Ocean acidification can reduce coral growth, alter coral-macroalgae interactions, and weaken reef resilience. This study develops a delayed coral-macroalgae-acidification-pressure model describing live coral cover, fleshy macroalgal cover, and a dimensionless effective acidification-pressure index. The model incorporates coral-macroalgae overgrowth, external stress input, natural relaxation, macroalgal-associated attenuation, coral-associated feedback, and a delayed coral response to acidification pressure. We establish positivity and boundedness of solutions, determine biologically feasible equilibria, derive local stability conditions, and analyze the effect of delay on the coexistence state. The analysis identifies a critical delay at which the stable coexistence equilibrium loses stability through a Hopf bifurcation. For the baseline parameter set, the bifurcation is supercritical and generates a local branch of orbitally asymptotically stable periodic orbits. Numerical simulations, sensitivity analysis, and robustness tests support the analytical findings and show how coral stress sensitivity, external forcing, and reef-scale feedbacks influence stability thresholds and coral persistence. These results provide a mechanistic framework for examining how delayed ecological responses to acidification may promote oscillatory reef dynamics.
Continue reading ‘Delay-induced Hopf bifurcation in a coral-macroalgae system under carbon-driven acidification stress’Posts Tagged 'community composition'
Delay-induced Hopf bifurcation in a coral-macroalgae system under carbon-driven acidification stress
Published 6 November 2026 Science Leave a CommentTags: algae, biological response, BRcommunity, community composition, communitymodeling, corals, growth, modeling, mortality
Multiscale pH fluctuations on a stable algal reef community (SE Sardinia, Tyrrhenian Sea)
Published 5 November 2026 Science Leave a CommentTags: abundance, algae, biogeochemistry, biological response, bryozoa, chemistry, cnidaria, community composition, corals, field, Mediterranean, otherprocess, porifera
Highlights
- Mean Tyrrhenian surface pH is 8.33, but drops to 8.07 at Capo Carbonara coralligenous.
- High-frequency pH fluctuations are twice the open-sea mean multidecadal pH decrease.
- Intrusion of Atlantic water and Saharan dust outbreaks affect local pH variability.
- Coralligenous assemblage had long-lived, stable components and seasonal turf development.
- Future shifting boundaries of variability by OA may impair Coralligenous tolerance.
Abstract
The Mediterranean Sea is threatened by ocean acidification and warming, in combination with habitat loss, pollution, invasive species, and overexploitation. Assessing local high-frequency pH variability in the context of relevant basin-scale time series data is essential to understand ecosystem vulnerability. We report the results of the Italian national pH monitoring based on the Marine Strategy Framework Directive, and the pH dynamics observed at Capo Carbonara. An experimental station equipped with a pH sensor and CTD probe was deployed at 32 m depth on a sandy bottom bordered by Coralligenous assemblages. Physical and biogeochemical variables were continuously recorded over 345 days and analyzed through additive time series decomposition. The benthic assemblages were surveyed by photographic and destructive sampling in summer and autumn 2016 and spring 2017 on algal reef and sandy bottom, to describe the biological components undergoing and contributing to the pH fluctuations. Seasonal pH variability ranged up to 0.2 units annually and 0.1 units daily, with maxima in January and minima in August, while the range of pH on the basin scale had higher mean values and exceeded local variability. Assemblage changes were driven by algal turf development and the invasive Caulerpa cylindracea. Coralligenous taxa appear stable, despite the substantial natural pH variability, shaped by meteo-marine conditions, water mass circulation, Saharan dust inputs, and benthic biological processes, with primary producers and calcifiers exerting a key influence. The ongoing trend of increasing temperatures and decreasing pH may threaten the Coralligenous ability to cope with the shifting future boundaries of such variability.
Continue reading ‘Multiscale pH fluctuations on a stable algal reef community (SE Sardinia, Tyrrhenian Sea)’Oxidative stress as a potential mechanistic link between climate change and aquatic biodiversity loss
Published 4 November 2026 Science Leave a CommentTags: abundance, adaptation, algae, biological response, calcification, community composition, corals, echinoderms, fish, light, mollusks, mortality, multiple factors, nutrients, otherprocess, oxygen, performance, photosynthesis, physiology, phytoplankton, plastics, protists, reproduction, review, temperature, zooplankton
Climate change is rapidly altering aquatic ecosystems through rising temperatures, ocean acidification, hypoxia, ultraviolet radiation, salinity fluctuations, and interacting environmental stressors. These changes impose substantial physiological challenges on aquatic organisms, with oxidative stress representing an important mechanistic pathway linking environmental disturbances to biological responses across multiple levels of organization. This review synthesizes current evidence on oxidative stress responses associated with climate change-related environmental stressors across aquatic taxa, including fish, aquatic invertebrates, corals, phytoplankton, macroalgae, amphibians, and polar and deep-sea organisms. We examine the mechanisms underlying reactive oxygen species production, disruption of antioxidant defenses, and oxidative damage, while critically evaluating biochemical, molecular, and omics-based biomarkers for environmental stress assessment. Particular emphasis is placed on how oxidative stress may translate from cellular and organismal responses into changes in growth, reproduction, behavior, survival, species distributions, population dynamics, community structure, biodiversity, and ecosystem resilience. We also highlight limitations of current biomarker approaches, including species-specific variability, methodological inconsistencies, and difficulties in extrapolating laboratory findings to natural ecosystems. Future research should prioritize integrated multi-biomarker and multi-stressor approaches, long-term ecological monitoring, standardized protocols, and the integration of omics, environmental DNA, remote sensing, and artificial intelligence. Overall, oxidative stress biomarkers provide complementary tools for assessing climate-change impacts on aquatic biodiversity and ecosystem resilience.
