Coastal marine ecosystems are increasingly threatened by multiple stressors such as ocean acidification and deoxygenation, but how these co-occurring stressors interact is often poorly understood. This is especially true for tropical coral reefs where deoxygenation is an emerging yet understudied threat. Using hypoxia response curves combined with rigorous pH control, we show that acidification alters hypoxia sensitivity and oxyregulation of reef-building corals in a species-specific manner: three species exhibited increased sensitivity to various degrees, while the fourth showed enhanced tolerance. Consequently, acidification pushes critical hypoxia thresholds into oxygen regimes already prevalent on reefs today, potentially driving shifts in community composition and accelerating risks to reef resilience as these stressors intensify in the future. Our findings challenge assumptions of uniform coral vulnerability under multi-faceted climate change, emphasizing the need for trait-based approaches and to account for stressor interactions in predictive models to better anticipate coral reef futures under rapid climate change.
Continue reading ‘Ocean acidification alters hypoxia sensitivity and oxyregulation in reef-building corals’Posts Tagged 'North Atlantic'
Ocean acidification alters hypoxia sensitivity and oxyregulation in reef-building corals
Published 9 June 2026 Science Leave a CommentTags: biological response, BRcommunity, chemistry, corals, laboratory, North Atlantic, physiology
Large-scale atmospheric circulation and its impact on the Baltic Sea region: controls, predictability and consequences
Published 15 May 2026 Science ClosedTags: North Atlantic, review
Large-scale Euro-Atlantic variability, shaped by the polar jet stream, governs weather and climate in the Baltic Sea region, thereby impacting the physical and biogeochemical properties of the Baltic Sea ecosystem. This review synthesizes how key atmospheric circulation features and modes of climate variability, including the North Atlantic Oscillation, atmospheric blocking and the Atlantic Multidecadal Variability, influence the Baltic Sea region. By integrating evidence from the published literature, observational datasets, and both global and regional climate model simulations, we assess established as well as potential linkages to key climatic variables, including temperature, precipitation, and storm activity, across temporal scales ranging from synoptic events to multidecadal variability. We then evaluate how these climate controls cascade into ecosystem-relevant processes, namely oxygen dynamics, primary productivity and ocean acidification. Although physical links are already established, the pathways connecting large-scale atmospheric patterns to biogeochemistry are still poorly constrained, partly because dedicated field studies and targeted model experiments are limited. We outline priority research needs to enhance near-term predictability and reduce uncertainty in future projections for the Baltic Sea.
Continue reading ‘Large-scale atmospheric circulation and its impact on the Baltic Sea region: controls, predictability and consequences’Mechanistic drivers of climate-induced reproductive collapse in African catfish: multi-stressor interactions under IPCC scenarios
Published 14 May 2026 Science ClosedTags: adaptation, biological response, fish, laboratory, mortality, North Atlantic, physiology, reproduction
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.
Continue reading ‘Mechanistic drivers of climate-induced reproductive collapse in African catfish: multi-stressor interactions under IPCC scenarios’Projected future of African marine ecosystems under climate change and stratospheric aerosol injection
Published 8 May 2026 Science ClosedTags: biological response, modeling, multiple factors, North Atlantic, phytoplankton, regionalmodeling, salinity, temperature
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.
