High-resolution temporal biogeochemical variations in a seagrass-coral cohabitate ecosystem: day-night, rain, and coral spawning

Published 14 May 2026 Science Leave a Comment

Highlights

  • Seagrass-coral habitats act as CO2 sources driven by intense nighttime respiration
  • High-resolution data enable predictive modeling of DIC, DOC, and POC dynamics
  • Metabolic cues govern DIC, while temperature and alkalinity regulate POC and DOC
  • Episodic coral spawning and rainfall trigger rapid ocean acidification
  • Short-term disturbances dramatically shift organic and inorganic nutrient loads

Abstract

Seagrass meadows and coral reefs are global hotspots for productivity, yet they are often studied in isolation despite their intense biogeochemical connectivity. Significant gaps remain in understanding how coupled inorganic and organic processes within the water column drive blue carbon services in such mixed habitats, particularly during rapid environmental disturbances. Here, we investigated a unique, intertwined ecosystem in the Dongsha Atoll, where massive Porites corals are distributed on seagrass meadows, creating a natural laboratory for studying water column carbon biogeochemistry. During a 10-day sampling period, we collected continuous hydrological and discrete biogeochemical data at two- to four-hour intervals. Our results reveal that the dissolved inorganic carbon (DIC) covaried with dissolved oxygen and pH in strong diurnal patterns, which were governed by photosynthesis and respiration. As an outcome, variable but mostly high pCO2 values (141–2070 μatm) indicate the seagrass meadow was a source of CO2 to the atmosphere due to strong night-time respiration. Particulate organic carbon (POC) increased with temperature but showed no diurnal pattern. Dissolved organic carbon (DOC) showed a weak diurnal pattern and was linked to variations in POC and total alkalinity, highlighting the tight coupling between the organic production of the meadow and the inorganic chemistry of the calcification framework. Additionally, coral spawning led to a surge in organic content and changed inorganic nutrient levels. Rainfall events significantly acidified the ocean and enhanced submarine groundwater discharge to the seagrass-coral habitat. The distinctive contributions of this study are the extremely high temporal resolution of discrete samples, allowing the simultaneous tracking of multiple organic and inorganic pools during natural disturbances. The high-resolution data provide fundamental information for parametrizing models that explain DIC, POC, and DOC, which yield insights into organic carbon cycling in seagrass meadow-coral habitats.

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Mechanistic drivers of climate-induced reproductive collapse in African catfish: multi-stressor interactions under IPCC scenarios

Published 14 May 2026 Science Leave a Comment

Climate change is increasingly disrupting freshwater ecosystems in sub-Saharan Africa, posing severe threats to the reproductive success and population viability of key fish species. This study investigated the mechanistic effects of elevated temperature across a gradient and the combined impact of elevated temperature, acidification and hypoxia under a simulated future climate scenario (IPCC SSP5-8.5) on the reproductive physiology and early life stages of Clarias gariepinus in the Cross River Estuary. Single-stressor trials examined the effect of temperature (28–38°C) on oestrogen synthesis, cortisol levels and gonadosomatic index (GSI). A combined-stressor scenario (35°C, pH 6.2, dissolved oxygen 2 mg/L) was used to simulate predicted climate conditions. Each treatment was replicated across triplicate tanks, with 10 broodstock per tank, over an 8-week period. Environmental parameters were tightly controlled using aquarium heaters, aerators and pH regulators. Combined stressors markedly disrupted reproductive function. Oestrogen synthesis ceased at 34°C, coinciding with a sharp decline in GSI (r2 = 0.81, p < 0.001). Cortisol concentrations increased fourfold under concurrent heat and hypoxia. Cortisol concentrations increased fourfold under heat and hypoxia co-stress. Larval performance also declined sharply, with prey capture efficiency reduced by 33% at pH 6.0 and cumulative mortality reaching 82% by day 5 under combined-stressor conditions. Habitat suitability models projected a 71% reduction in spawning habitat availability in the estuary by 2070 under the SSP5-8.5 scenario. Genetic screening revealed a significant correlation (r2 = 0.63, p = 0.004) between heat shock protein 70 (HSP70) allele frequency and larval survival, indicating potential for adaptive resilience. These findings suggest a compounded vulnerability of C. gariepinus to climate-related stressors and highlight the potential need for targeted conservation efforts. Recommended interventions include habitat restoration, enhancement of dissolved oxygen regimes and selective breeding programmes to support thermal and hypoxic tolerance in vulnerable populations.

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Understanding natural ecosystems: biogeochemical modelling

Published 14 May 2026 Web sites and blogs Leave a Comment

Why do we study ocean biogeochemistry?

The ocean has a huge and diverse range of ecosystems, from shallow coastal waters to the vast open sea and the deep seafloor. Each one supports life that’s adapted to its own specific environment and food webs. Ultimately, at the base of almost all marine ecosystems are tiny, microscopic organisms: the phytoplankton.

Why Does the Ocean’s Carbon Cycle Matter?

