Coral reefs are vital marine ecosystems that harbor a significant proportion of the ocean’s biodiversity. However, these ecosystems are increasingly threatened by anthropogenic activities, particularly the emission of greenhouse gases leading to climate change and ocean acidification. Ocean acidification refers to the reduction in pH of marine waters due to the absorption of CO₂ from the atmosphere, forming carbonic acid (H₂CO₃), which dissociates into bicarbonate (HCO₃−) and hydrogen ions (H+), thus lowering pH. This sequence of reactions leads to an increase in hydrogen ion concentration, causing a decrease in pH. The reduction in carbonate ions (CO₃2−) is particularly detrimental to marine calcifiers, including corals, which rely on carbonate for the formation of their calcium carbonate (CaCO₃) skeletons. Coral reefs are constructed by the deposition of CaCO₃ by coral polyps. Zooxanthellae, symbiotic algae living within coral tissues, provide essential nutrients through photosynthesis, facilitating calcification. Acidification disrupts this symbiotic relationship by impairing photosynthetic efficiency and reducing the availability of carbonate ions necessary for skeletal growth. As ocean acidification progresses, the concentration of carbonate ions diminishes, making it energetically more challenging for corals to secrete their skeletons, thereby slowing growth rates and compromising structural integrity. Coral bleaching occurs when corals, under stress, expel their zooxanthellae, leading to a loss of pigmentation and a decline in energy reserves. Stressors include elevated sea temperatures, pollution, and acidification. The loss of zooxanthellae not only deprives corals of their primary food source but also disrupts calcification processes. Thermal stress is a predominant factor in coral bleaching. Elevated sea temperatures can destabilize the photosynthetic machinery of zooxanthellae, producing reactive oxygen species (ROS) that damage both the algae and coral tissues. Prolonged exposure to high temperatures exacerbates acidification effects, intensifying bleaching events. The decline in coral health due to bleaching and acidification has profound ecological impacts, including the loss of habitat for numerous marine species, reduced biodiversity, and compromised fisheries. Socioeconomically, coral reef degradation affects tourism, coastal protection, and the livelihoods of communities dependent on reef resources. Reduction of CO₂ emissions through global policy agreements and renewable energy adoption. Local conservation efforts, such as marine protected areas (MPAs) have the potentials to enhance reef resilience. Conservation efforts may be complemented by research into coral species and strains with higher tolerance to acidification and thermal stress, potentially involving selective breeding and genetic modification. Marine water acidification and coral bleaching are intricately linked phenomena driven by anthropogenic climate change. The decline of coral reefs signals a broader environmental crisis that necessitates urgent scientific, policy, and community responses to mitigate adverse effects and foster adaptive resilience in marine ecosystems.
Continue reading ‘Marine water acidification and coral bleaching’Posts Tagged 'corals'
Marine water acidification and coral bleaching
Published 10 December 2024 Science ClosedTags: biological response, BRcommunity, corals, mitigation, protists, review
Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability
Published 6 December 2024 Science ClosedTags: adaptation, biological response, calcification, corals, field, laboratory, mesocosms, molecular biology, otherprocess, photosynthesis, physiology, South Pacific
Corals residing in habitats that experience high-frequency seawater pCO2 variability may possess an enhanced capacity to cope with ocean acidification, yet we lack a clear understanding of the molecular toolkit enabling acclimatisation to environmental extremes or how life-long exposure to pCO2 variability influences biomineralisation. Here, we examined the gene expression responses and micro-skeletal characteristics of Pocillopora damicornis originating from the reef flat and reef slope of Heron Island, southern Great Barrier Reef. The reef flat and reef slope had similar mean seawater pCO2, but the reef flat experienced twice the mean daily pCO2 amplitude (range of 797 v. 399 μatm day−1, respectively). A controlled mesocosm experiment was conducted over 8 weeks, exposing P. damicornis from the reef slope and reef flat to stable (218 ± 9) or variable (911 ± 31) diel pCO2 fluctuations (μatm; mean ± SE). At the end of the exposure, P. damicornis originating from the reef flat demonstrated frontloading of 25% of the expressed genes regardless of treatment conditions, suggesting constitutive upregulation. This included higher expression of critical biomineralisation-related genes such as carbonic anhydrases, skeletal organic matrix proteins, and bicarbonate transporters. The observed frontloading corresponded with a 40% increase of the fastest deposited areas of the skeleton in reef flat corals grown under non-native, stable pCO2 conditions compared to reef slope conspecifics, suggesting a compensatory response that stems from acclimatisation to environmental extremes and/or relief from stressful pCO2 fluctuations. Under escalating ocean warming and acidification, corals acclimated to environmental variability warrant focused investigation and represent ideal candidates for active interventions to build reef resilience while societies adopt strict policies to limit climate change.
