuso 2009) and benthic foraminifera (Schmidt et al. 2014) as well as on many life history stages of invertebrates (Gibson et al. 2011).
The presence of local stressors may put additional pressure on coral reef organisms, compromising their potential to withstand global environmental changes. However, the combined effects of many stressors are unknown. For instance, few studies have investigated the interactive effects of OA and light availability on corals and calcareous algae (Comeau et al. 2013; Marubini et al. 2001; Dufault et al. 2013), the interactive effects of OW and eutrophication on benthic foraminifera (Uthicke et al. 2011) as well as the interactive effects of OW and herbicides on scleractinian corals (Negri et al. 2011).
Furthermore, multifactorial experiments have been conducted on scleractinian corals with more than two stressors interacting (Comeau et al. 2014; Langdon and Atkinson 2005) including global and local stressors.
1.6
Knowledge gaps & research questions
Previous studies have particularly concentrated on the responses of scleractinian corals to the global stressor OA. Many other organism groups, such as calcareous algae, coralline algae or foraminifera which also play a critical role in coral reef ecosystems, have been less intensely studied and their re-sponses to altered environments are not fully understood. While some coral reef organisms are neg-atively impacted, others seem to be able to acclimatize to environmental changes. Individual stud-ies also came to contradictory conclusions potentially due to specstud-ies- and/or region-specific responses. Moreover, different methodologies implemented in the experimental setup, such as the duration of ex-periments, or the method to simulate OA conditions, may have a substantial effect on how organisms
respond to this particular stressor. For instance, in the early years of OA research experimental stud-ies often utilized hydrochloric acid (HCl) in order to reduce seawater pH and Ω. But HCl addition only reduces pH and Ω without increasing the DIC concentrations (Riebesell et al. 2010), as under fu-ture rises of atmospheric pCO2. Elevated DIC offers higher CO2and HCO3– availability for auto- and mixotrophic organisms, which may be DIC limited in their photosynthesis and/or calcification under present-day environmental conditions and may benefit under elevated DIC concentrations. Thus, it is important to investigate the effects of stressors at the species level and to use methods in experiments that closely resemble natural environments, to try to understand future changes to coral reef ecosystems. Coral reef organisms are increasingly affected by OA and coastal runoff, but the effects of many of these interactions on coral reef calcifiers are unknown. For instance, photosynthesis is an important factor in OA research, since photosynthetic CO2 uptake in the light and respiratory CO2 release in darkness alter the seawater carbonate chemistry internally and externally. Photosynthesis may buffer against OA as long as enough light is available, but may exacerbate negative OA effects in the dark or when not enough light is available. But knowledge about the mechanisms of OA effects in the light and in the dark is scarce. Reduced light availability, which indirectly results from coastal runoff, may affect photosynthesizing and calcifying organisms and their responses to OA, but so far this important interaction has been widely overlooked.
Photosynthesizing and calcifying organisms can be negatively affected by OA and eutrophication, but at the same time their photosynthesis and calcification can be limited by the supply of DIC and DIN. Increased DIN under eutrophication conditions and increased DIC under OA conditions may have negative, but potentially also positive effects. Yet, these interactions are barely investigated. Moreover, much of the previous work, that has studied the effects of elevated DIN, has used treatment levels beyond realistic concentrations which may lead to biased outcomes that are not environmentally relevant. Field studies offer an alternative to investigate the effects of eutrophication between areas with high and low DIN concentrations. However, high DIN concentrations in the field co-occur with other stressors, such as reduced light availability, and are difficult to study in combination with OA. Thus, investigating the effects of increased DIC and DIN under manipulated conditions with naturally occurring concentrations may help to understand the impacts of OA and eutrophication on coral reef organisms.