The ocean plays a dominant role in the Earth’s carbon cycle. It holds more than 90% of the planet’s carbon and absorbs around 25% of our carbon dioxide (CO₂) emissions. This uptake reduces the amount of CO₂ left in the atmosphere to cause climate warming. Understanding how the ocean’s carbon cycle works is a critically important area of research.

Marine ecosystems play a significant part in the ocean’s natural carbon cycle by transporting carbon from the surface to the deep ocean. This process is known as the “biological carbon pump” (BCP). However, climate-driven changes in ocean temperature, circulation, and mixing are expected to reduce the supply of deep nutrients that fuel the BCP. This may disrupt its vital role in storing carbon.”

How Does Ocean Biogeochemistry Affect Human Communities?

Focusing more directly on human concerns, marine productivity is ultimately what provides us with resources like fisheries. Marine ecosystems support global fisheries, which collectively employ 62 million people and feed about 3.2 billion, sustaining regional economies.

In coastal areas, seaweeds provide ecosystem services like pollution remediation and have a natural value we can all appreciate. On top of that, the wider ocean carbon cycle could potentially be leveraged by marine carbon dioxide removal (mCDR) technologies. These aim to remove CO₂ from the atmosphere and eventually help reduce the extent of climate warming.

So, studying how marine ecosystems operate, and how they might change, is a major goal for our ecosystems modelling group.

What is MEDUSA?

MEDUSA (Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration and Acidification) describes the surface ocean ecosystem with a simple, size-based model (nutrient-phytoplankton-zooplankton-detritus). It simulates the linked biogeochemical cycles of carbon, nitrogen, silicon, iron, and oxygen. We use MEDUSA in detailed, high-resolution simulations to help understand how human systems, including fisheries, may change in the future.

MEDUSA is typically run inside physical models of the ocean. This means its components respond to properties like temperature and salinity, and are transported around the ocean by currents. We can then compare the geographical and seasonal output from our models with observational data from ships, autonomous platforms, or satellites. This helps us work out how good a job the model is doing and how we can improve it.

Visit the MEDUSA website

How Does MEDUSA Contribute to Climate Research?

An important part of our work comes from MEDUSA serving as the marine biogeochemistry component of the UK’s state-of-the-art Earth system model, UKESM. Through UKESM, MEDUSA contributes to the international climate simulations that inform the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports. This helps improve our global understanding of how the ocean influences climate.

Using UKESM also allows our group to better study the links between marine ecosystems and the wider atmosphere and land systems. This integrated approach lets us examine how changes in one part of the Earth system cascade through to affect others.

Why is the Research Important for the Future?

Ocean biogeochemistry is important for understanding the ocean’s carbon cycle and its ecosystems, so crucial for both tackling global-scale challenges such as climate change and knowing how we can mitigate these or adapt to them.

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Anti-predatory responses of Mytilus coruscus to the combined effects of ocean acidification and microplastics

Published 13 May 2026 Science Leave a Comment
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Highlights

  • 1.Predator cues can significantly induce byssal secretion in Mytilus coruscus.
  • 2.Ocean acidification inhibits the anti-predatory responses of Mytilus coruscus.
  • 3.Microplastics exerts sublethal effects on the byssus of Mytilus coruscus.
  • 4.The presence of predators amplifies the mild disturbances caused by ocean acidification and microplastics.
  • 5.The combined stress shows a synergistic inhibitory trend on the anti-predatory capability of Mytilus coruscus.

Abstract

Ocean acidification (OA) and microplastics (MPs) pollution are major abiotic stressors in coastal ecosystems. Byssus is the core structural trait for Mytilus coruscus to defend against predators, and it is vulnerable to environmental stress, which in turn impairs its anti-predator function. However, the anti-predator response characteristics of M. coruscus byssus and the interaction mechanisms among OA, MPs and predation pressure from Charybdis japonica remain unclear under their combined stress. The study conducted acute exposure experiments, measuring five key byssus indicators: secretion frequency, quantity, diameter, volume and tensile strength, to explore the variation characteristics of the byssus-based anti-predator function of M. coruscus under multi-stressor conditions. Results showed that predators served as a key biological signal to trigger the anti-predator responses and significantly promoted byssus secretion; OA had the most prominent inhibitory effect on byssus function; MPs exposure only induced sublethal disturbances with no significant effects on core anti-predator indicators. Furthermore, the combined stress of ocean acidification and microplastics exhibited a synergistic trend, impairing the byssus-centered anti-predatory defense capacity of M. coruscus. This study provides experimental evidence for analyzing the variation patterns of mussel byssus under multiple stressors and suggests that future marine ecological risk assessments should focus on the interactions between biotic and abiotic stressors to more accurately predict the dynamic changes of coastal ecosystems.

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OA-ICC bibliographic database updated

Published 12 May 2026 Science Leave a Comment

An updated version of the OA-ICC bibliographic database is available online.