Continue reading ‘Oxidative stress as a potential mechanistic link between climate change and aquatic biodiversity loss’Anthropogenic CO2-induced seawater acidification suppressed dimethylsulfide emissions in the northwestern Pacific marginal seas
Published 4 November 2026 Science Leave a CommentTags: biogeochemistry, biological response, community composition, field, North Pacific, phytoplankton, prokaryotes
Marine dimethylsulfide (DMS) emissions exert a pivotal control on climate regulation via aerosol formation. Nevertheless, the biogeochemical cycle of DMS under seawater acidification remains poorly understood. Here we present integrated biogeochemical analyses that combine field observations, historical datasets, process-based modeling, and ship-based incubation experiments to elucidate pH-dependent regulatory mechanisms governing the cycling of DMS and its precursor dimethylsulfoniopropionate (DMSP) across the northwestern Pacific marginal seas. Our findings identify pH as the key driver of DMS spatial variability; moreover, DMS removal processes are highly sensitive to pH. Structural equation modeling reveals pH-driven cascading impacts on DMS mediated by dinoflagellate biomass. Incubation experiments further demonstrate that decreasing pH reduces high DMSP-producer abundance and suppresses both DMS biological production and removal rates, collectively inhibiting net DMS accumulation. These findings indicate that seawater acidification under the high-emission SSP5-8.5 scenario will reduce global marginal seas DMS emissions by 35%–66% by 2100, which may intensity regional and global warming. Our research provides new insights into the feedback mechanisms linking marine sulfur biogeochemical cycles and global climate change.
Continue reading ‘Anthropogenic CO2-induced seawater acidification suppressed dimethylsulfide emissions in the northwestern Pacific marginal seas’Long-term stress induced by low bicarbonate alkalinity causes intestinal oxidative stress, gut microbiota imbalance and metabolic disorder in Scylla paramamosain
Published 3 November 2026 Science Leave a CommentTags: abundance, biological response, community composition, crustaceans, fisheries, molecular biology, morphology, mortality, North Pacific, otherprocess, physiology, prokaryotes
Highlights
- Low bicarbonate induces acid-base imbalance and oxidative stress
- Opportunistic pathogen Klebsiella is a potential biomarker of the LB group.
- Low bicarbonate affects chitin synthesis and gut barrier.
- Low bicarbonate affects NDAA and gut microbiota.
Abstract
To investigate the effects of low bicarbonate alkalinity on intestinal health of Scylla paramamosain, we systematically evaluated the growth survival, intestinal antioxidant enzyme activities, and expression profiles of genes involved in immunity, inflammation, apoptosis and osmoregulation under low alkalinity conditions. Meanwhile, integrated intestinal microbiome and metabolome analyses were performed. The results showed that low bicarbonate alkalinity significantly reduced the survival and molting rates of S. paramamosain. It markedly elevated the activities of intestinal SOD, CAT and GSH-Px, as well as the expression levels of inflammation-related genes (IL-16, RELISH, LITAF), apoptosis-related genes (CASPASE7, BAX, BCL2) and osmoregulation-related genes (NKA, NHE, Cl−/HCO₃−), while suppressing the expression of immune genes (proPO, ALF1, LZM) (P<0.05). Low bicarbonate alkalinity disrupted the intestinal microbiota structure of S. paramamosain, accompanied by a decreased abundance of the phylum Bacteroidota and a significant increase in the abundance of the genus Klebsiella (P<0.05). A total of 714 differential metabolites were identified by metabolomic analysis, which were mainly annotated into Fatty Acyls, Glycerophospholipids, and Steroids and steroid derivatives. Multiple carbohydrate metabolism pathways were significantly enriched and participated in the regulation of Fructose 6-Phosphate (F6P). Integrated microbiome-metabolome analysis revealed that N,N-dimethyl arachidonoyl amine (NDAA) may cooperate with intestinal microorganisms to regulate the stress tolerance of S. paramamosain under low bicarbonate alkalinity stress. Based on the physiological and biochemical characterization of the intestine, this study elucidated the adaptive characteristics of S. paramamosain under low bicarbonate alkalinity. The findings provide important theoretical basis and practical significance for the saline-alkaline aquaculture of S. paramamosain.