Continue reading ‘Projected future of African marine ecosystems under climate change and stratospheric aerosol injection’The influence of localized water quality on Eastern oysters (Crassostrea virginica) and their internal microbiome under changing environmental conditions
Published 5 May 2026 Science ClosedTags: biological response, laboratory, mollusks, morphology, North Atlantic, physiology, prokaryotes
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 ClosedTags: algae, biological response, field, mitigation, North Atlantic, phytoplankton
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’Ocean acidification and harmful algal blooms combine to suppress the growth and survival of North Atlantic bivalve larvae
Published 29 April 2026 Science ClosedTags: algae, biological response, community composition, laboratory, mollusks, mortality, North Atlantic, otherprocess, reproduction
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’Decadal shifts in hypoxia and acidification reveal changing anthropogenic pressures on bottom waters of a coastal shelf
Published 20 April 2026 Science ClosedTags: chemistry, field, North Atlantic
Coastal systems provide habitat that sustains valuable shellfisheries but are subject to dissolved oxygen (DO) and/or carbonate chemistry impairment from anthropogenic pressures such as eutrophication and increasingly, climate change. Although extreme events can have disproportional negative ecological impacts, their ephemeral nature and a lack of baseline monitoring data make them challenging to characterize. Through assessments of historical records and a series of modern-day cruises, this study documented the magnitude and extent of summer hypoxia and acidification in the coastal shelf bottom waters of an urban shelf ecosystem, the New York Bight, before and during a devastating hypoxic event in 1976 and at present. In 1974, the most severe DO (2.39 mg L−1) and carbonate chemistry [pHN: 7.47; aragonite saturation state (ΩAr): 0.45] conditions occurred as a halo around a now derelict sewage disposal site, while averaging 4.43 mg L−1 (DO), 7.84 (pH), and 1.25 (ΩAr) across the region that August. During the mass mortality event of 1976, extremely low DO (< 1 mg L−1), pHN (< 7.5), and ΩAr (< 0.5) levels were observed across bottom waters during summer. Comparisons of modern subsurface chemistry to that of 1974—a year with ocean dumping but no mass mortality—indicated increases in bottom water DO, with evidence to suggest that ocean acidification has dampened the concomitant increases in ΩAr over the intervening half-century. This study highlights the impacts of ocean dumping and the threat of ocean acidification to systems that are experiencing or recovering from coastal hypoxia.
Continue reading ‘Decadal shifts in hypoxia and acidification reveal changing anthropogenic pressures on bottom waters of a coastal shelf’Register now: life on the extremes: why ocean acidification hits differently on the coasts
Published 16 April 2026 Events ClosedTags: North Atlantic
Tuesday, May 19, 2026 – 7:00pm – 8:30pm
Event Details
The ocean and other water bodies absorb nearly a third of human-emitted carbon dioxide (CO2). However, once dissolved, CO2 lowers the water’s pH, and makes it more acidic—a phenomenon known as ocean acidification. In coastal waters like Chesapeake Bay, acidification plays out differently than in the open ocean. In this talk, SERC ecologist Whitman Miller will explore the surprising role marine biota play in coastal acidification. He’ll also reveal how emerging technology and automated measurements are painting a new, more dynamic picture of coastal water bodies, where chemistry can shift drastically between day and night, between tides and between seasons—and what these shifts mean for life in coastal waters more broadly.
This event is part of the Smithsonian Environmental Research Center (SERC)’s free evening science talks, and it will be recorded! Closed captions will be available during the live stream and on the recording. By signing up on Zoom, you’ll be able to watch live and receive a link to the recording a few days after the live stream. SERC seeks to showcase a wide variety of topics and perspectives for its evening science talks. Views expressed during these talks belong to the individual speakers and not the Smithsonian.
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Continue reading ‘Register now: life on the extremes: why ocean acidification hits differently on the coasts’Coexpression among eastern oyster host and microbiome genes suggests coordinated regulation of calcifying fluid chemistry
Published 13 April 2026 Science ClosedTags: biological response, BRcommunity, laboratory, molecular biology, mollusks, North Atlantic, physiology, prokaryotes
Significance
Oysters and many marine animals build shells by controlling the chemistry of extracellular fluids where minerals form, yet whether microbes in these fluids influence calcification remains unclear. We show that oysters maintain favorable conditions for mineral formation by regulating the carbonate chemistry of the shell-forming fluid, and that resident microbes respond to these changes by expressing nitrogen- and sulfur-cycling genes capable of altering pH, alkalinity, and carbonate availability. Many of these microbial transcripts were tightly correlated with oyster immune and signaling genes, suggesting that host and microbiome processes may be linked within the calcifying environment. These findings point to a host–microbiome interaction in the regulation of calcifying-fluid chemistry that directly links microbial activity to the carbonate chemistry underlying biomineralization.
