Posts Tagged 'North Atlantic'

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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 Closed
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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 Closed
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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 Closed
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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.

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Mangrove-driven acidification and shell dissolution on intertidal oyster reefs in a subtropical estuary

Published 4 August 2025 Science Closed
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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.

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Long-term pH trends across depth in coastal areas of the southeastern Bay of Biscay

Published 1 August 2025 Science Closed
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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.

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Species-specific mechanisms of benthic foraminifera in response to shell dissolution

Published 31 July 2025 Science Closed
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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.

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Unraveling natural carbonate variability in Narragansett Bay, RI using multiple high temporal resolution pH time series

Published 30 July 2025 Science Closed
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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.

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Seasonal upwelling drives surface water biogeochemistry with implication for ocean acidification along the Northwest African coast

Published 25 July 2025 Science Closed
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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.

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River alkalinization and ocean acidification face off in coastal waters

Published 22 July 2025 Press releases Closed
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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)

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Timing of calcification and environmental variability determine pH proxy fidelity in coastal calcifying macroalgae

Published 21 July 2025 Science Closed
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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.

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Morphological responses of a temperate intertidal foraminifer, Haynesina sp., to coastal acidification

Published 17 July 2025 Science Closed
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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.

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Cross-generational plasticity in Atlantic silversides (Menidia menidia) under the combined effects of hypoxia and acidification

Published 17 July 2025 Science Closed
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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.

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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 Closed
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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.

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Harnessing nature’s buffer: assessing the role of bivalve shells in coastal alkalinity regeneration

Published 15 July 2025 Science Closed
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Bivalve shells, a natural alkaline material, play a crucial role in coastal carbon cycles by influencing total alkalinity (TA) and dissolved inorganic carbon (DIC). This study investigated oyster shell dissolution in Narragansett Bay, Rhode Island, under varying pCO2 conditions, revealing TA regeneration rates of 4–56 μmol L-1 d-1, which could mitigate localized ocean acidification (OA). Notably, significant dissolution occurred even in oversaturated waters (Ωcalcite > 1) due to corrosive microenvironments created by microbial respiration. Although shell formation (calcification) emits CO2, TA regeneration (shell dissolution) buffers OA when the carbonate chemistry of the water is corrosive, offsetting the initial CO2 emissions. Therefore, recycling shells enhances ecosystem resilience by buffering acidification stress for OA-sensitive organisms. This research highlights the need to revisit shell management policies to promote sustainable aquaculture and sheds light on the potential of incorporating this nature-based alkaline material into ocean alkalinity enhancement strategies for improved coastal carbon management.

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Observations of Sargassum carbon influx and biogeochemical impact in La Parguera Marine Reserve

Published 15 July 2025 Science Closed
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The massive influx of pelagic Sargassum spp. species, also known as Sargassum inundation events (SIEs), first arrived at the Caribbean’s coastal waters in 2011. These events have been linked to hypoxia, among other ecological disturbances. Here, we report data from 2022 on (1) an assessment of the relative magnitude of particulate organic carbon (POC) load arising from SIEs into the La Parguera Marine Reserve (LPMR) basin off the southwest coast of Puerto Rico and (2) the biogeochemical impact of SIE in a nearshore mangrove key within the reserve, Monsio Jose Key Bay (MJKB). Our analysis yields that the carbon influx increased by 20% in the LPMR basin and by 103% in MJKB. Weekly observations of Sargassum input, along with the collection and analysis of water samples in MJKB, evidenced a cause-effect relation between Sargassum carbon loading and frequency of hypoxic (DO < 2 mg·L-1) and critically acidic conditions (Aragonite saturation, Ω < 2.0). During the 2022 Sargassum season, hypoxic conditions were detected in 43% of samples collected in MJKB. Considering the modulation of biogeochemical parameters by changes in tide height (Δh) and wind speed (m·s-1), stepwise multiple regression analyses (RDA-AIC model selection) showed that significant parameters influencing DO, pH, and Ω include the Sargassum carbon influx and Δh (p < 0.05). These findings strongly support the hypothesis that the additional input of POC influx enhances microbial mineralization rates responsible for depressed oxygen concentrations and acidic conditions, which could be detrimental to coastal ecosystems. This is particularly concerning in areas prone to SIEs where geomorphological features facilitate the entrainment of floating materials. Proper management requires the identification of vulnerable sites and Sargassum removal. Ongoing efforts towards that goal are underway for LPMR.