Continue reading ‘Long-term stress induced by low bicarbonate alkalinity causes intestinal oxidative stress, gut microbiota imbalance and metabolic disorder in Scylla paramamosain’Current knowledge of marine crustaceans in Mauritius and their global importance in a changing climate
Published 30 October 2026 Science Leave a CommentTags: abundance, biological response, community composition, crustaceans, fisheries, otherprocess, performance, physiology, reproduction, review
Marine crustaceans are ecologically and socio-economically important components of coastal and marine ecosystems; however, in Mauritius, knowledge of their biodiversity, functional roles, and responses to climate change remains limited and fragmented. This narrative review synthesizes available information on Mauritian marine crustaceans, with particular emphasis on the class Malacostraca, while identifying key knowledge gaps and research priorities relevant to their ecological importance and climate-change vulnerability at both local and global scales. Although existing records document 61 crustacean families in Mauritius, these data are sparse, outdated, and largely based on historical surveys, highlighting the urgent need for updated inventories and long-term monitoring. Globally, marine crustaceans act as trophic intermediaries, ecosystem engineers, and scavengers, contributing to nutrient cycling, sediment dynamics, and habitat stability. They support fisheries, aquaculture, tourism, and cultural practices, and provide valuable bioresources such as chitin, chitosan, and other bioactive compounds with applications in regeneratiom engineering, medicine, agriculture, environmental remediation, and biotechnology. Trade patterns further emphasize their economic importance, revealing export-oriented dynamics in Mauritius, instead of local consumption, that result in a net reliance on imports. Climate change poses an escalating threat through ocean warming, acidification, and increasing environmental variability, affecting DNA repair, protein synthesis, haemolymph, metabolic performance, calcification, reproduction, immunity, behavior, and species interactions. These stressors are further compounded by habitat degradation, altered symbiotic interactions and food-web disruption. The scarcity of empirical studies from Mauritius underscores the need for integrative, multi-stressor, and long-term research to support effective conservation, fisheries management, and climate resilience.
Continue reading ‘Current knowledge of marine crustaceans in Mauritius and their global importance in a changing climate’Monsoon-linked gut microbiome variation in a tropical sea urchin: a single-reef case study from the Arabian Sea
Published 29 October 2026 Science Leave a CommentTags: biogeochemistry, biological response, community composition, echinoderms, field, Indian, molecular biology, otherprocess, physiology, prokaryotes
Highlights
- Stomopneustes variolaris gut microbiota shows clear seasonal structuring in response to monsoon-driven biogeochemical variability.
- The gut microbiota of Stomopneustes variolaris is dominated by Bacteroidota, and most diverse during winter and spring inter-monsoon.
- Gut microbial composition covaries with seasonal oxygen, pH, temperature, and nutrient gradients.
- The sea urchin gut microbiome shows seasonal plasticity under monsoon-linked stress.
Abstract
Tropical coastal ecosystems of the Eastern Arabian Sea (EAS) experience pronounced monsoon-driven shifts in water-column biogeochemistry, yet their influence on the gut-associated microbiomes of benthic invertebrates remains poorly understood. Sea urchins are ecologically important grazers in reef-associated habitats, and their gut microbiota may reflect both environmental and dietary variability. Here, we provide an exploratory characterisation of the gut-associated microbiome of the sea urchin Stomopneustes variolaris from the Grande Island archipelago (Goa, India) across four monsoon-associated periods: Winter monsoon (WM), Spring-inter monsoon (SIM), Summer monsoon (SM), and Fall-inter monsoon (FIM). Using 16S rRNA gene sequencing, we analysed gut tissue and gut digesta from S. variolaris alongside environmental samples (seawater, sediment, and seaweed). Bacteroidota dominated the urchin gut microbiome, whereas Proteobacteria were more abundant in environmental samples. Gut microbial diversity was highest in WM and SIM and lowest during SM and FIM. Exploratory analyses indicated that gut microbial composition varied temporally, with taxa affiliated with sulphur-cycling lineages more prevalent during sampling points associated with low-oxygen monsoon phases (SM and FIM) and Firmicutes and organic matter-associated taxa more prominent during comparatively oxygenated periods (WM and SIM). Ordination analyses suggested an association between gut and environmental microbial assemblages and gradients in dissolved oxygen, temperature, pH, nutrients, and pCO2. This study provides baseline insights into the gut microbiome of a tropical echinoid from an understudied region and highlights monsoon-associated patterns in microbial community composition, forming a foundation for future functional and experimental investigations.
Graphical abstract
Unlocking spatial ecological assessment for tropical seagrass habitats using a new rapid assessment method (SEARAM)
Published 29 October 2026 Science Leave a CommentTags: biological response, community composition, field, Indian, methods, otherprocess, phanerogams
Highlights
- Rapid and standardized assessment of tropical seagrass ecological state.
- Multimetric index combining structure and vitality indicators.
- Spatial mapping of seagrass fragmentation and degradation.
