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The Effects Of Ocean Warming And Acidification On Corallinaceae Coralline Algae
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Book Synopsis The Effects of Ocean Warming and Acidification on Corallinaceae Coralline Algae by : Jessie Ann Short
Download or read book The Effects of Ocean Warming and Acidification on Corallinaceae Coralline Algae written by Jessie Ann Short and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: [Truncated] Coralline algae (Rhodophyta, Corallinaceae) are a ubiquitous group of calcifying red macroalgae, which form an integral component of a diverse range of ecosystems worldwide. The effects of environmental change on ecologically important taxa, such as the coralline algae, have major implications for the future fate of marine ecosystems. Understanding how particular habitats will be affected by environmental change is currently of great interest, as this knowledge will contribute to the effective protection and management of the marine environment in the coming decades. Coralline algae are sensitive to the increases in seawater temperature and CO2 predicted with global climate change due to the negative effects of these changes on the process of calcification. In contrast, fleshy (non-calcifying) algal species can respond in a positive manner to ocean warming and acidification. As such, a shift in dominance from calcifying to fleshy algal species is predicted for many marine communities. Since coralline and fleshy algae occupy many of the same benthic habitats, understanding how differential responses to environmental change will affect the interaction between them is important for predicting future changes in community structure. Thus, the general aims of this thesis were to assess the effects of ocean warming and acidification on 1) coralline algal metabolism and 2) the interaction between coralline algae and fleshy algae.
Book Synopsis The Effects of Light, Temperature, and Ocean Acidification on the Physiology and Ecology of Tropical Crustose Coralline Algae by : Amy A. Briggs
Download or read book The Effects of Light, Temperature, and Ocean Acidification on the Physiology and Ecology of Tropical Crustose Coralline Algae written by Amy A. Briggs and published by . This book was released on 2016 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Ocean Acidification by : National Research Council
Download or read book Ocean Acidification written by National Research Council and published by National Academies Press. This book was released on 2010-09-14 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ocean has absorbed a significant portion of all human-made carbon dioxide emissions. This benefits human society by moderating the rate of climate change, but also causes unprecedented changes to ocean chemistry. Carbon dioxide taken up by the ocean decreases the pH of the water and leads to a suite of chemical changes collectively known as ocean acidification. The long term consequences of ocean acidification are not known, but are expected to result in changes to many ecosystems and the services they provide to society. Ocean Acidification: A National Strategy to Meet the Challenges of a Changing Ocean reviews the current state of knowledge, explores gaps in understanding, and identifies several key findings. Like climate change, ocean acidification is a growing global problem that will intensify with continued CO2 emissions and has the potential to change marine ecosystems and affect benefits to society. The federal government has taken positive initial steps by developing a national ocean acidification program, but more information is needed to fully understand and address the threat that ocean acidification may pose to marine ecosystems and the services they provide. In addition, a global observation network of chemical and biological sensors is needed to monitor changes in ocean conditions attributable to acidification.
Book Synopsis Coralline Algae: Globally Distributed Ecosystem Engineers by : Laurie Carol Hofmann
Download or read book Coralline Algae: Globally Distributed Ecosystem Engineers written by Laurie Carol Hofmann and published by Frontiers Media SA. This book was released on 2020-07-08 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Effects of Ocean Acidification, Elevated Temperature and Herbivory on Tropical Crustose Coralline Algae by : Maggie Dorothy Johnson
Download or read book The Effects of Ocean Acidification, Elevated Temperature and Herbivory on Tropical Crustose Coralline Algae written by Maggie Dorothy Johnson and published by . This book was released on 2011 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Effects of Warming and Ocean Acidification on Calcification and Photosynthesis of Arctic Coralline Red Algae Under Summer Light Conditions by : Dana Hellemann
Download or read book Effects of Warming and Ocean Acidification on Calcification and Photosynthesis of Arctic Coralline Red Algae Under Summer Light Conditions written by Dana Hellemann and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Impacts of Ocean Acidification on Coralline Algae by : Chenchen Shen
