Posts Tagged 'North Pacific'

Acidification dominates over hypoxia in controlling estuarine nitrogen removal Dynamics under coupled stressors

Published 8 July 2026 Science Leave a Comment
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As critical transitional zones between land and sea, estuaries are confronting the dual threats of increasing acidification and hypoxia driven by human activities and climate change. However, the combined effects of these stressors on estuarine nitrogen removal processes remain poorly understood. In this study, using stable-isotope tracing and molecular techniques in the Yangtze estuary, we found that hypoxia promoted N removal, yet concurrent acidification can override this effect, leading to net inhibition and a consequent reduction in estuarine nitrogen removal capacity. However, in seasonally hypoxic zones, these combined stressors generally enhanced nitrogen removal rates (by up to 34.4%), which suggests a degree of resilience under such perturbations. Nevertheless, the concurrent acidification–hypoxia in seasonally hypoxic areas stimulated N2O emissions (8.5–44.4%), which may intensify climate forcing and thereby further exacerbate these environmental stressors. Metagenomic and quantitative PCR analyses corroborated these response patterns, revealing coordinated changes in the abundance and expression of key nitrogen-removal genes, as well as divergent microbial response strategies and niche differentiation under acidification–hypoxia stress. This study elucidates the previously overlooked interactive effects of acidification and hypoxia on estuarine nitrogen removal, providing a mechanistic basis for refining biogeochemical models to improve the reliability of simulations under multiple stressors.

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Aragonite saturation state in the East China Sea during fall 2022: roles of temperature, biology, and mixing

Published 30 June 2026 Science Closed
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This work presents a comprehensive spatial distribution of aragonite saturation state (Ωara) during fall 2022 across the entire shelf of the East China Sea (ECS), a marginal sea of the North Pacific. Our observations revealed pronounced spatial heterogeneity in Ωara. Specifically, surface Ωara was higher in the southeastern ECS in (3.22−3.41), which is influenced by the Taiwan Warm Current and the Kuroshio, than the northern ECS (2.23−2.60), which is affected by the Yellow Sea and the Changjiang River. The lowest Ωara values (1.73−2.20) occurred beneath the mixed layer on the southeastern ECS shelf. Correlation analyses and a one-dimensional diagnostic model identified biological activity and temperature as primary controls on the spatial variability of Ωara. For example, on the southeastern ECS shelf, within the mixed layer, both biological activities and temperature increased Ωara, accounting for ~45% and ~33% of the total absolute contribution of each process. While below the mixed layer, these two processes decreased Ωara, accounting for approximately -38% and -24% of the total absolute contribution. Additionally, water mass mixing substantially influenced Ωara within interaction zones, such as in the intrusion areas of the Yellow Sea and Changjiang River waters. Projections indicate that under future elevated atmospheric carbon dioxide conditions (RCP6.0 and RCP8.5), sea surface Ωara will continue to decline, but the magnitude of decline will be smaller in the northern ECS than in the southeastern ECS, reflecting the carbonate system’s intrinsic buffering effect.

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Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification

Published 18 June 2026 Science Closed
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Body size is a fundamental characteristic of all living organisms that determines physiological functions and life-history traits. Ecological theory predicts that ocean acidification can cause body size reductions, confirmed by several studies reporting miniaturization in ectotherms. Based on this prediction, we would expect a broad suite of species to show similar plastic body-size responses to elevated CO2. Using four natural climate change analogues of ocean acidification across the northern and southern hemispheres, we quantified body size alterations across 18 marine invertebrate and fish taxa to test for climate-driven miniaturization. Only three species consistently showed body-size reductions under ocean acidification: one urchin and two fish species. In contrast, 15 other species, ranging from highly calcified to non-calcified, displayed unchanged or increased body sizes or inconsistent miniaturization. If body-size miniaturization responses were consistently reproducible across taxa we would have observed it more frequently, suggesting that species responses to ocean acidification are more variable than previously thought and likely vary depending on a species’ physiology and life history. Thus, rather than entire communities undergoing miniaturization, species are likely to display a spectrum of responses, with some exhibiting size reductions, others demonstrating physiological resistance to elevated CO2, and others potentially benefiting from the indirect effects of ocean acidification.

