Increased atmospheric CO2 levels lead to ocean acidification, threatening coral reefs. However, certain coral species thrive in naturally acidified environments, offering unique opportunities to explore potential acclimatization or adaptation strategies. We assessed the physiological and biochemical parameters of Porites cf. lobata. colonies from control and acidified sites in the Palau Archipelago. Using a holistic approach, we compared markers related to trophic state, symbiotic state, physiology, energy storage, and redox status, along with calcification and oxidative metabolism. Our findings indicate that these colonies can acclimatize to low-pH conditions by utilizing CO2 more effectively. The increased passive diffusion of CO2 through their tissues enables them to maintain photosynthesis and calcification rates by reallocating energy that would typically go toward bicarbonate uptake. However, this energy reallocation cannot maintain skeleton density. Corals expend energy to elevate pH in the extracellular calcifying fluid, which is highly energy-demanding and reduces lipid reserves, potentially compromising long-term resilience. Despite the heightened energy production requirements, oxidative stress does not appear to worsen; the colonies exhibited lower antioxidant defenses and protein damage under low-pH conditions. The absence of metabolic suppression due to stable respiration rates and increased biomass suggests modifications in metabolic pathways, likely shifting toward a Warburg-like effect. These findings highlight the potential for some corals to tolerate near-future ocean acidification, the trade-offs associated with this resilience, and the potential for cascading effects on reef ecosystems. Further research should explore corals metabolic pathways as potential coping mechanisms.
Continue reading ‘Coping with ocean acidification: metabolic shifts in Porites corals from the Palau Archipelago’Posts Tagged 'corals'
Coping with ocean acidification: metabolic shifts in Porites corals from the Palau Archipelago
Published 9 September 2025 Science ClosedTags: adaptation, biological response, calcification, corals, field, growth, North Pacific, otherprocess, photosynthesis, physiology, respiration
Multidecadal decoupling between coral calcifying fluid and seawater saturation states
Published 1 September 2025 Science ClosedTags: biological response, calcification, chemistry, corals, field, South Pacific
Ocean acidification poses a threat to coral skeleton formation via reductions in the saturation state of aragonite (ΩAr) in seawater. Given that corals precipitate their skeletons from a calcifying fluid supplied by seawater, reductions in seawater ΩAr should, in theory, confound calcification. Here, we reconstruct up to 200 years of coral calcifying fluid ΩAr, using Raman spectroscopy techniques, at approximately monthly resolution in two Porites sp. skeletal cores from the Coral Sea region to investigate (i) the regulation of coral calcifying fluid ΩAr and (ii) the skeletal calcification response to industrial-era ocean acidification. Our results reveal a significant increase in calcifying fluid ΩAr, suggesting that some corals may adjust to the pace of acidification in the wild more effectively than suggested by short-term laboratory studies.
Continue reading ‘Multidecadal decoupling between coral calcifying fluid and seawater saturation states’Acclimation mechanisms of reef-building coral Acropora gemmifera juveniles to long-term CO2-driven ocean acidification
Published 27 August 2025 Science ClosedTags: adaptation, biological response, corals, laboratory, molecular biology, morphology, North Pacific, otherprocess, physiology, reproduction
Ocean acidification (OA) is a major threat to the sexual recruitment of reef-building corals. Acclimation mechanisms are critical but poorly understood in reef-building corals to OA during early life stages. Here, Acropora gemmifera, a common Indo-Pacific coral cultured in in situ seawater from Luhuitou reef at three levels of pCO2 (pH 8.14, 7.83, 7.54), showed significantly delayed larval metamorphosis and juvenile growth, but adapted to long-term high pCO2. Differentially expressed genes (DEGs) emerged as a time- and dose-dependent mode of short-term response (3 days post settlement, d p.s.) and long-term acclimation (40 d p.s.), with more DEGs responding to high pCO2 (pH 7.54) than to medium pCO2 (pH 7.83). High pCO2, a presumed threatening seawater baseline for A. gemmifera juveniles, activated DNA repair, macroautophagy, microautophagy and mitophagy mechanisms to maintain cellular homeostasis, recycle cytosolic proteins and damaged organelles, and scavenge reactive oxygen species (ROS) and H+, but at the cost of delayed development through cell cycle arrest associated with epigenetic and genetic regulation at 3 d p.s.. However, A.gemmifera juveniles acclimated to high pCO2 by up-regulating cell cycle, transcription, translation, cell proliferation, cell-extracellular matrix, cell adhesion, cell communication, signal transduction, transport, binding, Symbiodiniaceae symbiosis, development and calcification from 3 d p.s. to 40 d p.s., when energy reallocation and metabolic suppression occurred for high demand but short-term energy limitation in coral cells undergoing flexible symbiosis. All results indicate that acclimation mechanisms of complicated gene expression improve larval and juvenile resilience to OA for coral population recovery and reef restoration.
