The persistence of reef building corals is threatened by human-induced environmental change. Maintaining coral reefs into the future requires not only the survival of adults, but also the influx of recruits to promote genetic diversity and retain cover following adult mortality. Few studies examine the linkages among multiple life stages of corals, despite a growing knowledge of carryover effects in other systems. We provide a novel test of coral parental conditioning to ocean acidification (OA) and tracking of offspring for 6 months post-release to better understand parental or developmental priming impacts on the processes of offspring recruitment and growth. Coral planulation was tracked for 3 months following adult exposure to high pCO2 and offspring from the second month were reciprocally exposed to ambient and high pCO2 for an additional 6 months. Offspring of parents exposed to high pCO2 had greater settlement and survivorship immediately following release, retained survivorship benefits during 1 and 6 months of continued exposure, and further displayed growth benefits to at least 1 month post release. Enhanced performance of offspring from parents exposed to high conditions was maintained despite the survivorship in both treatments declining in continued exposure to OA. Conditioning of the adults while they brood their larvae, or developmental acclimation of the larvae inside the adult polyps, may provide a form of hormetic conditioning, or environmental priming that elicits stimulatory effects. Defining mechanisms of positive acclimatization, with potential implications for carry over effects, cross-generational plasticity, and multi-generational plasticity, is critical to better understanding ecological and evolutionary dynamics of corals under regimes of increasing environmental disturbance. Considering environmentally-induced parental or developmental legacies in ecological and evolutionary projections may better account for coral reef response to the chronic stress regimes characteristic of climate change.
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Environmentally-induced parental or developmental conditioning influences coral offspring ecological performance
Published 14 September 2020 Science ClosedTags: adaptation, biological response, corals, laboratory, morphology, mortality, North Pacific, otherprocess, performance, reproduction
Responses of coral gastrovascular cavity pH during light and dark incubations to reduced seawater pH suggest species-specific responses to the effects of ocean acidification on calcification
Published 7 September 2020 Science ClosedTags: biological response, calcification, corals, laboratory, physiology
Coral polyps have a fluid-filled internal compartment, the gastrovascular cavity (GVC). Respiration and photosynthesis cause large daily excursions in GVC oxygen concentration (O2) and pH, but few studies have examined how this correlates with calcification rates. We hypothesized that GVC chemistry can mediate and ameliorate the effects of decreasing seawater pH (pHSW) on coral calcification. Microelectrodes were used to monitor O2 and pH within the GVC of Montastraea cavernosa and Duncanopsammia axifuga (pH only) in both the light and the dark, and three pHSW levels (8.2, 7.9, and 7.6). At pHSW 8.2, GVC O2 ranged from ca. 0 to over 400% saturation in the dark and light, respectively, with transitions from low to high (and vice versa) within minutes of turning the light on or off. For all three pHSW treatments and both species, pHGVC was always significantly above and below pHSW in the light and dark, respectively. For M. cavernosa in the light, pHGVC reached levels of pH 8.4–8.7 with no difference among pHSW treatments tested; in the dark, pHGVC dropped below pHSW and even below pH 7.0 in some trials at pHSW 7.6. For D. axifuga in both the light and the dark, pHGVC decreased linearly as pHSW decreased. Calcification rates were measured in the light concurrent with measurements of GVC O2 and pHGVC. For both species, calcification rates were similar at pHSW 8.2 and 7.9 but were significantly lower at pHSW 7.6. Thus, for both species, calcification was protected from seawater acidification by intrinsic coral physiology at pHSW 7.9 but not 7.6. Calcification was not correlated with pHGVC for M. cavernosa but was for D. axifuga. These results highlight the diverse responses of corals to changes in pHSW, their varying abilities to control pHGVC, and consequently their susceptibility to ocean acidification.
Paracellular transport to the coral calcifying medium: effects of environmental parameters
Published 4 September 2020 Science ClosedTags: biological response, calcification, corals, laboratory, physiology
Coral calcification relies on the transport of ions and molecules to the extracellular calcifying medium (ECM). Little is known about paracellular transport (via intercellular junctions) in corals and other marine calcifiers. Here, we investigated whether the permeability of the paracellular pathway varied in different environmental conditions in the coral Stylophora pistillata. Using the fluorescent dye calcein, we characterised the dynamics of calcein influx from seawater to the ECM and showed that increases in paracellular permeability (leakiness) induced by hyperosmotic treatment could be detected by changes in calcein influx rates. We then used the calcein-imaging approach to investigate the effects of two environmental stressors on paracellular permeability: seawater acidification and temperature change. Under conditions of seawater acidification (pH 7.2) known to depress pH in the ECM and the calcifying cells of S. pistillata, we observed a decrease in half-times of calcein influx, indicating increased paracellular permeability. By contrast, high temperature (31°C) had no effect, whereas low temperature (20°C) caused decreases in paracellular permeability. Overall, our study establishes an approach to conduct further in vivo investigation of paracellular transport and suggests that changes in paracellular permeability could form an uncharacterised aspect of the physiological response of S. pistillata to seawater acidification.