Continue reading ‘Extreme environmental variability induces frontloading of coral biomineralisation genes to maintain calcification under pCO2 variability’Varying effects of climate change on the photosynthesis and calcification of crustose coralline algae: implications for settlement of coral larvae
Published 4 December 2024 Science ClosedTags: algae, biological response, BRcommunity, calcification, corals, laboratory, molecular biology, multiple factors, photosynthesis, physiology, reproduction, temperature
Highlights
- Corals maintain settlement preferences under future climate conditions
- Future climate conditions negatively affect crustose coralline algae physiology
- Physiological responses to future climate conditions varied by algal species
Abstract
Coral recruitment is critical to the maintenance of healthy coral reef ecosystems. Many coral species settle preferentially on certain crustose coralline algae (CCA) (e.g., Hydrolithon boergesenii) over others (e.g., Paragoniolithon solubile). Calcifying organisms like CCA are particularly susceptible to ocean acidification (OA), and settlement behavior of larvae may be compromised as seawater temperatures increase (ocean warming; OW) and pH levels decrease as a result of climate change. Here, we examine the effects of future seawater conditions (OW and OA) on the calcification and photosynthetic efficiency of two CCA species, H. boergesenii and Pa. solubile. We also examine the effects of conditioning CCA in combined OA and OW on the settlement preferences of three coral species, Acropora palmata, A. cervicornis and Porites astreoides. Acropora palmata and Po. astreoides demonstrated a preference for H. boergesenii over Pa. solubile in choice experiments after short-term treatment (7–21 days) and this preference was not affected by future seawater conditions. A. cervicornis did not demonstrate a CCA preference under any treatment. Po. astreoides did not demonstrate a CCA preference in no-choice assays and settlement was unaffected by OW and OA even after the longest exposure (99 days). Both CCA had reduced photosynthetic efficiency after exposure to future seawater conditions. However, net calcification rate was reduced in H. boergesenii but not Pa. solubile after exposure to future seawater conditions. These results demonstrate that while climate change may differentially affect the physiological functioning of various species of CCA, coral settlement preferences are unlikely to be altered.
Continue reading ‘Varying effects of climate change on the photosynthesis and calcification of crustose coralline algae: implications for settlement of coral larvae’Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature
Published 25 November 2024 Science ClosedTags: biological response, BRcommunity, corals, laboratory, molecular biology, mortality, multiple factors, North Pacific, photosynthesis, physiology, primary production, protists, reproduction, respiration, temperature
Climate change destabilizes the symbiosis between corals and Symbiodiniaceae. The effects of ocean acidification and warming on critical aspects of coral survical such as symbiotic interactions (i.e., carbon and nitrogen assimilation and exchange) during the planula larval stage remain understudied. By combining physiological and stable isotope techniques, here we show that photosynthesis and carbon and nitrogen assimilation (H13CO3− and 15NH4+) in Pocillopora damicornis coral larvae is enhanced under acidification (1000 µatm) and elevated temperature (32 °C). Larvae maintain high survival and settlement rates under these treatment conditions with no observed decline in symbiont densities or signs of bleaching. Acidification and elevated temperature both enhance the net and gross photosynthesis of Symbiodiniaceae. This enhances light respiration and elevates C:N ratios within the holobiont. The increased carbon availability is primarily reflected in the 13C enrichment of the host, indicating a greater contribution of the algal symbionts to the host metabolism. We propose that this enhanced mutualistic symbiotic nutrient cycling may bolster coral larvae’s resistance to future ocean conditions. This research broadens our understanding of the early life stages of corals by emphasizing the significance of symbiotic interactions beyond those of adult corals.
Continue reading ‘Symbiodiniaceae algal symbionts of Pocillopora damicornis larvae provide more carbon to their coral host under elevated levels of acidification and temperature’The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean
Published 25 November 2024 Science ClosedTags: algae, biological response, BRcommunity, calcification, corals, dissolution, field, laboratory, mitigation, North Atlantic, photosynthesis, primary production, respiration
The ongoing increase in anthropogenic CO₂ emissions since the industrial revolution has accelerated ocean acidification (OA) by introducing CO₂ into seawater, forming carbonic acid and reducing pH levels. This acidification threatens marine calcifiers by weakening their capacity to build calcium carbonate structures and promoting the dissolution of existing skeletons. Nonetheless, calcifying organisms may contribute to mitigating OA effects. This study explores the roles of corals (rolling Siderastrea radians, a seagrass dweller) and free-living calcifying coralline algae (back reef) in CO₂ mitigation in seawater. Field experiments were conducted on Isla Grande (Corales del Rosario and San Bernardo National Natural Park, Colombian Caribbean), to observe the diel variations in photosynthesis and calcification of these uncommon reef builders across different times of the day. Results demonstrate diel shifts influenced by photosynthesis/respiration and calcification/dissolution, with free-living coralline algae exhibiting higher productivity and calcification rates than corals during the day. Notably, free-living coralline algae displayed pronounced hysteresis, reflecting high sensitivity to light. These findings underscore the significant role of free-living coralline algae in marine carbon cycling, suggesting a more substantial impact on CO₂ mitigation than previously recognized. Conserving free-living coralline algae and their habitats is thus critical for supporting marine ecosystem health and resilience amidst global change, warranting further research into their metabolic responses to inform conservation strategies.