Download or read book Impacts of Ocean Acidification on Coralline Algae written by Chenchen Shen and published by . This book was released on 2017 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oceanic uptake of rising anthropogenic CO2 emissions has caused the emergence of ocean acidification as a major threat to marine ecosystems worldwide. Along eastern boundary current systems, seawater is naturally acidified due to coastal upwelling of low pH seawater from depth. Compounded by ocean acidification, upwelling regions are expected to become increasingly corrosive to calcifying organisms, potentially forcing them beyond their physiological tolerance windows. In my dissertation, I focused on the impacts of ocean acidification on calcareous coralline algae in the California Current System. Using coralline algae in rocky intertidal habitats as model organisms, I extend the implications of ocean acidification from the organismal level to the broader community level. Global environmental change implies not only gradual changes in the mean values of environmental variables but also an increase in variability and the likelihood of rare, extreme events. In Chapter 2, I conducted a laboratory experiment to explore potential interactions between two different types of environmental stressors. Specifically, I tested the effects of elevated pCO2, including variable pCO2 treatments, and a severe desiccation event on the coralline species, Corallina vancouveriensis. I found that C. vancouveriensis growth was negatively impacted by both elevated pCO2 and desiccation stress, although their combined effects were approximately additive rather than synergistic. Furthermore, while high pCO2 at constant levels only caused small reductions in algal growth over a two-week period, these effects were exacerbated by pCO2 variability. One criticism of laboratory experiments testing species responses to environmental change is that they isolate organisms under simplified conditions. The potential of overlooking important biotic or abiotic factors present in the natural environment limits the inferences that can be made from laboratory studies. In Chapter 3, I conducted a reciprocal removal experiment at two field sites and two wave exposures to investigate potential changes in the interactions between coralline and fleshy turf-forming algae since the 1980s. I used as a baseline the results from a similar study conducted nearly 30 years ago that failed to detect spatial competition between coralline and fleshy algae. Despite the progression of ocean acidification over the last three decades, my results indicated that the lack of competition between coralline and fleshy algae persists to this day, with results consistent across both sites and wave exposures. The findings in Chapter 3 refer to present-day interactions, but in the future, ocean acidification is expected to be detrimental to coralline algae while potentially benefitting fleshy algae. Both coralline and fleshy algae form turf habitats that shelter diverse epifaunal communities. Thus, changes in the algal composition of turf habitats may lead to broader changes encompassing epifaunal communities, depending on the degree of specialization displayed in epifaunal habitat associations. In Chapter 4, I compared the abundance, richness, and community composition of epifauna between coralline and fleshy turf habitats at four sites along the Oregon-California coast. I found that epifauna were more abundant in coralline turfs due to higher turf density. However, epifaunal richness and community composition were similar between turf types, indicating high levels of redundancy in habitat provision between coralline and fleshy algae. Since most species of epifauna tended to be turf generalists, they may be resistant to the potential indirect effects of ocean acidification involving declines in coralline turf habitat. My dissertation combined a variety of standard ecological methodologies to help translate ocean acidification impacts from the organismal level to the community level. Overall, while I found that elevated pCO2 decreased coralline growth in the laboratory, evidence from the field suggested a capacity for communities to resist the effects of ocean acidification and remain resilient. In the natural environment, ocean acidification impacts may be moderated by multiple environmental variables working in different directions, the temporal dynamics of stressors allowing for periods of recovery, and species interactions having dampening effects. One way forward to unite theories of change with those of resistance is to identify ecosystem indicators and critical thresholds that may help provide a more comprehensive view of ecosystem functioning and stability in the face of global change.
Book Synopsis Coralline Algae: Past, Present, and Future Perspectives by : Laurie Carol Hofmann
Download or read book Coralline Algae: Past, Present, and Future Perspectives written by Laurie Carol Hofmann and published by Frontiers Media SA. This book was released on 2022-12-28 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Combined Effects of Ocean Acidification with Morphology, Water Flow, and Algal Acclimation on Metabolic Rates of Tropical Coralline Algae by : Sarah Merolla
