The increasing emission of carbon dioxide (CO2) is altering seawater chemistry, lowering ocean pH and threatening marine biodiversity. Predicting how marine biota will be adversely affected by ocean acidification (OA) remains a key challenge. Here, we document that functional morphological traits offer a more robust metric of calcifier sensitivity to OA than taxonomic diversity alone. Using benthic foraminifera from a Mediterranean CO2 vent system, we identify an empirically derived pH threshold beyond which community structure and function shift markedly. Applying this threshold to end-of-century projections under Shared Socioeconomic Pathway SSP5-8.5 reveals that most western Mediterranean coastal zones will exceed critical acidification levels by 2090–2100. These results highlight the susceptibility of the Mediterranean coastal ecosystems to OA under high-emission scenarios, underscoring the risk of widespread biodiversity loss and impaired ecosystem functioning. Our approach provides a trait-based framework for forecasting ecosystem responses to OA and informing adaptation strategies in climate-sensitive marine regions.
Continue reading ‘Ocean acidification pushes Mediterranean marine calcifiers toward a tipping point’Posts Tagged 'dissolution'
Ocean acidification pushes Mediterranean marine calcifiers toward a tipping point
Published 10 November 2026 Science Leave a CommentTags: biological response, community composition, dissolution, field, Mediterranean, modeling, molecular biology, morphology, otherprocess, protists, regionalmodeling, vents
Ocean acidification impairs the chiton shadow defensive response via degradation of aragonitic lenses
Published 9 November 2026 Science Leave a CommentTags: biological response, dissolution, laboratory, mollusks, morphology, North Pacific, performance, physiology
Ocean acidification (OA) has the potential to disrupt the behavior of marine organisms by altering the function of γ-aminobutyric acid type A (GABAA) receptors. In addition, OA can impair sensory performance by reducing the calcification of mineralized sensory structures. Some species of polyplacophoran mollusks (chitons) possess calcified visual organs (aragonitic lenses) that contribute to shadow defense responses triggered by sudden decreases in overhead illumination. Therefore, we hypothesized that OA affects this response by impairing GABAA-mediated signaling or lens calcification. To test this hypothesis, we exposed chitons to “control” or acidified seawater and examined their shadow defensive behavior with and without gabazine, a GABAA antagonist known to restore OA-induced GABAergic dysfunction. Although gabazine did not eliminate behavioral differences between the control and acidified groups, acidification reduced the response strength, suggesting that factors other than GABAA-mediated signaling may contribute to the observed behavioral impairment. Microscopic observations revealed clouding of aragonitic lenses under acidic conditions, suggesting reduced optical performance. Overall, our results indicate that OA-induced degradation of calcified lens structures is associated with impaired shadow defense responses and may contribute to behavioral dysfunction. To the best of our knowledge, this study provides the first evidence that acidification-induced physical and optical changes in the visual anatomy can alter behavioral performance in animals.
Continue reading ‘Ocean acidification impairs the chiton shadow defensive response via degradation of aragonitic lenses’Metabolic dynamics of an offshore coral reef in the central Red Sea: observations from autonomous sensors
Published 9 November 2026 Science Leave a CommentTags: abundance, algae, biogeochemistry, biological response, calcification, chemistry, community composition, corals, dissolution, field, methods, otherprocess, photosynthesis, physiology, porifera, primary production, Red Sea, respiration
Abstract
Coral reefs are increasingly threatened by local and global stressors. Traditional visual reef monitoring methods are time-intensive and provide only a snapshot of reef condition. Recent efforts aim to measure reef metabolism, or the balance of net community production (NCP) and net community calcification (NCC), as coral reef carbonate budgets shift globally toward declining NCC and greater NCP influence. Resolving these metabolic changes requires comprehensive, high-resolution biogeochemical measurements unattainable by traditional sampling alone. This work reports the novel multi-month deployment of a high-resolution, autonomous total alkalinity (TA) sensor alongside pH, partial pressure of CO2, and dissolved oxygen (DO) sensors at Cement Wreck, a central Red Sea offshore reef. Observations from the back reef and fore reef revealed strong diel variability and distinct reef-zone biogeochemical dynamics linked to contrasting benthic compositions. On the back reef, pH and DO were tightly coupled and closely matched a Redfield-based model (𝑅2=0.943), while the fore reef relationship was weaker (𝑅2=0.145). TA observations allowed characterization of the back reef carbonate system, with TA–DIC stoichiometry yielding a slope of 0.26, indicating NCP accounted for approximately 87% of observed carbonate system variability. Compared to global reefs, Cement Wreck exhibits high % NCP contribution. However, the observed 2023 TA–DIC slope closely matches those from Red Sea observations from 1997 to 2013, suggesting that while reefs around the world shift, Red Sea reefs like Cement Wreck represent a persistent metabolic state. Scaled-up autonomous deployments, like the one presented here, will better enable predictions of global reef health in future conditions.