Continue reading ‘Acclimation mechanisms of reef-building coral Acropora gemmifera juveniles to long-term CO2-driven ocean acidification’Ocean acidification and nitrate enrichment can mitigate negative effects of soft coral (Xenia) competition on hard coral (Stylophora pistillata) endosymbionts
Published 21 August 2025 Science ClosedTags: biological response, BRcommunity, community composition, corals, growth, laboratory, multiple factors, nutrients, otherprocess, physiology, phytoplankton
The combination of ocean acidification (OA) and eutrophication can undermine the physiological performance of reef-building corals during competition for benthic space, leading to shifts towards non-accreting organisms like soft corals. We conducted a 28-day laboratory orthogonal experiment to test if acidification (950 µatm pCO2) and moderate to high nitrate enrichment (4 and 8 µmolL−1) negatively affect the hard coral Stylophora pistillata while physically competing with the soft coral Xenia spp. We measured photosynthetic efficiency (PE) in hard corals and growth rate, Symbiodiniaceae density, and chlorophyll-a concentration in both hard and soft corals as proxies for their condition and responses to competition. Competition with the soft coral reduced PE, Symbiodiniaceae and chlorophyll-a contents of S. pistillata, while acidification alone and coupled with nitrate enrichment mitigated endosymbiont responses. The growth and chlorophyll-a concentrations of Xenia spp. were decreased by competition, but the soft coral was consistently benefited under nitrate enrichment. These results highlight that competition alone has a stronger negative impact on hard corals than on soft corals. Our study provides experimental evidence on how OA and eutrophication interact and shape coral dynamics, an overlooked but urgent topic in predicting reef futures under environmental change.
Continue reading ‘Ocean acidification and nitrate enrichment can mitigate negative effects of soft coral (Xenia) competition on hard coral (Stylophora pistillata) endosymbionts’Tubastraea coccinea (Lesson, 1830), a coral species with high invasive potential, can benefit from the synergistic effects of ocean warming and acidification
Published 14 August 2025 Science ClosedTags: biological response, calcification, corals, laboratory, morphology, multiple factors, North Atlantic, reproduction, respiration, temperature
Temperature rise and pH decrease, coupled with increasing maritime traffic, are inducing modifications in the distribution of many exotic species, such as Tubastraea coccinea, a species with high invasive potential recently recorded in the Canary Islands. This study assessed the effect of the expected end-of-century temperature and pH (26°C and pH 7.50) on this coral species through manipulative laboratory experiments conducted over different time periods (30 days vs. 80 days). The impact of acidification, warming, and time on variables such as weight, buoyant weight, number of new polyps, area, respiration, calcification and reproduction rates were analysed. Results revealed a negative effect of acidification on growth and respiration rates of T. coccinea, with significant differences between experimental treatments in weight, buoyant weight, number of polyps, area, and respired carbon. However, in future, T. coccinea may not be adversely affected by low pH values, as the negative effect is mitigated when colonies are exposed to 26°C. Using different experimental periods showed how this species’ response is liable to change over time under future climate change conditions.
Continue reading ‘Tubastraea coccinea (Lesson, 1830), a coral species with high invasive potential, can benefit from the synergistic effects of ocean warming and acidification’Skeleton-forming responses of reef-building corals under ocean acidification
Published 7 August 2025 Science ClosedTags: biological response, corals, laboratory, molecular biology, morphology, North Pacific
Ocean acidification is becoming more prevalent and may contribute to coral reef degradation, yet our understanding of its role in global reef decline remains limited. Therefore, there is an urgent need to study the impact of reduced pH levels on the growth patterns of major reef-building corals. Here, we studied the skeleton-forming strategies of 4 widely distributed coral species in a simulated acidified habitat with a pH of 7.6 to 7.8. We reconstructed and visualized the skeleton-forming process, quantified elemental calcium loss, and determined gene expression changes. The results suggest that different reef-building corals have diverse growing strategies in lower pH conditions. A unique “cavity-like” forming process starts from the inside of the skeletons of Acropora muricata, which sacrifices skeletal density to protect its polyp–canal system. The forming patterns in Pocillopora damicornis, Montipora capricornis, and Montipora foliosa were characterized by “osteoporosis”, exhibiting disordered skeletal structures, insufficient synthesis of adhesion proteins, and low bone mass, correspondingly. In addition, we found that damage from acidification particularly affects pre-existing skeletal structures in the colony. These results enhance our understanding of skeleton-forming strategies in major coral species under lower pH conditions, providing a foundation for coral reef protection and restoration amidst increasing ocean acidification.