Continue reading ‘The role of rolling corals and free-living calcifying coralline algae in the management of greenhouse gas CO2 in the Colombian Caribbean’Challenges and opportunities towards meeting the United Nations’ Sustainable Development Goals from coral and seaweed ecosystems in an era of climate change
Published 22 November 2024 Science ClosedTags: algae, biological response, corals, mitigation, policy, review, socio-economy
Global climate change scenarios due to anthropogenic responses jeopardize ecosystem sustainability and hinder progress toward achieving the United nations (UN-SDGs). Achieving “natural carbon solutions” from terrestrial ecosystems is challenging due to decreasing arable land and increasing marginal land. Marine ecosystems representing a wider “natural carbon solutions” have also been severely impacted by climate change. Among marine ecosystems, coral reefs and seaweed communities are the key ecosystem engineers that support a wide range of marine life, facilitate nutrient cycling, and provide essential ecosystem services with a pivotal role in sustaining coastal economies and livelihoods. Notably, these communities compete for space within the reef ecosystem and suffer from loss of diversity and richness due to climate change. Therefore, assessing the climate change resilience of both the corals and seaweeds is essential to evaluate and design long-term adaptation strategies, ecological innovations, and science-informed policies to conserve, restore, and sustainably manage economic services. This review article aims to highlight (1) the physiological response and resilience of corals and seaweeds to environmental changes, (2) the impact of climate change on their ecosystems and economic services, (3) their potential contributions towards the United Nations’ sustainable goals, (4) progressive efforts applied for their restoration, and (5) the potential complementary value of large-scale seaweed aquaculture as a carbon sink.
Continue reading ‘Challenges and opportunities towards meeting the United Nations’ Sustainable Development Goals from coral and seaweed ecosystems in an era of climate change’Expanding cold-water coral reef knowledge towards deep-sea ecosystem management
Published 13 November 2024 Science ClosedTags: biological response, corals, physiology, South Pacific
The deep sea is our planet’s largest and least explored ecosystem. Once thought to be a barren abyss devoid of life, we have learned the deep sea is home to diverse ecosystems. One such deep-sea ecosystem that supports biodiversity is cold-water coral (CWC) reefs. Less studied than their tropical counterparts, CWC reefs provide a range of ecosystem services such as carbon storage, pharmaceutical development, and fisheries. Threats from climate change and increasing anthropogenic deep-sea activity make protecting and managing CWC reef futures exceptionally important. Scientific advances over the last decades have allowed us to better understand CWC reef ecosystems, though we remain far off from achieving effective ecosystem management. The overall aim of this thesis is to guide CWC reef management through expanding knowledge of these ecosystems. Despite the majority of CWC reef area being composed of dead framework, most research has focused on understanding live coral responses to climate change. Dead framework supports the highest levels of biodiversity in a CWC reef system and contributes significantly to carbon and nitrogen cycling. Live corals and dead coral skeletons are vulnerable to different environmental stressors. To understand reef composition and accurately predict their futures under climate change, the proportion of live coral colonies to the entire reef structure must be quantified. Chapter 2 of this thesis guides CWC reef management through increasing our knowledge of depth’s role in driving live and dead reef proportions. In Chapter 2, the live and dead proportions of CWC Solenosmilia variabilis reefs are quantified across four seamount features in the southwest Pacific Ocean. Images of CWC reefs are analysed with significant differences in the proportions of live coral between reefs at the Louisville Seamount Chain and Graveyard Seamount Complex. Depth is identified as a driver of live and dead reef proportions in these regions, with a larger proportion of live coral at shallow depths and dead intact framework at deeper depths. Additionally, the proportion of live coral in the Graveyard Seamount Complex remained stable between 2015 and 2020, despite significant differences in the surface areas of live coral, dead intact framework, and the reef. These results indicate reef proportions can be used to estimate the amount of dead intact framework threatened by the shallowing aragonite saturation horizon (ASH) due to ocean acidification at each site, which can help inform which sites could be protected as possible climate change refugia. Identifying depth as a driver of reef proportions quantifies reef health, identifies reef threats, and predicts reef impacts, all of which increases our knowledge of current and future reef conditions. Ocean acidification (OA) is a critical stressor and leads to dissolution of exposed calcium carbonate (CaCO3) in aragonite-undersaturated waters — a direct threat to dead CWC skeletons. This increased coral porosity from climate stressors threatens the structural integrity of the entire reef framework and could lead to a direct loss of habitat through crumbling. Laboratory studies have largely explored how skeletons grown under favourable conditions respond to exposure in OA conditions. We do not yet know if CWC skeletons grown in OA conditions are as robust as those grown in favourable conditions or if CWC skeletal structures are built differently in ideal and OA conditions. Chapter 3 of this thesis guides CWC reef management through increasing our knowledge of the 3-dimensional (3D) crystallographic structure of CWC. In Chapter 3, 3D volumes of CWC skeletal samples from above and below the ASH are compared using Electron Backscatter Diffraction (EBSD). Aragonite needles grow radially from Rapid Accretion Deposits (RAD) which join with neighbouring crystal structures to create the skeletal building blocks called sclerodermites. From large RADs, sequential imaging shows aragonite needles radiate with a preferred growth direction perpendicular to the calcification interface before rotating out of plane. Crystal size and