Coastal zones are key players in the global carbon cycle, yet the temporal dynamics of their carbonate system, particularly in tropical rhodolith habitats, remain understudied. This study assessed seasonal and spatial variability in carbonate chemistry in Gairaca Bay, a protected tropical bay within Tayrona National Natural Park, Colombian Caribbean. Sampling was conducted in 2023–2024 across three habitats: a rhodolith bed (1, 7, 15 m depth), the bay entrance (outer bay, 10 m depth), and a shallow sandy-bottom area (inner bay, 1 and 6 m depths). Temperature, salinity, and total scale pH (pHT) were measured in situ; total alkalinity (TA) was determined via open-cell titration, and dissolved inorganic carbon (DIC), pCO2, bicarbonate (HCO3–), carbonate (CO32-), and aragonite saturation state (Ωarag) were calculated. Seasonal and spatial patterns were analyzed using PERMANOVA. Significant seasonal differences were found in temperature (F = 248.42, p < 0.05), salinity (F = 49.02, p < 0.05), TA (F = 7.65, p < 0.001), and DIC (F = 2.54, p < 0.001), with no significant variation among sites or depths. Upwelling periods were cooler and saltier (25.9 ± 1.14 °C; 34.48 ± 0.46), with elevated TA and DIC, and slightly lower pHT and Ωarag. Non-upwelling periods were warmer (30.0 ± 0.76 °C), less saline (33.36 ± 0.28), and had higher pHT and Ωarag. Seasonal delta analysis indicated greater variability during non-upwelling, linked to enhanced freshwater discharge. The outer bay showed the highest variability in pHT and Ωarag, while the inner bay was most stable for TA and DIC. The rhodolith bed bottom exhibited high TA variability but stability in pHT and Ωarag, especially during non-upwelling. Seasonal processes, including upwelling and freshwater inputs, drive carbonate system variability in Gairaca Bay. The stability of pHT and Ωarag in the rhodolith bed bottom suggests a potential role as a biogeochemical refuge in acidification-prone tropical environments.
Continue reading ‘Temporal dynamics of the carbonate system in a tropical rhodolith bed from a protected Caribbean bay’Posts Tagged 'North Atlantic'
Temporal dynamics of the carbonate system in a tropical rhodolith bed from a protected Caribbean bay
Published 1 September 2025 Science ClosedTags: chemistry, field, North Atlantic
What doesn´t kill you makes you stronger: the sea urchin Arbacia lixula living on volcanic CO2 vents
Published 1 September 2025 Science ClosedTags: adaptation, biological response, echinoderms, field, morphology, North Atlantic, otherprocess, vents
Anthropogenic CO2 emissions drive ocean acidification (OA), which reduces seawater pH and carbonate ion availability, threatening calcifying organisms such as sea urchins. This study examines the long-term effects of OA on Arbacia lixula using a natural volcanic CO2 vent at Fuencaliente, La Palma (Canary Islands) as an analogue of future conditions. We analyzed the external morphology, skeletal strength, mineralogy, and growth of A. lixula across three sites that differed consistently in mean pH (from 8.14 to 7.65 during low tide). Sea urchins from low pH conditions were smaller, with shorter spines and reduced jaw-to-diameter ratios, yet their tests showed higher fracture resistance than those from ambient conditions. Additionally, individuals from acidified zones showed altered growth dynamics, with fewer growth rings. Skeletal changes and growth alterations are consistent with modified mineralization processes and dietary shifts toward non-calcareous food sources. This study highlighting the morphological plasticity and resilience of A. lixula under persistent natural acidification, offering insight into how sea urchins may respond in a high-CO2 ocean.