Continue reading ‘Skeleton-forming responses of reef-building corals under ocean acidification’Ocean acidification threatens Niue’s coral reefs: a call for global action
Published 6 August 2025 Web sites and blogs ClosedTags: corals, South Pacific
Ocean acidification, driven by anthropogenic carbon dioxide (CO₂) emissions, poses a severe threat to coral reef ecosystems worldwide, with significant implications for small island nations like Niue. This article examines the specific impacts of ocean acidification on Niue’s coral reefs, which are vital to the island’s biodiversity, economy, and cultural heritage. Through a situational analysis of Niue’s reefs and a review of global literature, the study highlights the chemical processes of acidification, its ecological consequences, and the socio-economic ramifications for Niue’s communities. The paper further explores the role of intergovernmental organizations and international treaties in addressing this crisis, emphasizing the need for coordinated global action. Recommendations are provided to mitigate acidification impacts through local conservation efforts, regional collaboration, and international policy advocacy. This article underscores the urgency of integrating ocean acidification into global climate agendas to protect vulnerable ecosystems like Niue’s coral reefs.
Continue reading ‘Ocean acidification threatens Niue’s coral reefs: a call for global action’Dynamics of ocean acidity, CO2 fluxes and metabolic rates on a shallow reef of Weizhou Island: a buoy-based observational study
Published 5 August 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, dissolution, field, North Pacific, physiology, respiration
Highlights
- Diel cycles of reef seawater pH, calcification, and production were documented through a 37-day high-frequency time series.
- Daily net ecosystem production and calcification maintain a strong linear relationship even during dark periods.
- The studied reef exhibited persistent daily net heterotrophy and net CaCO3 dissolution for over weeks.
Abstract
The metabolic processes of calcification and production serve as crucial indicators of how environmental changes impact reef health. Previous studies suggest that Net Ecosystem Production (NEP) primarily drives Net Ecosystem Calcification (NEC) in the short-term. However, the functional relationship between these two carbon metabolisms remains poorly understood. We employed a mooring buoy approach to obtain simultaneous, high-frequency data of seawater pH, aragonite saturation state, CO2 fluxes, and carbon metabolic rates over a coral reef on Weizhou Island for 37 consecutive days. Our findings revealed a strong linear correlation between NEC and NEP across both diel cycles and day-to-day timescales—this relationship held even when analyzing nighttime periods alone. This indicates an intrinsic link between carbon metabolisms that can operate independently of light. Furthermore, we observed predominantly negative daily NEC and NEP values, indicating persistent net CaCO3 dissolution and net heterotrophy across the studied reef for over weeks. Our results suggest that CaCO3 dissolution is more likely to occur in waters with heterotrophic conditions, implying that heterotrophy contributes to CaCO3 dissolution. This tight coupling could be explained by reef sediment dissolution through the Carbonate Critical Threshold (CCT) mechanism. Our study highlights the significance of ambient respiration in driving reef ecosystem-scale CaCO3 dissolution, especially in reefs with low live hard coral coverage. This process releases alkalinity into the seawater, helping to neutralize respiration-induced acidification. Additionally, we identified a higher rate of respiratory CO₂ release as the primary driver of CO2 emissions from the studied reef.
