As shown in the studies of the present thesis different organisms varied in their responses to OA condi-tions. These differences were attributed to species-specific OA effects, but also to other environmental or experimental factors that can influence the effects of OA on the response parameters measured. For instance, the duration of experiments (short- vs. long-term), the seawater supply of experimental tanks (filtered vs. unfiltered), the experimental light regimes (natural and parabolic vs. artificial and linear), or the experimental treatments (past, present-day and future) all may have effects on the organisms’
responses to OA and the conclusions able to be drawn. Ultimately, the setup that is best to implement will depend on the research question and the organisms under investigation. Thus, the experimental design should be chosen carefully to make studies comparable and to allow for extrapolations to natural environments in order to improve the knowledge about impacts of OA and other stressors on future coral reef ecosystems. Suggestions for future research are to consider the different mechanisms of OA effects in the light and in the dark. As shown in the present thesis, coral reef organisms and their community composition will be increasingly affected by OA and OW. But inshore communities will also be ex-posed to increasing coastal runoff in the future. Thus, future research is encouraged to investigate the interactive effects of all three factors. Moreover, several local stressors appear rather acute than chronic, but knowledge about the potential of organisms to recover to the original state after short-term (weekly) pulses of certain stressors, such as reduced light availability or elevated DIN, is rare and warrants further investigation.
In conclusion, evidence from studies of this thesis suggests that coral reef ecosystems will change under the projected environmental shifts during the 21stcentury. These anthropogenically induced eco-logical changes are already happening today and will continue to happen in the future. The question whether organisms are able to withstand or go extinct depends not only on their ability to acclimatize to the rapidly changing environmental conditions, but also on their ability to find their place in the ecosys-tem changing around them. Even if creatures (including humans) are not directly impacted by OA, OW or coastal runoff they may be affected indirectly by ecological changes through loss of habitat, food sources, or sources for income. If carbon emissions are drastically reduced within the next few years a time-delayed effect of already stored greenhouse gases in the atmosphere will lead to future rises in extreme temperature events (Ortiz et al. 2014). Hence, immediate and drastic reductions in carbon emis-sions and coastal pollution are encouraged to increase chances of future survival of coral reef organisms.
In the present thesis, it was shown that coastal runoff can have additional negative effects in combina-tion with global stressors on coral reef organisms. Thus, by reducing runoff effects organisms will gain some time or might be better able to acclimatize to inevitable environmental alterations on the global scale. Environmental action plans, such as management of fertilizer usage and sedimentation sources,
should be implemented at the regional scale to decrease the pressure from global stressors on coral reef organisms which may help to preserve future coral reefs.
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Abbreviations and glossary
AIMS Australian Institute of Marine Science ANOVA Analysis of variance
AOI area of interest CaCO3 calcium carbonate CCA crustose coralline algae Chla chlorophylla
CO2 carbon dioxide CO32– carbonate Cinorg inorganic carbon Corg organic carbon
COTS crown of thorns seastar Ctot total carbon
DIC dissolved inorganic carbon, DIC = [CO2] + [HCO3–] + [CO32–]
DIN dissolved inorganic nutrients (ammonium, phosphate, nitrate and nitrite) Ek minimum saturation irradiance
GBR Great Barrier Reef GHG greenhouse gases H2CO3 carbonic acid HCl hydrochloric acid
HCO3– hydrogen carbonate, bicarbonate IEA International Energy Agency
IPCC Intergovernmental Panel on Climate Change LAT lowest astronomical tide
LBF large benthic foraminifera mya million years ago
µM micro mol per liter
NBS National Institute of Standards and Technology NERP National Environmental Research Program
NH4+ ammonia
NIST National Institute of Standards and Technology NO2– nitrite
NO3– nitrate
NOAA National Oceanic & Atmospheric Administration OA ocean acidification
OW ocean warming
Ω calcium carbonate saturation state Ωar aragonite saturation state
Ωca calcite saturation state PAM pulse amplitude modulation
PAR photosynthetically available radiation pers. comm. personal communication
PO43– phosphate
POM particulate organic matter P-I photosynthesis vs. irradiance Pmax maximum photosynthetic capacity Pnet net oxygen production
pCO2 carbon dioxide partial pressure
PNG Papua New Guinea
ppt parts per thousand
RCP representative concentration pathway SRES Special Report on Emission Scenarios SST sea surface temperature