The database currently contains 9,838 references and includes citations, abstracts and assigned keywords. Updates are made every month.

The database is available as a group on Zotero. Subscribe online or, for a better user experience, download the Zotero desktop application and sync with the group OA-ICC in Zotero. Please see the “User instructions” for further details.

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Leveraging AI-driven predictors of enzyme pH optima to unravel microbial adaptation to environmental pH

Published 12 May 2026 Science Leave a Comment
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It is well-known that pH (potential of hydrogen) influences enzyme catalytic activity (Schomburg and Salzmann, 1991; Nelson et al., 2021). The pH optimum (pHopt), at which an enzyme displays maximal catalytic activity, is therefore critical for enzyme design and applications (Zhang et al., 2025). To identify suitable enzymes for target pH environments or optimize enzymatic performance in biotechnology, enzyme engineering requires efficient characterization of kinetic properties across large numbers of amino acid sequences. However, experimental determination of pHopt for numerous sequences is time-consuming, labor-intensive, and costly. To address these limitations, computational approaches based on machine learning have been developed for rapid prediction of enzyme pHopt, supporting applications in protein engineering.

Recent advances, exemplified by EpHod (enzyme pH optimum prediction with deep learning) (Gado et al., 2025), enable prediction of the enzyme pHopt directly from protein sequences. The EpHod model leverages embeddings from the protein language model (PLM) ESM-1v and achieves a root mean squared error (RMSE) of 1.25 pH units on the held-out test data (Gado et al., 2025). To further improve predictive performance, an increasing number of AI-driven tools have been developed. For instance, (Zhang et al. 2025) introduced the model VENUS-DREAM, which employs the PLM ESM-2 and reduces the RMSE to 0.809. These AI-powered tools are revolutionizing enzyme discovery and design by enabling high-throughput prediction of pHopt.

Similarly, studies of microbial adaptation to environmental pH frequently require knowledge of enzyme pHopt. This information can be used to investigate the underlying adaptive mechanisms. However, experimental determination of pHopt for large-scale enzyme sequences remains impractical due to high costs and low throughput. Fortunately, the high-throughput predictive capacity of these AI-driven tools offers a powerful alternative for obtaining enzyme pHopt values, which can facilitate investigations into the mechanisms by which microorganisms adapt to environmental pH. The potential applications are illustrated with examples below.

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Scientists collaborate with aquaculture industry on ocean acidification resiliency

Published 12 May 2026 Web sites and blogs Leave a Comment

An innovative new research project led by William & Mary’s Batten School & VIMS is bringing together scientists, shellfish farmers and community planners to prepare for emerging environmental challenges related to ocean and coastal acidification (OCA) in the Chesapeake Bay.

“It isn’t something that we’re thinking about on a daily basis, but that doesn’t mean that we shouldn’t begin planning for it now,” said Marcia Berman, co-founder of Cappahosic Oyster Company. “Aquaculture is a vulnerable industry, and more science is always welcome in helping us prepare.”

Supported by a $1.2 million grant from the National Oceanic and Atmospheric Administration’s Ocean Acidification Program, the Regional Vulnerability Assessment (NOAA RVA) study combines traditional coastal and marine science with community research to develop adaptation resources and strategies for the aquaculture industry.

With an advisory committee comprised of Batten School & VIMS experts, members of the region’s shellfish industry and community planners, work is now underway to develop a dynamic, web-based dashboard featuring user-friendly tools that will support businesses and municipalities through complex decision-making processes in the decades ahead.

An invisible shellfish stressor approaches from both land and sea  

OCA is the result of both global and local processes. On a global scale, acidification occurs when the ocean absorbs excess carbon dioxide from the atmosphere, reducing the water’s pH and making it more acidic. In coastal regions like the Chesapeake Bay, freshwater runoff introduces nutrients to coastal waters, inducing processes that can lead to further acidification.

“It’s this hidden stressor sneaking up on us and on the shellfish,” said Rivest, an associate professor at the Batten School of Coastal & Marine Sciences & VIMS and the project’s primary investigator (PI). “Animals like oysters and clams that build their shells out of calcium carbonate provide valuable environmental services and are particularly vulnerable to acidification. Understanding the impact of [OCA] on shellfish, and on shellfish farmers, is critical if we want to support the ecosystems and communities that depend on them.”

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Divergent responses of the diatom Thalassiosira weissflogii to ocean acidification during light and dark periods

Published 11 May 2026 Science Leave a Comment
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Given the limited understanding of discrepancies in responses of diatoms to ocean acidification (OA), we comparatively investigated the physiological and transcriptional performances of a diatom Thalassiosira weissflogii acclimated to OA (pHt drop of 0.35–0.41) between day and night periods. We found that OA enhanced its specific growth rate (up to 10%) in the light period by upregulating light reaction, Calvin cycle and H+ pumps to cope with the decreased pH. On the other hand, OA reduced its apparent specific growth rate (14%) in the dark period due to additive pH drop caused by OA-enhanced respiratory CO2 release. In the dark period, the cells could not effectively cope with the decreased pH since H+ pumps were downregulated. Consequently, OA did not affect cell growth during a 24 h diel cycle. These findings suggest that daytime positive and night negative effects of OA on diatoms could be responsible for differential results observed under different conditions, with implications for possible seasonal and latitudinal effects of OA.