orientation are compared between samples collected from above and below the ASH to understand differences in skeletal structure and better predict reef futures under OA. Neither aragonite crystal size or sclerodermite length were significantly different between the sample taken from below and above the ASH. Increasing our understanding of CWC 3D crystallographic structure above and below the ASH quantifies reef health, identifies reef threats, and predicts reef impacts, increasing our knowledge of current and future reef conditions. There are more CWC reefs in the world which have not yet been discovered, and thus cannot be managed. Therefore, increasing global capacity to carryout baseline deep-sea research is crucial to ensuring adequate protection and management for these vulnerable marine ecosystems. Limited at-sea training opportunities make it difficult to ensure the next generation of deep-sea scientists are properly trained in sea-going research methods. However, telepresence and remote learning can be used to increase the number of active participants on deep-sea expeditions. Chapter 4 of this thesis guides CWC reef management through increasing our knowledge of the effectiveness of virtual ship-to-shore training for increasing deep-sea capacity. Chapter 4 explores the 2021 iMirabilis2 expedition’s use of telepresence to virtually involve early career researchers from several countries in deep-sea science. Post expedition, a survey of onshore participants was conducted to assess and quantify the effectiveness of the peer-to-peer early career researcher ship-to-shore scheme. During the expedition, live, interactive training via WhatsApp and Zoom was accessed more than traditional static, unidirectional methods of blog posts and pre-recorded videos. All respondents either agreed or strongly agreed the scheme provided an inclusive and accessible platform to share deep-sea science. These results suggest similar schemes could be used to supplement shorter duration at-sea training or used prior to a seagoing experience to better prepare early career researchers, increasing inclusivity. Creating an inclusive and accessible platform to virtually share at-sea deep-sea science increases capacity for deep-sea exploration which can lead researchers to discover more CWC reefs. Through quantifying reef health, identifying reef threats, predicting reef impacts, and increasing capacity for deep-sea exploration, this thesis expands knowledge of CWC reef ecosystems to guide deep-sea ecosystem management.
Continue reading ‘Expanding cold-water coral reef knowledge towards deep-sea ecosystem management’Drivers of biological diversity and responses to global changes in marine invertebrates
Published 12 November 2024 Science ClosedTags: adaptation, biological response, BRcommunity, community composition, corals, echinoderms, Indian, laboratory, molecular biology, otherprocess, reproduction
Human activities, in particular global changes (e.g., ocean warming – OW and ocean acidification – OA) are projected to drive some marine species to extinction within the coming decades. Marine invertebrates are amongst the most vulnerable to these changes due to the increased energetic cost to maintain intracellular pH homeostasis. To mitigate extinction, organisms may migrate, acclimate or adapt genetically. While these mechanisms are increasingly documented, they are not fully understood. This knowledge is critical for assessment of extinction risks, an important index for effective conservation and management of marine biodiversity. This thesis aims to increase our understanding on the drivers of biological diversity and sensitivity of marine invertebrates to OW and OA. Specifically, I assess (1) the quality of inferences on adaptive evolution in recent publications on responses of marine invertebrates to OW or OA and summarize the current knowledge and identify the gaps (Paper I); (2) the drivers of genetic diversity, structure, connectivity among Acropora austera populations across Mozambique coral reefs (Paper II); (3) the sensitivity to low pH in larvae of the sea urchin, Tripneustes gratilla, from subtidal and intertidal seagrass meadows with contrasting pH variability at Inhaca Island, Mozambique (Paper III); (4) the role of natural fluctuation in pH on the response of larvae of the sea urchin Echinus esculentus to low pH (Paper IV). Field genome scans surveys, laboratory experiments and systematic literature review were used. My systematic literature review (Paper I) highlights that publication on adaptive responses of marine invertebrates to OW or OA used more frequently strong methods for inferences of genetic change, such as common garden experiments and molecular genetic analysis. Methods for weaker inferences, such as comparison to model prediction, were less frequently used. On the other hand, reciprocal transplants, the stronger method for inferring adaptive change was less used in comparison with weaker methods such as phenotypic and genotypic selection. I also showed different levels of genetic variability and connectivity between populations of corals along the Mozambique coast. These geographic differences in levels of genetic diversity and connectivity may be explained by oceanographic factors and mode of reproduction of the corals (Paper II). Larvae of the sea urchin T. gratilla from Inhaca Island had reduced fitness when exposed to low pH. Moreover, larvae from adults collected in an intertidal habitat were more sensitive to low pH as compared to larvae from adults collected in a subtidal population. This result reveals population specific responses to low pH and challenges current theories that predict higher tolerance in individuals living in habitats with higher pH range (Paper III). Under present day natural variability in pH, the extreme low pH does not appear to be the main driver of biological responses in larvae of the sea urchin E. esculentus and adaptation to such conditions might be associated with a cost of plasticity but not a cost of canalization (Paper IV). Overall, this thesis shows that oceanographic factors and natural variability in pH influence the levels of genetic diversity and biological sensitivity in populations of marine invertebrates. These parameters should be considered to better evaluate the ability of marine invertebrates to withstand environmental changes and to sustain the provision of ecological functions, and guide conservation strategies.