Continue reading ‘Dynamics of ocean acidity, CO2 fluxes and metabolic rates on a shallow reef of Weizhou Island: a buoy-based observational study’Mid-Miocene warmth pushed fossil coral calcification to physiological limits in high-latitude reefs
Published 28 July 2025 Science ClosedTags: biological response, calcification, corals, field, growth, morphology, paleo
The history of resilience of organisms over geologic timescales serves as a reference for predicting their response to future conditions. Here we use fossil Porites coral records of skeletal growth and environmental variability from the subtropical Central Paratethys Sea to assess coral resilience to past ocean warming and acidification. These records offer a unique perspective on the calcification performance and environmental tolerances of a major present-day reef builder during the globally warm mid-Miocene CO2 maximum and subsequent climate transition (16 to 13 Ma). We found evidence for up-regulation of the pH and saturation state of the corals’ calcifying fluid as a mechanism underlying past resilience. However, this physiological control on the internal carbonate chemistry was insufficient to counteract the sub-optimal environment, resulting in an extremely low calcification rate that likely affected reef framework accretion. Our findings emphasize the influence of latitudinal seasonality on the sensitivity of coral calcification to climate change.
Continue reading ‘Mid-Miocene warmth pushed fossil coral calcification to physiological limits in high-latitude reefs’Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island
Published 15 July 2025 Science ClosedTags: adaptation, biological response, BRcommunity, community composition, corals, field, molecular biology, North Pacific, otherprocess, phytoplankton, prokaryotes, vents
Ocean acidification (OA), driven by rising atmospheric CO2, presents a serious threat to marine biodiversity, especially within coral reef ecosystems. Natural analogue sites, such as the high-pCO2 seep at Iōtorishima Island in Japan, offer insights into future conditions. This study investigated the holobiont communities of Symbiodiniaceae and bacteria in the zoantharian Palythoa tuberculosa at Iōtorishima and compared them to specimens from control sites in Okinawa and Hawaiʻi. Using amplicon sequencing of the dinoflagellate internal transcribed spacer 2 (ITS2) region of ribosomal DNA and microbial 16S rRNA gene, we detected significant shifts in both Symbiodiniaceae and bacterial communities under high-pCO2 conditions at Iōtorishima. Specifically, P. tuberculosa at the seep site had reduced Symbiodiniaceae diversity, predominatly featuring Cladocopium C1 and C3 types. Additionally, its bacterial communities showed lower richness with distinct taxonomic profiles, including increased levels of Mollicutes and Vibrio spp. These results highlight the potentially adverse effects of OA on hexacoral holobionts and emphasize the need for detailed, high-resolution studies across various holobiont species and geographic locations. The shifts observed specifically in Symbiodiniaceae and bacterial communities at the Iōtorishima seep suggest that holobionts may exhibit plasticity in response to environmental stress, which has implications for resilience and adaptation of zoantharians and other reef organisms amid climate change. This research provides crucial baseline data for predicting future coral reef compositions in an OA-affected world.
Continue reading ‘Shifts in coral reef holobiont communities in the high-CO2 marine environment of Iōtorishima Island’Impact of ocean acidification on fish health and marine ecosystem dynamics
Published 11 July 2025 Science ClosedTags: algae, biological response, corals, fish, mollusks, phanerogams, phytoplankton, review, zooplankton
Ocean acidification (OA) causes an increase in carbon dioxide (CO2) and a reduction in the pH of ocean waters. This chapter reviews the current literature to investigate the adverse effects of OA on fish health and marine ecosystem dynamics. OA poses serious threats to marine biodiversity and ecosystem dynamics. Fish experience severe physiological problems such as impaired growth, development, tissue damage, Impaired behavioral changes, sensory and brain functions, and disruption in predator-prey interactions due to acidification with a 74% decline in survival rates of egg and larval stages. Besides affecting fish, OA also affects marine ecosystem dynamics: reducing calcification rates in calcifying species, increasing seagrass production, causing effects on habitat-forming species, and disrupting the food web. Vulnerable species, such as coral reef fish, show high sensitivity, risking the stability of their habitats. The United Nations recognized the OA as a threat to marine biodiversity through the Convention on Biodiversity. The future research needs to focus on understanding fish and marine animals’ adaptive mechanisms to OA, its interaction with other stressors, and global collaboration to address the underlying causes of OA.
Continue reading ‘Impact of ocean acidification on fish health and marine ecosystem dynamics’Groundwater discharge found to alter coral reef ecosystems
Published 11 July 2025 Press releases ClosedTags: corals, South Pacific
Groundwater directly affects water chemistry in coral reefs and triggers a cascade of changes in the coastal ecosystem, according to a new study led by University of Hawaiʻi at Mānoa oceanographers. The researchers describe the effect as a “Goldilocks scenario”—too much groundwater has a negative impact, and when the input is “just right,” the reef benefits.