Continue reading ‘What doesn´t kill you makes you stronger: the sea urchin Arbacia lixula living on volcanic CO2 vents’Wind control of the interannual ocean-biogeochemical variability in the South Atlantic Bight
Published 29 August 2025 Science ClosedTags: biogeochemistry, chemistry, modeling, North Atlantic, regionalmodeling
In the South Atlantic Bight (SAB), changes in the strength and proximity to the coast of the Gulf Stream are thought to be primary factors determining the shelf-break upwelling rate. However, it is still not clear if and to what extent those factors influence cross-shelf nutrient fluxes and shape the ocean biogeochemistry at interannual and longer timescales. Here, we use a high-resolution regional ocean-biogeochemical model, an ocean reanalysis product, and a satellite-derived chlorophyll dataset to investigate the interannual ocean-biogeochemical variability in the SAB during 1993-2022. Regional model outputs suggest that year-to-year changes in phytoplankton production are indeed largely driven by upwelling of cold and nutrient-rich water to the shelf-break. The upwelling variability, reflected in bottom temperature and vertically integrated production patterns, is strongly linked to surface velocity changes in the Gulf Stream near the shelf break, but weakly related to the depth-integrated Gulf Stream transport. The Gulf Stream’s velocity changes, and the temperature and production anomalies, are well correlated to the alongshore wind stress, suggesting that local wind is the leading driver of the shelf-break upwelling variability. Those relationships are also supported by circulation patterns from ocean reanalysis and satellite chlorophyll anomalies. Finally, we examine the simulated carbonate system changes linked to the slope-shelf interchanges, finding that shelf-break upwelling significantly increases bottom acidification, a pattern linked to the low carbonate concentration in the slope waters. Our study thus provides new insight to better constrain the impacts of the Gulf Stream and local wind on the SAB biogeochemical variability.
Continue reading ‘Wind control of the interannual ocean-biogeochemical variability in the South Atlantic Bight’Within and cross-generational effects of elevated seawater pCO2 on larval bay scallops Argopecten irradians (L)
Published 27 August 2025 Science ClosedTags: adaptation, biological response, growth, laboratory, mollusks, morphology, mortality, North Atlantic, otherprocess, reproduction
Bivalve larvae are highly susceptible to ocean acidification (OA), but there is little knowledge of the capacity of bivalve species to acclimate or adapt to changing ocean conditions. It is challenging to compare results among studies of OA reported in the literature, as there is little consistency among studies in water chemistry across OA treatments used or how OA conditions were determined. In addition, it is difficult to predict from short-term experiments how populations might respond across generations. The bay scallop, Argopecten irradians, is a good model species for such experiments because of its short generation time and importance commercially and ecologically. Bay scallops were exposed to OA conditions from embryos to metamorphosis across two generations. Ocean acidification treatment levels included historical or preindustrial “low” (pCO2 ∼450 µatm), current average “moderate” (∼800 µatm), and future “high” (∼1,350 µatm). In the first generation, high OA had negative effects on larval performance, with no survival to metamorphosis, preventing its inclusion in the second generation. Moderate OA reduced performance (survivorship and growth) relative to the low OA. In the second generation, however, there was no difference in survival between the moderate and low OA treatments, but the difference in size at metamorphosis remained. These results suggest that over two generations, bay scallops either acclimated or adapted to moderate OA. Further work is needed to determine the extent to which long-term, generational adaptation to OA is possible in the bay scallop.
Continue reading ‘Within and cross-generational effects of elevated seawater pCO2 on larval bay scallops Argopecten irradians (L)’The development and plasticity of acid excretion mechanisms in early life stage red drum, Sciaenops ocellatus
Published 21 August 2025 Science ClosedTags: biological response, fish, laboratory, molecular biology, North Atlantic, physiology, reproduction
Highlights
- Components of acid-base pathways are present and stable in very early development.
- NHE3 is localized to the apical pit of epithelial ionocytes.
- Epithelial proton excretion is responsive to elevated CO2 and governed by NHEs.
- nhe2/3 transcript abundance is elevated following development in high CO2.
- Low level CO2 causes reductions in survival.
Abstract
Ocean acidification (OA) has been shown to affect early life stage fishes in a variety of ways, including reduced survival and growth, and increased tissue damage. Yet, there is also substantial interspecies variability in the sensitivity of early life stage fishes to high CO2, and it has been theorized that this may relate to the ontogeny of systemic acid-base regulatory pathways; an area that has been surprisingly understudied in obligate marine species. Here, we used an integrative set of approaches to describe the development and plasticity of acid excretion pathways in developing red drum (Sciaenops ocellatus), a marine fish native to the Gulf of Mexico. We observed mRNA expression of relevant transporters and ionocytes immediately post-hatch (36 h post-fertilization, hpf) with relatively stable abundance throughout the pre-metamorphic stages. Consistent with work in adults and seawater acclimated euryhaline larvae, we demonstrate strong co-localization of acid excretion proteins within a single epithelial ionocyte cell-type. Measurements of epithelial Δ[H]+, an indicator of proton efflux, showed that by 72 hpf larvae had CO2-responsive EIPA-sensitive acid excretion, confirming the presence of sodium proton exchanger (NHE)-mediated acid excretion. Elevated mRNA expression of nhe2 and nhe3 was induced following exposure to 5500 and 12,000 μatm CO2, which coincided with the absence of further survival effects relative to lower dose CO2. Overall, these data confirm that red drum have fully functional epithelial acid excretion pathways in early life, and that plasticity in these pathways may offer survival benefits.