Scientific Significance Statement

Progressive ocean acidification (OA) due to continuous dissolution of anthropogenic CO2 into seawater is known to affect diatoms that contribute to approximately 20% of the Earth’s primary production. However, impacts of OA on diatoms through a daily cycle remain poorly understood. Our data provide compelling evidence from both physiological and molecular aspects that OA enhances growth of a diatom during the light period by upregulating its photosynthetic CO2 fixation against the stress of decreased pH, but decreases its apparent specific growth rate during the night period due to the aggravated stress of pH drop from respiratory CO2 release overlaid with OA. These findings align well with transcriptional imprints, suggesting the essential role of light in modulating the effects of OA on diatoms, with implications for possible seasonal and latitudinal effects of OA given the changing lengths of daytime.

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Aragonite saturation state and coral reefs health assessment in Sri Lanka

Published 11 May 2026 Science Leave a Comment
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Ocean acidification (OA) and nutrient enrichment can separately or together threaten coral reefs by reducing calcification efficiency and increasing physiological stress, ultimately weakening reef resilience. Therefore, the study evaluates the prevailing OA level over the Sri Lankan coral reef areas using the aragonite saturation state (ΩAr) and assesses the nitrate (NO3−), and phosphate (PO43−) concentrations over the coral sites. The study was conducted on coral reefs on the eastern coast (EC), southern coast (SC), northern coast (NC), and west coast (WC) of Sri Lanka from April to June 2024. A total of 63 seawater samples were collected around each coastal site for analysis. The ΩAr were supersaturated (ΩAr > 1) and ranged from 2.98 ± 0.04 to 4.92 ± 0.12. Throughout the study period, the study sites had ΩAr values exceeding 2.92 ± 0.16, indicating that the nation’s corals were resilient to deterioration, and the comparative analysis demonstrates that these sites were not vulnerable to OA. However, the NC exhibited significantly (P < 0.05) the lowest ΩAr values (3.2 ± 0.64), positioning the regions near the lower bound of optimal calcification conditions. While ΩAr values indicate low OA stress during sampling, elevated NO3− concentrations (2 – 5 μmol L−1) in SC (2.19 ± 1.28 µmol L−1) and WC (3.52 ± 1.48 µmol L−1) may exacerbate coral bleaching during thermal stress events, representing a co-stressor rather than OA effect. Coral bleaching HotSpot (HS) identification emphasizes how spatially distributed HS are from January to June. The OA risk assessment confirmed that climate change will bring high risk to the coral calcification, reproduction, and damage to the breeding ground, which impact on the ecology and economy of Sri Lanka.

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Controls on boron isotope ratios in marine bivalve shells: insights from a controlled experiment across pH and temperature gradients

Published 8 May 2026 Science Leave a Comment
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Documenting spatial and temporal patterns of ocean acidification and understanding the way marine organisms build carbonate skeletons is critical to assessing their potential vulnerability to present and future stressors. The boron isotopic composition (δ11Bc) of many marine carbonates provides insight into the pH at the site of calcification within biocalcifiers and, by extension, the pH of ambient seawater when the carbonate formed. The modification of seawater carbonate chemistry at the site of calcification by marine calcifiers and the utility of different taxa as paleo-pH proxy archives remains an area of active research. Despite the significance of marine bivalves to ecosystem function, high-resolution paleoclimatic studies, and the shellfish industry, their biocalcification mechanisms, controls on internal pH, and potential for reconstructing records of past seawater pH remain unclear. To address these gaps, a 20.5-week flowthrough tank experiment was conducted in which four species of commercially important bivalves from the northwest Atlantic Ocean were grown in tanks with controlled pHT (pH 7.4 to 8.0) and temperature conditions (6 to 12 °C). A total of 106 shell samples from 99 individuals of adult and juvenile Arctica islandica (ocean quahog), juvenile Mercenaria mercenaria (northern quahog or hard clam), juvenile Mya arenaria (soft-shell clam) and juvenile Placopecten magellanicus (Atlantic sea scallop) were analyzed from this controlled experiment to assess the seawater pH, temperature, and growth rate controls on shell δ11Bc.These four bivalve species, grown under identical, controlled conditions, showed differential responses to the same seawater temperature and pH, likely due to differences in how they regulate the pH of their internal fluids. Juvenile P. magellanicus and juvenile M. mercenaria demonstrated significant relationships (R≥0.60; p-value <0.006) between tank pHT and δ11Bc, suggesting potential utility as proxies for past ambient seawater pH. Conversely, the δ11Bc of juvenile A. islandica and juvenile M. arenaria did not yield a strong relationship with seawater pHT but instead yielded significant relationships with shell growth rate (linear extension), with a positive relationship for M. arenaria and a negative relationship for juvenile A. islandica. The δ11B results from the few (n=9) adult A. islandica shells measured show the most variability across the range of pH and temperatures (range of 16‰) and no significant relationship was found with seawater pH or growth rate. Despite rigorous oxidative cleaning of samples, the data suggest that adult A. islandica shells contain boron-rich organic phases resistant to traditional cleaning techniques. This suggests that the next step in the development of boron-based pH proxies in A. islandica requires additional research into robust cleaning and sampling methods of periostracum and other organics. Despite the need for further investigations to constrain growth rate effects and cleaning techniques in A. islandica and M. arenaria, there is potential for developing paleo-pH proxies from P. magellanicus and M. mercenaria to better understand spatial and temporal patterns of past, present and future ocean acidification.