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Temporal trends of ocean acidification in the Gulf of Guinea and the potential impact on socio economic development

Published 15 July 2025 Science Closed
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Ocean acidification, primarily driven by increased atmospheric CO₂, poses significant environmental and socioeconomic threats, particularly in vulnerable regions like the Gulf of Guinea. This study analyses historical pH trends, spatial variations, and projected acidification scenarios using data from CMIP6 models and NOAA observational records, focusing on the Gulf of Guinea’s unique ecological and economic challenges. Findings indicate a steady decline in pH from 8.20 to 8.08 between 1750 and 2010, with pronounced deviations linked to industrial activities and rising atmospheric CO₂ concentrations. Seasonal fluctuations and upwelling events exacerbate acidification in this high-productivity region, intensifying the vulnerability of marine biodiversity and fisheries. Projections for 2050–2100 under SSP2 4.5 and SSP5-8.5 scenarios reveal further pH declines, with potential hotspots emerging in coastal areas. These changes threaten critical ecosystems, such as shellfish habitats, and threaten food security and economic stability for communities dependent on marine resources. The study underscores the necessity of regional monitoring programs, international collaboration, and mitigation strategies, including carbon emission reductions, ecosystem-based adaptation, and sustainable aquaculture practices. This research highlights the Gulf of Guinea’s heightened sensitivity to acidification due to its unique biogeochemical processes and socioeconomic dependencies. It advocates for integrating science, policy, and local initiatives to address these challenges. Targeted interventions, such as mangrove restoration and regional partnerships, can strengthen resilience and provide valuable insights for global ocean acidification management efforts.

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Mollusc epifaunal assemblages are simplified due to habitat shifts under ocean acidification

Published 14 July 2025 Science Closed
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Highlights

  • Ocean acidification can modify the structure of marine communities.
  • The macroalga Halopteris sp. supports a rich community of associated molluscs.
  • Halopteris sp. from an acidified site support fewer and less diverse assemblages.
  • Most abundant species were present both at the acidified and reference sites.
  • Biodiversity of molluscs will be simplified under acidified conditions.

Abstract

Ocean acidification can have profound effects on marine organisms, particularly those that rely on calcium carbonate for shell and skeleton formation, resulting in structural changes to marine ecosystems. Here, we contrast the structure of marine mollusc communities (epifauna) associated with an abundant shallow-water macroalga, Halopteris scoparia, in an area with seawater carbonated by natural CO2 seeps and three reference sites, off the Azores archipelago. Epifaunal mollusc abundance and diversity were significantly lower at the CO2 seep compared to reference sites whilst species accumulation curves and Jaccard multivariate analyses showed that the mollusc assemblage was consistently less diverse at the CO2 seep. Most of the abundant epifaunal species that were present at the CO2 seep were also found at reference sites, but less common or rare species were generally absent from the former. We conclude that while some molluscs are likely to cope with ocean acidification, the overall biodiversity of epifaunal molluscs will be simplified under these conditions in a future ocean.

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Chemical and biological oceanographic conditions in the Labrador Sea from 2019 to 2023

Published 10 July 2025 Newsletters and reports Closed
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The Atlantic Zone Off-Shelf Monitoring Program samples the AR7W line annually. This report summarises trends from 2019-2023 for three regions: AR7W-W (Labrador shelf and slope), AR7W-C (central Labrador Sea), and AR7W-E (Greenland shelf and slope). Samples revealed a continued increase in dissolved inorganic carbon and a decrease in pH from 2019 to 2023. Mean concentration of CFC-12 decreased in 2020, and SF6 continued its steady increase. Mean temperature from 0-100 m in the Labrador Sea was above normal in 2019, below normal on the next mission (2022), and near or above normal in 2023. Surface (0-100 m) nutrients were mainly below normal from 2019-2023, which could be attributed to mission timing. However, below-average deep nutrients (>100 m, less impacted by sampling timing) suggests a profound change in the biogeochemistry of the Labrador Sea. Integrated (0-100 m) chlorophyll-a was below normal in 2019 and in AR7W-E in 2022-2023, but above normal elsewhere, with a record high value in AR7W-C in 2022 caused by an unusually large bloom of Phaeocystis spp.. Satellite data revealed high variability in the timing of the spring and fall blooms and surface average chlorophyll-a concentration. Mesozooplankton abundances showed high interannual variability since 2019.