SD standard deviation
SE standard error
TA total alkalinity, TA= [HCO3−] +2[CO32−] + [B(OH)4−] + [OH−]−[H+] UIPAC International Union of Pure and Applied Chemistry
ZMT Leibniz Center for Marine Tropical Ecology
List of Tables
1.1 Dissolved inorganic nutrient (phosphate, ammonium, nitrate+nitrite and nitrite) con-centrations of the study sites . . . 18 2.1 Mean carbonate system parameters of long- and short-term experiments. Carbonate
system parameters were calculated from measured TA, DIC, salinity, temperature and pressure. Standard deviations are given in brackets. SW=seawater . . . 39 2.2 Linear Model ANOVA results for growth rate, maximum quantum yield and chlorophyll
acontent ofA. radiata,H. depressaandM. vertebralisin the long-term experiment . . . 44 2.3 Linear Model ANOVA results for oxygen production and respiration rates ofH. depressa
andM. vertebralisafter long- and short-term exposition . . . 47 2.4 Regression parameters and Linear Model ANOVA results of light response experiments . 48 3.1 Carbonate system parameters of water samples from in-situ collections (ntotal =86)
(Dobu Island and Upa-Upasina, 2012, 2013), incubations (ntotal =30) (Upa-Upasina, 2012) and transplant experiment (ntotal =50) (Upa-Upasina, 2012). Data is given as mean and standard deviation . . . 66 3.2 Linear Model ANOVA results for physiological and skeletal parameters ofH. digitata
and H. opuntia with control and seep site as source of variation. Asterisks indicate significant differences of response variables between control and seep site . . . 70 4.1 Carbonate system parameters of experimental conditions. Data is given as means and
standard deviations . . . 92 4.2 Mixed Model ANOVA results forA. milleporaandH. opuntia . . . 96 4.3 Summary of effects of treatment variables on response parameters forA. milleporaand
H. opuntia. Decreases > 100% are possible due to decalcification. ‘ns’ indicates no significant treatment effect, ‘measured additive effects’ represent differences of means between the control pCO2/high light and high pCO2/low light treatment . . . 98 5.1 Mean (±SD) carbonate system parameters of experimental treatment conditions.
Treat-ments consisted of 400, 700 and 1100 µatm pCO2and 0.4 and 1.9 µmol DIN . . . 117 5.2 Mean (± SD) water quality parameters of experimental treatment conditions.
Treat-ments consisted of 400, 700 and 1100 µatm pCO2and 0.4 and 1.9 µmol NOx . . . 118 5.3 Mixed Model ANOVA results of OA and elevated DIN on response parameters of
or-ganisms investigated. Asterisks indicate significant treatment effects . . . 128
5.4 Continuation of Mixed Model ANOVA results of OA and elevated DIN on response parameters of organisms investigated. Asterisks indicate significant treatment effects . . 129 6.1 Temperature (n∼200) and carbonate system parameters (n=10) of experimental tanks.
Data is given as means (±SD) . . . 147 6.2 Generalized Linear Model results for effects of temperature, pCO2and the interaction
of both on response parameters of the epilithic community and CCA andPeyssonnelia spp. Tukey contrasts represent significantly different treatment groups (1, 2, 3, 4) from temperature (25.0, 26.1, 26.5 and 27.7 °C) and pCO2(360, 440, 650, 940 µatm) . . . 150 6.3 Summary of individual and interactive effects of temperature and pCO2on growth of the
investigated epilithic community and final cover of CCA andPeyssonneliaspp. Results are given as means (±SD). Asterisks indicate significant treatment effects . . . 151 7.1 Summary of experimental results from the different studies presented in this thesis . . . 166 7.2 Summary of significant treatment effects on response variables of experimental species
from the different studies presented in this thesis. Green arrows indicate an increase, red arrows a decrease and circles no significant treatment effect on response parameters compared to control conditions . . . 167
List of Figures
1.1 Trends in atmospheric CO2concentrations with long-term projections following RCP2.6-RCP8.5 (modified from IPCC 2013) . . . 6 1.2 Trends in global ocean surface pH with long-term projections following RCP2.6-RCP8.5
(modified from IPCC 2013) . . . 7 1.3 Illustration of research objectives with individual and interactive effects of global and
local stressors in sequence as covered in this thesis . . . 15 1.4 Experimental species (a)Acropora millepora, (b)Acropora tenuis, (c)Seriatopora
hys-trix, (d)Halimeda digitata, (e)Halimeda opuntia, (f) crustose coralline algae, (g) Peysson-nelia spp., (h) Amphistegina radiata, (i)Heterostegina depressaand (j) Marginopora vertebralis . . . 16 1.5 Map of study sites for experiments in Papua New Guinea and Australia . . . 19
2.1 Growth (n=40-60), maximum quantum efficiency (n=40-70) and chlorophylla con-tent (n=27-30) ofA. radiata,H. depressaandM. vertebralisafter six weeks of experi-mental treatment. Whiskers represent upper and lower extremes. Data shown in graphs are untransformed . . . 43 2.2 Net photosynthesis and dark respiration (n=9) ofH. depressaandM. vertebralisafter
six weeks of experimental treatment. Whiskers represent upper and lower extremes.