Plain Language Summary
Globally, coral reefs are threatened by rising temperatures, changes in seawater chemistry, pollution, and overfishing. The health of coral reefs is traditionally monitored by reef community composition through visual analysis, however changes in surrounding seawater chemistry can provide insight into reef processes and holistically monitor reef health. Here, we deploy a newly developed total alkalinity (TA) sensor, alongside commercially available pH and oxygen sensors on a coral reef in the Red Sea. Autonomous sensors allow the collection of high-resolution data on reef seawater chemistry, including daily cycles and changes over time, with a cost per data point much lower than traditional discrete samples. Furthermore, the TA sensor allows us to evaluate the relative balance between the reef-building processes and reef-eroding processes occurring, which are important parameters when evaluating a reef’s present and future health. We found that the reef studied here was strongly influenced by organic production, and that this signal closely matched Red Sea observations from the last 25 years. This suggests that some Red Sea reefs may represent a persistent metabolic state rather than a recent shift. The Red Sea lacks high-resolution carbonate-system observations, and this deployment contributes to baseline understanding of Red Sea reef metabolism and carbonate budgets.
Continue reading ‘Metabolic dynamics of an offshore coral reef in the central Red Sea: observations from autonomous sensors’Active calcifying fluid pH upregulation facilitates resilience of the coral Tubastraea aurea to ocean acidification
Published 4 November 2026 Science Leave a CommentTags: biological response, corals, dissolution, field, morphology, North Pacific, physiology, vents
Ocean acidification poses a critical threat to marine calcifiers, yet the physiological mechanisms allowing certain species to thrive in high-CO₂ environments remain poorly understood. Kueishan Island (Taiwan) provides a unique natural laboratory to address this gap. While nearby non-vent reefs support diverse coral communities, the strongly acidified hydrothermal vent fields at Kueishan Island are dominated by the azooxanthellate coral Tubastraea aurea. Here, we tested whether this persistence is driven by regulation of the calcifying microenvironment. Using skeletal boron isotope (δ¹¹B) composition and scanning electron microscopy (SEM), we reconstructed calcifying-fluid pH (pHCF) and assessed skeletal microstructure in specimens from the vent site (HV, pH ~6.6) and a reference site (FU, pH ~8.0). Despite a ~1.4-unit difference in ambient seawater pH (pHSW), the estimated pHCF was indistinguishable between sites (HV 8.45 ± 0.02, FU 8.38 ± 0.01), resulting in a markedly larger ΔpH (pHCF − pHSW) at the vents. While SEM analysis revealed no gross dissolution at the resolution examined, vent colonies were smaller than reference counterparts, suggesting possible growth constraints under extreme conditions (exploratory given limited colony replication). These findings indicate that T. aurea maintains elevated pHCF in exceptionally low-pH seawater, highlighting a physiological capacity that could contribute to skeletal maintenance under future acidified oceans.