Continue reading ‘The development and plasticity of acid excretion mechanisms in early life stage red drum, Sciaenops ocellatus’Ocean and coastal acidification monitoring priorities for the Northeast US and Eastern Canada
Published 20 August 2025 Newsletters and reports ClosedTags: North Atlantic, policy
The Interagency Working Group on Ocean Acidification Monitoring Prioritization Plan 2024 calls for Coastal Acidification Networks to identify the ocean and coastal acidification (OCA) monitoring needs most important for their regions. The Northeast Coastal Acidification Network (NECAN) organized a webinar series to study regional needs, which culminated with a workshop in November 2023. This workshop led to the identification of six priority new Monitoring Needs in addition to the maintenance of current monitoring efforts:
- Improve spatial and temporal scale of monitoring co-located OCA variables and biological measurements to better resolve variability of acidification dynamics in concert with biological processes
- Increase subsurface monitoring to understand how conditions vary at depth
- Increase the number of high-frequency monitoring assets that measure at least two of four carbon parameters
- Increase near-real-time and rapid response observing capacity for episodic events
- Determine fluxes and rates that would help parameterize and constrain regional modeling efforts to understand past conditions and project future trends
- Increase spatial coverage of “climate”-quality observations
This report presents monitoring needs and opportunities for consideration by coastal managers, decision makers, researchers, and monitoring groups. It offers options to apply new capacity or funding to the expansion of OCA monitoring in the NECAN region. Writing the report led to the identification of eight cross-cutting actions which will lead to the implementation of these Monitoring Needs:
- Expand monitoring beyond carbonate chemistry to provide a complete assessment of OCA, its effects, and future trends.
- Enhance or leverage existing monitoring platforms for a cost-effective and collaborative approach to creating a more complete OCA monitoring system in the NECAN region.
- Expand the NECAN membership to include protected area experts, terrestrial biogeochemists and hydrologists, fisheries experts, social scientists, Tribal liaisons, project leads from large assessments, and other important stakeholders, rights holders and decision makers.
- Increase funding in the Northeast to both sustain currently-stretched efforts and grow a more robust ocean acidification monitoring program.
- Pursue immediate implementation of proxy approaches or interim strategies for measurements with technological or capacity limitations, while new technologies are being developed.
- Synthesize monitoring information to advance the understanding of OCA in the region.
- Deploy monitoring assets strategically, with end-user needs in mind, ensuring that the collected data is accessible, relevant, and useful for decision-making.
- Share NECAN’s experience in developing these recommendations with other Coastal Acidification Networks and regional monitoring programs.
A climate vulnerability assessment for U.S. highly migratory fishes in the Atlantic Ocean
Published 18 August 2025 Science ClosedTags: biological response, fish, North Atlantic, review
Climate change will continue to alter key physical and biological oceanographic processes throughout the global ocean, modifying environmental conditions for U.S. highly migratory fish species found in the Atlantic Ocean. The Atlantic Highly Migratory Species Climate Vulnerability Assessment evaluated the vulnerability of 58 species and stocks to projected ocean conditions, using a combined qualitative and quantitative analysis of species sensitivity (physiological, ecological, and behavioral attributes) and estimated exposure to possible future ocean stressors. Key modeled environmental variables included bottom and sea surface temperature, sea surface oxygen, and ocean acidification (pH), whereas the most influential biological attributes considered were population growth rate, stock size, and stock status. We produced vulnerability rankings (i.e., low, moderate, high, and very high) based on biological attribute sensitivity and exposure to the environmental variables, and separate analyses including estimated ability of distributional shifts, predicted directional effects of climate change, certainty, and data quality scores for the species and stocks assessed, with exceptions for species with undetermined geographic distributions. Of the 58 species and stocks assessed, 4 had very high vulnerability to climate change, 14 had high vulnerability, 22 had moderate vulnerability, 6 had low vulnerability, and 12 could not be assigned a rank. The majority (n = 45) of species and stocks had high ability for distributional shifts in response to projected changes in climate. Further, directional effect results suggest that climate change impacts on the majority of species and stocks will be neutral, implying that these species have life history or behavioral traits that impart some level of resilience and adaptability to the impacts of climate change. These results provide information for use in ecosystem-based fisheries management, particularly for prioritization of vulnerable species and stocks in conservation activities and research endeavors.