Abstract
Marine animals that build shells, such as oysters, carefully regulate the chemistry of their internal calcifying fluids, but the molecular mechanisms behind this control, as well as whether microbes play a role in calcification, are poorly understood. To better understand oysters’ molecular mechanisms and the role of their calcifying-fluid microbes, we conducted experiments that simulated a tidal cycle, measured calcifying fluid pH and total dissolved inorganic carbon, and characterized host and microbial gene expression via transcriptomics. These experiments showed that calcifying fluid pH remained relatively stable throughout tidal pH fluctuations, with corresponding increases in oyster transcripts for ion transport and acid–base regulation. These data provide direct evidence that tidal fluctuations drive rapid changes in oyster calcifying fluid chemistry. Most surprisingly, increases in microbial transcripts related to nitrogen and sulfur cycling correlated to higher calcifying fluid DIC, and coexpression network analysis revealed patterns of gene expression that linked oyster immune and neural pathways to microbial redox processes, providing molecular evidence of potential host modulation of microbial metabolism. Together, these results reveal that oysters actively regulate their calcifying fluid pH over short timescales, and the endemic microbiome metabolic responses can yield metabolites that influence calcifying fluid pH, alkalinity, and ultimately calcification. These data offer a perspective on oyster physiological capacity and, most importantly, the potential role of microbes in oyster calcification. In light of ongoing changes in ocean pH and temperature, oysters provide a model for studying animal–microbial responses to environmental acidification and how their interactions may shape biomineralization.
Continue reading ‘Coexpression among eastern oyster host and microbiome genes suggests coordinated regulation of calcifying fluid chemistry’Climate change influence on salinity, temperature, dissolved oxygen and pH in Biscayne Bay (Florida): two decades of observations (2001–2021)
Published 8 April 2026 Science ClosedTags: chemistry, field, North Atlantic
Highlights
- Research Highlight 1: Biscayne Bay is transitioning from an estuarine to a more marine regime due to sea level rise.
- Research Highlight 2: Salinity is increasing at canal mouths, with saltwater intrusion detected in bottom layers.
- Research Highlight 3: Global warming has raised Bay water temperature, and the past decade has been the warmest on record.
- Research Highlight 4: Ocean acidification is influencing the Bay.
Abstract
An evaluation of 20 years (2001-2021) of monthly data from a long-term monitoring program was performed to determine the temporal, seasonal and spatial changes in the distribution of salinity, temperature, dissolved oxygen, and pH, to identify the potential impacts of climate change on Biscayne Bay, the largest estuary on the Atlantic coast of Florida. Data were evaluated by decade, season, and zone. Decade 2 showed higher salinity in four of eight zones, along with saltwater intrusion in the bottom layer of some canals. The zones most influenced by the Atlantic Ocean did not show decadal salinity changes. In decade 2, the overall median temperature in-creased (+0.5◦C), with North Bay exhibiting the highest increase (+0.8◦C). In decade 2, dissolved oxygen was higher in four zones, while pH decreased in six zones, suggesting that ocean acidification is also influencing the Bay. Temperature, dissolved oxygen, and pH displayed pronounced seasonal patterns across zones. Collectively, these results suggest that sea level rise and climate change are gradually transforming Biscayne Bay from an estuarine system to one that is more marine in nature.