Calcification and organic productivity at the world’s southernmost coral reef
Published 4 September 2020 Science ClosedTags: biological response, BRcommunity, calcification, corals, field, physiology, respiration, South Pacific
Highlights
- High-latitude coral reefs are hotspots of ocean change and vulnerable to bleaching.
- Coral ecosystem calcification in winter was lower than most studied ecosystems.
- The reef was net heterotrophic in the winter and net respiratory in the summer.
- Detailed bathymetric observations reduce uncertainties in metabolic calculations.
- Summer calcification was not driven by temperature or aragonite saturation state.
Abstract
Estimates of coral reef calcification and organic productivity provide valuable insight to community functionality and the response of an ecosystem to stress events. High-latitude coral reefs are expected to experience rapid changes in calcification rates and become refugia for tropical species following climate change and increasing bleaching events. Here, we estimate ecosystem-scale calcification and organic productivity at the world’s southernmost coral reef using seawater carbon chemistry observations (Lord Howe Island, Australia). We reduce uncertainties in metabolic calculations by producing a detailed bathymetric model and deploying two current meters to refine residence time and volume estimates. Bathymetry-modelled transect depths ranged from 74% shallower to 20% deeper than depths averaged from reef crest/flat current meters, indicating that higher-resolution depth observations help to reduce uncertainties in reef metabolic calculations. Rates of ecosystem calcification were 56.6 ± 14.8 mmol m−2 d−1 in the winter and 125.3 ± 39.4 mmol m−2 d−1 in the summer. These rates are lower than most other high-latitude reefs according to our compilation of high-latitude coral ecosystem metabolism estimates. Coral cover ranged from 14.7 ± 2.3% in winter to 19.8 ± 2.1% in the summer. A concurrent bleaching event and cyclone occurred during summer sampling (February – March 2019), resulting in 47% of corals bleached at the study site and 2% mortality due to cyclonal damage. Therefore, it is likely that the summertime Gnet rates underestimate baseline calcification. Our results enable future assessments of long-term change, but do not resolve the impact of bleaching at Lord Howe Island.
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Controls on the spatio-temporal distribution of microbialite crusts on the Great Barrier Reef over the past 30,000 years
Published 3 September 2020 Science ClosedTags: chemistry, corals, field, methods, morphology, paleo, South Pacific
Highlights
- Comprehensive dataset of reefal microbial crusts over the past 30,000 years.
- Modern 3D analysis to assess heterogeneity of microbialites in reef frameworks.
- Radiocarbon ages show microbialite development coeval with and postdating framework.
- Microbialite thickness correlates with changes in carbonate saturation level and pH.
Abstract
Calcification of microbial mats adds significant amounts of calcium carbonate to primary coral reef structures that stabilizes and binds reef frameworks. Previous studies have shown that the distribution and thicknesses of late Quaternary microbial crusts have responded to changes in environmental parameters such as seawater pH, carbonate saturation state, and sediment and nutrient fluxes. However, these studies are few and limited in their spatio-temporal coverage. In this study, we used 3D and 2D examination techniques to investigate the spatio-temporal distribution of microbial crusts and their responses to environmental changes in Integrated Ocean Drilling Program (IODP) Expedition 325 (Great Barrier Reef Environmental Changes) fossil reef cores that span 30 to 10 ka at two locations on the GBR reef margin. Our GBR microbialite record was then combined with a meta-analysis of 17 other reef records to assess global scale changes in microbialite development (i.e., presence/absence, thickness) over the same period. The 3D results were compared with 2D surface area measurements to assess the accuracy of 2D methodology. The 2D technique represents an efficient and accurate proxy for the 3D volume of reef framework components within the bounds of uncertainty (average: 9.45 ± 4.5%). We found that deep water reef frameworks were most suitable for abundant microbial crust development. Consistent with a previous Exp. 325 study (Braga et al., 2019), we also found that crust ages were broadly coeval with coralgal communities in both shallow water and fore-reef settings. However, in some shallow water settings they also occur as the last reef framework binding stage, hundreds of years after the demise of coralgal communities. Lastly, comparisons of crust thickness with changes in environmental conditions between 30 and 10 ka, show a temporal correlation with variations in partial pressure of CO2 (pCO2), calcite saturation state (Ωcalcite), and pH of seawater, particularly during the past ~15 kyr, indicating that these environmental factors likely played a major role in microbialite crust development in the GBR. This supports the view that microbialite crust development can be used as an indicator of ocean acidification.