Continue reading ‘Active calcifying fluid pH upregulation facilitates resilience of the coral Tubastraea aurea to ocean acidification’Tolerance measured at one developmental stage mispredicts climate resilience in an animal with a complex life cycle
Published 2 November 2026 Science Leave a CommentTags: adaptation, biological response, dissolution, growth, laboratory, mollusks, morphology, mortality, North Atlantic, otherprocess, physiology, reproduction
Forecasts of whether marine species can evolve fast enough to survive climate change rely largely on single-stage tolerance assays, tacitly assuming that tolerance measured at one developmental stage reflects adaptive capacity across the organism’s life cycle. We test this assumption in a common marine bivalve (Mercenaria mercenaria) and find that it fails in sign, not degree: larval and post-metamorphic tolerance to end-century ocean acidification are strongly negatively correlated (r = −0.53, 95% CI [−0.69, −0.33]) across family-level, pedigree-conditioned and animal model estimates, with pervasive rank reversals among the top performers of each stage. A multivariate analysis of the among-family covariance matrix G shows why: under acidification, 57% of the among-family variance collapses onto a single dominant axis that loads positively on every larval trait and negatively on every post-metamorphic trait, whereas under ambient conditions the same families show no cross-stage covariance at all. Acidification therefore does not merely depress performance—it reorganizes the genetic architecture into a cross-stage conflict. Under ramping RCP 8.5 forcing this conflict geometry dictates the direction—not merely the magnitude—of adaptation: only balanced multi-stage selection preserves family diversity, whereas single-stage selection systematically erodes the opposite axis. In complex life cycles, resilience is a geometric property of ontogeny that forecasts cannot compress into a single-stage without inverting the sign of the answer.
Continue reading ‘Tolerance measured at one developmental stage mispredicts climate resilience in an animal with a complex life cycle’Global projections of coral reef sediment dissolution in the 21st century
Published 22 October 2026 Science ClosedTags: biological response, chemistry, communitymodeling, corals, dissolution, globalmodeling, modeling
Abstract
Coral reefs build carbonate frameworks, but ocean acidification threatens to reverse this role by accelerating dissolution of permeable reef sediments. We combined Earth system model projections across five emission pathways with an aragonite saturation state-dissolution relationship to project global reef sediment dissolution through 2100. Under stringent mitigation, less than 2% of reef area experiences dissolution by 2100, compared with 30% under intermediate emissions and nearly all reefs under high emissions. Cumulative calcium carbonate loss reaches 2.5 gigatonnes under the highest-emission pathway, accompanied by 0.7 gigatonnes of potential carbon dioxide uptake that is globally negligible but signals framework degradation. Model-derived aragonite saturation states exceeded in situ observations in most regions, suggesting that reef sediment dissolution may begin earlier than gridded projections indicate. The southern Central Pacific emerges as a candidate acidification refugium warranting reef-scale evaluation. Continued high emissions could shift reefs from net carbonate accretion toward widespread structural loss.
Plain Language Summary
Human carbon emissions are making the oceans more acidic, threatening not only living corals but also the carbonate sand and rubble that help build and support reef structures. Using climate model projections and reef observations, we estimated how reef sediment dissolution may change worldwide through 2100. Under high-emission scenarios, nearly all coral reefs are projected to experience sediment dissolution by the end of the century, with cumulative calcium carbonate losses reaching 2.5 billion metric tons. Although this process can absorb carbon dioxide, the amount is far too small to meaningfully slow climate change and instead reflects the physical breakdown of reef structures. The southern Central Pacific may acidify more slowly and could offer some protection, but local water chemistry and heat stress must be evaluated before the region can be considered a reliable refuge.