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Cross-seasonal influence of China Coastal Current water on spring carbonate system in the northern South China Sea

Published 15 June 2026 Science Closed
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This study investigates the carbonate system in the northern South China Sea shelf off the Pearl River estuary during the spring of 2023. Contrary to the typical distribution pattern observed in river-dominated coast where dissolved inorganic carbon (DIC) increases offshore, field observations revealed higher DIC in inshore waters (> 1980 µmol kg− 1) than in offshore seawaters (< 1970 µmol kg− 1), with DIC in the coastal zone being 20.9±8.8 µmol kg− 1 higher than that offshore. An end-member mixing model indicated that the high DIC coastal water was primarily attributed to mixing with the remnant high-DIC southward winter China Coastal Current water. In addition, biological processes and air-sea CO2 exchange also played important roles. Two representative regions were examined: the inshore high-DIC region and the offshore low-DIC region. In the inshore high-DIC region, biological processes and air-sea CO₂ exchange increased DIC by 11.6 ± 3.0 (relative to air-sea CO2 equilibrium) and 1.1 ± 7.0 µmol kg− 1 (relative to conservative mixing), respectively. In the offshore low-DIC region, biological processes decreased DIC by 5.1 ± 3.5 µmol kg− 1, whereas air-sea CO2 exchange increased DIC by 9.9 ± 2.8 µmol kg− 1. Overall, this study highlights the dominant role of the cross-seasonal influence of the remnant water of the coastal current, as well as the secondary but significant contributions of biological activity and air-sea CO2 exchange to the DIC distribution in coastal regions.

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Response mechanism of Sepia esculenta larvae under global warming, ocean acidification and salinity fluctuation: Integrated biochemical and transcriptome profiling

Published 12 June 2026 Science Closed
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Highlights

  • Analysis based on global warming, ocean acidification and salinity fluctuation.
  • Multi-angle analysis of Sepia esculenta under temperature, pH and salinity stress.
  • Different stress enhanced the immune defense and antioxidant defense of S.esculenta.
  • The hub genes closely related to stress resistance were identified and screened out.

Abstract

The Sepia esculenta occupies a significant economic proportion in the squid family, and it is also the squid with the largest economic value in the northern sea area of China. With the occurrence of global warming, ocean acidification and ocean salinity fluctuations, it has caused serious negative effects on the development of the S. esculenta artificial breeding industry. Therefore, in the research, we employed weighted gene co-expression network analysis (WGCNA) to investigate the effects of three environmental factors, including salinity, temperature and pH, on the molecular mechanism of S. esculenta larvae, and proved the reliability of transcriptome results through physiological indicators. Enrichment analysis of each module indicated that environmental exposure markedly influenced immune function, oxidative stress responses, and other physiological processes in S. esculenta larvae. Our research elucidates the comprehensive response mechanism of S. esculenta under different environmental stresses, clarifies the significant molecular pathways essential for its growth and development.

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Ocean acidification, more than warming or heatwaves, constrains shoaling behaviour in a range-extending fish through habitat simplification

Published 8 June 2026 Science Closed
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  1. Social context is a critical yet underexplored determinant of behavioural resilience to climate change. Group living can buffer individuals against environmental stress through enhanced vigilance, reduced predation risk and improved foraging efficiency.
  2. However, whether these behavioural expressions persist under chronic (warming, acidification) and acute (marine heatwaves) climate stressors remains unclear. Using natural climate analogues spanning present-day, ocean warming and combined warming–acidification reefs, we quantified how shoal size influences behavioural expression in a range-extending reef fish (Pomacentrus coelestis).
  3. Across all climate conditions, fish in larger shoals consistently exhibited higher foraging and activity levels and reduced risk-avoidance behaviours, whereas direct effects of warming, acidification and heatwaves on behaviour were negligible.
  4. In contrast, ocean acidification most likely constrained collective behaviour indirectly by simplifying benthic habitats, where fish densities were 84% lower than at the warming reef, resulting in shoals that were up to 79% smaller than the Warming and Control reefs.
  5. Combined, our data suggest that shoal size mediates behavioural expression between foraging and predator avoidance and that acidification-driven habitat simplification can alter behavioural expression indirectly by reducing fish densities and the formation of large shoals.
  6. We conclude that climate change can indirectly modify behavioural expression in shoal-forming fishes through habitat-driven erosion of social structure.
Continue reading ‘Ocean acidification, more than warming or heatwaves, constrains shoaling behaviour in a range-extending fish through habitat simplification’

Seasonal upwelling shapes coral reef community structure and photophysiology on the Pacific Coast of Costa Rica