Ocean acidification has impacted coral growth on the Great Barrier Reef
Published 31 August 2020 Science ClosedTags: biological response, calcification, communitymodeling, corals, growth, modeling, morphology, multiple factors, South Pacific, temperature
Ocean acidification (OA) reduces the concentration of seawater carbonate ions that stony corals need to produce their calcium carbonate skeletons, and is considered a significant threat to the functional integrity of coral reef ecosystems. However, detection and attribution of OA impact on corals in nature are confounded by concurrent environmental changes, including ocean warming. Here we use a numerical model to isolate the effects of OA and temperature, and show that OA alone has caused 13±3% decline in the skeletal density of massive Porites corals on the Great Barrier Reef since 1950. This OA‐induced thinning of coral skeletons, also evident in Porites from the South China Sea but not in the central equatorial Pacific, reflects enhanced acidification of reef water relative to the surrounding open ocean. Our finding reinforces concerns that even corals that might survive multiple heatwaves are structurally weakened and increasingly vulnerable to the compounding effects of climate change.
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Effects of future climate on coral-coral competition
Published 20 August 2020 Science ClosedTags: biological response, corals, field, laboratory, mesocosms, morphology, multiple factors, North Atlantic, photosynthesis, temperature
As carbon dioxide (CO2) levels increase, coral reefs and other marine systems will be affected by the joint stressors of ocean acidification (OA) and warming. The effects of these two stressors on coral physiology are relatively well studied, but their impact on biotic interactions between corals are poorly understood. While coral-coral interactions are less common on modern reefs, it is important to document the nature of these interactions to better inform restoration strategies in the face of climate change. Using a mesocosm study, we evaluated whether the combined effects of ocean acidification and warming alter the competitive interactions between the common coral Porites astreoides and two other mounding corals (Montastraea cavernosa or Orbicella faveolata) common in the Caribbean. After 7 days of direct contact, P. astreoides suppressed the photosynthetic potential of M. cavernosa by 100% in areas of contact under both present (~28.5°C and ~400 μatm pCO2) and predicted future (~30.0°C and ~1000 μatm pCO2) conditions. In contrast, under present conditions M. cavernosa reduced the photosynthetic potential of P. astreoides by only 38% in areas of contact, while under future conditions reduction was 100%. A similar pattern occurred between P. astreoides and O. faveolata at day 7 post contact, but by day 14, each coral had reduced the photosynthetic potential of the other by 100% at the point of contact, and O. faveolata was generating larger lesions on P. astreoides than the reverse. In the absence of competition, OA and warming did not affect the photosynthetic potential of any coral. These results suggest that OA and warming can alter the severity of initial coral-coral interactions, with potential cascading effects due to corals serving as foundation species on coral reefs.
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Distribution of deep-water scleractinian and stylasterid corals across abiotic environmental gradients on three seamounts in the Anegada Passage
Published 18 August 2020 Science ClosedTags: abundance, biological response, chemistry, corals, field, North Atlantic, otherprocess
In the Caribbean Basin the distribution and diversity patterns of deep-sea scleractinian corals and stylasterid hydrocorals are poorly known compared to their shallow-water relatives. In this study, we examined species distribution and community assembly patterns of scleractinian and stylasterid corals on three high-profile seamounts within the Anegada Passage, a deep-water throughway linking the Caribbean Sea and western North Atlantic. Using remotely operated vehicle surveys conducted on the E/V Nautilus by the ROV Hercules in 2014, we characterized coral assemblages and seawater environmental variables between 162 and 2,157 m on Dog Seamount, Conrad Seamount, and Noroît Seamount. In all, 13 morphospecies of scleractinian and stylasterid corals were identified from video with stylasterids being numerically more abundant than both colonial and solitary scleractinians. Cosmopolitan framework-forming species including Madrepora oculata and Solenosmilia variabilis were present but occurred in patchy distributions among the three seamounts. Framework-forming species occurred at or above the depth of the aragonite saturation horizon with stylasterid hydrocorals being the only coral taxon observed below Ωarag values of 1. Coral assemblage variation was found to be strongly associated with depth and aragonite saturation state, while other environmental variables exerted less influence. This study enhances our understanding of the factors that regulate scleractinian and stylasterid coral distribution in an underreported marginal sea and establishes a baseline for monitoring future environmental changes due to ocean acidification and deoxygenation in the tropical western Atlantic.