- Links between habitat condition, environment, and megafauna.
- A practical tool for coastal monitoring and impact mitigation.
Abstract
Seagrass meadows are key coastal ecosystems supporting biodiversity, carbon storage, and essential trophic functions, yet they are increasingly threatened by anthropogenic and climatic pressures. Based on the Seagrass Meadows Rapid Assessment Method (SEARAM), a standardized protocol grounded in seagrass biodiversity indicators (SBIs), we developed a reliable and operational index to assess seagrass ecological state at high spatial resolution. Using 536 circular plots and 144 faunal stations across three intertidal reef habitats in Mayotte (Western Indian Ocean), SEARAM integrates structural and vitality sub-indices into a composite seagrass ecological state index (SESI), spatialized by geostatistical interpolation and analyzed using ANOVA, PCA, and multiple regression models. Results revealed highly fragmented meadows dominated by Halodule uninervis and Halophila ovalis, with low canopy height (5 ± 2 cm) and substantial epiphyte loads (37 ± 17%). The inner fringing reef flat showed the poorest ecological state (SESI = 4.8 ± 0.7/10), whereas the barrier reef (5.4 ± 0.8/10) and exposed fringing reef flat (5.6 ± 0.8/10) exhibited moderate scores. Key environmental drivers (turbidity, grain size, pH), significantly explained spatial patterns of seagrass structure and vitality, confirming the influence of sediment and light regimes. Functional relationships were also demonstrated between seagrass condition and associated fauna, particularly green turtle density and dugong feeding traces. SEARAM proved to be a rapid and robust tool for diagnosing tropical seagrass states. Its multimetric framework connects benthic condition to habitat suitability for megafauna, offering an operational foundation for ecological monitoring, management, and impact mitigation within the Avoid–Reduce–Offset (ARO) doctrine.
Graphical abstract
Coastal benthic ecosystems in a changing ocean: a mini review
Published 29 October 2026 Science Leave a CommentTags: biogeochemistry, biological response, BRcommunity, community composition, corals, otherprocess, review
Coastal benthic ecosystems are shaped by the combined effects of climate change and anthropogenic pressures. Ocean warming, acidification, and deoxygenation interact with eutrophication, pollution, bottom trawling, and coastal development, altering biodiversity, habitat structure, and functioning from shallow coasts to continental margins. Benthic communities, comprising infaunal and epifaunal taxa, regulate key processes including nutrient cycling, sediment dynamics, and carbon burial, thereby underpinning benthic-pelagic coupling and biogeochemical dynamics. Rising temperatures and marine heatwaves drive widespread losses of habitat-forming species, while ocean acidification constrains calcification. Warming, acidification, hypoxia, eutrophication, and pollution increasingly simplify assemblages, and alter trophic pathways and performance. Interactions among stressors can amplify organismal sensitivity and push ecosystems towards ecological thresholds. However, many knowledge gaps remain. Recent methodological advances, including environmental DNA metabarcoding, automated imaging, trait-based analyses, and multi-stressor experiments, are improving the detection of ecosystem changes at large and our mechanistic understanding of ecosystem responses to ongoing change. By summarizing the various stressors that benthic habitats and taxa face, their interactions and potential outlooks, this review provides a concise synthesis of current understanding and identifies key knowledge gaps for future research and management under accelerating climate change.
Continue reading ‘Coastal benthic ecosystems in a changing ocean: a mini review’Surviving together: evolutionary dependency, community dynamics, and mortality in marine microbial communities
Published 26 October 2026 Science Leave a CommentTags: abundance, adaptation, biological response, community composition, growth, laboratory, light, molecular biology, mortality, multiple factors, nutrients, otherprocess, photosynthesis, physiology, phytoplankton, primary production, prokaryotes, reproduction, respiration, temperature
Oligotrophic regions of the world ocean sustain vast phytoplankton populations despite extremely low nutrient levels. However, the mechanisms governing their coexistence, interdependence, and mortality are poorly understood. This dissertation investigates how evolutionary dependency, community feedback, and regulated cell death (RCD) jointly shape the stability of marine microbial communities using the Prochlorococcus/Parasynechococcus/Alteromonas model system.
In Chapter 1, I argue that the Black Queen (BQ) hypothesis—which posits that microbes lose costly metabolic functions supplied by community partners—provides a unifying framework for understanding phytoplankton ecology. This framework helps resolve longstanding puzzles, including the paradox of the plankton and the evolutionary maintenance of RCD in unicellular organisms. Building on this framework, Chapter 2 uses transcriptomic analysis of Alteromonas in co-culture with picocyanobacteria to demonstrate that community composition induces greater changes in gene expression than pCO₂ alone. Reduced 2-phosphoglycolate/glycolate exudation by Prochlorococcus under elevated pCO₂ may disrupt the helper heterotroph effect underlying this cyanobacterium’s BQ dependency.