Continue reading ‘Global projections of coral reef sediment dissolution in the 21st century’Crustose coralline algae buffer shallow reef environments from dissolution
Published 11 August 2026 Science ClosedTags: algae, biological response, chemistry, dissolution, field
Ocean acidification threatens coral reefs by reducing seawater pH and carbonate saturation state. Crustose coralline algae are particularly vulnerable because their high-magnesium calcite skeletons dissolve more readily than coral aragonite skeletons. However, this dissolution may increase alkalinity and buffer reef-water chemistry. Here we show, using repeated low-tide observations and in situ incubations in a shallow reef system in the southern Great Barrier Reef, that reef-water pH varies by more than one unit over the day (7.47 – 8.61), reaching levels comparable to those projected for the end of this century. Nighttime respiration promotes dissolution of high-magnesium calcite produced by crustose coralline algae, increasing alkalinity and helping maintain seawater supersaturated with respect to aragonite. At the same time, isolated coral incubations experience a greater decline in pH and aragonite saturation state in the absence of this buffering effect. These findings suggest that high-magnesium calcite-producing communities may help partially buffer reefs against future acidification.
Continue reading ‘Crustose coralline algae buffer shallow reef environments from dissolution’Skeletal growth and loss of the cold-water coral Lophelia pertusa from multiple environmental drivers in a year-long experiment
Published 27 March 2026 Science ClosedTags: biological response, corals, dissolution, growth, laboratory, morphology, mortality, multiple factors, North Atlantic, oxygen, physiology, respiration, temperature
Colony-forming scleractinian cold-water corals (CWCs) are important ecosystem engineers, forming complex 3-dimensional habitats in the deep sea, which in turn sustain high biodiversity. They are threatened by future environmental changes such as ocean acidification, warming, deoxygenation, and food limitation, but little is known about the effect of these drivers in combination or on the long-term. We conducted a year-long aquarium experiment with Lophelia pertusa (syn. Desmophyllum pertusum) under projected end-of-century conditions, investigating the combined effect of differences in pH (8.1 and 7.7), temperature (9°C and 12°C), oxygen concentration (100% and 90%) and food supply (100% and 60%) on coral survival, growth, respiration rates, skeletal dissolution and energetic reserves. Growth rates of L. pertusa decreased significantly in both multiple driver treatments, resulting in negative and more variable growth rates. However, growth rates only started to decrease after 4.5 months, clearly showing a delayed response. In addition, survival rates and energetic reserves were slightly lower in multiple driver treatments, whereas L. pertusa was not affected by reduced oxygen concentration examined as a single factor. Negative growth rates in multiple driver treatments were driven by dissolution of bare skeletal parts due to reduced seawater pH and temporary aragonite undersaturation, visualised here through micro-computed tomography images. While live CWCs may be able to cope with projected future environmental changes over the timescale of 1 year, ocean acidification will lead to dissolution of the dead skeletal framework of CWC reefs and net loss, reducing the complexity and associated biodiversity of these reefs. However, the challenge remains in closing the gap between long-term experiments and the much longer-term chronic exposure of CWCs to projected environmental changes.
Continue reading ‘Skeletal growth and loss of the cold-water coral Lophelia pertusa from multiple environmental drivers in a year-long experiment’Effects of long-term exposure to ocean acidification on the Patagonian scallop Zygochlamys patagonica (P.P. king, 1832), a strategic fishery resource in the Southwest Atlantic ocean
Published 12 March 2026 Science ClosedTags: biological response, dissolution, fisheries, laboratory, mollusks, morphology, mortality, South Atlantic
Highlights
- Scallops were resilient to low pH within the present range of natural variability.