Published 3 June 2026 Science Closed
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Reef-building corals form the calcium-carbonate frameworks that underpin tropical coral reefs, yet global coral cover has declined by ~50% in recent decades, due to marine heatwaves and other stressors. Identifying refugia environments, such as upwelling systems, that buffer stress, promote recovery, and enhance resilience by promoting physiological plasticity that supports thermotolerance is therefore critical. Here, we compared benthic community composition, coral percent cover, and photo-physiology between an upwelling location in the Gulf of Papagayo and a non-upwelling location in Sámara on the Pacific coast of Costa Rica. Waters in Papagayo were cooler, more acidic, and richer in chlorophyll a. Reefs at this location exhibited higher crustose coralline algae, higher sea urchin cover, and lower macroalgae cover, compared to Sámara. Papagayo also showed higher stony coral cover, driven by Pocillopora spp., while Sámara was dominated by massive, heat-tolerant Porites spp.. When significant, photophysiological measurements showed 9.7 – 44.5% higher photosynthetic efficiency (Fv’/Fm’) in Papagayo corals and 19.94 – 42.75 % higher maximum photosynthetic rates (Pmax) in Sámara corals. These results highlight how contrasting environmental regimes within a relatively small geographic area can shape distinct coral community compositions and photophysiological strategies, with implications for identifying areas of reef persistence or refugia.

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Upper-ocean variability of the marine carbonate system in the Northeast Pacific

Published 2 June 2026 Science Closed
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In the Northeast Pacific, the marine carbonate system’s variability across timescales is not well constrained. Here, we quantify observed seasonal and non-seasonal variability in Dissolved Inorganic Carbon (DIC), partial pressure of carbon dioxide (pCO2) and aragonite saturation state  Ω� and discuss potential drivers. We used three decades of observations from four Line P time series stations, the longest marine carbonate system time series in the Northeast Pacific (1990–2019). To gauge the spatial extent of the variability patterns, we used output from a global ocean model representing the observed period. In the Northeast Pacific, seasonal and non-seasonal pCO2 variability at 10 m was minimal, mostly damped by the opposing influence of DIC and temperature changes at both seasonal and interannual timescales. For DIC and Ω�, the seasonal cycle dominated total variability in the top 60–70 m, with mean-transect 10 m seasonal amplitudes of 35 ± 3 μmol kg−1 and 0.31 ± 0.04, respectively. In the upper 60–70 m, the magnitude of non-seasonal variability was at least half that of the seasonal variability for most variables. From five climate indices examined, we focused on the basin-scale Pacific Decadal Oscillation index (PDO) to investigate potential drivers of non-seasonal variability, with 20%–40% of the non-seasonal variability in DIC and Ω� associated to this index. In the Northeast Pacific, positive PDO periods were linked to a mean reduction in 10 m DIC of 5 μmol kg−1 and an increase in 10 m Ω� of 0.04 for each PDO unit increase, which could potentially reduce the occurrence and severity of ocean acidification events. The opposite could be expected during negative PDO periods.

Plain Language Summary

Using 30 years of observations from the Northeast Pacific, we characterized sources of variability for three marine carbonate system variables: , dissolved inorganic carbon (DIC) and the saturation state of aragonite (an common indicator of ocean acidification). The  seasonal and non-seasonal variability was minimal in the top 10 m. The seasonal cycle of DIC and aragonite saturation state was the major contributor to total variability in the top 60–70 m, and not detectable below. Also, in the top 70 m of the water column, up to 20%–40% of the DIC and aragonite saturation state non-seasonal variability was associated to the Pacific Decadal Oscillation index (PDO). The PDO is a statistics-derived index that captures variability patterns influencing the whole Pacific basin and has a positive and negative phase. We found that a warmer than usual upper water column in the Northeast Pacific during a positive PDO phase, potentially driven by reduced mixing, was linked to a lower DIC and higher values of aragonite saturation state. The opposite could be expected during negative PDO periods. Knowing the magnitude of natural variability in the marine carbonate system is important to identify the emergence of ocean acidification and other human-driven changes in the ocean.

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Present and future seawater CO2 chemistry across multiple coral reef habitats and scales at Dongsha Atoll and Taiping Island in the South China Sea