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Projected future of African marine ecosystems under climate change and stratospheric aerosol injection

Published 8 May 2026 Science Leave a Comment
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Stratospheric Aerosol Injection (SAI) has been proposed as a potential strategy to cool the planet. The ARISE-SAI-1.5 approach, which employes a moderate emission scenario, is simulated to limit future global warming to 1.5°C by injecting aerosols into the stratosphere in the year 2035. However, the climate response to this SAI scenario, particularly along the African coast, remains unclear. In this study, we investigate the potential impacts of climate change under the SSP2-4.5 scenario and ARISE-SAI-1.5 on regional African marine ecosystems through key biological (chlorophyll), physical (salinity, temperature), and chemical (nitrate, acidification, and dissolved oxygen) parameters. Our results indicate that climate change may reduce productivity in African coastal ecosystems, with chlorophyll concentrations decreasing between 10% and 62%. Sea surface temperatures are projected to rise by 1.5°C along the entire coast by 2069, while surface salinity increases up to 0.3 g/kg, except for a slight decrease of up to 0.1 g/kg along the Congolese-Angolan coast. This salinity dipole in the Gulf of Guinea results from enhanced precipitation and river discharge, reinforced by stratification that traps freshwater at the surface. Additionally, climate change drives ocean acidification and may expand the oxygen minimum zone in the Gulf of Guinea, with oxygen levels decreasing by 10%–30% at depths of 100–200 m. Although ARISE-SAI-1.5 may help reduce surface oxygen depletion, it may not significantly mitigate subsurface oxygen loss or continued acidification. Nevertheless, it may reduce some negative climate change impacts on marine ecosystems by stabilizing chlorophyll levels, sea surface temperatures, and salinity.

Plain Language Summary

Stratospheric Aerosol Injection is being explored as a way to cool the planet and limit future global warming, for instance, to 1.5°C in the scenario we explore here (ARISE-SAI-1.5). However, its effects on the ocean, especially along the African coast, are not fully understood. This study examines key factors such as chlorophyll, water temperature, salinity, and oxygen levels to assess changes in marine ecosystems. Our findings show that climate change could reduce productivity, with chlorophyll levels dropping by 10%–62%. Sea surface temperatures are expected to rise by 1.5°C by 2069, and salinity will increase along most coastal areas. The low-oxygen zone in the Gulf of Guinea may expand, making deep waters less habitable for marine life. While the SAI we study here helps slow oxygen loss near the surface, it does not prevent deeper waters from losing oxygen or the ocean from becoming more acidic. However, it can still reduce some harmful effects of climate change by stabilizing chlorophyll levels, temperatures, and salinity.

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Coupled ocean warming and acidification reduce shell integrity and bioenergetics in juvenile Mytilus coruscus

Published 7 May 2026 Science Leave a Comment
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Under realistic climate change scenarios, marine bivalves face compounding stressors from concurrent ocean warming and acidification. Research has established the separate effects of these factors; however, the synergy driving physiological adaptation in mollusks has yet to be fully elucidated. We assessed the physiological responses of an ecologically significant mussel, Mytilus coruscus, to 2 mo exposure under varying environmental conditions (25°C/28°C and pH 7.7/8.1). Key metrics included shell properties, flesh weight, antioxidant defenses, bioenergetics, and gene expression. Compared to control groups, experimental groups showed reductions in shell hardness and compressive strength, >10% decrease in flesh weight, and 40-52% suppression of carbonic anhydrase and Ca2+-ATPase activities. Molecular analyses of the mantle tissue demonstrated compromised mitochondrial energy transduction (>40% reduction in ATP6 expression) alongside upregulated stress response markers (>2.1-fold COX3 increase). Notably, cellular energy allocation declined, accompanied by depletion of energy reserves (proteins, lipids, carbohydrates), indicating metabolic prioritization toward stress compensation. These findings elucidate how coupled stressors disrupt homeostasis through multilevel interactions, forcing energy trade-offs between defense mechanisms and growth processes, and confirm the tissue-specific vulnerability of the mantle and individual resilience of bivalves under multifactorial climate change.