Continue reading ‘Climate change influence on salinity, temperature, dissolved oxygen and pH in Biscayne Bay (Florida): two decades of observations (2001–2021)’Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish
Published 2 April 2026 Science ClosedTags: adaptation, biological response, fish, laboratory, morphology, mortality, North Atlantic, otherprocess, reproduction
Ocean acidification (OA) is a major climate-related threat to fish that can disrupt the regulation of the reproductive axis of fish, impacting reproductive success. However, previous studies have only focused on a single reproductive cycle and reported increased fecundity in some species exposed to OA. Since acclimation over several reproductive cycles can occur, it is necessary to evaluate successive reproductive cycles for predicting the actual resilience of species to OA. In this study we assessed the impact of lifetime exposure to different ocean pH/pCO2 levels (Current condition, Moderate OA and High OA) on the sexual maturation and spawning phenology of the European sea bass, over its two first reproductive periods. We tested the hypothesis that OA would exert its greatest impact at the onset of puberty (first reproduction). Accordingly, High OA exposure induced an earlier onset of puberty in both sexes, resulting in a longer spawning period and an increased fecundity. These effects were reduced during the second reproductive season. However, OA affected egg quality and sperm motility profile during the second reproductive season, leading to a total mortality at hatching of embryos spontaneously produced. This mortality was not observed in embryos produced through hormone-induced oocyte maturation and in vitro fertilisation. These results suggest that OA affects the regulation of oocyte maturation and/or the synchronisation of eggs and sperm release. The OA-driven shift in spawning may misalign with optimal environmental conditions for offspring survival. This increases the population’s vulnerability and could favour species whose reproduction is more resilient to OA.
Continue reading ‘Ocean acidification affects the timing of puberty and the reproductive output in a marine temperate fish’Skeletal growth and loss of the cold-water coral Lophelia pertusa from multiple environmental drivers in a year-long experiment
Published 27 March 2026 Science ClosedTags: biological response, corals, dissolution, growth, laboratory, morphology, mortality, multiple factors, North Atlantic, oxygen, physiology, respiration, temperature
Colony-forming scleractinian cold-water corals (CWCs) are important ecosystem engineers, forming complex 3-dimensional habitats in the deep sea, which in turn sustain high biodiversity. They are threatened by future environmental changes such as ocean acidification, warming, deoxygenation, and food limitation, but little is known about the effect of these drivers in combination or on the long-term. We conducted a year-long aquarium experiment with Lophelia pertusa (syn. Desmophyllum pertusum) under projected end-of-century conditions, investigating the combined effect of differences in pH (8.1 and 7.7), temperature (9°C and 12°C), oxygen concentration (100% and 90%) and food supply (100% and 60%) on coral survival, growth, respiration rates, skeletal dissolution and energetic reserves. Growth rates of L. pertusa decreased significantly in both multiple driver treatments, resulting in negative and more variable growth rates. However, growth rates only started to decrease after 4.5 months, clearly showing a delayed response. In addition, survival rates and energetic reserves were slightly lower in multiple driver treatments, whereas L. pertusa was not affected by reduced oxygen concentration examined as a single factor. Negative growth rates in multiple driver treatments were driven by dissolution of bare skeletal parts due to reduced seawater pH and temporary aragonite undersaturation, visualised here through micro-computed tomography images. While live CWCs may be able to cope with projected future environmental changes over the timescale of 1 year, ocean acidification will lead to dissolution of the dead skeletal framework of CWC reefs and net loss, reducing the complexity and associated biodiversity of these reefs. However, the challenge remains in closing the gap between long-term experiments and the much longer-term chronic exposure of CWCs to projected environmental changes.
Continue reading ‘Skeletal growth and loss of the cold-water coral Lophelia pertusa from multiple environmental drivers in a year-long experiment’Ocean acidification disrupts the biomineralization process in the oyster Crassostrea virginica via intracellular calcium signaling dysregulation
Published 20 March 2026 Science ClosedTags: biological response, laboratory, molecular biology, mollusks, morphology, North Atlantic, physiology, reproduction
Calcium is a key component in the shell and skeleton structure, serving as a second messenger for regulating biomineralization across many species. Ocean acidification (OA) is well-studied for causing shell dissolution in marine bivalve species by disordering calcium deposition. However, the regulatory pathway of calcification affected by OA remains unclear. This study assessed eastern oyster (Crassostrea virginica) to determine how calcium signaling responds to elevated pCO2 and influences shell formation. Under elevated pCO2, increased calcium influx was found in mantle epithelial cells, followed by the upregulation of calmodulin, a primary sensor of intracellular calcium. Expression levels of shell matrix proteins (SMPs), representing shell construction conditions, were significantly upregulated in the CO2-induced mantle cells. Larval C. virginica exhibited developmental stage-dependent alterations in calcium signaling and SMPs disarrangement stimulated by pCO2. Pharmaceutical blockage of the calcium binding on calmodulin induced abnormal expression of downstream genes and shell matrix changes consistent with those caused by elevated pCO2. Restored SMPs expressions in CO2-treated mantle cells were achieved by rescuing the level of calcineurin, a downstream effector of calmodulin. These findings suggest that shell deformities under OA are primarily caused by the disruption of the calcium-calmodulin signaling pathway in mantle epithelial cells.