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Climate vulnerability assessment of fish and invertebrates in the U.S. South Atlantic large marine ecosystem

Published 9 July 2025 Science Closed
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Trait-based climate vulnerability assessment (CVA) is a rapid and repeatable approach to simultaneously assess the vulnerability of a large number of species to projected regional changes in climate. We conducted the first CVA in the U.S. South Atlantic Large Marine Ecosystem for 71 ecologically, economically, and culturally important fish and invertebrate species. The CVA was conducted by a 16-member panel based on scoring 12 biological sensitivity attributes and seven climate exposure factors. About two-thirds of the species were considered highly vulnerability to future climate projected under the RCP 8.5 emissions scenario, with diadromous species, invertebrates, and deepwater reef fishes the most vulnerable functional groups. Ocean acidification, sea surface temperature, and salinity were the exposure factors with the greatest influence on climate vulnerability, while population growth rate, population status, and early life history traits were the most important biological sensitivity attributes. More than two-thirds of the species had high potential for shifts in geographic distribution, due mostly to the prevalence of broadcast spawning, extensive larval dispersal, and high adult mobility of many species, and the generalist habitat requirements of several estuary-dependent and hard-bottom reef species. Some shifts in distribution have already occurred though potential relationships to environmental conditions associated with climate are not well-understood. Uncertainty analyses confirmed the robustness of the climate vulnerability rankings, but comparison of alternative types of elicited informed judgement did not always agree, suggesting higher uncertainty in climate vulnerability for some species. In addition, several species may benefit under future climate conditions, and climate effects on some species considered to be highly vulnerable may be of relatively small magnitude. These results can be used to prioritize conservation, research, and management efforts, and identify key uncertainties related to the impacts of future climate on fishery resources in the U.S. South Atlantic region.

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Something in the water: how kelp is helping Maine’s mussels boom

Published 8 July 2025 Media coverage Closed
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On a glimmering May morning, Tom Briggs pilots a 45ft aluminium barge through the waters of Casco Bay for one of the final days of the annual kelp harvest. Motoring past Clapboard Island, he points to a floating wooden platform where mussels have been seeded alongside ribbons of edible seaweed.

“This is our most productive mussel site,” says Briggs, the farm manager for Bangs Island Mussels, a Portland sea farm that grows, harvests and sells hundreds of thousands of pounds of shellfish and seaweed each year. “When we come here, we get the biggest, fastest-growing mussels with the thickest shells and the best quality. To my mind, unscientifically, it’s because of the kelp.”

A growing body of science supports Briggs’s intuition. The Gulf of Maine is uniquely vulnerable to ocean acidification, which can impede shell development in mussels, clams, oysters and lobster, threatening an industry that employs hundreds of people and generates $85m to $100m (£63m to £74m) annually.

Atmospheric carbon dioxide from fossil fuels is the main driver of declining ocean pH, increasing the acidity of the world’s oceans by more than 40% since the preindustrial era and by more than 15% since 1985. Add carbon runoff from growing coastal communities, regular inflows of colder, more acidic water from Canada, and intense thermal stress – the Gulf of Maine is warming three times faster than the global average – and you’re left with a delicate marine ecosystem and key economic resource under threat.

Enter kelp. The streams of glistening, brownish-green seaweed that Bangs Island seeds on lines under frigid November skies and harvests in late spring are a natural answer to ocean acidification because they devour carbon dioxide. Sensors placed near kelp lines in Casco Bay over the past decade have shown that growing seaweed changes water chemistry enough to lower the levels of carbon dioxide in the immediate vicinity, nourishing nearby molluscs.

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