Chapter 3 integrates co-culture experiments, RNA-seq, metabolomics, and mathematical modeling to demonstrate that the stable coexistence of Prochlorococcus and Parasynechococcus is maintained by an “Ouroboros network” of feedback loops. In this network, resource competition, carbon exudation, BQ dependency, and possibly RCD collectively stabilize the community across environmental gradients and during adaptation to changing conditions.
Chapter 4 resolves the cellular mechanisms underlying RCD in these cyanobacteria, showing that differences in cell death modes and the number of checkpoint-linked mortality events between taxa are associated with divergent life-history strategies. These findings suggest that carbon released at these checkpoints may shape interactions with helper Alteromonas, linking individual cell death to community-level interdependencies.
In conclusion, these findings converge on a new resolution to the paradox of the plankton: coexistence in resource-limited environments emerges from interdependent metabolic exchanges, feedback, and regulated cell death shaped by multilevel selection. I propose that together, these processes form an “altruistic bargain” in which stability arises from self-constraint rather than competition alone. Because these interactions are environmentally sensitive, climate change, including warming and acidification, may disrupt the dependencies that sustain microbial diversity and ecosystem function in the world ocean.
Continue reading ‘Surviving together: evolutionary dependency, community dynamics, and mortality in marine microbial communities’Long-term coral responses to high CO2: insights from volcanic vents and semi-enclosed bays
Published 20 October 2026 Science ClosedTags: abundance, adaptation, biological response, community composition, corals, mortality, multiple factors, North Pacific, otherprocess, oxygen, physiology, South Pacific, temperature, vents
This chapter provides a comprehensive review of natural laboratories used to study the effects of ocean acidification (OA) on coral reefs, emphasizing volcanic CO2 vents and semi-enclosed bays. It examines key environmental conditions at these study sites and their implications for coral physiology, biodiversity, and reef resilience. Two prominent natural analogues are highlighted: the Shikine Island warm-temperate shallow CO2 vent system in Japan and the semi-enclosed lagoon of Bouraké in New Caledonia.
Shikine Island represents a unique high-latitude coral environment influenced by the Kuroshio Current. The island’s CO2 vents provide a natural setting to investigate the community level effects of ocean acidification and how elevated CO2 levels interact with ocean warming and influence coral tropicalization. Findings suggest that while some corals persist at high CO2 levels, biodiversity declines significantly, with sensitive species unable to establish stable populations. Corals growing in these conditions exhibit reduced calcification, and the community structure shifts toward simpler, lower-complexity ecosystems dominated by turf algae. These results indicate that ocean acidification may act as a constraint on the poleward expansion of tropical corals, counteracting warming-induced range shifts.
In contrast, the semi-enclosed lagoon of Bouraké experiences extreme environmental fluctuations in pH, oxygen, and temperature, providing a window into the multifactorial stressors coral reefs may face in the future. Despite prolonged exposure to acidified, hypoxic, and thermally variable waters, corals in Bouraké demonstrate remarkable resilience. The system harbors diverse coral assemblages, with species exhibiting metabolic adjustments, increased heterotrophy, and shifts in symbiotic algae communities. This site suggests that coral ecosystems can develop physiological adaptations that enhance their survival in extreme conditions, offering valuable insights into the potential for long-term acclimatization.
By comparing these two contrasting natural analogues, this chapter highlights the complex interplay between acidification, warming, and other environmental stressors on coral reefs. While both sites provide critical insights into the future of coral ecosystems, they also underscore the urgent need for continued research and conservation efforts to mitigate the effects of climate change on marine biodiversity.
Continue reading ‘Long-term coral responses to high CO2: insights from volcanic vents and semi-enclosed bays’Environmental regulation of interspecific interactions among macrobenthic seaweeds and its implications for community phase transition
Published 15 October 2026 Science ClosedTags: algae, community composition, otherprocess, review
Macrobenthic seaweeds are key species in temperate and boreal nearshore rocky ecosystems, and their interspecific interactions profoundly affect the species composition, spatial distribution and dynamic succession of the community. This paper systematically reviews the mechanisms of interspecific competition and facilitative effects among macrobenthic seaweeds. We also examine their environmental regulation and impacts on community phase transitions. Competition mainly centers on three major resources: light, space and nutrients. It manifests as an asymmetric hierarchical structure, in which canopy-forming species exert a disproportionate repressive effect on lower algal layers through light competition. Facilitative effects are realized through several mechanisms. These include canopy shading to mitigate heat stress and water loss, physical structure building to create complex habitats, and nutrient retention with chemical microenvironment regulation. Moreover, the relative strengths of facilitation and competition shift systematically across environmental stress gradients. Multi-trophic level regulation further shapes community diversity maintenance mechanisms through the suppression of dominant species by vegetative predators and the cascading effect of top predators on vegetative predators. In the context of global change, physiological asymmetries driven by oceanic heat waves are tilting the competitive balance in favor of opportunistic turf algae. These algae form a lock-in state through the triple positive feedbacks: physical barriers, biogeochemical deterioration, and chemosensory exclusion. This significantly decreases the resilience of algal field recovery. Tropical coral-macroalgae phase transition is highly consistent with the degradation of temperate algal fields in terms of driving logic. They follow the law of coupling resource competition imbalance, downward regulatory relaxation, and positive feedback lock-up. This paper suggests several priorities for future research. Studies should focus on the nonlinear response of multifactor interaction, the quantitative correlation between key functional traits and community resilience, and the establishment of a cross-ecosystem comparison framework. These efforts will provide theoretical support for predicting and adaptively managing offshore ecosystems under global change.