Data shown in graphs are untransformed . . . 45 2.3 Net photosynthesis and respirationn=6-9 ofH. depressaandM. vertebralisafter
short-term exposure. Whiskers represent upper and lower extremes. Data shown in graphs are untransformed . . . 46 2.4 Photosynthesis irradiance (P-I) curve forM. vertebralis in two different experimental
treatments. Black symbols represent the control treatment (pCO2=496 µatm);n=9, R2=0.96, p<0.001. White symbols represent the high CO2treatment (pCO2=1662 µatm);n=9, R2=0.98, p<0.001. Data are given as means±1 SE of 9 replicates in 3 experimental runs, each treatment. Data shown in graph are untransformed . . . 48 3.1 (a) Map of Papua New Guinea, Milne Bay Province and Normanby Island with locations
of seep sites at Dobu Island and Upa-Upasina. (b)H. digitatagrowing at the CO2seep site (Upa-Upasina). (c)H. opuntiagrowing at the CO2 seep site (Upa-Upasina). (d)H.
opuntiagrowing next to CO2bubbles (Dobu Island) . . . 65 3.2 Carbonate system parameters of water samples collected aboveHalimedaspecies
grow-ing at Dobu Island and Upa-Upasina control and seep site. Each dot represents a water sample collected above the corresponding species (green = control site, red = seep site).
Dotted lines indicate ambient (green) levels and predicted future (red) levels following the most pessimistic ‘representative concentration pathway’ RCP8.5. Solid lines (red) represent mean values of water samples for each species, collected at the seep site . . . . 71 3.3 In-situ light-, dark- and net calcification rates ofH. digitata andH. opuntia grown at
control and CO2 seep site. Brackets indicate significant differences in ANOVAs, with significance levels∗p<0.05,∗∗p<0.001,∗ ∗ ∗p<0.0001 . . . 72 3.4 In-situ rates of net photosynthesis ofH. digitataandH. opuntia grown at control and
CO2seep site . . . 73 3.5 Total-, organic- and inorganic carbon content and Corg: Cinorgratio ofH. digitataandH.
opuntiagrown at control and CO2seep site. Brackets indicate significant differences in ANOVAs, with significance levels∗p<0.05,∗∗p<0.001,∗ ∗ ∗p<0.0001 . . . 74
3.6 δ13C andδ15N signatures ofH. digitataandH. opuntiagrown at control and CO2seep site and transplanted from control to control and control to seep site. Brackets indicate significant differences in ANOVAs, with significance levels∗ p<0.05,∗∗ p<0.001,
∗ ∗ ∗ p<0.0001 . . . 75 4.1 Growth rates, net-, light- and dark calcification rates ofA. millepora andH. opuntia
after 16 days exposure to experimental conditions. Data was pooled across pCO2 and light treatment because there was no significant interaction. X-axes represent OA treat-ments in µatm pCO2and light treatments in µmol photons m−2s−1. Whiskers represent lower and upper extremes. Brackets indicate significant differences in ANOVAs, with significance levels∗ p<0.05,∗∗ p<0.001,∗ ∗ ∗ p<0.0001 . . . 95 4.2 Gross-, net photosynthesis, respiration and Chlacontent of ofA. milleporaandH.
op-untiaafter 16 days exposure to experimental conditions. Data was pooled across pCO2 and light treatment because there was no significant interaction. X-axes represent OA treatments in µatm pCO2and light treatments in µmol photons m−2s−1. Whiskers rep-resent lower and upper extremes. Brackets indicate significant differences in ANOVAs, with significance levels∗ p<0.05,∗∗ p<0.001,∗ ∗ ∗ p<0.0001 . . . 97 5.1 Growth of A. tenuis, S. hystrix and H. opuntia after three weeks experimental
treat-ment. X-axes represent pCO2treatments in µatm and DIN treatments in µmol L−1NOx. Whiskers represent upper and lower extremes. Plots illustrate pooled data, due to non-significant interactions . . . 121 5.2 Light-, dark- and net calcification ofA. tenuis,S. hystrixandH. opuntiaafter three weeks
experimental treatment. X-axes represent pCO2treatments in µatm and DIN treatments in µmol L−1NOx. Whiskers represent upper and lower extremes. Plots illustrate pooled data, due to non-significant interactions . . . 122 5.3 Net photosynthesis, dark respiration and gross photosynthesis ofA. tenuis,S. hystrixand
H. opuntiaafter three weeks experimental treatment. X-axes represent pCO2treatments in µatm and DIN treatments in µmol L−1 NOx. Whiskers represent upper and lower extremes. Plots illustrate pooled data, due to non-significant interactions . . . 123 5.4 Light-, dark-, and net NOxuptake ofA. tenuis,S. hystrixandH. opuntiaafter three weeks
experimental treatment. X-axes represent pCO2treatments in µatm and DIN treatments in µmol L−1NOx. Whiskers represent upper and lower extremes. Plots illustrate pooled data, due to non-significant interactions . . . 124