Continue reading ‘A climate vulnerability assessment for U.S. highly migratory fishes in the Atlantic Ocean’Molecular markers of stress in the sea urchin embryo test: analysing the effect of climate change and pollutant mixtures on Paracentrotus lividus larvae
Published 15 August 2025 Science ClosedTags: biological response, echinoderms, laboratory, molecular biology, morphology, multiple factors, North Atlantic, plastics, reproduction, temperature, toxicants
Highlights
- Combined effects of ocean stressors on sea urchin larvae were analysed.
- RNA-seq revealed key transcriptional changes under stressor combinations.
- Larval growth and deformities worsened with acidification and warming.
- Biomarkers for early detection of stress in marine larvae were identified.
- Insights contribute to predicting organismal responses to climate change.
Abstract
Climate change and pollution represent critical stressors for marine ecosystems, particularly for calcifying organisms such as the sea urchin Paracentrotus lividus. This study examines the combined effects of ocean acidification (OA), ocean warming (OW), and microplastics (MP) loaded with chlorpyrifos (CPF), a broad-spectrum organophosphate insecticide, on sea urchin larvae, evaluating growth and molecular endpoints. Experimental treatments simulated future ocean conditions predicted for 2100, exposing larvae to varying temperature and pH levels, alongside CPF-contaminated MP. RNA sequencing (RNA-seq) was utilized to assess gene expression changes, revealing significant transcriptional shifts in metabolic, cellular, and developmental pathways. Morphological responses showed reduced larval growth, exacerbated under OA and OW conditions. Molecular analyses identified key upregulated pathways associated with stress response, including nitrogen metabolism and extracellular matrix remodelling, while downregulated genes involved DNA stability, cell cycle regulation, and enzymatic activities. These findings suggest a dual compensatory and deleterious response to combined stressors. Notably, temperature acted as a modulator of stressor effects, amplifying oxidative stress and metabolic costs at higher temperatures. Potential biomarkers, such as genes involved in actin regulation and embryonic development, were identified, offering possible tools for early detection of environmental stress. This study highlights the compounded impacts of anthropogenic and climate-induced stressors on marine invertebrates, emphasizing the need for integrative molecular approaches in ecotoxicology. Our findings contribute to the understanding of organismal adaptation and vulnerability in the face of global climate change and pollution, informing conservation strategies for marine ecosystems.
Continue reading ‘Molecular markers of stress in the sea urchin embryo test: analysing the effect of climate change and pollutant mixtures on Paracentrotus lividus larvae’Tubastraea coccinea (Lesson, 1830), a coral species with high invasive potential, can benefit from the synergistic effects of ocean warming and acidification
Published 14 August 2025 Science ClosedTags: biological response, calcification, corals, laboratory, morphology, multiple factors, North Atlantic, reproduction, respiration, temperature
Temperature rise and pH decrease, coupled with increasing maritime traffic, are inducing modifications in the distribution of many exotic species, such as Tubastraea coccinea, a species with high invasive potential recently recorded in the Canary Islands. This study assessed the effect of the expected end-of-century temperature and pH (26°C and pH 7.50) on this coral species through manipulative laboratory experiments conducted over different time periods (30 days vs. 80 days). The impact of acidification, warming, and time on variables such as weight, buoyant weight, number of new polyps, area, respiration, calcification and reproduction rates were analysed. Results revealed a negative effect of acidification on growth and respiration rates of T. coccinea, with significant differences between experimental treatments in weight, buoyant weight, number of polyps, area, and respired carbon. However, in future, T. coccinea may not be adversely affected by low pH values, as the negative effect is mitigated when colonies are exposed to 26°C. Using different experimental periods showed how this species’ response is liable to change over time under future climate change conditions.