- Negative impacts were observed under true ocean acidification scenario, including:
- Increased mortality & decreased shell mass condition index
- Dissolution of the external shell surface modifying shell ornamentation
- Shell disarticulation leading to the lost ability to swim
- During depuration time were observed:
- A recovery of the scallops’ vital functions when the stressor (low pH) was not present
- No recovery for shell mass condition index, shell ornamentations and disarticulated scallops
- No new disarticulated scallops
Abstract
Ocean acidification (OA) is a global process leading to a decrease in seawater pH. It is a direct consequence of the increase in CO2 emissions due to human activities with documented impacts on marine species and ecosystems. Effects of a long-term OA exposure (6 months) followed by a 2 months depuration period were evaluated on the Patagonian scallop Zygochlamys patagonica, an important seafood species of the Southwest Atlantic Ocean. Scallops were exposed to three target pHs, (1) pH 7.93, the mean annual pHT at the sampling site, (2) pH 7.83, the minimum value of the natural variability recorded at the sampling site and, (3) pH 7.53, a 0.3 pH unit below the minimum pH. Mortality, shell growth, and shell mass, adductor muscle mass and gonadal mass condition indices were measured at the beginning of the experiment and after 3, 6 and 8 months of exposure. Decreased pH led to a significant increase in mortality and decrease in the shell mass condition index. Shell growth was minimal over the course of the experiment with no effect of pH. The external shell surface showed a gradual dissolution and discolouration over the 6 months exposure to low pH. Shell disarticulation due to ligament damage was also observed in 29% of the animals exposed to low pH after 6 months resulting in loss of swimming ability of scallops, whereas no disarticulated animals were recorded in the high pH treatment. These results show the vulnerability of this species to future OA conditions with implications for the ecosystem services it provides, such as a decline in scallop numbers, greater vulnerability to predation and lower quality of commercial products.
Continue reading ‘Effects of long-term exposure to ocean acidification on the Patagonian scallop Zygochlamys patagonica (P.P. king, 1832), a strategic fishery resource in the Southwest Atlantic ocean’Experimental observations on ultrastructure of scales of red seabream (Pagrosomus major) for seawater pH monitoring
Published 18 February 2026 Science ClosedTags: biological response, dissolution, fish, laboratory, morphology, North Pacific
Ocean acidification monitoring relies predominantly on field test and numerical modeling, while bioindicators are emerging as practical and economic approaches for seawater pH monitoring. Here, we report indoor dissolution experiments on the scale of red seabream (Pagrosomus major) under varied pH (from 7.1 to 7.9), showing that the mean aspect ratio of ventral ctenii and caudal/ventral lepidonts negatively correlated with pH. We propose to employ these ultrastructures of fish scale to be a novel bioindicator for marine pH reconstruction. This semiquantitative proxy would be applicable to both contemporary biomonitoring and paleo-oceanic pH reconstruction for the extensive occurrences of fish in modern oceans and fossil records.
Continue reading ‘Experimental observations on ultrastructure of scales of red seabream (Pagrosomus major) for seawater pH monitoring’Mussel periostracum protects against shell dissolution
Published 6 August 2025 Science ClosedTags: biological response, dissolution, laboratory, mollusks, morphology
Reductions to seawater pH challenge the shell integrity of marine calcifiers. Many molluscs have an external organic layer (the periostracum) that limits exposure of underlying shell to the outside environment, which could potentially help combat shell dissolution under corrosive seawater conditions. We tested this hypothesis in adult California mussels, Mytilus californianus. We quantified shell dissolution rates as a function of periostracum cover across three levels of reduced pH (7.7, 7.5, and 7.4 on the total scale). Since periostracum can also be eroded over time, we additionally conducted a first-pass examination of whether differing surface textures induced by abrasional processes might influence dissolution rates. We contextualized this set of experiments with measurements of mussel periostracum cover in multiple intertidal habitats. Our results indicate a threefold reduction in shell dissolution rate as periostracum cover increases from 10 to 85% of shell surface area. Dissolution was higher in lower-pH treatments and in treatments where periostracum removal resulted in shells with rougher surface texture, potentially due to increased microtopographic surface area of underlying shell exposed to corrosive seawater. Periostracum loss in the field was greater for mussels at higher shoreline elevations and in sunnier locations, where heat, ultraviolet radiation, and desiccation at low tide may weaken attachment of the periostracum to the shell and. These findings highlight the potential for protective structures of marine organisms to help confront increasingly acute global environmental stressors.