Continue reading ‘Drivers of biological diversity and responses to global changes in marine invertebrates’Ecophenotypic variation in a cosmopolitan reef-building coral suggests reduced deep-sea reef growth under ocean change
Published 7 November 2024 Science ClosedTags: biological response, communitymodeling, corals, field, Mediterranean, modeling, morphology, North Atlantic, South Atlantic
Sensitivity of reef-building corals to environmental factors has far-reaching ecosystem implications, especially in the limited number of cold-water coral (CWC) species that form reefs in the deep sea. Understanding CWC responses to large-scale oceanographic variation in their natural habitat can elucidate their sensitivity to global anthropogenic stressors. Here, we use skeletal samples to analyse fine-scale phenotypic variation in the widespread reef-building CWC Desmophyllum pertusum (Lophelia pertusa) in relation to broad physicochemical gradients in different sites across the Atlantic Ocean and Mediterranean Sea. We find evidence, amidst local and regional differentiation, of species-wide growth responses to physicochemical factors, mainly affecting corallite length, width and their ratio (slenderness). Our results suggest that higher temperature and lower oxygen levels negatively affect skeletal linear extension and budding rate of polyps. As also hinted by the reduced corallite length and slenderness in less developed reefs, these widespread responses may lead to a general decline in CWC reef growth rates as a long-term consequence of ocean warming and deoxygenation. Given this relevance, such responses can be used to model reef growth in a changing ocean.
Continue reading ‘Ecophenotypic variation in a cosmopolitan reef-building coral suggests reduced deep-sea reef growth under ocean change’Coral reefs: a maker of changing ecosystem
Published 4 November 2024 Science ClosedTags: corals, mortality, review
Highlights
- Corals with high N levels create the situation of nutrient starvation syndrome.
- Ocean acidification condition produces excess CO2, more HCO3–, and less CO32- ions.
- Around 55% of world’s coral reef species are endangered by overfishing.
- Various app and video game such as the NeMO-Net team help to defend coral reefs.
Abstract
Coral reefs are the backbone of the economies of tropical regions. The structure of coral reefs saves property damage, loss of life, and erosion problems by buffering the shoreline against 97% of the energy from storms, waves, and floods. They act as the arsenal of very powerful chemical weapons to defend themselves. Healthy coral reefs not only support the ecosystem on Earth but also give a platform to commercial and subsistence fisheries. Monitoring coral reef status and trends is very crucial to notify the policy, management, and science so the cause of the collapsing of the reef system needs to be addressed. In the current scenario, the coral reefs are going through the bad phase of over-fishing, climate change, pollution, excess nutrients, etc. By controlling these factors with the additional help of modern era tools (various apps), we can minimize the effect of the above raising factor and save the world’s most spectacular beauty: The corals just to keep oceans fairly blue. As coral reefs are for each and everyone, so everyone makes sure to secure the life of coral reefs.
Continue reading ‘Coral reefs: a maker of changing ecosystem’Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification
Published 31 October 2024 Science ClosedTags: biological response, BRcommunity, calcification, community composition, corals, laboratory, mesocosms, mitigation, molecular biology, mortality, multiple factors, otherprocess, temperature
Significance
Coral reefs are exceptional ecosystems and support hundreds of millions of people around the world, yet they are under severe threat due to ocean warming and acidification. Reefs are predicted to collapse over the next few decades under these climate change stressors, with grave consequences for society. Contrary to predictions of near total destruction, this study shows that with effective climate change mitigation, coral reefs will continue to change, but global reef collapse may still be avoidable.
Abstract
Coral reefs are among the most sensitive ecosystems affected by ocean warming and acidification, and are predicted to collapse over the next few decades. Reefs are predicted to shift from net accreting calcifier-dominated systems with exceptionally high biodiversity to net eroding algal-dominated systems with dramatically reduced biodiversity. Here, we present a two-year experimental study examining the responses of entire mesocosm coral reef communities to warming (+2 °C), acidification (−0.2 pH units), and combined future ocean (+2 °C, −0.2 pH) treatments. Contrary to modeled projections, we show that under future ocean conditions, these communities shift structure and composition yet persist as novel calcifying ecosystems with high biodiversity. Our results suggest that if climate change is limited to Paris Climate Agreement targets, coral reefs could persist in an altered state rather than collapse.