Continue reading ‘Tubastraea coccinea (Lesson, 1830), a coral species with high invasive potential, can benefit from the synergistic effects of ocean warming and acidification’Mechanisms of ocean acidification in Massachusetts Bay: insights from modeling and observations
Published 11 August 2025 Science ClosedTags: chemistry, modeling, North Atlantic, regionalmodeling
Massachusetts Bay in the northeastern United States is highly vulnerable to ocean acidification (OA) due to reduced buffering capacity from significant freshwater inputs. We hypothesize that acidification varies across temporal and spatial scales, with short-term variability driven by seasonal biological respiration, precipitation–evaporation balance, and river discharge, and long-term changes linked to global warming and river flux shifts. These patterns arise from complex nonlinear interactions between physical and biogeochemical processes. To investigate OA variability, we applied the Northeast Biogeochemistry and Ecosystem Model (NeBEM), a fully coupled three-dimensional physical–biogeochemical system, to Massachusetts Bay and Boston Harbor. Numerical simulation was performed for 2016. Assimilating satellite-derived sea surface temperature and sea surface height improved NeBEM’s ability to reproduce observed seasonal and spatial variability in stratification, mixing, and circulation. The model accurately simulated seasonal changes in nutrients, chlorophyll-a, dissolved oxygen, and pH. The model results suggest that nearshore areas were consistently more susceptible to OA, especially during winter and spring. Mechanistic analysis revealed contrasting processes between shallow inner and deeper outer bay waters. In the inner bay, partial pressure of pCO2 (pCO2) and aragonite saturation (Ωa) were influenced by sea temperature, dissolved inorganic carbon (DIC), and total alkalinity (TA). TA variability was driven by nitrification and denitrification, while DIC was shaped by advection and net community production (NCP). In the outer bay, pCO2 was controlled by temperature and DIC, and Ωa was primarily determined by DIC variability. TA changes were linked to NCP and nitrification–denitrification, with DIC also influenced by air–sea gas exchange.
Continue reading ‘Mechanisms of ocean acidification in Massachusetts Bay: insights from modeling and observations’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’Long-term pH trends across depth in coastal areas of the southeastern Bay of Biscay
Published 1 August 2025 Science ClosedTags: chemistry, field, North Atlantic
Highlights
- We examined pH trends over time across depth in the Basque coast upon 21733 observations during 2002-2022.
- Significant pH decreases over time (0.022 to 0.041 units decade-1) across 0-100m likely driven by the global increase of atmospheric CO2.
- Marked seasonality and higher ocean acidification rates in deeper relative to surface layers tied to environmental factors and the biological activity.
- Importance of pH monitoring in coastal areas to warn on the effect of ocean acidification on marine ecosystems.
Abstract
Increased CO2 concentrations in the atmosphere have triggered ocean acidification over the past decades in the global ocean. However, regional efforts of pH monitoring across the southern Bay of Biscay´s Basque coast remain elusive, with only a few short-term studies limited to the ocean’s surface. Here we examine pH trends over time across the Basque coast using 21733 observations of long-term data collected during 2002-2022 with quarterly CTD casts from surface down to 100 m at three coastal sites. Results revealed significant pH decreases over time in all depth layers (0.5-100 m) at the three coastal sites (0.022 to 0.041 units decade-1), presumably driven by the global increase of atmospheric CO2. Across depth, the pH trends observed also showed significantly higher ocean acidification rates with depth. Seasonally, observed changes ranged from wintertime highs of 8.18 ± 0.07 to summertime lows of 8.14 ± 0.05, with a mean seasonal amplitude of about ∼0.04 pH units. The observed pH seasonality and vertical patterns appeared to be tied to the combined effect of environmental factors alongside the development of the thermocline as well as to differences in the biological activity across the water column. Taken together, these findings highlight the importance of pH monitoring in coastal areas to warn on the effect of ocean acidification on marine ecosystems and the services they provide to society.