Status of corals along the Sindh coast of Pakistan: prevailing environmental conditions, their impacts on community structure and conservation approaches
Published 14 August 2020 Science ClosedTags: abundance, biological response, chemistry, community composition, corals, field, Indian, otherprocess
Highlights
• Describes status of corals along the Sindh coast of Pakistan.
• Prevailing physico-chemical conditions in coastal waters of Sindh, Pakistan.
• Impacts of physico-chemical conditions on corals distribution patterns.
• Existing threats and future conservation plans.
Abstract
Reef system across the globe is facing serious anthropogenic threats and impacts. The present study describes the status of corals, prevailing stresses and their impacts on community structure along the Sindh coast of Pakistan. In the current study, 21 species of hard corals were recorded. All together, 50 live coral species recorded from the coastal waters of Pakistan. High diversity occurred at Churna Island (15 species). A little bit patch reef formation was observed at Churna Island (dive sites 2 and 3) while scattered colonies were recorded in coastal habitats. Porites species were found dominating both in coastal and offshore environments. Overall, temperature and nutrient concentrations were found to be fluctuating than what corals prefer, however, pH concentrations were found in normal ranges. Calcium, carbon and oxygen were recorded as major elements incorporated in coral skeletons. Possible causes of limited coral fauna and a confined distribution pattern appeared to be linked with local factors (strong wave action, high nutrient concentrations, temperature fluctuations, past geological events, reversal monsoon and overfishing) rather than global changes. Other impacts, for example diving tourism, coral mining or collection for ornaments or sale are minor. Prevailing stresses, increase in the construction of local infrastructure in coastal areas and unmanaged tourism indicates that in future, the level of pollution will further increase in coastal areas. As a result, a further shift in community structure will occur and it appears that only Porites will survive in the coastal waters of Pakistan. Future protection efforts should focus on regular monitoring and establishing of an effective Marine Protected Area at least around the shallow habitats of the Churna Island.
The role of aspartic acid in reducing coral calcification under ocean acidification conditions
Published 12 August 2020 Science ClosedTags: biological response, calcification, corals, laboratory, molecular biology, morphology, South Pacific
Biomolecules play key roles in regulating the precipitation of CaCO3 biominerals but their response to ocean acidification is poorly understood. We analysed the skeletal intracrystalline amino acids of massive, tropical Porites spp. corals cultured over different seawater pCO2. We find that concentrations of total amino acids, aspartic acid/asparagine (Asx), glutamic acid/glutamine and alanine are positively correlated with seawater pCO2 and inversely correlated with seawater pH. Almost all variance in calcification rates between corals can be explained by changes in the skeletal total amino acid, Asx, serine and alanine concentrations combined with the calcification media pH (a likely indicator of the dissolved inorganic carbon available to support calcification). We show that aspartic acid inhibits aragonite precipitation from seawater in vitro, at the pH, saturation state and approximate aspartic acid concentrations inferred to occur at the coral calcification site. Reducing seawater saturation state and increasing [aspartic acid], as occurs in some corals at high pCO2, both serve to increase the degree of inhibition, indicating that biomolecules may contribute to reduced coral calcification rates under ocean acidification.