Download or read book The Combined Effects of Ocean Acidification with Morphology, Water Flow, and Algal Acclimation on Metabolic Rates of Tropical Coralline Algae written by Sarah Merolla and published by . This book was released on 2017 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Coral reefs are currently facing multiple stressors that threaten their health and function, including ocean acidification (OA). OA has been shown to negatively affect many reef calcifiers, such as coralline algae that provide many critical contributions to reef systems. Past studies have focused on how OA independently influences coralline algae, but more research is necessary as it is expected that the effects of OA on coralline algae will vary depending on many other factors. To better understand how algal morphology, water flow, and algal acclimation interact with OA to affect coralline algae, three studies were conducted in Moorea, French Polynesia, from June 2015 to July 2016. In January 2016, I tested the hypothesis that algal individuals with higher morphological complexity would exhibit faster metabolic rates under ambient pCO2 conditions, but would also demonstrate higher sensitivity to OA conditions. For three species of crustose coralline algae, Lithophyllum kotschyanum, Neogoniolithon frutescens, and Hydrolithon reinboldii, algal individuals with more complex morphologies demonstrated faster rates of calcification, photosynthesis, and respiration in the ambient pCO2 treatment than individuals with simpler morphological forms. There also appeared to be a relationship between morphology and sensitivity to OA conditions, with calcification rates negatively correlated with higher morphological complexity. In the summers of 2015 and 2016, I conducted three experiments examining the effects of water flow and OA on different morphologies of coralline algae to test the hypotheses that increased flow would enhance metabolic rates and mitigate the effects of OA, and that algae with more complex morphologies would be more responsive to increased water flow and more sensitive to OA conditions. A field experiment investigating the effects of water flow on Amphiroa fragilissima, L. kotschyanum, N. frutescens, and H. reinboldii detected enhanced rates of calcification, photosynthesis, and respiration with increased flow, and this relationship appeared to be the strongest for the crustose algal species with the highest structural complexity. A flume manipulation examining the combined effects of water flow and OA on A. fragilissima, L. kotschyanum, N. frutescens, H. reinboldii, and Porolithon onkodes suggested that coralline algal species with high structural complexity were the most sensitive to OA conditions. Finally, A. fragilissima and L. kotschyanum were maintained in different pCO2 and water flow conditions in a long-term mesocosm experiment, which indicated that flow was unable to mitigate the effects of OA on coralline algae. In the summer of 2016, I investigated the acclimation potential of A. fragilissima and L. kotschyanum to OA, and predicted that the original treatment conditions would induce phenotypic modifications that would influence algal responses to the end treatment. There were negative effects of long-term exposure of coralline algae to elevated pCO2 conditions on calcification and photosynthesis, though partial acclimation in calcification to OA was observed. The instantaneous exposure of elevated pCO2 had negative impacts on algal calcification, but had a nominal effect on photosynthesis. No effects of long-term or instantaneous exposure to elevated pCO2 were observed for respiration. The results of these studies indicate that the coralline algal response to OA conditions will likely be complex and depend on numerous factors including water flow, morphology, and acclimation potential. Therefore, it is critical that future studies further investigate the effects of these factors; specifically examining the mechanisms that underlie these responses in order to better predict the future of coralline algae and thus coral reef ecosystems in a more acidic ocean.
Book Synopsis Red Coralline Algae and Climate Change by : Maren Isabelle Pauly
Download or read book Red Coralline Algae and Climate Change written by Maren Isabelle Pauly and published by . This book was released on 2015 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: Past ocean acidification recorded in the geological record facilitates the understanding of rates and influences of contemporary pCO2 enrichment. High resolution proxies of pCO2 and pH can be used to reconstruct components of the palaeocarbonate system. At present, most pH reconstructions are made using boron isotopes, however, there is some uncertainty associated with vital effects and isotopic fractionation. In addition to contemporary ocean acidification, marine organisms currently experience thermal stress associated with increasing atmospheric temperatures. Here we present a study of the influences of multiple stressors on the growth and structure of a marine carbonate, predicted to occur within this century, and a novel structural proxy for carbonate chemistry; Mg-O bond strength in coralline algae. Free living Lithothamnion glaciale algae were incubated in control (380ppm pCO2), moderate acidification (750ppm pCO2) and high acidification (1000ppm pCO2) at ambient and enhanced (+2°C) temperature conditions for 24 months. Coralline algae growth (linear extension) was highly dependent on temperature, with +2°C samples experiencing significantly reduced growth. No significant correlation was found between pCO2 and growth, indicating L. glaciale's ability to acclimatize. Relative magnesium concentration and Mg-O bond strength within the high-Mg skeleton cyclically over an annual cycle. For all seasons there was a positive linear relationship between pCO2 concentration and bond strength mediated by positional disorder of the calcite lattice. Structural preservation of the carbonate chemistry system in coralline algal high Mg calcite represents an alternative approach to reconstructing marine carbonate chemistry parameters based on skeletal structure rather than chemistry.