Freshwater from land that flows into the ocean beneath the sea surface, termed submarine groundwater discharge, was found to increase nutrient availability, change acidity of the seawater, and impact the process by which corals build their skeletons. This research, published recently in Ecological Monographs, provides critical insights into the complex interactions between the land and ocean.
“Submarine groundwater discharge is a widespread and underappreciated land–sea connection that delivers terrestrial nutrients and carbon to coastal ecosystems,” said Nyssa Silbiger, lead author of the study, associate director of the Uehiro Center for the Advancement of Oceanography, and associate professor in the Department of Oceanography at the UH Mānoa School of Ocean and Earth Science and Technology. “This profoundly influences coral reef health by triggering a cascade of chemical and biological changes that alter the cycling of carbon in these ecosystems.”
The fundamental connection between land and sea through the flow of freshwater is a universal principle recognized as important for coastal health across all cultures. Porous volcanic islands throughout the tropics deliver much of this water through rivers and streams, but a major fraction emerges unseen directly into the coral reefs that ring these islands. This submarine groundwater discharge has long been recognized by Pacific peoples as important, with seeps frequently named and associated with specific communities of algae and fish relevant to subsistence. The new research has helped define the complex interplay of chemistry and biology that makes these inputs so important to the ecology of coral reefs.
Continue reading ‘Groundwater discharge found to alter coral reef ecosystems’Terrestrial nutrient inputs restructure coral reef dissolved carbon fluxes via direct and indirect effects
Published 11 July 2025 Science ClosedTags: biogeochemistry, BRcommunity, calcification, chemistry, corals, field, South Pacific
The addition of terrestrial inputs to the ocean can have cascading impacts on coastal biogeochemistry by directly altering the water chemistry and indirectly changing ecosystem metabolism, which also influences water chemistry. Here, we use submarine groundwater discharge (SGD) as a model system to examine the direct geochemical and indirect biologically mediated effects of terrestrial nutrient subsidies on a fringing coral reef. We hypothesize that the addition of new solutes from SGD alters ecosystem metabolic processes including net ecosystem production and calcification, thereby changing the patterns of uptake and release of carbon by benthic organisms. SGD is a common land–sea connection that delivers terrestrially sourced nutrients, carbon dioxide, and organic matter to coastal ecosystems. Our research was conducted at two distinct coral reefs in Moʻorea, French Polynesia, characterized by contrasting flow regimes and SGD biogeochemistry. Using a Bayesian structural equation model, our research elucidates the direct geochemical and indirect biologically mediated effects of SGD on both dissolved organic and inorganic carbon pools. We reveal that SGD-derived nutrients enhance both net ecosystem production and respiration. Furthermore, the study demonstrates that SGD-induced alterations in net ecosystem production significantly influence pH dynamics, ultimately impacting net ecosystem calcification. Notably, the study underscores the context-dependent nature of these cascading direct and indirect effects resulting from SGD, with flow conditions and the composition of the terrestrial inputs playing pivotal roles. Our research provides valuable insights into the interplay between terrestrial inputs and coral reef ecosystems, advancing our understanding of coastal carbon cycling and the broader implications of allochthonous inputs on ecosystem functioning.
Continue reading ‘Terrestrial nutrient inputs restructure coral reef dissolved carbon fluxes via direct and indirect effects’Coral calcification mechanisms across a natural environmental mosaic in Hawai’i
Published 9 July 2025 Science ClosedTags: adaptation, biological response, chemistry, corals, field, North Pacific, otherprocess, physiology
Coral calcification is key to coral reef growth and function but may be compromised under increasing global and local stressors. Corals modify the carbonate chemistry of their calcifying fluid to facilitate calcification, but little is known about how these mechanisms vary across the substantial differences in reef seawater conditions that can occur over as little as a few kilometers. Here, we used boron-based geochemical proxies (δ11B, B/Ca) to investigate how three common Hawaiian coral species (Montipora capitata, Porites compressa, Porites lobata) regulate the carbonate chemistry of the calcifying fluid along a natural environmental mosaic of seawater carbonate chemistry and significant wave height. We found that calcification mechanisms were governed by complex species and site interactions: while all species generally differed from each other in their calcifying fluid chemistry, they also responded differently to site-specific environmental conditions. These results highlight that there are varying degrees of calcification mechanism plasticity in response to changing environmental conditions. Furthermore, species-specific patterns of pH upregulation inside the calcifying fluid were good predictors of calcification responses to ocean acidification and warming in at least two of the three species, with M. capitata being a clear winner under future ocean conditions. Our findings provide important insights into how corals calcify across a natural environmental mosaic and highlight the differential potential for an adaptive capacity in calcification mechanisms in the face of intensifying climate change.