Continue reading ‘Ocean acidification disrupts the biomineralization process in the oyster Crassostrea virginica via intracellular calcium signaling dysregulation’UConn helps sea scallop communities adapt to ocean warming
Published 19 March 2026 Web sites and blogs ClosedTags: fisheries, modeling, mollusks, North Atlantic
UConn Marine Sciences Associate Professor Samantha Siedlecki co-leads a project to incorporate data on historic and projected ocean conditions to predict the growth of scallops across vast geographic regions and more than a century of time. The project uses a novel tool developed by UConn Ph.D. candidate Halle Berger. Photo by NOAA.
In the coastal waters stretching from Maine to Virginia, Atlantic sea scallops rival lobster as the top shellfish caught in the wild. This delectable mollusk supports one of the most valuable fisheries in the U.S., generating $360 million in revenue annually, and making the U.S. a global leader in wild scallop fishing.
A combination of conservation measures has helped the industry weather the effects of overfishing. Now, warming and acidifying oceans are posing new threats and prompting new solutions.
A team of researchers co-led by UConn Associate Professor of Marine Sciences Samantha Siedlecki, Shannon Meseck, of NOAA’s Northeast Fisheries Science Center, and Robert “Bobby” Murphy, a social scientist with NOAA’s Northeast Fisheries Science Center, is exploring how environmental data can be used to develop a new management approach adapted for and responsive to a changing ocean. With the support of a three-year grant of just over $1 million from NOAA’s Ocean Acidification Program (OAP), the project will integrate oceanographic modeling, industry engagement, and socioeconomic research to create actionable strategies for industry and management. The project is one of six announced by OAP in November aimed at helping U.S. coastal communities adapt to ocean acidification.
“This is one of the earliest attempts to forecast optimal regions for Atlantic sea scallop growth, based on both carbon content and ocean temperature,” says Siedlecki.
Continue reading ‘UConn helps sea scallop communities adapt to ocean warming’Novel in situ CO2 enrichment system reveals seagrass meadows are a refugium against coastal acidification for North Atlantic bivalves
Published 18 March 2026 Science ClosedTags: biological response, BRcommunity, chemistry, growth, laboratory, mollusks, mortality, North Atlantic, phanerogams
While the accumulation of anthropogenic CO2 in the atmosphere is causing a decline in global ocean pH, many eutrophic estuaries are already experiencing acidification due to accelerated respiration driving the consumption of dissolved oxygen (DO) and production of CO2, decreasing available carbonate ions (CO32-) and threatening marine calcifiers. Here, a novel in situCO2 enrichment system was constructed to examine the effects of coastal acidification on the growth and survival of two species of North Atlantic bivalves (Argopecten irradians and Crassostrea virginica) in two distinct estuarine habitats: a seagrass meadow and an unvegetated sandy bottom in an open water estuary. The in-situ system captured natural diel dynamics as ambient chambers displayed chemistry nearly identical to the surrounding water, while CO2-enriched, acidified chambers maintained a consistent ~Δ 0.3–0.5 pH offset. At the unvegetated sandy bottom site, A. irradians and C. virginica displayed significant reductions in growth and survival in the acidified chambers (pHT = 7.3–7.5; saturation state of aragonite, ΩAr = 0.6–0.9) relative to ambient conditions (pHT = 7.6–7.9; ΩAr = 1.6–2). At the seagrass site, while growth of A. irradians and C. virginica in the acidified treatments (pHT = 7.3–7.7; ΩAr = 0.7) receiving the same delivery of CO2 was, again, significantly slowed compared to the control (pHT = 7.5–8.1; ΩAr = 2 – 2.8), the growth reduction, mortality rates, and levels of acidification were attenuated compared to the sandy bottom experiment, evidencing the ability of seagrass to buffer seawater and serve as a potential acidification refuge for bivalves. Collectively, the novel experimental CO2 enrichment system constructed for this project demonstrates that coastal acidification can have deleterious effects on marine bivalve populations, and that future conditions as well as the habitat refuge offered by seagrasses must be considered when developing management and restoration plans for temperate estuaries.