Continue reading ‘Mussel periostracum protects against shell dissolution’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’Mangrove-driven acidification and shell dissolution on intertidal oyster reefs in a subtropical estuary
Published 4 August 2025 Science ClosedTags: biological response, BRcommunity, chemistry, dissolution, field, mollusks, morphology, North Atlantic, phanerogams
Tropicalization, resulting from warmer minimum temperatures, has allowed mangroves to expand poleward and increase in abundance in historical ranges. Since 1984, mangrove abundance on intertidal oyster reefs in Mosquito Lagoon, Florida, USA, has increased by 198% due to tropicalization. Oysters provide abundant ecosystem services including engineering reef habitat and water filtration, but shells are prone to dissolution in acidic conditions. Mangroves are associated with soil acidification and therefore may alter the pH of oyster reef sediment. The goal of this research was to determine if mangroves acidify oyster reef porewater (i.e. water within the sediment) and determine if mangrove-correlated acidification caused oyster shell dissolution as indicated by shell mass loss. Porewater, up to 10 cm depth, was collected monthly for 2 yr, and the pH was compared between 4 habitats: mudflats, oyster-dominated reefs (oyster reefs), transitioning reefs (oyster reefs with mangroves), and mangrove-dominated sites (mangrove islands). Porewater was more acidic with mangroves present. Transitioning reefs had a mean pH of 7.13 compared to oyster-dominated reefs (mean pH: 7.52). To measure shell dissolution, bags containing 10 pre-weighed oyster shells were deployed and re-weighed after 6, 12, and 24 mo. After 24 mo, mangrove-dominated sites lost more shell mass (8% loss) compared to oyster-dominated sites (1% loss). Transitioning reefs had intermediate shell mass loss. Combined, these data suggest that mangrove expansion on intertidal oyster reefs can negatively impact oysters. With oyster reef habitats in global decline, understanding new sources of degradation, including mangrove-driven acidification, is crucial to supporting conservation and restoration efforts.
Continue reading ‘Mangrove-driven acidification and shell dissolution on intertidal oyster reefs in a subtropical estuary’Shell dissolution rates differ fourfold between mussel species
Published 1 August 2025 Science ClosedTags: biological response, dissolution, laboratory, mollusks, North Pacific
Ocean acidification poses a critical threat to marine calcifiers globally and is particularly severe in the California Current System, where ecologically and economically important bivalves experience reduced calcification under climate change. Marine mussels display differential habitat preferences, with species like Mytilus californianus favouring fully saline environments and M. trossulus inhabiting sites with greater freshwater input. Determining abiotic dissolution rates of these species under ocean acidification is essential for predicting future consequences of climate change for coastal populations. We examined shell dissolution rates of mussel congeners under a range of pH (6.5–9.3) and aragonite saturation states (0.1–9.0). We also experimentally quantified the relative importance of dissolution from interior versus exterior shell surfaces. M. trossulus exhibited fourfold higher shell dissolution rates than M. californianus. When the shell interior was sealed against seawater exposure, dissolution rates decreased significantly in both species, indicating high abiotic dissolution on the shell interior. Results demonstrate that dissolution rates can vary between congeners inhabiting the same biogeographic region. Our finding that freshwater-tolerant M. trossulus has higher abiotic dissolution under ocean acidification is important because low salinity may further retard calcification, altering future intertidal population structure along freshwater-influenced coastlines.
Continue reading ‘Shell dissolution rates differ fourfold between mussel species’Vulnerability to ocean acidification of marine calcifying organisms cannot be predicted from the mineral type in their shells
Published 31 July 2025 Science ClosedTags: biological response, dissolution, review
Scientific Significance Statement
Anthropogenic CO2 is acidifying the surface ocean water, a process called ocean acidification (OA). This process can result in conditions that are corrosive for seashells with more “delicate” calcium carbonate shells. An important debate in OA research centers on the degree of vulnerability of the calcium carbonate shell forming groups. It is widely believed that the vulnerability can be simply inferred from the particular mineral type forming the shells (related to the mineral’s solubility). This idea is widespread and has found its way into policy reports. We argue that the idea is over-simplified and can lead to wrong assessments of vulnerability to OA. Shell dissolution kinetics is not only a function of the mineral type but also of microstructure and organic content. This means that vulnerability assessments in, for example, some models and policy reports have to be revised.