Continue reading ‘Experimental coral reef communities transform yet persist under mitigated future ocean warming and acidification’The dilemma of Luhuitou fringing reefs: net dissolution in winter and enhanced acidification in summer
Published 24 October 2024 Science ClosedTags: algae, calcification, chemistry, corals, North Pacific
Global coral reef ecosystems have been severely degraded due to the combined effects of climate change and human activities. Changes in the seawater carbonate system of coral reef ecosystems can reflect their status and their responses to the impacts of climate change and human activities. Winter and summer surveys in 2019 found that the ecological community of the Luhuitou coral reef flat was dominated by macroalgae and corals, respectively, contrasting with the conditions 10 years ago. The Luhuitou fringing reefs were sources of atmospheric CO2 in both seasons. In winter, the daily variation range of dissolved inorganic carbon (DIC) in Luhuitou coral reefs was up to 450 µmol/kg, while that of total alkalinity (TA) was only 68 µmol/kg. This indicated that the organic production was significantly higher than the calcification process during this period. The TA/DIC was approximately 0.15, which was less than half of that in healthy coral reefs; hence, photosynthesis-respiration processes were the most important factors controlling daily changes in the seawater carbonate system. The net community production (NCP) of the Luhuitou coral reef ecosystem in winter was as high as 47.65 mmol C/(m2·h). While the net community calcification (NCC) was approximately 3.35 and −4.15 mmol CaCO3/(m2·h) during the daytime and nighttime respectively. Therefore, the NCC for the entire day was −21.9 mmol CaCO3/(m2·d), indicating a net autotrophic dissolved state. In summer, the acidification was enhanced by thunderstorms and heavy rain with the highest seawater partial pressure of CO2 (pCO2) and lowest pHT. Over the past 10 years, the increase rate of seawater pCO2 in Luhuitou reef was approximately 13.3 µatm/a***, six times that of the open ocean, while the decrease rate of pH was approximately 0.008 3/a, being five times that of the global ocean. These findings underscore the importance of protecting and restoring Luhuitou fringing reef, as well as similar reefs worldwide.
Continue reading ‘The dilemma of Luhuitou fringing reefs: net dissolution in winter and enhanced acidification in summer’Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification
Published 14 October 2024 Science ClosedTags: calcification, corals, North Pacific, physiology, primary production
Recovery of ecosystem function in the aftermath of climate extremes such as cyclones and marine heat waves occurs in contest of highly variable environmental conditions and more chronic disturbances such as ocean acidification, which can further alter community structure and function. The present study investigated short-term responses of reef-scale primary production (Net Ecosystem Production; NEP), calcification (Net Ecosystem Calcification; NEC) and community structure in 2018 and again five years later in 2022 on a coral reef flat in Lizard Island on Australia’s Great Barrier Reef, between and following multiple consecutive stressors, namely two cyclones (2014 and 2015) and back-to-back bleaching events (2016–2017 and 2020). NEC in 2022 was highly variable compared to what it was in 2018. Conversely, NEP was higher in 2022 even though light availability was often reduced by cloud cover. High variability in NEC indicated that environmental parameters may have immediate impacts on carbonate chemistry in seawater and may largely and quickly affect short-term recovery trajectories. Therefore, comparison of metabolic rates over short time scales across decades should be done with caution. We also found that cover of calcifiers and particularly algae were highest in coral rubble suggesting that typical benthic surveys in the open reef flat largely underestimate their abundance and possible contribution to NEP and NEC. This study adds to the evidence that NEC and NEP might not be exclusively related to coral cover and likely not tied to vertical reef accretion.
Continue reading ‘Unraveling the influence of environmental variability and cryptic benthic assemblages on reef-scale primary production and calcification’Widespread scope for coral adaptation under combined ocean warming and acidification
Published 27 September 2024 Science ClosedTags: biological response, BRcommunity, calcification, corals, mesocosms, molecular biology, mortality, multiple factors, North Pacific, temperature
Reef-building coral populations are at serious risk of collapse due to the combined effects of ocean warming and acidification. Nonetheless, many corals show potential to adapt to the changing ocean conditions. Here we examine the broad sense heritability (H2) of coral calcification rates across an ecologically and phylogenetically diverse sampling of eight of the primary reef-building corals across the Indo-Pacific. We show that all eight species exhibit relatively high heritability of calcification rates under combined warming and acidification (0.23–0.56). Furthermore, tolerance to each factor is positively correlated and the two factors do not interact in most of the species, contrary to the idea of trade-offs between temperature and pH sensitivity, and all eight species can co-evolve tolerance to elevated temperature and reduced pH. Using these values together with historical data, we estimate potential increases in thermal tolerance of 1.0–1.7°C over the next 50 years, depending on species. None of these species are probably capable of keeping up with a high global change scenario and climate change mitigation is essential if reefs are to persist. Such estimates are critical for our understanding of how corals may respond to global change, accurately parametrizing modelled responses, and predicting rapid evolution.
Continue reading ‘Widespread scope for coral adaptation under combined ocean warming and acidification’Ocean acidification does not prolong recovery of coral holobionts from natural thermal stress in two consecutive years
Published 24 September 2024 Science ClosedTags: adaptation, biological response, BRcommunity, calcification, corals, laboratory, mortality, multiple factors, North Pacific, nutrients, otherprocess, physiology, protists, zooplankton
Under predicted future ocean conditions, corals will experience frequent and intense thermal stress events while simultaneously being exposed to chronic ocean acidification. Yet, some corals will likely be more resistant and/or resilient to these predicted conditions than others and may be critical to reef persistence in the future. Following natural thermal stress in two consecutive years (2014 and 2015), we evaluated the effects of feeding and simulated ocean acidification on the physiological recovery of Montipora capitata and Porites compressa sourced from Kāneʻohe Bay and Waimānalo Bay, Hawaiʻi. Following the 2014 thermal stress event, simulated ocean acidification did not slow recovery of the holobiont and feeding enhanced recovery. However, feeding did not decrease susceptibility to the 2015 thermal stress event, and simulated ocean acidification did not increase susceptibility. Recovery strategies employed between species and between sites clearly differed, highlighting that coral reef restoration and management should consider species-level and site-specific vulnerabilities. Overall, our findings call attention to the immediate threat which ocean warming presents, the lack of additional stress to the holobiont from ocean acidification, the importance of heterotrophy in coral resilience, and the potential significance of additional local biotic stressors (i.e., predator outbreaks) for coral resiliency under annual thermal stress.