Book Synopsis The Combined Effects of Ocean Acidification with Fleshy Macroalgae and Filamentous Turfs on Tropical Crustose Coralline Algae by : Lansing Yun Perng
Download or read book The Combined Effects of Ocean Acidification with Fleshy Macroalgae and Filamentous Turfs on Tropical Crustose Coralline Algae written by Lansing Yun Perng and published by . This book was released on 2019 with total page 111 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Ecophysiology of Coral Reef Primary Producers by : Maggie Dorothy Johnson
Download or read book Ecophysiology of Coral Reef Primary Producers written by Maggie Dorothy Johnson and published by . This book was released on 2016 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Natural heterogeneity and global change are key environmental drivers of ecosystem structure and function in both terrestrial and marine ecosystems. At the foundation of all food webs are the primary producers, which require macronutrients and photosynthetic substrate in order to fix inorganic carbon into organic sugars and fuel energy transfer into food webs. This dissertation is an examination of the ecophysiology, or the interaction of organismal physiology with the environment, of key benthic primary producers on coral reefs. Reef-building corals and algae are the most abundant primary producers on coral reefs, and I use coarse functional groupings categorized as reef-building corals, fleshy macroalgae, calcareous macroalgae, crustose coralline algae (CCA) and turf algae assemblages. I assessed the influence of, 1) a natural gradient in inorganic nutrient availability, and, 2) simulated global change on the ecophysiology of corals and algae by functional group. The Southern Line Islands are an archipelago of islands that span the equatorial upwelling region and demonstrate predictable heterogeneity in inorganic nutrient availability. The dominant species of corals and algae demonstrated higher pigment concentrations and photosynthetic efficiency across the archipelago as a function of increasing inorganic nutrient concentrations. This suggests that natural fluxes of inorganic nutrients have an important positive influence on primary producers. I then conducted laboratory experiments on Palmyra Atoll and in Moorea, French Polynesia to test the effects of ocean acidification (OA) and warming on different functional groups of algae. Across a suite of species, OA increased the growth of fleshy macroalgae and turf algae assemblages, but decreased growth and calcification of calcareous macroalgae and CCA. Ocean acidification had a stronger effect than warming on the biomass of turf algae assemblages. Positive effects of OA on turf algae metabolism were increased by warming. These findings suggest that fleshy and calcifying algae respond differently to global change stressors. Ocean acidification has the potential to increase growth and productivity of fleshy algae, while concurrently decreasing growth and calcification of calcifying algae. Anthropogenic activities are increasingly altering the natural environment, and the results of this dissertation improve our ability to predict the response of corals and algae to increasing exposure to nutrients, OA and warming in the near-future ocean.
Book Synopsis The Effects of Ocean Acidification on the Reproduction of Coralline Red Algae by : Jian Wei Lai
Download or read book The Effects of Ocean Acidification on the Reproduction of Coralline Red Algae written by Jian Wei Lai and published by . This book was released on 2012 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Characterizing the Response of Coralline Algae to Ocean Acidification and Nutrient Changes in the California Current System by : Sandy Letzing
Download or read book Characterizing the Response of Coralline Algae to Ocean Acidification and Nutrient Changes in the California Current System written by Sandy Letzing and published by . This book was released on 2013 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ocean acidification (OA) has emerged as an important focus of research and policy in this decade. Ocean acidification specifically refers to changes in the inorganic carbon system in the ocean resulting from its absorption of human-released CO2 from the atmosphere. Anthropogenic atmospheric CO2 levels are rapidly increasing; much of this is dissolved and absorbed in the ocean (~30%) where it reacts with seawater altering fundamental properties including pH, pCO2 and saturation state of carbonate minerals. This change is of concern because of the potential of OA to disrupt biological processes, particularly those processes associated with calcification (Byrne, 2011; Diaz-Pilido, Anthony, Kline, Dove, & Hoegh-Guldberg, 2012). For this study, I chose to investigate red coralline algae as a model organism because OA is predicted to have effects on calcification and photosynthesis, and because of the importance of coralline algae as an ecological engineer, which can be found in shallow water habitats globally. While the response of coralline algae to OA is a serious concern, there remains very limited data on the interactions of OA with other ocean conditions (e.g., temperature, nutrients, and light) that may alter or modify the effects of low pH on coralline algae communities. One nutrient in particular, phosphorus is known to have inhibiting effects on calcification in long-term studies. My objective was to describe the short-term effects of a range of elevated pCO2 and phosphorus levels both alone, and together, on calcification and photosynthetic rates of Corallina vancouveriensis. I exposed these algae to a range of pCO2 and phosphate concentrations and measured changes in total alkalinity, pH, and DO in acute exposure trials (
Book Synopsis The Effects of Nutrient Addition and Ocean Acidification on Tropical Crustose Coralline Algae by : Bridget Francine Shayka