In future, all coral reef organisms will be affected by a combination of OA and OW, regardless of the presence of local stressors. Knowledge gaps still exist in the responses of organisms and particularly their community composition to combinations of OA and OW. In addition, most experimental designs included future environmental scenarios, but only few studies included past pCO2and temperature treat-ments similar as seen on coral reefs a few decades ago. By including past treattreat-ments in experimental designs, organisms’ performance can be investigated under past, present-day and future environmental
conditions.
In summary, the objectives of the present thesis are to investigate (see also Fig. 1.3):
1. how photosynthesizing and calcifying coral reef organisms are affected by future ocean acidifica-tion scenarios, and whether they respond differently to ocean acidificaacidifica-tion condiacidifica-tions.
2. how decreased light availability affects the response of photosynthesizing and calcifying coral reef organisms to ocean acidification.
3. whether increased dissolved inorganic carbon and -nitrogen have interactive effects on photosyn-thesizing and calcifying coral reef organisms.
4. how photosynthesizing and calcifying coral reef organisms and their communities respond to com-binations of past and future ocean acidification and warming scenarios.
Ocean
Acidification
foraminifera, calcareous algae+
Ocean
Acidification
corals, calcareous algae+
Ocean
Acidification
corals, calcareous algae Ocean Warming Eutrophi-cation Turbidity+
Ocean
Acidification
epilithic communitiesFigure 1.3: Illustration of research objectives with individual and interactive effects of global and local stressors in sequence as covered in this thesis
1.7
Experimental species
Scleractinian corals Acropora millepora, Acropora tenuis and Seriatopora hystrix (Fig. 1.4a-c) are three common and widespread species found on the GBR and throughout the tropical Indo-Pacific Region (Veron 2000). They host endosymbiotic algae, are important primary- and carbonate producers and ac-count for reef development. With their complex, three-dimensional structure they also provide habitat for a vast range of invertebrates and reef fish. Corals use aragonite, a more soluble form of the carbonate minerals, for calcification and thus are assumed to be more susceptible to OA than calcite depositing organisms. Responses of the coral A. millepora towards combinations of OA and decreased light avail-ability were investigated in Chapter 4. Responses of A. tenuis and S. hystrix towards combinations of OA and eutrophication were studied in Chapter 5.
1cm 1 cm 1 mm 1 mm 1 mm 1 cm 1 cm 1 mm 1 mm 1 mm (a) (b) (c) (d) (e) (f) (g) (h) (h) (i) (j) 1 cm
Figure 1.4: Experimental species (a) Acropora millepora, (b) Acropora tenuis, (c) Seriatopora hystrix, (d) Halimeda digitata, (e) Halimeda opuntia, (f) crustose coralline algae, (g) Peyssonnelia spp., (h) Amphistegina radiata, (i) Heterostegina depressa and (j) Marginopora vertebralis
The calcareous green algae Halimeda opuntia and Halimeda digitata (Fig. 1.4d, e) are crucial pri-mary producers commonly found on tropical coral reefs (Littler and Littler 2003; Littler and Littler 2000). Halimeda spp. meadows considerably contribute to carbonate production and habitat formation
and provide habitat for many invertebrate species (Wefer 1980; Rees et al. 2007; Freile et al. 1995; Fukunaga 2008). Halimeda spp. also utilize aragonite as skeletal mineral, suggesting higher OA sensi-tivity than calcite depositing organisms. H. opuntia and H. digitata were investigated in regard to their ability to grow under natural OA conditions at tropical CO2seeps in Chapter 3. Responses of H. opuntia towards combinations of OA and decreased light availability were investigated in Chapter 4. Moreover, responses of H. opuntia towards combinations of increased DIC and DIN were investigated in Chapter 5.