Continue reading ‘Ocean acidification does not prolong recovery of coral holobionts from natural thermal stress in two consecutive years’Carbon budgets of coral reef ecosystems in the South China Sea
Published 20 September 2024 Science ClosedTags: biological response, calcification, corals, North Pacific, primary production
The coral reef ecosystem is one of the most productive ecosystems in the ocean, and is also an important calcium carbonate deposition region. Because excess production is very low in coral reefs, organic carbon reservoirs are very limited. During the calcification process, each mole of CaCO3 will produce 1 mol of CO2, approximately 60% of which will be released into the atmosphere through the sea-air interface. This causes coral reefs to be large inorganic carbon reservoirs, but at the same time, most coral reefs act as atmospheric CO2 sources (which also act as sinks in some coral reefs). Therefore, clarifying the sea-air CO2 exchange flux and carbon storage is critical for understanding the carbon cycle in coral reef ecosystems. In this paper, we summarize the carbon cycle processes in the coral reefs of the South China Sea (SCS) and estimate the total CO2 budget and carbon reserves. According to current research, the coral reefs in this area act as a source of atmospheric CO2, releasing 0.37−1.59 × 1011 g C a-1 into the atmosphere. Owing to their extremely high biological productivity and carbonate productivity, the carbon reserves of coral reefs in the SCS range from 1.66–3.78 × 1012 g C a-1, which is an order of magnitude greater than the CO2 emissions at the sea–air interface. Overall, coral reefs in the SCS are important carbon storage areas. As the current results are still approximate, a more comprehensive and in-depth investigation is needed to clarify the carbon source/sink processes, regulatory mechanisms, and carbon storage capacity of SCS coral reefs.
Continue reading ‘Carbon budgets of coral reef ecosystems in the South China Sea’Anthropogenic climate change will likely outpace coral range expansion
Published 26 August 2024 Science ClosedTags: biological response, communitymodeling, corals, modeling, review
Past coral range expansions suggest that high-latitude environments may serve as refugia, potentially buffering tropical biodiversity loss due to climate change. We explore this possibility for corals globally, using a dynamical metacommunity model incorporating temperature, light intensity, pH, and four distinct, interacting coral assemblages. This model reasonably reproduces the observed distribution and recent decline of corals across the Indo-Pacific and Caribbean. Our simulations suggest that there is a mismatch between the timescales of coral reef decline and range expansion under future predicted climate change. Whereas the most severe declines in coral cover will likely occur within 60–80 years, significant tropical coral range expansion requires centuries. The absence of large-scale coral refugia in the face of rapid anthropogenic climate change emphasises the urgent need to reduce greenhouse gas emissions, and mitigate non-thermal stressors for corals, both in the tropics and high-latitudes.
Continue reading ‘Anthropogenic climate change will likely outpace coral range expansion’Boron isotopic compositions of middle Miocene to recent shallow-water carbonates from the South China Sea: assessing diagenetic effects and implications for paleoclimate changes
Published 23 August 2024 Science ClosedTags: biological response, corals, laboratory, paleo
Highlights
- A high-resolution δ11B dataset for carbonates from the South China Sea.
- Limestone without strong recrystallization can record ambient seawater pH.
- Diagenetic processes do not affect δ11B records of marine limestone.
- Dolomites should be excluded as archives for seawater δ11B.
Abstract
The partial pressure of atmospheric CO2 (pCO2) significantly influences global climate change and biological evolution through geological history. Boron isotopic composition (δ11B) in carbonates has been used to reconstruct the paleo-pH of seawater, providing insight into atmospheric pCO2 levels. However, the fidelity of δ11B records in marine carbonates due to diagenesis remains uncertain. Here, to understand how diagenetic processes influence B isotopic records in marine carbonates, we examined B concentrations and δ11B values of modern corals (from Hainan Island), unconsolidated shallow pushcores (Jiuzhang A and Jiuzhang B from Nansha Islands, South China Sea), and a long drillcore (XK-1 from Xisha Islands, South China Sea) covering the Late Miocene to Holocene periods. Our coral samples show a uniform δ11B range (20.16 ± 0.85%), consistent with previously published values for modern corals in other open oceans. The δ11B values of the unlithified carbonate sediments from Jiuzhang A and B pushcores vary within a narrow range (18.70 ± 0.84%), yielding pH and CO2 concentrations consistent with the range between modern and pre-industrial values. Since we did not observe any statistically significant covariations between traditionally established diagenetic proxies (such as δ13C, δ18O, Mn/Sr, and Al/Ca) and δ11B values for non-dolomitized samples in the XK-1 drillcore, we suggest that δ11B values of bulk limestones are not significantly affected by typical diagenesis (meteoric, mixed-diagenetic, and marine diagenetic processes), likely due to limited post-depositional recrystallization of our study carbonates. In contrast, dolomitization significantly decreases δ11B values of bulk carbonates, rendering dolomites unsuitable as archives for reconstructing seawater δ11Bborate values. Our study supports that marine limestone with limited recrystallization or dolomitization have the potential to record ambient seawater pH values with high resolution. The established secular seawater pH variations based on XK-1 δ11B records provide information about ocean acidification over the past 5.1 million years.