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Ordovician sedimentary processes and related driving forces: Jordan, Arabian Plate

Published 7 May 2026 Science Leave a Comment
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The Ordovician-Lower Silurian siliciclastics deposited on the Jordanian Platform represent a transitional sedimentary system between their granitoid Gondwana source area and the Paleo-Tethys. While fluvial fining upward cycles (FUCs) of quartz arenite dominate braid plain deltas/upper shore face environments of the Lower Ordovician, arkosic tempestite and oxygen-deficient bituminous pelite/tuffite cycles cover upper/lower shore face environments of the Sandbian and Katian. The mineral deficit (feldspar, unstable heavy minerals) relates to acid sturz-rain events during volcanic degassing (SO2, HCl, HF, NOx) sourced in an Infracambrian/Cambrian Large Igneous Province (LIP) around S Sinai/Wadi Araba Rift-Zone. The change of sedimentary architectural elements/lithofacies types during the Upper Darriwilian took place after an L-chondrite of the Main Asteroid Belt (MAB) crossed the Earth’s orbit (~470 Ma), which resulted in some small meteorite craters (i.e., Lockne). Through the Sandbian and Katian, this insignificant impact series was accompanied by massive tephra production during worldwide explosive subduction-related volcanic arc magmatism. During the Upper Ordovician High Stand-System Tract (HST), the glass-bearing tephras were transformed under marine conditions into montmorillonite (K-bentonite), contributing to green tuffitic pelite interbedded with storm-generated arkosic clastics. Transtensional tectonics (pull-apart type) caused the main Ordovician-Silurian unconformity (“paleovalleys”) in SE Jordan and Saudi Arabia. Their sedimentary fills expose arkosic FUCs originated by shallow-water turbidites during the Hirnantian. The intensive explosive volcanism generated almost continuously negative climate forcing (“cosmic winter”) by tephra, aerosols, smog, and clouding that led to regional glaciation in the S Hemisphere. The abrupt 87Sr/86Sr-ratio decrease accompanies, at the Sandbian base, the onset of magmatism, while δ13C excursions follow a Transgressive System Tract (TST) and three T-maxima indicating increasing phytoplankton growth. The undulation—0% mirrors a cyclicity of volcanic events, climate forcing, Eh, and pH conditions. The δ18O rise shows a continuous CO2 assimilation until its stop (~1200 ppm CO2) and the following formation of black-shale facies.

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Ocean acidification does not affect the trophic transfer of Ag, Co, and Zn in the cuttlefish Sepia officinalis

Published 6 May 2026 Science Leave a Comment
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Highlights

  • Trophic transfer of metallic radiotracer was assessed in cuttlefish under low pH condition.
  • High assimilation of Ag, Co and Zn in juvenile cuttlefish via diet.
  • Ocean acidification (pH 7.63) does not affect metal trophic transfer.
  • Digestive gland is main storage site for Ag and Co.
  • Zn displays broader tissue distribution.

Abstract

Cephalopods are known to efficiently accumulate metals and may therefore play an important role in the trophic transfer of contaminants within marine food webs. However, the influence of environmental changes such as ocean acidification on trace element assimilation and retention in these organisms remains poorly understood. In the present study, the trophic transfer of three trace elements (Ag, Co, and Zn) was investigated in juvenile cuttlefish Sepia officinalis under two seawater pH conditions representative of present-day (pH 7.92) and near-future ocean acidification scenarios (pH 7.63). Using radiotracer techniques and a pulse-chase feeding experiment with radiolabelled shrimp, we quantified assimilation efficiencies, depuration kinetics, and tissue distribution of these elements following a single contaminated meal. Juvenile cuttlefish showed high assimilation efficiencies for all three trace elements: 94–100% for Ag and Co, and 77–78% for Zn. Depuration kinetics revealed element-specific retention patterns, with biological half-lives of several weeks to months for Ag and Zn, whereas Co was eliminated more rapidly. Tissue distribution showed a strong organotropism towards the digestive gland, which acted as the main storage compartment for Ag and Co, while Zn showed a wider distribution across tissues. No significant differences in assimilation efficiencies, depuration kinetics, or tissue distribution were observed between pH treatments. These results suggest that moderate ocean acidification scenarios projected for the coming century are unlikely to significantly affect trophic transfer and internal handling of trace elements in juvenile cuttlefish.

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Effects of ocean acidification on radular tooth material properties in Littorina littorea (Gastropoda, Mollusca)

Published 6 May 2026 Science Leave a Comment
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Ocean acidification is known to affect calcified structures in marine organisms, yet its impact on non-calcified but functionally essential feeding tools remains poorly understood. The radula is a defining molluscan apomorphy, whose mechanical performance is critical for feeding and survival. Here we investigated the effects of reduced seawater pH on the radular teeth of the intertidal gastropod Littorina littorea. Individuals were maintained for seven weeks under acidified conditions (pH 7.5) or near-present-day conditions (pH 8.1) and compared with a field-collected control group. Radulae were analysed using scanning electron microscopy, confocal laser scanning microscopy, energy-dispersive X-ray spectroscopy, and nanoindentation.