Continue reading ‘Coral calcification mechanisms across a natural environmental mosaic in Hawai’i’Robustness of gametogenesis in the scleractinian coral, Tubastraea aurea, in the shallow-water hydrothermal vent field off Kueishan Island, northeastern Taiwan
Published 8 July 2025 Science ClosedTags: biological response, corals, field, North Pacific, reproduction, vents
Highlights
- Stony corals (Tubastraea aurea) can colonize in acidified shallow-water hydrothermal vent fields.
- T. aurea is a gynodioecious brooder; mostly females with a low percent of hermaphroditism.
- HV colonies maintained the similar gametogenic process and seasonal timing of reproduction as NHV colonies.
- Elevated gametogenic activity of vent T. aurea could facilitate success in extreme conditions.
- Hydrothermal vents as natural laboratories offer insights on the resiliency of scleractinians.
Abstract
Understanding the reproductive resiliency of scleractinian corals is imperative as ocean acidification and rising sea surface temperatures threaten the foundation of coral reef ecosystems. However, the limited temporal scales of laboratory and transplantation-based methods fail to consider evolutionary time frames offered by natural analogues of future climate conditions, like hydrothermal vents (HV). Accordingly, we characterized the presence of scleractinians surrounding a major shallow-water HV near Kueishan Island in northeastern Taiwan, identified a candidate species, Tubastraea aurea, and investigated its sexual reproductive strategies. Since this was the first study to describe the sexual reproduction of T. aurea, we characterized the gametogenetic process of T. aurea colonies from the HV and three non-HV locations (NHV1, NHV2, NHV3). Oogenesis was similar between HV and NHV sites and mature oocytes reached the same size. The seasonal timing of reproduction was comparable between HV and NHV1 colonies, likely related to the similar seasonal variation of water temperatures. HV colonies showed an even higher gametogenetic activity (100 % of polyps containing developing gametes in HV colonies versus 73.5 % in NHV colonies). As assessed by the presence of larvae, T. aurea is a brooder, with mostly female polyps (97.6 %,) and a low percent of hermaphroditism (2.4 %, as observed in 2 in HV and 1 in NHV colonies). This suggests that parthenogenesis may contribute to larval production. Taken together, we demonstrated the robustness of gametogenesis in T. aurea and propose the heightened reproductive effort of T. aurea at the Kueishan Island HV could be facilitating its success in acidified conditions. Overall, this study exemplified the importance of using unique ecosystems to uncover clues on scleractinian resiliency.
Continue reading ‘Robustness of gametogenesis in the scleractinian coral, Tubastraea aurea, in the shallow-water hydrothermal vent field off Kueishan Island, northeastern Taiwan’Phenotypic plasticity in Mediterranean gorgonians Eunicella singularis and Paramuricea clavata at high temperature and low pH
Published 2 July 2025 Science ClosedTags: adaptation, biological response, corals, laboratory, Mediterranean, molecular biology, multiple factors, otherprocess, performance, physiology, temperature
Highlights
- The oxygen consumption of the gorgonian corals increased at high temperatures.
- Energy reserves were not affected by high temperature, low pH or their interaction.
- The global DNA methylation in Eunicella singularis was not affected by high temperature, low pH, or their combination.
- Global DNA methylation in Paramuricea clavata decreased under high temperature and low pH.
- High temperature alone caused more DEGs in E. singularis than low pH or combined treatment.
Abstract
The Mediterranean gorgonian octocorals are threatened by acidification, warming and marine heat waves. Phenotypic plasticity is critical for slow-growing gorgonians, as adaptation through natural selection might not be fast enough to cope with rapid environmental changes. DNA methylation (DNAm) is a type of (trans)generational phenotypic plasticity mechanism that may help slow-growing corals better withstand the effects of environmental changes by adjusting gene expression. This study aimed to assess the physiological responses and epigenetic modifications associated with phenotypic plasticity in the Mediterranean gorgonians Eunicella singularis and Paramuricea clavata exposed to warming (+4 °C), acidification (−0.35 pHT units) and their combination over two weeks. In addition, RNA-Seq-based differential gene expression analysis was performed for E. singularis.