Continue reading ‘Boron isotopic compositions of middle Miocene to recent shallow-water carbonates from the South China Sea: assessing diagenetic effects and implications for paleoclimate changes’Lipid droplets in endosymbiotic Symbiodiniaceae spp. associated with corals
Published 20 August 2024 Science ClosedTags: biological response, BRcommunity, chemistry, corals, protists
Symbiodiniaceae species is a dinoflagellate that plays a crucial role in maintaining the symbiotic mutualism of reef-building corals in the ocean. Reef-building corals, as hosts, provide the nutrition and habitat to endosymbiotic Symbiodiniaceae species and Symbiodiniaceae species transfer the fixed carbon to the corals for growth. Environmental stress is one of the factors impacting the physiology and metabolism of the corals-dinoflagellate association. The environmental stress triggers the metabolic changes in Symbiodiniaceae species resulting in an increase in the production of survival organelles related to storage components such as lipid droplets (LD). LDs are found as unique organelles, mainly composed of triacylglycerols surrounded by phospholipids embedded with some proteins. To date, it has been reported that investigation of lipid droplets significantly present in animals and plants led to the understanding that lipid droplets play a key role in lipid storage and transport. The major challenge of investigating endosymbiotic Symbiodiniaceae species lies in overcoming the strategies in isolating lesser lipid droplets present in its intercellular cells. Here, we review the most recent highlights of LD research in endosymbiotic Symbiodiniaceae species particularly focusing on LD biogenesis, mechanism, and major lipid droplet proteins. Moreover, to comprehend potential novel ways of energy storage in the symbiotic interaction between endosymbiotic Symbiodiniaceae species and its host, we also emphasize recent emerging environmental factors such as temperature, ocean acidification, and nutrient impacting the accumulation of lipid droplets in endosymbiotic Symbiodiniaceae species.
Continue reading ‘Lipid droplets in endosymbiotic Symbiodiniaceae spp. associated with corals’Effects of predicted future ocean acidification and dredging-induced turbidity on the scleractinian coral lipidome
Published 20 August 2024 Science ClosedTags: biological response, chemistry, corals, laboratory, physiology
Shallow-water coral reefs provide diverse ecosystem services and are thus considered a conservation priority. However, stony corals continue to face various threats. Lipids constitute ~30% of the dry tissue biomass in stony coral, which are vitally important for biological processes. Therefore, this study used a lipidomics approach to measure and characterize the lipidome of (1) three coral species, Porites rus, Porites lobata, and Pocillopora eydouxi, collected along a natural pH gradient created by the Maug Shallow Hydrothermal Vent (MSHV), and (2) from Acropora cervicornis, a coral species listed as threatened under the Endangered Species Act, following exposure to acute turbidity and sedimentation. Analyses of the (1) MSHV coral revealed lipidomic distinction across pH sites in P. lobata and P. rus. However, data from P. eydouxi may indicate resilience to acidification, supporting previous findings from metabolomics data. Of the top 25 most important spectral features driving distinctions across pH treatments, putatively annotated lipids classified as glycerophospholipids, glycerolipids, and sphingolipids were differently abundant in lower pH conditions for P. lobata and P. rus, while a single fatty acyl was also found to be altered in P. lobata under acidified conditions. Such lipids may help support and control cellular processes and maintain membrane stability and structure when exposed to lower pH conditions. Annotations were not assigned to over half of the features important for lipidomic distinction across pH sites in P. lobata and P. rus, limiting possible conclusions. Analyses of (2) A. cervicornis exposed to 96-h turbidity revealed no significant change in tissue regeneration or total lipids. Lipidomic changes were identified in the highest turbidity treatment (30 NTU), however, no significant differences in relative concentration of features important for lipidomic changes were detected. Tissue regrowth was significantly decreased in A. cervicornis exposed to turbidity and sedimentation during a 12-day experiment. Total lipids remained unchanged, although 12-day exposure to 15 NTU target turbidity and 96-h sedimentation periods impacted the A. cervicornis lipidome. Differences in relative concentration of features important for lipidomic distinction were not significant. This study provides important inaugural information regarding stony coral response to changes in environmental conditions that serves as a cornerstone for predicting coral composition shifts, may inform crucial conservation and management strategies, and will guide future investigations.
Continue reading ‘Effects of predicted future ocean acidification and dredging-induced turbidity on the scleractinian coral lipidome’