Epilithic algae, including crustose coralline algae (CCA) and Peyssonnelia spp. (Fig. 1.4f, g), play a critical role in the benthic community. They provide the substrate and olfactory cues for coral larvae settlement and metamorphosis (Heyward and Negri 1999; Harrington et al. 2004). In addition, they drive reef cementation and thus are important for reef development and reinforcement (Chisholm 2000; Chisholm 2003). CCA deposit high-Mg-calcite, the most soluble carbonate mineral and are presumed to be highly sensitive to OA related reduced Ω. Peyssonnelia spp. vary in their calcification intensity (Littler and Littler 2003) and deposit aragonite, which is more stable compared with high-Mg-calcite, potentially offering advantages over CCA. Responses of latter organisms towards combinations of OA and OW were studied in Chapter 6.
Large benthic foraminifera Amphistegina radiata, Heterostegina depressa and Marginopora verte-bralis (Fig. 1.4h-j) are unicellular organisms hosting endosymbiotic algae. Benthic foraminifera are utilized as biological indicators for ecosystem health (Hallock et al. 2003; Uthicke and Nobes 2008; Uthicke et al. 2010) and provide important information about water quality. Foraminifera are widespread over tropical coral reefs and play a crucial role in the production of carbonate sand for beaches and sand cays (Fujita et al. 2009; Doo et al. 2014). A. radiata and H. depressa deposit low-Mg-calcite, while M. vertebralisdeposits high-Mg-calcite and thus is considered to be more sensitive to OA. Responses of the latter foraminifera were investigated in regard to OA in Chapter 2.
1.8
Introduction to study sites
Field-studies and collections of specimens for laboratory experiments of this thesis have been conducted at four main sites from tropical Papua New Guinea (PNG) to tropical Australia (Fig. 1.5). Study sites were located at reefs next to Normanby Island in PNG, at Lizard Island in the northern GBR and around the Palm Islands in the central section of the GBR.
The particular feature of the study site in PNG (S 9° 49.446’, E 150° 49.055’) is that pure volcanic carbon dioxide is bubbling out of the seafloor (Fabricius et al. 2011). This changes the carbonate chem-istry of the surrounding seawater according to predictions for coral reefs of the entire globe by the end of this century (IPCC 2013). This ‘window to the future’ provides a unique opportunity to study coral
reef organisms living in their natural environment in OA conditions happening already today. The PNG study site is included in Chapter 3 of this thesis.
With low to medium background levels of DIN concentrations (Table 1.1) the Lizard Island study site (S 14° 40.768’, E 145°26.753’) was selected to conduct a multifactorial tank experiment under OA and eutrophication conditions. Specimens were collected in the Lizard Island lagoon and transplanted into experimental aquaria facilities on the island. In the experimental tanks CO2 and nitrate concentrations were manipulated to mimic interactive effects of OA and eutrophication on coral reef calcifiers. This study site is included in Chapter 5 of this thesis.
Table 1.1: Dissolved inorganic nutrient (phosphate, ammonium, nitrate + nitrite and nitrite) concentra-tions of the study sites
Site PO4 3-[µmol L-1] NH4+ [µmol L-1] NO3- + NO2 -[µmol L-1] NO2 -[µmol L-1] Upa-Upasina (PNG) 0.10 (0.04) 0.38 (0.13) 0.27 (0.07) 0.04 (0.01) Lizard Island 0.05 (0.01) 0.70 (0.14) 0.44 (0.10) 0.14 (0.02) Palm Islands 0.05 (0.01) 0.46 (0.14) 0.38 (0.27) 0.02 (0.01) Davies Reef 0.08 (0.06) 0.59 (0.19) 0.30 (0.09) 0.01 (0.01)
The Palm Islands (S 18° 37.549’, E 146° 29.246’) study site was primarily utilized to collect spec-imens for manipulative tank experiments which were conducted at the Australian Institute of Marine Science (AIMS) in Townsville. The Palm Islands are considered as an inshore location of the GBR. Particularly in the summer months, they are exposed to land-runoff with associated increases in dis-solved inorganic nutrients, decrease in light availability, reduced salinity and increased sedimentation from suspended solids. Specimens were collected here for experiments in Chapter 2 and Chapter 4.