The challenges of detecting and attributing ocean acidification impacts on marine ecosystems
Published 12 August 2020 Science ClosedTags: biological response, corals, mollusks, phanerogams, review, zooplankton
A substantial body of research now exists demonstrating sensitivities of marine organisms to ocean acidification (OA) in laboratory settings. However, corresponding in situ observations of marine species or ecosystem changes that can be unequivocally attributed to anthropogenic OA are limited. Challenges remain in detecting and attributing OA effects in nature, in part because multiple environmental changes are co-occurring with OA, all of which have the potential to influence marine ecosystem responses. Furthermore, the change in ocean pH since the industrial revolution is small relative to the natural variability within many systems, making it difficult to detect, and in some cases, has yet to cross physiological thresholds. The small number of studies that clearly document OA impacts in nature cannot be interpreted as a lack of larger-scale attributable impacts at the present time or in the future but highlights the need for innovative research approaches and analyses. We summarize the general findings in four relatively well-studied marine groups (seagrasses, pteropods, oysters, and coral reefs) and integrate overarching themes to highlight the challenges involved in detecting and attributing the effects of OA in natural environments. We then discuss four potential strategies to better evaluate and attribute OA impacts on species and ecosystems. First, we highlight the need for work quantifying the anthropogenic input of CO2 in coastal and open-ocean waters to understand how this increase in CO2 interacts with other physical and chemical factors to drive organismal conditions. Second, understanding OA-induced changes in population-level demography, potentially increased sensitivities in certain life stages, and how these effects scale to ecosystem-level processes (e.g. community metabolism) will improve our ability to attribute impacts to OA among co-varying parameters. Third, there is a great need to understand the potential modulation of OA impacts through the interplay of ecology and evolution (eco–evo dynamics). Lastly, further research efforts designed to detect, quantify, and project the effects of OA on marine organisms and ecosystems utilizing a comparative approach with long-term data sets will also provide critical information for informing the management of marine ecosystems.
Vulnerability and resilience of tropical coastal ecosystems to ocean acidification
Published 11 August 2020 Science ClosedTags: biological response, corals, Indian, review, South Atlantic, South Pacific
Ocean acidification leads to a wide variety of responses from tropical coastal ecosystems. Coral reefs are most vulnerable with most coral species exhibiting declining calcification rates with decreasing pH and carbonate chemistry parameters. Some corals show resilience to acidification likely due to active physiological regulation of their calcifying fluid. Other calcifying organisms, such as some foraminifera and coccolithophores, exhibit negative responses, whereas some symbiont-bearing calcifiers respond positively, to increasing acidification. Seagrasses and brown macroalgae thrive under acidified conditions, with increasing rates of primary productivity. Some tropical coastal fish species are resilient, and in some species, respond positively, to acidification. Some tropical species show complex, nonlinear responses to declining pH and carbonate chemistry. Factors that influence the ability of a species to adapt to and/or resist acidification include food supply, nutrient availability, temperature, diet, interactions with symbionts and other organisms and species and community diversity. Interactive effects of ocean acidification with other climate change parameters, such as elevated temperature, play an important but poorly understood role in determining the resilience and vulnerability of tropical coastal species, communities and ecosystems. Some short-lived species can undergo acclimation and/or adaptive evolution to increase fitness in the face of acidification. Biota living in tropical estuarine and nearshore environments, such as mangroves, seagrasses and intertidal and subtidal inshore benthos, are unlikely to be significantly affected by future acidification as such environments exhibit very wide variations in water and sediment pH and carbonate chemistry. Nearly all tropical coastal environments exhibit significant CO2 efflux to the atmosphere due to pCO2 and [CO32-] oversaturation caused by high rates of respiration and factors linked to fluvial discharge. Except for coral reefs, most calcifying organisms and upwelling regions, tropical estuarine and inshore ecosystems unaffected by eutrophication and other anthropogenic problems should be resilient to future acidification.
Vulnerability of global coral reef habitat suitability to ocean warming, acidification and eutrophication
Published 11 August 2020 Science ClosedTags: abundance, biological response, corals, multiple factors, nutrients, otherprocess, temperature
Coral reefs are threatened by global and local stressors. Yet, reefs appear to respond differently to different environmental stressors. Using a global dataset of coral reef occurrence as a proxy for the long‐term adaptation of corals to environmental conditions in combination with global environmental data, we show here how global (warming: sea surface temperature; acidification: aragonite saturation state, Ωarag) and local (eutrophication: nitrate concentration, and phosphate concentration) stressors influence coral reef habitat suitability. We analyse the relative distance of coral communities to their regional environmental optima. In addition, we calculate the expected change of coral reef habitat suitability across the tropics in relation to an increase of 0.1°C in temperature, an increase of 0.02 μmol/L in nitrate, an increase of 0.01 μmol/L in phosphate and a decrease of 0.04 in Ωarag. Our findings reveal that only 6% of the reefs worldwide will be unaffected by local and global stressors and can thus act as temporary refugia. Local stressors, driven by nutrient increase, will affect 22% of the reefs worldwide, whereas global stressors will affect 11% of these reefs. The remaining 61% of the reefs will be simultaneously affected by local and global stressors. Appropriate wastewater treatments can mitigate local eutrophication and could increase areas of temporary refugia to 28%, allowing us to ‘buy time’, while international agreements are found to abate global stressors.