Radulae from acid-treated individuals exhibited markedly increased tooth wear in the working zone despite largely preserved gross morphology. Wear was most pronounced at the cusps of central and lateral teeth and showed rounded profiles indicative of progressive abrasive wear. Acidic conditions caused pronounced changes in the outer tooth coating, including reduced silicon enrichment and substantial decreases in stiffness and hardness, while the inner tooth structure was only weakly affected. Confocal microscopy revealed treatment-specific autofluorescence patterns, suggesting pH-dependent alterations of the organic matrix. Differences between laboratory-maintained and field-collected individuals further indicate that feeding conditions influence radular tooth properties.

These results demonstrate that ocean acidification can impair radular function through material-level degradation of composite feeding structures, potentially reducing grazing efficiency and imposing sublethal fitness costs.

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The influence of localized water quality on Eastern oysters (Crassostrea virginica) and their internal microbiome under changing environmental conditions

Published 5 May 2026 Science Leave a Comment
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Oysters are found ubiquitously in estuaries along the Georgia coast, where marsh morphology and large daily tidal fluctuations create dynamic and stressful conditions to which oysters may be locally adapted. Based on water quality data from the Sapelo Island National Estuarine Research Reserve, it is evident that changing climatic conditions are rapidly causing shifts in water quality that may be adversely affecting oyster health, especially as ocean acidification alters the carbonate buffering capacity, increasing the amplitude of daily pH variations. Importantly, the rate of change of conditions are not uniform within estuaries, varying on spatial and temporal scales. The symbiotic relationship between oysters and their internal microbiome has been increasingly analyzed as a metric for oyster health. As filter feeders, oysters continuously introduce microorganisms into their hemolymph. Core families of bacteria, including Mycoplasmataceae, have been identified to be associated with healthy oysters. The abundance of core groups, or of pathogenic genera like Vibrio, can be used as an indicator of oyster condition. Utilizing reciprocal transplant and common garden tank designs, we examined how changing variability in localized water quality conditions drive oyster health using physical and microbial indicators, including oyster growth, condition index, and shifts in microbial community dynamics. Our results suggest that low pH conditions are detrimental to oyster physiology, inducing stress, leading to a reduction in overall health and growth. Low pH causes a shift within the microbial composition, altering community dynamics, and increasing the abundance of stress-related bacteria, including Arcobacteraceae and Vibrionaceae. Drivers of oyster health and host-associated microbial dynamics are site- and scale-dependent and will need further research to fully understand which biotic or abiotic factors are most influential in oyster conditions amidst low pH conditions. Oysters are increasingly used in nature-based restoration efforts to support reef recovery and salt marsh expansion, making it critical to understand how relocation influences oyster health. Our results indicate that oyster condition is driven by destination rather than origin, with relocation success dependent on water quality at the transplant site.

Continue reading ‘The influence of localized water quality on Eastern oysters (Crassostrea virginica) and their internal microbiome under changing environmental conditions’

Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations

Published 5 May 2026 Science Leave a Comment
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The oceanic uptake of anthropogenic CO2 has resulted in ocean acidification (OA). Macroalgae farming has the potential to mitigate OA by removing CO2 from the surface water via photosynthesis. However, continuous in-situ observations of marine carbonate chemistry related to macroalgae farming remain limited, leaving its effectiveness in addressing OA uncertain. To address these knowledge gaps, this study examined a 2-acre Saccharina latissima, sugar kelp, farm located at Point Judith, Rhode Island, as a case study to assess the potential of sugar kelp aquaculture in mitigating local OA. Over the full growing season from December 2022 to May 2023, high-temporal-resolution (every 30–60 minutes) measurements of surface temperature, salinity, dissolved oxygen and pH were taken inside and outside the kelp farm. The results demonstrate that sugar kelp farming does not significantly impact the carbonate system, thus providing negligible OA mitigation locally. Specifically, a temporary, local-scale CO2 reduction and higher pH occurred during very early kelp growth in early February, but was reversed by a higher surface CO2, exaggerating OA, starting in mid-February. Over the entire observation period, kelp growth resulted in a 5.1 ± 11.6 μatm increase of pCO2 per week compared to the control site in the surface, a signal which is small compared to the substantial natural variability. However, the minimal pCO2 difference at the kelp farm may be reflective of the relatively small cultivation area (2 acres) or depressed growth of phytoplankton, resulting from nutrient competition between the kelp and in-situ phytoplankton. This study underscores the need for future sustained observations to evaluate the impact of seaweed cultivation on OA mitigation and the carbon cycle at the ecosystem scale.