Continue reading ‘Long-term pH trends across depth in coastal areas of the southeastern Bay of Biscay’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’Unraveling natural carbonate variability in Narragansett Bay, RI using multiple high temporal resolution pH time series
Published 30 July 2025 Science ClosedTags: chemistry, field, North Atlantic
The increase in atmospheric carbon dioxide (CO2) over the last 200 years has largely been mitigated by the ocean’s function as a carbon sink. However, this continuous absorption of CO2 by seawater triggers ocean acidification (OA), a process in which water becomes more acidic and more depleted in carbonate ions that are essential for calcifiers. OA is well-studied in open ocean environments; however, understanding the unique manifestation of OA in coastal ecosystems presents myriad challenges due to considerable natural variability resulting from concurrent and sometimes opposing coastal processes—e.g. eutrophication, changing hydrological conditions, heterogeneous biological activity, and complex water mass mixing. Developing a mechanistic understanding of carbonate chemistry variability and its drivers across different time scales is a critical first step in identifying the anthropogenic OA signal against background variability and predicting future OA in coastal systems. This study analyzed high temporal resolution pH data collected during 2022 and 2023 from Narragansett Bay, RI—a mid-sized, urban estuary that since 2005 has undergone a 50% reduction in nitrogen loading—with weekly, discrete bottle samples to verify sensor data. Over a year’s worth of data revealed a distinct diurnal cycle of pH, with pH increasing during the day and decreasing during the night, with an average daily range between 0.05 and 0.1 pH units. Further, we observed a strong seasonal cycles with higher mean pH in winter (8.07 ± 0.15) and lower mean pH in summer (7.72 ± 0.07). By separating the drivers of pH variability into effects from temperature, salinity, water mass mixing, biological activity, and air-sea gas flux, we determined that biological production has the most significant influence on pH from daily to annual timescales and in episodic pH changes. To a lesser extent, the seasonal air-sea CO2 exchange and temperature cycle further modified pH on monthly to seasonal timescales. The dominant influence of biological activity in modulating pH has allowed Narragansett Bay’s nutrient reductions, which have been successful in increasing bottom water DO and pH conditions, to modestly reduce summertime surface pH through reduced primary production. This study offers an in-depth understanding of Narragansett Bay’s natural carbonate variability and highlights the sensitivity of an estuary to water management policy. These findings will benefit future OA prediction and will ultimately assist in making environmental management decisions in coastal estuaries with implications for multiple coastal stakeholders.
Continue reading ‘Unraveling natural carbonate variability in Narragansett Bay, RI using multiple high temporal resolution pH time series’Seasonal upwelling drives surface water biogeochemistry with implication for ocean acidification along the Northwest African coast
Published 25 July 2025 Science ClosedTags: biogeochemistry, chemistry, field, North Atlantic
This study assesses the impact of intensified upwelling on the marine carbonate system along the Northwest African coast, from Cape Blanc (21°N) to Cape Cantin (33°N), a region where ocean acidification observations remain limited. We analyze surface water variability using data from two oceanographic surveys conducted aboard the R/V Dr. Fridtjof Nansen in spring and autumn 2022. The analysis is based on observational data of temperature, salinity, dissolved oxygen, chlorophyll a, pH, total alkalinity, and derived carbonate system variables. In spring, upwelling was widespread across the study area, while in autumn it was more localized near Cape Draa (28°30’N), between Cape Boujdour and Dakhla (25°30N–23°30N), and at Cape Blanc (21°N). Both spring and autumn were influenced by low-oxygenated South Atlantic Central Water (SACW), which is rich in DIC (2160–2250 µmol/kg), and upwelled to the surface, lowering pH (~7.85–7.95) and aragonite saturation state (ΩAr ~1.5–2.5). The strongest acidification signals were observed in autumn at Cape Draa (28°30N) and Cape Blanc (21°N), where the lowest pH (7.8) and ΩAr (1.5), along with the highest DIC (2250 µmol/kg), were recorded. The study clearly shows that the lowest pH values and highest DIC concentrations were related to the influence of SACW upwelling at Cape Blanc. It was also evident that areas with high chlorophyll a coincided with higher ΩAr and pH in spring. This suggests that primary production (PP) during spring counteracts the effect of upwelled low-pH water along the coast. Areas of high PP, such as at Cape Draa (28°30N), experienced increased DIC levels and enhanced acidification after the bloom season, potentially influenced by organic matter remineralization. Our findings highlight the influence of upwelling and biological processes on surface carbonate chemistry along the Northwest African coast. This study emphasizes the necessity of long-term monitoring to assess ocean acidification trends and their ecological implications in this vulnerable region.