Controls on boron isotopes in a cold-water coral and the cost of resilience to ocean acidification
Published 21 July 2020 Science ClosedTags: biogeochemistry, biological response, calcification, corals, individualmodeling, laboratory, modeling, morphology, North Pacific
Coral skeletal growth is sensitive to environmental change and may be adversely impacted by an acidifying ocean. However, physiological processes can also buffer biomineralization from external conditions, providing apparent resilience to acidification in some species. These same physiological processes affect skeletal composition and can impact paleoenvironmental proxies. Understanding the mechanisms of coral calcification is thus crucial for predicting the vulnerability of different corals to ocean acidification and for accurately interpreting coral-based climate records. Here, using boron isotope (δ11B) measurements on cultured cold-water corals, we explain fundamental features of coral calcification and its sensitivity to environmental change. Boron isotopes are one of the most widely used proxies for past seawater pH, and we observe the expected sensitivity between δ11B and pH. Surprisingly, we also discover that coral δ11B is independently sensitive to seawater dissolved inorganic carbon (DIC). We can explain this new DIC effect if we introduce boric acid diffusion across cell membranes as a new flux within a geochemical model of biomineralization. This model independently predicts the sensitivity of the δ11B-pH proxy, without being trained to these data, even though calcifying fluid pH (pHCF) is constant. Boric acid diffusion resolves why δ11B is a useful proxy across a range of calcifiers, including foraminifera, even when calcifying fluid pH differs from seawater. Our modeling shows that δ11B cannot be interpreted unequivocally as a direct tracer of pHCF. Constant pHCF implies similar calcification rates as seawater pH decreases, which can explain the resilience of some corals to ocean acidification. However, we show that this resilience has a hidden energetic cost such that calcification becomes less efficient in an acidifying ocean
Emergent properties of branching morphologies modulate the sensitivity of coral calcification to high PCO2
Published 13 July 2020 Science ClosedTags: biological response, calcification, corals, field, laboratory, mesocosms, multiple factors, South Pacific, temperature
Experiments with coral fragments (i.e. nubbins) have shown that net calcification is depressed by elevated PCO2. Evaluating the implications of this finding requires scaling of results from nubbins to colonies, yet the experiments to codify this process have not been carried out. Building from our previous research demonstrating that net calcification of Pocillopora verrucosa (2–13 cm diameter) was unaffected by PCO2 (400 and 1000 µatm) and temperature (26.5 and 29.7°C), we sought generality to this outcome by testing how colony size modulates PCO2 and temperature sensitivity in a branching acroporid. Together, these taxa represent two of the dominant lineages of branching corals on Indo-Pacific coral reefs. Two trials conducted over 2 years tested the hypothesis that the seasonal range in seawater temperature (26.5 and 29.2°C) and a future PCO2 (1062 µatm versus an ambient level of 461 µatm) affect net calcification of an ecologically relevant size range (5–20 cm diameter) of colonies of Acropora hyacinthus. As for P. verrucosa, the effects of temperature and PCO2 on net calcification (mg day−1) of A. verrucosa were not statistically detectable. These results support the generality of a null outcome on net calcification of exposing intact colonies of branching corals to environmental conditions contrasting seasonal variation in temperature and predicted future variation in PCO2. While there is a need to expand beyond an experimental culture relying on coral nubbins as tractable replicates, rigorously responding to this need poses substantial ethical and logistical challenges.