Continue reading ‘Environmental regulation of interspecific interactions among macrobenthic seaweeds and its implications for community phase transition’Ocean acidification drives grazer niche convergence and trophic homogenization in benthic communities
Published 22 September 2026 Science ClosedTags: algae, annelids, biological response, BRcommunity, community composition, crustaceans, echinoderms, field, North Atlantic, otherprocess, performance, porifera, vents
Highlights
- Acidification compresses benthic community isotopic space via carbon homogenization.
- Functional groups show differential isotopic responses consistent with bottom-up trophic reorganization.
- Arbacia lixula shifts from a sponge-dominated diet to herbivory under low pH.
- Paracentrotus lividus maintains stable trophic niche despite acidification.
- Asymmetric grazer responses drive site-specific increases in isotopic niche overlap under acidification.
Abstract
Ocean acidification is expected to alter marine food webs, yet community-level evidence from long-term, naturally acidified systems remains limited. We used stable isotope ratios (δ13C and δ15N) to investigate how natural acidification restructures benthic trophic interactions, from basal resources to consumer niche dynamics, a naturally acidified system (pH gradient: 8.1 to ~7.4; pHT scale) spanning present-day to end-of-century projected conditions (SSP2–4.5 to SSP5–8.5). After accounting for local differences in the isotopic baseline, we found that: (1) community isotopic space contracted under acidification, with the carbon range decreasing as primary producers converged toward 13C-depleted values, while the nitrogen range expanded, indicating species-specific trophic adjustments; (2) functional groups responded asymmetrically, with primary producers showing the strongest δ13C shifts, filter-feeders remaining relatively stable, and omnivorous consumers showing reduced δ13C and δ15N values; (3) the two dominant sea urchin grazers responded in opposite directions — the macrophyte-based omnivore Paracentrotus lividus maintained stable isotopic values across the pH gradient, whereas the invertebrate-based omnivore Arbacia lixula exhibited pronounced isotopic shifts — resulting in markedly increased, though site-dependent, niche overlap at the most acidified sites (up to 27%); (4) Bayesian mixing models revealed that this convergence was driven by dietary shifts in A. lixula, which transitioned from a predominantly invertebrate-based diet (70–79% animal prey) toward algal-based feeding under acidification (19–24% animal prey), while P. lividus maintained relatively consistent dietary composition (50–70% algae). Together, these results indicate that acidification-driven homogenization of primary producers, combined with asymmetric consumer responses, compresses trophic niche space, with broad implications for the resilience and functioning of benthic ecosystems under future ocean change.
Graphical abstract
Along a natural CO2 gradient in the Canary Islands (pH 8.1–7.4, pHT scale; spanning present-day to end-of-century projected conditions, SSP2-4.5–SSP5-8.5), ocean acidification compresses community isotopic space through homogenization of primary producers. The two dominant sea urchin grazers respond asymmetrically: Paracentrotus lividus maintains a stable trophic niche, while Arbacia lixula shifts toward algal-based feeding, increasing niche overlap up to 27% at the most acidified sites.
Physiological responses of coralline algae to climate change
Published 18 September 2026 Science ClosedTags: adaptation, algae, biological response, calcification, community composition, field, laboratory, molecular biology, morphology, mortality, multiple factors, North Pacific, otherprocess, photosynthesis, reproduction, South Pacific, temperature, vents
Ocean acidification and ocean warming are among the most pressing threats to marine ecosystems, with significant implications for calcifying organisms such as crustose coralline algae (CCA). These habitat-forming species play critical ecological roles in reef systems, yet they are particularly vulnerable to ocean acidification and ocean warming. While laboratory studies have documented declines in coralline algal growth and calcification under elevated CO₂ and temperature, less is known about their responses in natural settings where environmental variability and potential acclimatization may modulate stress impacts. Furthermore, the interactive effects of multiple stressors across generations remain poorly understood, limiting our ability to predict ecosystem-level consequences of climate change. This thesis explores the physiological responses of coralline algae to ocean acidification, ocean warming, and marine heatwaves through complementary field and laboratory approaches. Using natural climate analogues, I investigated how CCA communities respond to chronic exposure to low pH and elevated temperatures in situ (Chapters 2 and 3). These natural systems provide unique opportunities to assess long-term acclimatization and identify potentially resilient populations. To disentangle the mechanisms underlying stress responses and examine multi-generational effects, I conducted a multigenerational, multi-stressor laboratory experiment exposing coralline algae to factorial combinations of elevated pCO₂ and temperature over successive generations (Chapter 4). Together, these approaches enabled assessment of single-driver impacts, stressor interactions, and the capacity for phenotypic plasticity and acclimatization under both fluctuating natural conditions and controlled experimental regimes. Results from natural analogues revealed species-specific variation in stress tolerance, with some CCA populations maintaining growth and calcification despite chronic exposure to conditions projected for year 2100. The laboratory experiment revealed that growth significantly declined when exposed to ocean acidification and the combined effect of ocean acidification and ocean warming over multiple generations. This research advances our understanding of how marine calcifiers respond to climate change across ecological and temporal scales. The findings have important implications for predicting ecosystem trajectories and identifying potential climate refugia in an increasingly acidic and warming ocean.