Continue reading ‘Seasonal upwelling drives surface water biogeochemistry with implication for ocean acidification along the Northwest African coast’River alkalinization and ocean acidification face off in coastal waters
Published 22 July 2025 Press releases ClosedTags: chemistry, North Atlantic
The Chesapeake Bay is the continental United States’ largest estuary, spanning approximately 320 kilometers (200 miles) between northeastern Maryland and Virginia Beach. Like many coastal ecosystems, its water chemistry is affected by agricultural runoff, chemical weathering, and increasing atmospheric carbon dioxide.
Although rising carbon dioxide levels have led to ocean acidification, land use changes and chemical weathering from acid rain have made inland rivers and streams generally more alkaline. But long-term pH trends in coastal waters, such as the Chesapeake Bay, are less clear.
Li et al. ran a simulation to analyze pH trends in the Chesapeake Bay between 1951 and 2010, revealing a complex web of factors that altered the bay’s pH over that 60-year period.
Nutrient runoff into the Chesapeake Bay increased between 1950 and 1980 before dropping in the 1990s, thanks primarily to decreased atmospheric deposition of nitrogen and to upgrades in wastewater treatment systems. Agricultural lime application and intensified chemical weathering, which also decrease acidity, became more common over the study period. In contrast, coal mining, drainage from which can increase water acidity, declined over the study period. Weather played a role as well: Typical spring rainfall, as well as particularly wet decades such as the 1970s, pushed the upper bay freshwater plume farther into the middle of the bay and increased the area’s pH.
The researchers examined all these factors and found that overall, the upper bay generally became more alkaline over time but that deeper waters in the middle and lower bay became more acidic. No long-term trend in the pH of the surface waters of the middle and lower bay was observed, as the effects of river alkalinization and ocean acidification mixed and essentially canceled each other out.
They found that river alkalinization had twice the effect on the Chesapeake Bay’s long-term pH trends compared with ocean acidification. Both processes played a greater role than coastal eutrophication did.
The researchers say their results suggest the potential effectiveness of ocean alkalinity enhancement, a geoengineering technique that adds alkaline minerals to the ocean, for increasing carbon dioxide removal from the atmosphere. (AGU Advances, https://doi.org/10.1029/2024AV001350, 2025)
Continue reading ‘River alkalinization and ocean acidification face off in coastal waters’Timing of calcification and environmental variability determine pH proxy fidelity in coastal calcifying macroalgae
Published 21 July 2025 Science ClosedTags: algae, biological response, chemistry, field, mesocosms, North Atlantic, paleo, physiology, South Pacific
Long-lived calcifying marine biota are increasingly used as paleo-archives for reconstructing ocean pH. They enable exploration of the rate and magnitude of ocean acidification in shallow-water ecosystems serving as proxies for environmental pH reconstruction. However, shallow water systems often have highly variable carbonate chemistry, and the impact of this on the accuracy of pH reconstructions from long-lived marine calcifiers is not known. In particular, a better understanding of the timing of calcification with respect to environmental pH cyclicity is needed. To test the fidelity of coastal environmental pH proxies, we assessed the synchronicity between calcification and in situ diel carbonate chemistry in a tropical (One Tree Island, Great Barrier Reef, Australia) and a temperate (Loch Sween, Scotland) location using calcifying macroalgae (rhodolith-forming coralline algae) as a model system. Calcification occurred primarily during daylight hours, meaning a recording bias was introduced when compared to the full diel pH range (< 0.02 pH units). This bias resulted in pH offsets up to 0.043 pH units over the period 1860–2020, representing up to 34% of the projected pH change from 1860 in the tropics and up to 1.8% in temperate latitudes. Therefore, when proxy records are used to extend modern instrumental records of pH, we find that this may lead to bias, indicating daytime, nighttime, and full diel pH records should be assessed separately. We suggest that temporal pH cycles should be characterized at a local scale to enable incorporation of potential biases in the application of calcifying marine macroalgae to reconstruct pH change.