Regional and species level responses of Scleractinian corals under global change within the Caribbean Sea
Published 2 July 2020 Science ClosedTags: biological response, calcification, corals, field, laboratory, mesocosms, molecular biology, morphology, multiple factors, North Atlantic, physiology, review, temperature
Human-induced global change has caused rapid increases in ocean temperature (warming) and declines in seawater pH (acidification), and are expected to have negative impacts on tropical reef-building corals globally. Abnormally high seawater temperatures disrupt the symbiosis between corals and their algal endosymbiont in a process known as ‘coral bleaching.’ During such bleaching events, calcification rates decline and physiological processes deteriorate. Additionally, corals rely heavily on elevated seawater pH in order to support and maintain production of their calcium carbonate skeletons. Together, changes in ocean temperatures and seawater pH pose serious threats to coral reefs, foundational ecosystems that provide habitat for countless essential fisheries, while also acting as natural buffers from storms and providing major economic support for tropical coastal communities. Identifying how these global scale stressors impact Caribbean coral reefs is critical in understanding community composition and coral abundance on future reefs. This dissertation employs an interdisciplinary suite of techniques to assess the impacts of ocean acidification and warming on the growth and physiology of Caribbean corals to improve understandings of the responses of coral under projected global change, and provide a framework for similar future studies. Through the use of a meta-analysis (Chapter 1), I identified trends in coral calcification throughout the Greater Caribbean Sea in response to experimental ocean acidification and warming, and performed quantitative assessment of experimental design effects on coral calcification rates. I then conducted a 93- day simulated ocean acidification and warming mesocosm experiment to identify growth (Chapter 2, 4) and physiological (Chapter 3) responses of several species of common Caribbean corals. The results from this work highlight the diversity of responses of Caribbean corals to projected global change at individual and species levels, as well as between the coral host and algal endosymbiont. Overall, the variation in growth and physiological responses of these important Caribbean coral species under ocean acidification and warming is critical in predicting the future ‘winners’ and ‘losers’ of Caribbean reefs as global change unfolds.
Air-sea CO2 flux in an equatorial continental shelf dominated by coral reefs (Southwestern Atlantic Ocean)
Published 29 June 2020 Science ClosedTags: biological response, calcification, chemistry, corals, South Atlantic
Highlights
•Air-sea CO2 fluxes and carbonate chemistry were investigated in coral reef-dominated waters (SW Atlantic).
•The relationship between nTA and nDIC evidenced occurrence of CaCO3 calcification in coral reefs.
•CaCO3 calcification increased the values of fCO2sw, and lowered the pHT and Ωara.
•Aquatic emissions of CO2 in coral reefs were higher than nearshore and offshore locations.
•The results have implications considering the carbon budget at the SW Atlantic Ocean.
Abstract
Coral reefs are ecosystems highly vulnerable to changes in seawater carbonate chemistry, including those related to the ocean acidification and global warming. Brazilian coral reefs contains the major area of reefs coverage in the Southwestern (SW) Atlantic Ocean, however, studies aimed at investigating the controls of seawater carbonate chemistry in coral reefs are still overlooked in Brazil. This study comprehends the first investigation of complete seawater carbonate chemistry parameters in a section of the equatorial continental shelf dominated by coral reefs in the SW Atlantic Ocean. The sampling included spatial continuous underway measurements of sea surface CO2 fugacity (fCO2sw), temperature (SST), salinity (SSS), and discrete investigations of total alkalinity (TA), dissolved inorganic carbon (DIC), bicarbonate (HCO3–), carbonate (CO32−), and saturation state of aragonite (Ωara). The study was conducted during a dry period (July-2019) in the Marine State Park of Pedra da Risca do Meio (PRM), a marine protected area dominated by coral reef communities. Overall, the coral-reef dominated waters presented higher values of fCO2sw (475 ± 28 μatm), and lower values of pHT (7.98 ± 0.008), CO32− (217 ± 5 μmol kg-1) and Ωara (3.49 ± 0.07), compared to nearshore regions without the influence of coral reef waters, where the averages of fCO2sw, pHT, CO32−, and Ωarawere, respectively, 458 ± 21 μatm, 8.00 ± 0.007, 224 ± 4 μmol kg-1, and 3.58 ± 0.05. The relationship between salinity-normalized TA (nTA) and salinity-normalized DIC (nDIC) showed a slope higher than 1 (1.26) in the coral reef, evidencing the occurrence of calcium carbonate (CaCO3) precipitation and prevalence of inorganic carbon metabolism. The CaCO3 precipitation involves the consumption of TA and DIC in a ratio 2:1, with production of CO2. This mechanism explains the higher values of fCO2sw in the coral reef-dominated waters. The values of fCO2sw were always higher than the atmospheric values (fCO2air), indicating a permanent source of CO2 in the study area during the sampled period. The calculated fluxes of CO2 at the air-sea interface averaged 8.4 ± 6.5 mmolC m-2 d-1 in the coral reef-dominated waters, and these data are higher than those verified in nearshore and offshore locations. These higher emissions of CO2 in coral reef-dominated waters evidence that the carbon budgets calculated for North and Northeastern continental shelf of Brazil must include these environments taking into account the widespread coral reef coverage in the region. This study also confirms that biogeochemical processes occurring in coral reefs are modifying the seawater carbonate chemistry, with implication in the context of the current process of ocean acidification.