A fourth study site was located mid-shelf off the Palm Islands at Davies Reef (S 18° 49.072’, E 147° 38.959’). A multifactorial tank experiment was conducted at the AIMS in Townsville and required initial growth of epilithic communities on artificial substrates. This substrate was deployed on Davies Reef over a period of five months. This study site is included in Chapter 6 of this thesis.
1.9
Publication outline
Included in this thesis are five data chapters of which two have been published as research articles in international, peer-reviewed journals. One article is accepted for publication and currently in press, and two articles are in preparation for submission.
Publication 1
Calcification and photobiology in symbiont-bearing benthic foraminifera and responses to a high CO2environment
Port Moresby Alotau Sydney Townsville Cairns Cooktown Brisbane 40.0ºS 30.0ºS 20.0ºS 10.0ºS 0º
140.0ºE 150.0ºE 160.0ºE
10.5ºS 10.0ºS 9.5ºS 150.5ºE 151.0ºE Cooktown Lizard Island 15.5ºS 15.0ºS 14.5ºS 145.5ºE Orpheus Island Pelorus Island Fantome Island 19.0ºS 18.5ºS 146.5ºE 147.0ºE Townsville Alotau Dobu Island Normanby Island Upa−Upasina Milne Bay
Vogel N., Uthicke S.
Published in the Journal of Experimental Marine Biology and Ecology (2012) 424-425: 15-24
In Chapter 2 ‘Calcification and photobiology in symbiont-bearing benthic foraminifera and re-sponses to a high CO2environment’ we conducted a six week tank experiment at the AIMS in Townsville in order to investigate the individual effects of OA on large benthic foraminifera. At the time this exper-iment was conducted the available information on how foraminifera will react to OA was scarce. With this experiment we contribute to the understanding of how future OA conditions may affect photobiol-ogy and calcification of the three large benthic foraminifera species Amphistegina radiata, Heterostegina depressaand Marginopora vertebralis. This experiment has been the first OA experiment at the AIMS using a CO2-injection system under flow-through conditions and was utilized to establish the technology and methodology for many upcoming experiments with the same experimental system. Chapter 2 has been published in the Journal of Experimental Marine Biology and Ecology (Vogel and Uthicke 2012).
Contributions: This project was initiated by N. Vogel and S. Uthicke. The experimental design was developed by N. Vogel and S. Uthicke. A field trip for the collection of experimental specimens was organized and realized by S. Uthicke and N. Vogel. Data sampling, analyzing and the writing of the manuscript was conducted by N. Vogel with improvements by S. Uthicke.
Publication 2
Calcareous green alga Halimeda tolerates ocean acidification conditions at tropical carbon dioxide seeps
Vogel N., Fabricius K. E., Strahl J., Noonan S. H. C., Wild C., Uthicke S. Published in Limnology and Oceanography (2015) 60.1: 263-275
Chapter 3 ‘Calcareous green alga Halimeda tolerates ocean acidification conditions at tropical car-bon dioxide seeps’ investigates the individual effects of OA on the ecology, physiology and skeletal characteristics of Halimeda spp. grown at tropical carbon dioxide seeps. This field study was conducted in Upa-Upasina, PNG where natural, unheated CO2seeps change the carbonate chemistry of the seawa-ter according to global projections for the upcoming decades due to OA. By now this is the only tropical CO2seep site worldwide and thus presents a unique opportunity to study the effects of OA on tropical coral reef organisms in their natural environment. This chapter has been published in Limnology and Oceanography (Vogel et al. 2015a).
Contributions: This project was initiated by N. Vogel, K. Fabricius and S. Uthicke. The experimental design for this study was developed by N. Vogel, with the help of J. Strahl, S. Noonan and S. Uthicke. A field trip to PNG was organized and realized by K. Fabricius, S. Noonan, S. Uthicke, N. Vogel and J. Strahl. Data sampling was conducted by N. Vogel with the help of S. Uthicke, J. Strahl and S.