High temperature, low pH and their combination did not cause tissue death or necrosis in the corals. Polyp activity in E. singularis increased at high temperatures. Warming increased oxygen consumption in both species. Energy reserves (protein, lipid, carbohydrate contents) were not affected by temperature, pH or their interaction in either species. The global DNA methylation (gDNAm) rate was ten times higher in P. clavata than in E. singularis. There was no effect of temperature, pH or their interaction on gDNAm in E. singularis. gDNAm in P. clavata decreased at high temperatures and low pH. Differential gene expression analysis indicated that high temperature induced the most extensive transcriptional changes in E. singularis, while low pH alone had the least impact. The combined stress of high temperature and low pH also led to notable up- and downregulation of gene expression. Heat stress in E. singularis caused widespread downregulation of transcription factors (TFs), particularly those in the zf-C2H2, AP-2, and HMG families. Conversely, the IRF, RFX, P53, and NRF1 families were upregulated, highlighting the complex transcriptional response to thermal stress. Overall, these physiological, transcriptomic and epigenetic alterations have the potential to negatively impact the fitness of these emblematic species and their associated ecosystems.
Continue reading ‘Phenotypic plasticity in Mediterranean gorgonians Eunicella singularis and Paramuricea clavata at high temperature and low pH’The seven sins of climate change: a review of rates of change, and quantitative impacts on ecosystems and water quality in the Great Barrier Reef
Published 1 July 2025 Science ClosedTags: biological response, BRcommunity, chemistry, corals, review, South Pacific
Highlights
- Reviewed rates of change for 7 climate change factors, quantifying impacts
- Climate change affects water quality, emphasising local management needs
- Extreme weather events are still the most destructive climate change factors
- Progressive climate factors will increase in importance, altering ecosystems.
- Ocean acidification may reach critical thresholds within decades.
Abstract
The term climate change encompasses many types of impacts and threats to the long-term outlook of coastal marine ecosystems. Based on a structured Evidence Summary methodology, this review synthesises the peer-reviewed knowledge on climate change impacts on the Great Barrier Reef (GBR). We summarise the observed and predicted region-specific rates of change for seven climate change factors; three representing episodic extreme weather events (heatwaves, tropical storms, and extreme rainfall events), and four chronic progressive climate change factors (rising temperatures, ocean acidification and sea level, and altered cloudiness/windiness). We extract key quantitative findings on their impacts on GBR ecosystems and associated organisms, especially coral reefs, seagrasses, mangroves and wetlands, and on GBR water quality. Quantifying GBR-wide effects requires data on their four dimensions: intensity, duration, spatial extent, and frequency. The review shows that to date, most damage to GBR ecosystems is inflicted by extreme weather events. Of the progressive climate change factors, ocean acidification is already altering some GBR ecosystem functions, potentially reaching a critical threshold within decades. The progressive climate change factors are already causing selective mortality and changes in communities. We document regional differences, and we outline the evidence of climate change impacts on GBR water quality, suggesting further cumulative effects. This review provides an overview of empirical data for modellers and ecologists, and for experimentalists to choose environmentally relevant treatment levels. Intensifying climate change disturbances increase the urgency of climate change mitigation, as well as effective local management to accelerate ecosystem recovery.
Continue reading ‘The seven sins of climate change: a review of rates of change, and quantitative impacts on ecosystems and water quality in the Great Barrier Reef’Species-specific proton and oxygen flux in Hawaiian corals under ocean acidification—a microsensor analysis of the concentration boundary layer
Published 30 May 2025 Uncategorized ClosedTags: biological response, corals, laboratory, North Pacific, physiology
Coral reefs are essential for the foundation of marine ecosystems. However, ocean acidification (OA) driven by rising atmospheric carbon dioxide (CO₂) threatens coral growth and biological homeostasis. In this study, we examined the microenvironmental fluxes of two Hawaiian coral species—Montipora capitata and Pocillopora acuta to elevated pCO₂, focusing on proton (H⁺) and oxygen (O₂) flux within the concentration boundary layer (CBL) at the zone of primary calcification (ZPC). Utilizing pH and O2 microsensors under controlled light and dark conditions, we characterized species-specific CBL traits and quantified material fluxes. Our results revealed that while both species maintained a positive net proton flux, P. acuta showed a pronounced reduction in dark proton efflux (-188%) and a significant increase in light O₂ flux (+ 175%), suggesting impaired metabolic and calcification dynamics. In contrast, M. capitata showed minimal changes in both flux parameters under similar OA conditions. Statistical analyses using linear models showed several significant interactions between species, treatment, and light conditions, identifying physical, chemical, and biological drivers for species responses to OA. We also present a conceptual model correlating external measures with internal physiologies to explain our findings. We indicate that OA exacerbates microchemical gradients in the CBL and potentially acts to reduce calcification in vulnerable species like P. acuta while highlighting the resistance of M. capitata. This study advances our understanding of how species-specific microenvironmental processes could influence coral responses to changing ocean chemistry.