Download or read book The Effects of Nutrient Addition and Ocean Acidification on Tropical Crustose Coralline Algae written by Bridget Francine Shayka and published by . This book was released on 2018 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the global population increases, the occurrence of multiple anthropogenic impacts on valuable coastal ecosystems, such as coral reefs, also increases. These stressors can be global and long-term, like ocean acidification (OA), or local and short-term, like nutrient runoff in some areas. The combination of these stressors can potentially have additive or interactive effects on the organisms in coral reef communities. Among the most important groups of organisms on coral reefs are crustose coralline algae (CCA), calcifying algae that cement the reef together and contribute to the global carbon cycle. This thesis studied the effects of nutrient addition and OA on Lithophyllum kotschyanum, a common species of CCA on the fringing reefs of Mo'orea, French Polynesia. Two mesocosm experiments tested the individual and interactive effects of OA and short-term nitrate and phosphate addition on L. kotschyanum. These experiments showed that nitrate and phosphate addition together increased photosynthesis, OA had interactive effects with nutrient addition, and after nutrient addition ended, calcification and photosynthetic rates changed in unpredictable ways in different OA and nutrient treatments. Because the results of the first two experiments showed impacts of nutrients even after addition stopped, two more mesocosm experiments were conducted to study the changes in photosynthesis and calcification over hourly time scales more relevant to a single nutrient pulse event. These two experiments revealed the existence of diurnal variation in light-saturated photosynthetic rate, but not calcification rate, under ambient and elevated pCO2. This pattern of increased maximum photosynthesis in the middle of the day can have important implications for how the time of nutrient runoff events during the day impacts CCA physiology. Finally, a field experiment was conducted to determine the effects of short- and long-term nutrient addition on L. kotschyanum. The results showed that a series of short-term nutrient additions did not increase photosynthesis or calcification rates above those in ambient nutrient conditions, but continual nutrient enrichment for 6 weeks increased photosynthetic rates. This increase in photosynthesis under only long-term enrichment shows the need for consideration of specific nutrient addition scenarios on coral reefs when predicting how the community will be affected.
Book Synopsis The Effect of Ocean Acidification on the Ecology of Two Tropical Crustose Coralline Algae (phylum Rhodophyta) by : Joshua Caraher-Fergusson Manning
Download or read book The Effect of Ocean Acidification on the Ecology of Two Tropical Crustose Coralline Algae (phylum Rhodophyta) written by Joshua Caraher-Fergusson Manning and published by . This book was released on 2017 with total page 92 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crustose coralline algae (CCA) are important members of coral reef communities. They accrete and consolidate the calcium carbonate framework of coral reefs, and some species are an important settlement substratum for coral larvae. CCA community composition is shaped, at least in part, by herbivory and competition. However, ocean acidification (OA) is negatively affecting CCA, with potential to affect CCA responses to herbivory (wounding) and their ability to compete for space. Changes in seawater chemistry because of OA cause reductions in the recruitment, abundance, and net calcification of CCA. In this thesis, the effects of OA on net calcification, regeneration of wounds, and competition was quantified for two species of CCA common in the back reefs of Mo'orea, French Polynesia; Porolithon onkodes and Lithophyllum insipidum. Three separate experiments were conducted in four flowing seawater tanks (flumes), each set to a different target pCO2 level representative of ambient (~ 400 μatm) or predicted end of the 21 century pCO2 (~ 700, 1000, and 1300 μatm). P. onkodes, was found to be the most abundant species of CCA in the back reefs of Mo'orea, followed by L. flavescens and L. insipidum. The abundance of P. onkodes is likely a direct result of its competitive ability. P. onkodes is thicker on average than the other common CCA in the back reefs of Mo'orea, and thicker species generally become dominant in areas of intense herbivory, such as coral reefs. In a flume experiment conducted from January to March 2016, net calcification declined 85% in P. onkodes at elevated pCO2 compared to a decline of 42% in L. insipidum, indicating that P. onkodes may be more negatively affected by OA. The differential responses to OA found here could alter the outcome of competitive interactions between P. onkodes and L. insipidum, leading to changes in the abundances of these species in CCA communities. Few studies have quantified the potential for OA to interact with natural disturbances, such as wounding of the thallus by herbivores. A flume experiment conducted from May to July 2016 found that there was a 58% reduction in the rate of vertical regeneration of artificial wounds within P. onkodes at elevated pCO2. This result could have important implications for the response of P. onkodes to grazing by excavating herbivores like parrotfish and sea urchins. Inability for CCA to recover from wounding, could increase the susceptibility of CCA to further wounding. In addition, the reductions in vertical regeneration of the wounds could also be indicative of reduced vertical growth rates. CCA with thicker thalli generally outcompete thinner CCA. Reduced vertical growth rates could reduce thallus thickness, and affect the outcome of competitive interactions among CCA. A flume experiment conducted from June to July 2016 found that there was no effect of elevated pCO2 on the outcome of competitive interactions between P. onkodes and L. insipidum. It is likely that this result may have been due to the relatively short duration of this experiment (one month). There was, however, an effect of the identity of the competitor on the proportion of live tissue remaining in focal individuals of P. onkodes. The proportion of live tissue remaining in focal individuals of P. onkodes was significantly lower in intraspecific pairings than in interspecific pairings or when paired with non-living substrate (controls). This result highlights the importance of including both intraspecific and interspecific interactions in future studies of the effects of OA on competition. Experiments of longer durations may elucidate the potential for elevated pCO2 to affect competition among CCA. CCA are ecologically important members of coral reefs. Changes in the community composition of CCA on coral reefs, because of altered competitive abilities under elevated pCO2, could affect the roles that CCA play in building and maintain coral reef ecosystems.