Continue reading ‘Novel in situ CO2 enrichment system reveals seagrass meadows are a refugium against coastal acidification for North Atlantic bivalves’Physiological responses of Swedish maerl to ocean acidification and warming
Published 17 March 2026 Science ClosedTags: algae, biological response, calcification, laboratory, multiple factors, North Atlantic, photosynthesis, respiration, temperature
Maerl, (Corallinales, Rhodophyta), are free-living calcareous algae found in coastal ecosystems. They form biogenic beds with complex structures in which other species can find refuge or on which other species can settle, which highlights their importance as an ecosystem. While many species have been investigated worldwide, maerl from the Swedish west coast are poorly studied. This report investigated both acidification and warming impacts on different physiological functions of Swedish maerl, including photosynthesis, respiration and calcification. The maerl were exposed to different pH levels and temperatures in both light and dark conditions to determine their physiological thresholds, where photosynthesis and respiration were measured via oxygen fluctuations, photosynthetic efficiency via PAM fluorometry and calcification via alkalinity titrations. It was found that neither photosynthetic nor respiratory oxygen exchange showed positive or negative trends when exposed to changes in pH. On the contrary, photosynthesis peaked at the natural ambient temperature of 16°C and respiration increased with increasing temperature. Photosynthetic efficiency also did not show any trends to pH changes. However, calcification showed a significant (p < 0.05) negative response to pH in both light and dark conditions, with the response more severe in dark conditions. This suggests that decreasing pH may induce skeletal dissolution, and that photosynthesis could help buffer internal responses to external conditions. Carbonate production at ambient conditions in the light was calculated to be 556 ± 54 g CaCO3 m-2 yr-1, showing that Swedish maerl are just as, if not more, productive than maerl found elsewhere. Overall, this report showed that photosynthetic and respiratory thresholds may not be reached with acidification and that temperature increases could instead have much more severe consequences. It also showed that calcification thresholds will be met sooner rather than later, depending on acidification rates, in darker conditions for maerl found in temperate and possibly polar regions.
Continue reading ‘Physiological responses of Swedish maerl to ocean acidification and warming’An invisible threat in Long Island’s waters
Published 16 March 2026 Media coverage ClosedTags: fisheries, North Atlantic
For generations, the waters surrounding Long Island have defined its identity — from the wide-open waterfronts of the South Shore to the shellfish beds of the North Shore. But beneath the surface, a quieter transformation is underway.
Ocean acidification is often called climate change’s “evil twin,” and refers to the lowering of the water’s pH, the scale used to measure the concentration of hydrogen ions in the water. While global warming refers to rising temperatures, acidification describes a shift in seawater chemistry.
…
On Long Island, acidification is not driven by global carbon emissions alone. Local factors intensify the problem. Nitrogen discharged from wastewater, septic systems and fertilizer runoff flows into bays and harbors, fueling harmful algal blooms. When those blooms die and decompose, the process consumes oxygen and releases additional carbon dioxide in the water, further lowering pH.