Continue reading ‘Species-specific proton and oxygen flux in Hawaiian corals under ocean acidification—a microsensor analysis of the concentration boundary layer’Fatty acid response of calcifying benthic Antarctic species to ocean acidification and warming
Published 22 May 2025 Science ClosedTags: Antarctic, biological response, corals, laboratory, mollusks, multiple factors, physiology, temperature
Highlights
- None of the species showed changes in the immune function in response to OA or OW.
- FA associated with cell membrane fluidity wasn’t affected in both species.
- 20:5n-3 and 20:1n-9 FA were negatively impacted in A. eightsii under OW.
- Both species appear capable of maintaining stable FA levels in these conditions.
Abstract
Ocean acidification (OA) and ocean warming (OW) are likely to alter the biochemical composition of certain organisms as a physiological response to these changing environmental conditions. Given the importance of fatty acids (FA) in energy transfer within marine food webs, this two-month laboratory study examines the response of two calcifying species from Potter Cove (Antarctica) – the bivalve Aequiyoldia eightsii and the coral Malacobelemnon daytoni – to predicted OA and OW, focusing on their FA profiles. Neither species showed significant changes compared to the control group in the composition of FA ratios associated with immune function and cell membrane fluidity in response to either OA or OW. Additionally, the FA composition related to inflammatory responses remained largely unaffected by the stressors, although the 20:5n-3 FA was negatively impacted in A. eightsii under high-temperature conditions. Overall, the FA composition in these species appears robust to near-future environmental changes.
Continue reading ‘Fatty acid response of calcifying benthic Antarctic species to ocean acidification and warming’Positive interactions in a warmer and more acidic ocean: crustose coralline algae holobionts enhance gorgonian larval settlement under climate change
Published 21 May 2025 Science ClosedTags: algae, biological response, BRcommunity, corals, laboratory, Mediterranean, molecular biology, multiple factors, physiology, prokaryotes, reproduction, temperature
Background: The increasing frequency of marine heatwaves is leading to mass mortality of gorgonians in the Mediterranean Sea, threatening some populations with local extinction. A better understanding of the dynamics of gorgonians’ early life stages under climate change is urgent to ensure their conservation. Crustose coralline algae (CCAs) and their associated bacteria are known to induce the larval settlement of several coral species through the production of chemical cues. The larvae of the white gorgonian Eunicella singularis have been observed to preferentially settle and metamorphose on CCAs. Here, we investigated this positive interaction, and explored how it might be altered by climate change. Specifically, we tested the capacity of two Mediterranean CCA holobionts, Macroblastum dendrospermum and Lithophyllum stictiforme, to foster E. singularis larval settlement after exposure to SSP5-8.5 projected conditions for 2100 (warming and acidification), combined or not with a simulated marine heatwave event.
Results: Our results showed a threefold increase of larval settlement in presence of the CCAs previously exposed to acidification and warming treatments. After these treatments, both CCAs hosted a consistently high abundance of bacteria belonging to the Pirellulaceae family, and exhibited a higher abundance of monosaccharides in their exudates. We hypothesize that the enhanced larval settlement was driven by the bacterial breakdown and utilization of CCA polysaccharides, in combination with their release through the CCA cell walls. This release may have been enhanced by a decalcification process induced by climate change conditions. Furthermore, we showed that CCAs act as sources of bacterial taxa that can establish and persist in adult E. singularis holobiont, independently of climate change effects.
Conclusions: Our results highlight that CCA-larvae interaction is critical for E. singularis recruitment success, especially under future climatic conditions, and influences the development of its microbiome. This research underscores the importance of studying positive interspecific interactions across biological levels (from microorganisms to macroorganisms) under climate change scenarios, and provides valuable insights that inform the conservation and restoration of the Mediterranean white gorgonian.
Continue reading ‘Positive interactions in a warmer and more acidic ocean: crustose coralline algae holobionts enhance gorgonian larval settlement under climate change’