Continue reading ‘Timing of calcification and environmental variability determine pH proxy fidelity in coastal calcifying macroalgae’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’Cross-generational plasticity in Atlantic silversides (Menidia menidia) under the combined effects of hypoxia and acidification
Published 17 July 2025 Science ClosedTags: biological response, fish, laboratory, molecular biology, mortality, multiple factors, North Atlantic, oxygen, physiology, reproduction
We investigated the potential for cross-generational plasticity to influence how offspring respond to hypoxia and ocean acidification (hereafter HypOA) in the coastal forage fish Atlantic silverside (Menidia menidia). Mature wild silversides were treated with a control (dissolved oxygen (DO):100% air saturation (a.s.) / pCO2: 650 µatm) or HypOA conditions (DO: 40% a.s. / pCO2: 2300 µatm) for 10 days prior to spawning. Their offspring were reared under both treatments in factorial experimental design. Parental environment had minimal effects on offspring phenotype: exposure to HypOA reduced survival and developmental rates regardless of parental treatment. However, RNAseq analysis revealed that direct offspring exposure to HypOA induced substantial transcriptional changes, with 1,606 differentially expressed transcripts (DETs) in larvae from control parents. These changes affected neural development, synaptic signaling, oxygen acquisition, and extracellular matrix organization. In contrast, larvae from HypOA-exposed parents exhibited a muted transcriptional response to HypOA, with only 4 DETs. Although we did not detect a statistically significant interaction between parental and offspring environments at the gene-wise level, a gene set test supported a consistent attenuation of expression changes in offspring from HypOA-treated parents. This pattern may be consistent with transcriptional frontloading, when stress-induced changes are retained and may modify future responses. However, because this effect did not improve offspring performance under HypOA, they are unlikely to represent an adaptive response. Instead, they may reflect non-adaptive carryover effects of parental exposure. Our findings highlight the potential for cross-generational effects to shape transcriptional plasticity, even in the absence of benefits to offspring.
Continue reading ‘Cross-generational plasticity in Atlantic silversides (Menidia menidia) under the combined effects of hypoxia and acidification’Acidification, warming, and nutrient management are projected to cause reductions in shell and tissue weights of oysters in a coastal plain estuary
Published 16 July 2025 Science ClosedTags: biological response, communitymodeling, fisheries, modeling, mollusks, morphology, multiple factors, North Atlantic, nutrients, respiration, temperature
Coastal acidification, warming, and nutrient management actions all alter water quality conditions that marine species experience, with potential impacts to their physiological processes. Decreases in calcite saturation state (ΩCa) and food availability, combined with warming water temperatures, pose a threat to calcifying organisms; however, the magnitude of future changes in estuarine systems is challenging to predict and is not well known. This study aims to determine how and where oysters will be affected by future acidification, warming, and nutrient reductions, and the relative effects of these stressors. To address these goals, an oyster growth model for Eastern oysters (Crassostrea virginica) was embedded in a 3-D coupled hydrodynamic-biogeochemistry model implemented for two tributaries in the lower Chesapeake Bay. Model simulations were forced with projected future conditions (mid-21st century atmospheric CO2 and atmospheric temperature under Representative Concentration Pathway (RCP) 8.5, as well as managed nutrient reductions) and compared with a realistic present-day reference run. Together, all three stressors are projected to reduce ΩCa and growth of oyster shell and tissue. Increased atmospheric CO2 is projected to cause widespread reductions in ΩCa. The resulting reductions in oyster shell and tissue growth will be most severe along the tributary shoals. Future warming during peak oyster growing seasons is projected to have the strongest negative influence on tissue and shell growth, due to summer water temperatures reducing filtration rates, enhancing shell dissolution and oyster respiration rates, and increasing organic matter remineralization rates, thus reducing food availability. Nutrient reductions will exacerbate deficits in oyster food availability, contributing to further reductions in growth. Quantifying the effects of these stressors provides insight on the areas in the lower bay where oysters will be most vulnerable to mid 21st-century conditions.
Continue reading ‘Acidification, warming, and nutrient management are projected to cause reductions in shell and tissue weights of oysters in a coastal plain estuary’