Continue reading ‘Evaluating the role of seaweed farming in ocean acidification mitigation: insights from high-frequency observations’

Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment

Published 30 April 2026 Science Closed
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Highlights

  • Reduced pH enhances ammonium toxicity on sea urchin embryos in filtered seawater.
  • In elutriates ammonium is a major driver of P. lividus embryotoxicity.
  • Data support setting ammonium thresholds in sediment quality frameworks.
  • Ocean acidification potentially increases ammonium toxicity for sea urchin larvae.

Abstract

Ammonium is a key component of coastal marine systems, originating from both natural and anthropogenic sources, with possible toxic effects on marine organisms depending on the concentration and pH. This study evaluates, for the first time, the combined effects of ammonium and seawater acidification on early development of the sea urchin Paracentrotus lividus under both laboratory conditions and exposure to environmental matrices derived by dredged sediments from harbor area. Embryos were incubated with increasing concentrations of ammonium in filtered seawater at pH 8.1 and 7.6, as well as in sediment elutriates from the Pescara harbor (Adriatic Sea, Italy), selected as a case study with relevant concentrations of ammonium (0.1–3.5 mg/L). A combined effect between ammonium and pH was observed, with increasing ammonium toxicity by ∼20% at pH 7. Moreover, in sediment elutriates, ammonium affect sea urchin embryo development, with EC50 ranging between 1.388 and 1.538 mg/L NH4+ at pH 8.1 and 7.6, respectively, without significant differences due to pH. Chemical analyses of sediments confirmed low levels of trace metals and organic pollutants, indicating that ammonium is the primary driver of embryotoxicity without a direct toxic effect of other contaminants. The results further underscore the need to integrate ammonium assessment into sediment quality frameworks and for management strategies, particularly in the context of future ocean acidification, to safeguard the early life stages of sensitive marine invertebrates.

Continue reading ‘Combined effects of ammonium and pH on sea urchin embryogenesis: insights for sediment quality assessment’

Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)

Published 29 April 2026 Science Closed
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Ocean acidification is expected to be particularly severe in Antarctic continental shelves due to enhanced anthropogenic carbon uptake in cold waters in response to rising atmospheric CO2, sea-ice retreat, freshening and climate-change feedbacks. Models suggest that undersaturated conditions with respect to aragonite (Ωar), a major form of calcium carbonate formed by marine species, could be reached as soon as 2052 for austral winter.  Here we present new ocean carbonate system observations from cruises conducted since 2010 in the Adélie Land coastal region in East Antarctica, along with data from a BCG-Argo float and results from a neural network model for the period 1985–2025. The region is a permanent CO2 sink and was most pronounced since 2006. The CO2 sink leads to a positive increase of surface water total CO2 concentrations (CT) (+0.44 ± 0.01 µmol.kg-1.yr-1) and to a progressive decrease of pH (-0.013 per decade) and Ωar (-0.035 per decade) for the winter season. The lowest surface Ωar of 1.2 was observed in winter 2024 from the float data, a critical limit for some marine species such as pteropod. A projection of the CT concentrations in the future, based on observed anthropogenic CO2 concentrations and emissions scenarios, suggests that aragonite saturation state (Ωar = 1) will occur in surface waters as soon as 2055 in the Adélie Land region, which is part of a larger area of East Antarctica proposed as a Marine Protected Area by the Commission for the Conservation of Antarctic Marine Living Resources since the early 2010s.

Continue reading ‘Acidification in coastal waters of Adélie Land, Antarctica (1985–2025)’

Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae

Published 29 April 2026 Science Closed
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While harmful algal blooms (HABs) and ocean acidification (OA) are environmental factors that can impair bivalves, the manner in which these two stressors may act and interact to impact bivalve larvae is poorly understood. This study exposed larvae of hard clams (Mercenaria mercenaria) and Eastern oysters (Crassostrea virginica) to a range of pCO2 levels found in estuaries (400–3,000 µatm) and three harmful algae, Alexandrium catenella, Dinophysis acuminata, and Margalefidinium polykrikoides, at densities found during HABs (500–7,000 cells mL-1), with one HAB species exposure per experiment. The combined OA and HAB treatment significantly reduced larval survival in all 21 experiments by 91 ± 4.6% (SE) compared to controls and reduced larval sizes in 92% of experiments by 40 ± 3.5%. Cultured M. polykrikoides had a stronger negative effect on larvae than cellular equivalent bloom populations. Densities of D. acuminata >750 cells mL-1 reduced larval survival and size (p < 0.01), but the addition of OA to D. acuminata did not suppress survival further. While the combined A. catenella and OA treatment reduced larval growth and survival at all densities (p < 0.01), A. catenella alone did not impact M. mercenaria survival or size at or below 1,000 cells mL-1 and did not impact C. virginica at any density. Oyster larvae were less impacted than hard clams by OA (33 vs. 67% of experiments) and by HABs (67 vs. 100% of experiments). Given the very low survival of bivalve larvae when exposed to combined HABs and OA in all experiments (<0.1–5%), bivalve restoration and conservation efforts should seek to avoid regions that experience these co-stressors.

Continue reading ‘Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae’

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