Noonan. Sample analyzing was conducted by N. Vogel. The manuscript was written by N. Vogel with improvements from all contributing authors.
Publication 3
Decreased light availability can amplify negative impacts of ocean acidification on calcifying coral reef organisms
Accepted for publication in Marine Ecology Progress Series (2015) doi:10.3354/meps11088
In Chapter 4 ‘Decreased light availability can amplify negative impacts of ocean acidification on calcifying coral reef organisms’ we conducted a two week tank experiment in order to investigate the individual and combined effects of OA and decreased light availability, which is a byproduct of coastal runoff, on the coral Acropora millepora and the calcareous green alga Halimeda opuntia. Because photosynthetic activity of organisms can alter the internal as well as external carbonate chemistry of the seawater, it is important to understand how a decrease in light availability will affect the response of organisms to OA. With this experiment we provide information on how organisms living inshore (susceptible to coastal runoff) may be affected in future OA conditions when light availability is reduced at the same time. This chapter is accepted for publication in Marine Ecology Progress Series (Vogel et al. 2015b).
Contributions: This project was initiated by N. Vogel, C. Wild and F. Meyer. The experimental design was developed by all contributing authors. A field trip for collection of experimental specimens was organized and realized by N. Vogel and S. Uthicke. Data sampling and analyzing was conducted by N. Vogel and F. Meyer. The manuscript was written by N. Vogel with improvements from S. Uthicke and C. Wild.
Publication 4
Effects of elevated dissolved inorganic carbon and nitrogen on the physiology of scleractinian corals and calcareous macroalgae under ocean acidification and eutrophication conditions Vogel N., Ow Y., Flores F., Collier C., Wild C., Uthicke S.
Chapter 5 ‘Effects of elevated dissolved inorganic carbon and nitrogen on the physiology of scle-ractinian corals and calcareous macroalgae under ocean acidification and eutrophication conditions’ investigates the individual and combined effects of OA and increased inorganic nitrate on corals Acrop-ora tenuisand Seriatopora hystrix and the calcareous green alga H. opuntia. We conducted a three week tank experiment in a controlled manipulated environment on Lizard Island, Australia. Experiments in-vestigating nutrient effects are often characterized by high nutrient background levels and even higher nutrient treatments which are unnaturally high and prevent an extrapolation of results to natural inshore
environments as found at the GBR. In this study nutrient background levels were low and were elevated to naturally relevant concentrations. This article is in preparation.
Contributions: This project was initiated by N. Vogel, Y. Ow and S. Uthicke. The experimental design was developed by N. Vogel, Y. Ow, S. Uthicke and C. Collier. A field trip to Lizard Island was organized by N. Vogel, Y. Ow and S. Uthicke. Data sampling was conducted by N. Vogel, Y. Ow, S. Uthicke and F. Flores. Data analyzing and manuscript writing was conducted by N. Vogel with improvements from all contributing authors.
Publication 5
Interactive effects of ocean acidification and warming on coral reef associated epilithic algal com-munities under past, present and future ocean conditions
Vogel N., Cantin N., Strahl J., Kaniewska P., Bay L., Wild C., Uthicke S.
In Chapter 6 ‘Interactive effects of ocean acidification and warming on coral reef associated epilithic algal communities under past, present and future ocean conditions’ we conducted a long-term experi-ment over six months with four temperature and four CO2treatments. In this experiment, we investigated the individual and combined effects of OA and OW on early assemblages of epilithic algal communities. This article is in preparation.
Contributions: This project was initiated by N. Vogel, N. Cantin and S. Uthicke. The experimental design was developed by N. Cantin, J. Strahl, P. Kaniewska, L. Bay and N. Vogel. Field trips were organized and realized by N. Cantin and P. Kaniewska. Data sampling was conducted by N. Vogel, N. Cantin and S. Uthicke. Data analyzing was conducted by N. Vogel. The manuscript was written by N. Vogel with improvements from all contributing authors.
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