Continue reading ‘Physiological responses of coralline algae to climate change’Comparative responses of coastal Arabian sea plankton to different ocean acidification simulation methods
Published 16 September 2026 Science ClosedTags: abundance, biological response, BRcommunity, community composition, Indian, laboratory, otherprocess, phytoplankton, prokaryotes, zooplankton
Ocean acidification (OA) is expected to alter marine phytoplankton communities by modifying seawater carbonate chemistry, with important implications for marine food webs and biogeochemical cycling. In this study, we tested the hypothesis that comparable pH reductions achieved through different acidification methods generate distinct carbonate chemistry conditions and consequently different biological responses. A 5-day microcosm experiment was conducted using natural phytoplankton assemblages collected from the coastal Eastern Arabian Sea. OA was simulated by HCl addition (acid), CO2 enrichment (CO2), and acid–base manipulation. Changes in carbonate chemistry, nutrients, phytoplankton community composition, pigments, bacteria, microzooplankton, and organic carbon pools were monitored. As expected, the three manipulation methods produced significantly different carbonate chemistry conditions despite comparable pH reductions. Repeated-measures ANOVA and Tukey’s post hoc analyses confirmed significant treatment effects for pH, pCO2, DIC, HCO3−, CO32−, and total alkalinity. By Day 5, CO2 enrichment significantly increased total phytoplankton abundance and promoted microplankton dominance, driven by bloom-like proliferation of Thalassiosira sp., whereas picoplankton declined significantly. Conversely, pennate diatoms, cyanobacteria, dinoflagellates, and coccolithophores exhibited weak or negative responses. Concurrent changes in phosphate, nitrite, autotrophic bacteria, and microzooplankton indicated that nutrient availability, microbial recycling, and grazing interacted with carbonate chemistry to regulate phytoplankton succession. Our findings demonstrate that phytoplankton responses in the oligotrophic Eastern Arabian Sea are governed by the combined effects of carbonate chemistry, nutrient dynamics, and ecological interactions rather than pH alone.
Continue reading ‘Comparative responses of coastal Arabian sea plankton to different ocean acidification simulation methods’Long term monitoring of coral reef fish populations under increasing ocean temperature and acidification stress
Published 11 September 2026 Science ClosedTags: biological response, BRcommunity, community composition, corals, fish, otherprocess
Coral reefs are especially sensitive to ocean warming and acidification caused by climate change and can have a major impact on reef-associated fish species and reef stability. This study analyzes the diversity of coral reef fishes over time using data from the National Coral Reef Monitoring Program (NCRMP) of NOAA from the year 2014 to 2024 from the Hawaiian Archipelago. The impacts of environmental factors such as sea surface temperature, ocean pH, and coral cover were evaluated on fish population structure. Shannon Diversity Index as the main statistical method to quantify the changes in biodiversity between monitoring years. The mean sea surface temperature (MST) ranged from 26.8°C in 2014 to 29.1°C in 2024, with a steady increase over the years, whereas the mean pH decreased from 8.12 to 7.95 over the years. During the same time frame, there was significant loss of coral cover, from 62% to 36%. The Shannon Diversity Index was then found to have decreased from 3.45 to 2.51, representing a loss of some 27.2% of biodiversity. The results indicate that the diversity of coral reef fishes is negatively correlated with environmental stress. Fish functional groups were further simplified, with habitat specialist fishes being more affected than generalist fishes under climate stress. The rising temperature and acidification of the oceans are important factors in the decline of coral reef fish. The continued monitoring and adaptive conservation strategies will be critical to ensure that reef biodiversity will persist into the future under different climate change scenarios.
Continue reading ‘Long term monitoring of coral reef fish populations under increasing ocean temperature and acidification stress’Physiology and hydrodynamics influence the susceptibility of reef-building corals to ocean acidification
Published 3 September 2026 Science ClosedTags: biological response, community composition, corals, growth, laboratory, otherprocess, physiology
Ocean acidification (OA) poses a major future threat to tropical coral reefs. This is primarily due to its effects on reef-building coral species, which vary in their susceptibility to this climate change stressor. However, the potential factors underlying the range of susceptibilities observed among reef-building corals remain poorly understood. Therefore, this doctoral thesis investigates the influence of species-specific physiology and water flow conditions on coral susceptibility to OA. Using an experimental, multi-scale approach, the present thesis addresses this knowledge gap in a total of four studies and focuses on the physiological response of three major reef-building coral genera (Acropora, Pocillopora, and Porites) to prolonged exposure of OA conditions (> three months).