Book Synopsis Assessing Ocean Acidification Impacts on the Reef Building Properties of Crustose Coralline Algae by : Merinda Catherine Nash
Download or read book Assessing Ocean Acidification Impacts on the Reef Building Properties of Crustose Coralline Algae written by Merinda Catherine Nash and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crustose coralline algae (CCA), and in particular Porolithon onkodes, play an important reef-building role in modern tropical coral reefs. CCA form thick crusts of Mg-calcite and grow over corals and loose substrate to bind these together. This binding and cementing process is fundamental to the development of structural reefs that are capable of withstanding the high-energy waves in the shallow to inter-tidal areas of the reef. As anthropogenic CO2 emissions continue to increase, the oceans absorb part of this extra CO2 and become more acidic, a process known as Ocean Acidification (OA). There are concerns that OA will have a negative affect on the reef-building capacity of coral reef organisms, in particular on CCA. This is because Mg-calcite is meta-stable and more susceptible to dissolution than aragonite, the mineral used by corals to build skeletons. The goal of this thesis work was to firstly understand the physical and mechanical properties that enable the CCA to cement the reef and withstand damage from high-energy waves, bioerosion and chemical dissolution. Secondly, to anticipate how OA may interfere with these reef-building properties. These goals were pursued by setting clear aims with associated specific objectives designed to elucidate information relevant to these questions. Methods were developed for X-ray diffraction to identify the mineral composition of CCA. Nanoindentation was investigated as a tool for determining the mechanical properties of CCA and the measurement of fracture toughness was found to return physically meaningful information relevant to structural reef development. Study of CCA calcification showed that cell wall Mg-calcite exhibited radial crystal morphology in agreement with published studies on temperate species. However, high-resolution imaging showed the radial crystals were made of banded stacked sub-micron grains within an organic framework. Dolomite was found not only as cell lining by submicron rhombs, but also as the primary calcification of hypothallial cell walls. Dolomite is shown to be resistant to bacterial erosion. A model is developed whereby it is proposed that dolomite formation is dependent on polysaccharide accumulation. Using nanoindentation, P. onkodes are found to be extraordinarily tough, on par with the measured fracture toughness for metamorphic minerals quartz and corundum. The fracture toughness is enabled by the presence of dolomite cell lining. Contrary to the literature, bacterial erosion is found to be a constructive, not destructive, process. A survey of P. onkodes from Heron Island fore reef and reef flat showed that dolomite was present in all the fore reef crusts but none of the reef flat crusts. The reef flat crusts did not have fracture resistance except where remineralised. The presence of dolomite cell lining was shown to decrease skeletal dissolution rates by an order of magnitude. OA experiments showed that skeletal dissolution rates increased with elevated pCO2, but dolomite continued to confer resistance to dissolution. pCO2 levels did not affect the skeletal Mg content or dolomite formation in living CCA. Of concern, and in agreement with the literature, bacterial erosion is accelerated under a combination of elevated pCO2 and temperatures, suggesting this may be the main threat to CCA reef-building in the future. The experimental findings were corroborated by results of a field survey along a natural pCO2 gradient. In summary, dolomite was found to be an essential component of modern reef development via its contribution to enabling CCA P. onkodes thick crust development and persistence. Reef building by CCA P. onkodes is likely to continue as pCO2 rises up until a tipping point is reached whereby bacterial erosion switches from constructive to destructive.