The result is a compounding effect: global atmospheric carbon dioxide combined with local nitrogen pollution accelerates acidification in shallow, enclosed estuaries.
Warming waters add another layer of stress. As temperatures rise, marine organisms’ metabolic demands increase, but warmer water holds less dissolved oxygen. Together, warming and acidification can weaken shellfish during their most vulnerable larval stages, making it harder for them to survive and build shells.
For Long Island’s oyster and clam farmers — industries that have experienced both revival and setbacks in recent decades — these chemical changes aren’t just theoretical. They are measurable, seasonal and, increasingly, part of daily operations.
Continue reading ‘An invisible threat in Long Island’s waters’Temperature and pH-dependent potassium currents of muscles of the stomatogastric nervous system of the crab, Cancer borealis
Published 13 March 2026 Science ClosedTags: biological response, crustaceans, laboratory, molecular biology, multiple factors, North Atlantic, physiology, temperature
HIGHLIGHTS
- Cancer borealis stomach muscles are sensitive to temperature and pH.
- Warming or alkalizing hyperpolarizes fibers and reduces synaptic response amplitude.
- qRT-PCR detects K2P gene transcripts CbKCNK1 and CbKCNK2 in muscles.
- CbKCNK1 and CbKCNK2 are candidates for the temperature and pH-dependent conductances.
SUMMARY
Marine crustaceans such as the crab Cancer borealis experience fluctuations in temperature and pH, yet their stomatogastric neuromuscular system must remain functional for feeding. We examined 16 of ∼40 stomach muscle pairs and found that warming consistently hyperpolarized muscle fibers (∼10 mV per 10°C) and reduced excitatory junctional potentials and currents. Muscle responses were also strongly influenced by extracellular pH, with an optimal range between pH 6.7 and 8.8; outside this window, abnormal activity emerged. Voltage-clamp analysis of gastric muscle gm5b revealed a temperature- and pH-sensitive conductance with a reversal potential near the potassium equilibrium potential and insensitivity to tetraethylammonium and barium, arguing against classical voltage-gated potassium channels. Quantitative RT-PCR detected expression of two putative two-pore domain potassium (K2P) channels in these muscles. Together, these results suggest that muscle excitability in C. borealis is shaped by temperature- and pH-sensitive potassium currents consistent with contributions from K2P channels.
Continue reading ‘Temperature and pH-dependent potassium currents of muscles of the stomatogastric nervous system of the crab, Cancer borealis’Trophic status and climatic stressors in the shallow coral reefs of the Cuban marine shelf
Published 12 March 2026 Science ClosedTags: chemistry, field, North Atlantic
The “Bojeo a Cuba” expedition (summer 2023) provided a synoptic, national-scale snapshot of oceanographic conditions around Cuba’s shallow coral reefs during a regional marine heatwave. At 66 sites across six regions, we evaluated key climatic stressors (sea surface temperature, pH, alkalinity) and trophic status indicators. Satellite-derived SST during each site’s sampling week revealed significantly warmer waters on the southern shelf (mean = 30.93 °C) than the northern shelf (mean = 29.21 °C, P < 0.01). In situ SST was consistently high (mean = 30.52 °C), documenting the heatwave’s intensity. pH (mean = 8.12) and total alkalinity (mean = 2343 µmol kg⁻¹) indicated a currently balanced carbonate system. Concentrations of dissolved inorganic nitrogen and phosphorus were below our methods’ quantification limits (1.61 µmol L⁻¹ for P-PO₄³⁻), while chlorophyll-a (mean = 0.04 µg L⁻¹) consistently classified waters as oligotrophic. This study establishes a critical summer baseline, confirming oligotrophic conditions while documenting the severity of thermal stress during the 2023 heatwave—the most immediate and uniform threat to Cuban reefs. Our findings underscore the vulnerability of these ecosystems to extreme warming events within the context of long-term Caribbean warming trends.
Continue reading ‘Trophic status and climatic stressors in the shallow coral reefs of the Cuban marine shelf’