Continue reading ‘Air-sea CO2 flux in an equatorial continental shelf dominated by coral reefs (Southwestern Atlantic Ocean)’Insights from extreme coral reefs in a changing world
Published 24 June 2020 Science ClosedTags: biological response, corals, review
Coral reefs are one of the most biodiverse and economically important ecosystems in the world, but they are rapidly degrading due to the effects of global climate change and local anthropogenic stressors. Reef scientists are increasingly studying coral reefs that occur in marginal and extreme environments to understand how organisms respond to, and cope with, environmental stress, and to gain insight into how reef organisms may acclimate or adapt to future environmental change. To date, there have been more than 860 publications describing the biology and/or abiotic conditions of marginal and extreme reef environments, most of which were published within the past decade. These include systems characterized by unusually high, low, and/or variable temperatures (intertidal, lagoonal, high-latitude areas, and shallow seas), turbid or urban environments, acidified habitats, and mesophotic depth, and focus on reefs geographically spread throughout most of the tropics. The papers in this special issue of Coral Reefs, entitled Coral Reefs in a Changing World: Insights from Extremes, build on the growing body of literature on these unique and important ecosystems, providing a deeper understanding of the patterns and processes governing life in marginal reef systems, and the implications that these insights may have for the future of tropical coral reefs in our rapidly changing world.
Continue reading ‘Insights from extreme coral reefs in a changing world’
Prior exposure to elevated pCO2 does not affect calcification of a tropical scleractinian when returned to ambient pCO2
Published 18 June 2020 Science ClosedTags: biological response, calcification, corals, laboratory, South Pacific
Highlights
•Coral reefs experience biologically-driven pCO2 oscillations
•Calcification of A. retusa with two pCO2 exposure histories differed.
•When subsequently placed in common pCO2 environment, calcification was similar.
•Some corals are capable of a reversible plastic response of calcification.
Abstract
Coral reefs experience biologically-driven pCO2 oscillations that are predicted to become more extreme in magnitude and duration under ocean acidification (OA) regimes. Understanding the plasticity of responses in common reef-building corals to oscillations in pCO2 will allow for better predictions of their function in future seawater conditions. This study explored the effects of variation in seawater pCO2 on coral calcification using experiments conducted over one month between 9 April 2018 and 18 May 2018. Branches (~4-cm long) of Acropora retusa were sampled from colonies at 10-m depth on the fore reef of Mo’orea, French Polynesia (17° 28′ 53.9004″ S, 149° 49′ 50.5992″ W). We tested the hypothesis that depressed calcification caused by elevated pCO2 (~1000 μatm) is relaxed (i.e., calcification increases) upon return to ambient pCO2 (~400 μatm). Corals first were incubated in ambient or elevated pCO2 for 19 days, with the result that calcification integrated over this period was reduced by 31% under elevated pCO2. The same corals were then incubated at ambient pCO2 for 11 days, during which calcification was independent of the experimental pCO2 exposure history. Our results suggest that a quick relaxation of pCO2-depressed calcification in A. retusa following cessation of high pCO2 indicates that corals are capable of a reversible plastic response of calcification when confronted by pCO2 oscillations.
Continue reading ‘Prior exposure to elevated pCO2 does not affect calcification of a tropical scleractinian when returned to ambient pCO2’How does the sexual reproduction of marine life respond to ocean acidification?
Published 16 June 2020 Science ClosedTags: algae, biological response, corals, physiology, reproduction, review
Recent research indicates that synchronicity of sexual reproduction in coral spawning events is breaking down, leading to aging populations and decreased recruitment success. In this perspective, we develop a hypothesis that this phenomenon could be caused by ongoing ocean acidification (OA). We hypothesize, that the underlying physiological machinery could be the carbon concentrating mechanism (CCM). The endosymbiotic zooxanthellae of corals could use this mechanism to sense calm water motion states in a comparable way to that known from macroalgae. In macroalgae, it is well-established that dissolved inorganic carbon (DIC) acts as the trigger for signaling low water motion. Hence, evolutionarily developed signals of low water motion, suited for gamete-release, may be misleading in the future, potentially favoring opportunistic species in a broad range of marine organisms.
Continue reading ‘How does the sexual reproduction of marine life respond to ocean acidification?’