Continue reading ‘Vulnerability to ocean acidification of marine calcifying organisms cannot be predicted from the mineral type in their shells’Species-specific mechanisms of benthic foraminifera in response to shell dissolution
Published 31 July 2025 Science ClosedTags: biological response, dissolution, laboratory, light, mortality, multiple factors, North Atlantic, performance, photosynthesis, protists, respiration
Highlights
- Living specimens and empty tests of two benthic foraminifera species were cultured in different pH and light conditions.
- In acidic conditions, greater dissolution of empty tests compared to living specimens was observed.
- No differences in the degrees of dissolution between the two species were observed.
- Living foraminifera have active mechanism(s) to tolerate acidification.
Abstract
Ammonia confertitesta and Haynesina germanica are two common estuarine benthic foraminifera subject to sediment acidification. Nevertheless, mechanisms involved in their response to acidification are still poorly understood. Since H. germanica is kleptoplastic and photosynthetically active, unlike A. confertitesta, these species were cultured in controlled experiments to determine whether these mechanisms could mitigate acidification-induced shell dissolution. Both living and dead specimens were incubated at two pH (8.0 and 6.8) and two light conditions (0 and 24 μmol photon m-2.s-1) for 18 days. For each species, respiration and photosynthesis rates were calculated based on oxygen measurements. At the end of incubation, foraminiferal viability was assessed with CellTracker Green™ biomarker, and each test was categorised according to a dissolution scale (DS) using SEM. For both species, in acidic conditions, the tests of dead specimens were significantly more dissolved than the tests of living specimens, suggesting active mechanisms providing tolerance to acidification. For the living specimens, no significant difference in the DS distribution was observed between the two species at both conditions, suggesting that kleptoplast photosynthetic activity in H. germanica does not provide additional resistance to acidification. Until at least day 12, respiration data revealed a different biological activity for the two species, and we observed distinct behaviours (e.g., encystment and pseudopod emission). These suggest each species exhibits species-specific responses to cope with acidification. On day 18, respiration rates and binocular observations showed low biological activity, suggesting dormancy or death. Further investigation is required to identify the cellular mechanisms involved to counter acidification stress.
Continue reading ‘Species-specific mechanisms of benthic foraminifera in response to shell dissolution’Morphological responses of a temperate intertidal foraminifer, Haynesina sp., to coastal acidification
Published 17 July 2025 Science ClosedTags: biological response, dissolution, laboratory, morphology, North Atlantic, protists
Coastal acidification could have widespread impact on marine organisms, affecting the ability of calcifying organisms to build shells and skeletons through calcium carbonate precipitation. As an abundant group of calcifying organisms, some protists within the phylum Foraminifera demonstrate potential success under elevated partial pressure of carbon dioxide (pCO2) due to their ability to modulate intracellular pH. However, little is known about their responses under more extreme acidification conditions that are already seen in certain coastal environments. Here we exposed specimens of Haynesina sp., which belongs to a genus that is prevalent in temperate intertidal salt marshes, to moderate (pCO2 = 2386.05+/−97.14 μatm) and high acidification (pCO2 = 4797.64+/−157.82 μatm) conditions through the duration of 28 days. We demonstrate that although this species is capable of withstanding moderate levels of coastal acidification with little impact on overall test thickness, it can experience precipitation deficiency and even dissolution of the calcareous test under highly elevated pCO2. Interestingly, such a deficit was primarily seen among live foraminifera, as compared to dead specimens, throughout the four-week experiment. This study suggests that a combination of environmental stress and the physiological process of test formation (i.e., calcite precipitation) could induce thinning of the test surface. Therefore, with the acceleration of coastal acidification due to anthropogenic production of CO2, benthic foraminifera and other calcifying organisms among coastal ecosystems could reach a tipping point that leads to thinning and dissolution of their calcareous tests, which in turn, will impair their ecological function as a carbon sink.