The results showed that (1) variable decreases in coral growth under OA were mediated by differential changes in maintenance and cellular stress parameters. This physiological interplay was genus-specific for Acropora and Pocillopora, and was species-specific for Porites spp. Moreover, assessments of the combined effects of OA and changes in water flow conditions indicated that (2) temporarily reduced water flow may mitigate OA effects on Acropora and Porites spp. Still, simultaneous changes in seawater chemistry and flow led to changes in coral physiology with complex and species-specific patterns. Finally, at the microscale, characterisation of the effects of OA and water flow on the concentration boundary layer (CBL) at the coral surface revealed that (3) OA was an overall weak modulator of this layer, regardless of flow conditions and CBL variability among species. Despite minor OA effects, however, the results also suggested that the CBL had a limited OA-buffering capacity due to thin pH gradients across the CBL. Nonetheless, low flow potentially enhanced CBL sheltering from acidified seawater by elevating pH at the coral surface.
In summary, this thesis provides evidence that both species physiology and water flow conditions shape coral susceptibility to OA in species-specific patterns and contributes novel insights into the potential links, between colony and CBL levels, involved in shaping it. Furthermore, the findings of this thesis showcase the potential of low-flow environments as refugia for coral species under OA and highlight the importance of including reef hydrodynamics in future OA scenarios, which will require consideration of different spatial and temporal scales. Altogether, the knowledge provided here may help improve projections of coral community dynamics under future OA and inform conservation efforts.
Continue reading ‘Physiology and hydrodynamics influence the susceptibility of reef-building corals to ocean acidification’Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica
Published 28 August 2026 Science ClosedTags: biological response, community composition, corals, echinoderms, field, North Pacific, otherprocess, photosynthesis, physiology
Reef-building corals and coralline algae form the calcium carbonate frameworks that underpin tropical coral reefs, yet in some locations, coral cover has declined by ~50% in recent decades due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that may buffer stress, promote recovery, and could enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photophysiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and had higher chlorophyll-a concentrations. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin abundance, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp. Photophysiological parameters were significantly different between locations. Specifically, photosynthetic efficiency (Fv′/Fm′) was 10–45% higher, and maximum photosynthetic rate (Pmax) was 20–40% lower in corals from Papagayo than in those from Sámara. These results reveal that two locations differing in environmental regime within a relatively small geographic area also differ in coral community composition and photophysiological features. Although further research is needed to resolve whether these environmental contrasts shape the observed biological differences, the observed patterns are consistent with the hypothesis that such regimes may support reef persistence or refugia, providing a basis for future work to test this hypothesis directly.
Continue reading ‘Coral reef community structure and photophysiology differ between upwelling and non-upwelling locations on the Pacific Coast of Costa Rica’Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Published 24 August 2026 Science ClosedTags: algae, biological response, BRcommunity, community composition, otherprocess, photosynthesis, physiology, review
Calcium carbonate formation in coastal macroalgal ecosystems via multiple pathways
Highlights
- Focused on a novel inorganic carbon sequestration pathway of non-calcifying macroalgae.
- Clarified algae-bacteria synergistic driving mechanism for calcium carbonate precipitation.
- Systematically sorted out potential mineralizing microbial taxa within the phycosphere and their core metabolic pathways.
Abstract
Macroalgae are dominant primary producers that drive carbon sequestration in coastal ecosystems. Macroalgal carbon sequestration primarily refers to the long-term storage of macroalgae-derived organic carbon in the ocean. However, calcium carbonate (CaCO3) formation is frequently observed in non-calcifying macroalgal environments, suggesting the existence of an overlooked inorganic carbon process in macroalgal ecosystems. Here, we introduce multiple pathways that may drive CaCO3 formation in macroalgal ecosystems. These include the effects of macroalgal photosynthesis and carbon-concentrating mechanisms on the seawater carbonate system, the role of phycosphere interfacial properties in facilitating CaCO3 nucleation, and the macroalgae-bacteria synergy that promotes CaCO3 formation. We identified several current knowledge gaps—the unclear carbon sequestration or source effect of CaCO3 formation in macroalgal ecosystems and the stability of CaCO3 minerals in macroalgal ecosystems—that require further investigation. This review advances the understanding of macroalgal carbon cycling beyond organic pathways and emphasizes the importance of a comprehensive assessment of macroalgal carbon sequestration, including that of inorganic carbon.
Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean
Published 17 August 2026 Science ClosedTags: biological response, community composition, Indian, laboratory, otherprocess, photosynthesis, physiology, phytoplankton
Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.
Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’