Continue reading ‘Morphological responses of a temperate intertidal foraminifer, Haynesina sp., to coastal acidification’Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply
Published 26 June 2025 Science ClosedTags: biological response, chemistry, dissolution, laboratory, mesocosms, mollusks, morphology, multiple factors, physiology, South Pacific
Soft-sediment habitats are crucial for marine coastal ecosystems, supporting diverse biodiversity both above and below the sediment. Ocean acidification, driven by rising CO2 and nutrient influx, enhances heterotrophic metabolism, raising CO2 levels and lowering pH. These alterations complicate the dynamics of tidal flat, emphasizing the need for further research into their impact on biodiversity. Within these ecosystems, deposit- and suspension-feeding bivalves play crucial roles. Tagelus dombeii, a bivalve mollusc found in soft sediments, exhibits burrowing behavior linked to food supply and is of significant commercial value in southern Chile. This study assessed the response capacity of T. dombeii to key stressors associated with global ocean change, such as ocean acidification and food availability. Our results revealed significant differences in pH levels between the water column and pore water from the sediment in experimental mesocosms. T. dombeii was affected by ocean acidification and food availability in terms of its morphological traits (i.e. length, width, height and growth rate), while oxygen consumption was influenced only by the interaction between acidification and food supply. Notably, heart rate remained constant but increased when food supply was low. Our study suggests that T. dombeii exhibits partial tolerance to variations in seawater pH and carbonate chemistry, possibly due to its natural exposure to acidic pore water, but it is sensitive to food availability. These plastic physiological responses suggest that T. dombeii may be less vulnerable to future global change scenarios, demonstrating potential resilience and ecological success in its natural habitat.
Continue reading ‘Infaunal bivalves exhibit resilience to ocean acidification but remain sensitive to food supply’Pteropods as early-warning indicators of ocean acidification
Published 6 May 2025 Science ClosedTags: Antarctic, biological response, BRcommunity, chemistry, community composition, dissolution, field, mollusks, morphology, otherprocess, zooplankton
Aragonite undersaturation (Ωar < 1) events are projected to rapidly increase in frequency and duration in the Antarctic Weddell Sea by 2050. Thecosome pteropods (pelagic snails) are bioindicators of ocean acidification (OA) because their aragonite shell dissolves easily at low Ωar saturation states. Here, we describe the shell dissolution state of the pteropod Limacina helicina antarctica in relation to the water column Ωar in the southern Weddell Sea during austral summer 2018 as benchmark for future monitoring of ongoing OA. Ωar depth profiles at the sampling sites were consistently close to or in the range of threshold levels (Ωar ~ 1.1–1.3) for pteropod shell dissolution. Pteropods contributed up to 69% of total mesozooplankton biomass, and their distribution correlated positively with Ωar and chlorophyll a concentration. When analyzed with scanning electron microscopy, 78% of the investigated shells exhibited dissolution, and 50–69% showed the more severe Type II dissolution exceeding current projections of pteropod shell dissolution for the Southern Ocean. But importantly, in our study, only two specimens had the most severe Type III dissolution. Dissolution often co-occurred with and occurred in scratch marks of unclear origin supporting notions that an intact periostracum protects the shell from dissolution. Where dissolution occurred in the absence of scratches or absence of evidence of periostracum breaches, microscale/nanoscale breaches may have been an important pathway for dissolution commencement supporting recent findings of a reduction of the organic shell content caused by low Ωar/low pH. The dissolution benchmark we provide here allows future application of pteropods as early-warning indicators of presumably progressing OA in the Weddell Sea.
Continue reading ‘Pteropods as early-warning indicators of ocean acidification’