Published 22 May 2026 Science Closed
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Coral reefs consist of diverse benthic habitats that influence seawater CO2 chemistry variability on multiple spatial and temporal scales. Understanding the present-day seawater CO2 chemistry variability across both habitat-specific and reef-wide scales is critical to accurately predict the effects of future environmental change. Here, we utilize autonomous sensors and discrete seawater samples across diverse habitats at multiple scales ranging from habitat-specific (inner lagoon, patch reefs and seagrass beds; 0.02–0.72km2) to reef-wide scales at Dongsha Atoll (250km2) and Taiping Island (20km2) to characterize seawater chemistry. Across all habitats, daily mean pH ranged from 7.79–8.60 with mean diel variability ranging from 0.19–0.91. Spatially, pH variability ranged from 0.08 (patch reef) to 1.29 (inner lagoon). Biogeochemical modification of seawater chemistry was dominated by organic carbon cycling at individual habitat scales, whereas inorganic carbon cycling dominated at the scale of Dongsha Atoll. The largest alkalinity depletion (net calcification) was associated with patch reef habitats, whereas the highest alkalinity repletion was associated with a semi-enclosed lagoon. Under two climate change scenarios (linear dissolved inorganic carbon increase derived from historical observations and the CMIP6 SSP5-8.5 pathway), pH and/or aragonite saturation state (ΩAr) observations across all habitats in this study are projected to be below proposed thresholds for net reef accretion (pH < 7.7: inner lagoon ~ 10–13%; seagrass beds ~ 21–44%; patch reefs ~ 0–100%; atoll-wide ~ 4–98% of observations) or net dissolution (ΩAr < 2.92: inner lagoon ~ 10–18%; seagrass beds ~ 44–75%; patch reefs ~ 77–100%; atoll-wide ~ 94–100% of observations) by the year 2100. The results highlight the importance of habitat-specific and scale-conscious assessments of future coral reef environmental conditions.

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Impacts of coinciding ocean acidification and warming on the fatty acid profile of the pteropod Limacina helicina within the Northeast Pacific coastal region

Published 19 May 2026 Science Closed
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Under global climate change, co-occurrence of ocean acidification (OA) and warming poses a substantial threat to marine ecosystems. The present study focused on the Strait of Georgia within the Northeast Pacific region, where conditions of aragonite undersaturation exist year-round across the majority of the water column, with further intensification expected under OA. These conditions coincide with persistent rises in mean seasonal seawater temperatures and increased prevalence of acute stressor events, such as marine heatwaves and low-pH upwelling events. Limacina helicina, a pteropod species well-represented within the region’s zooplankton communities, is susceptible to OA and warming, with documented impacts including altered shell development, growth, and survival. To date, however, there has been minimal investigation into the effects of OA and warming on the species’ fatty acid profile under regionally-relevant conditions, thereby contributing to a lack of understanding of how impacts at lower trophic levels may relay across ecosystems. To address this knowledge gap, we examined the survival and fatty acid profile of L. helicina under future conditions via a laboratory experiment during which pteropods were exposed to singular and coinciding warming (mean summer seawater temperature + 4 °C) and OA (Ωarag < 1) conditions, with fatty acid analyses carried out via gas chromatography at 48-h and 5-d timepoints. OA conditions significantly altered fatty acid proportions at 48 h, and there was an additional interactive effect of OA and warming. Temperature significantly affected survival at 5 d, although experimental starvation conditions likely confounded this result. Additionally, fatty acid analyses of L. helicina picked from historical plankton samples collected in the region over 2014–2023 were carried out to examine time-series changes in fatty acid profiles in relation to temperature records. Results indicated no significant differences in fatty acid fractions among years, though there was suggestion of a changing proportion of myristic acid over a number of year groups. Overall, findings suggest that short-term OA conditions may result in altered fatty acid composition in pteropods, potentially leading to shifts in nutritional quality and associated impacts on trophic energy transfer.

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Changes in salinity impact nitrogen removal and carbon preservation in coastal wetlands sediment

Published 18 May 2026 Science Closed
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Highlights

  • Coastal freshening suppressed N removal via denitrification while accelerating net organic carbon mineralization.
  • Salinity shaped N removal vs. N retention and carbonate vs. alkalinity balance through sulfate availability.
  • Salinity changes had concurrent implications for coastal eutrophication and ocean acidification.

Abstract

Coastal wetlands naturally remediate nitrogen (N) pollution through microbial pathways that either remove reactive N via denitrification and anammox, or retain it via dissimilatory nitrate reduction to ammonium (DNRA). The balance among three processes is closely linked to the carbon (C) cycle, as both heterotrophic denitrification and DNRA consume organic C and release alkalinity. While salinity fluctuations can disrupt these processes through direct ionic stress or sulfur (S) cycling, their net impact on N removal and C preservation services remains unclear. Here, we deployed microcosm experiments using mangrove sediments under a large salinity gradient (0-30 psu). We quantified N transformation rates using 15N isotope tracing technique, combined with geochemical analysis, and functional genes quantification. Freshening from ambient 30 psu to 10 psμ decreased N removal efficiency by ∼20%. This decline was caused by reduced denitrification, whereas anammox and DNRA were unaffected. Meanwhile, lower salinity appears to have stimulated C decomposition via reduced ionic stress. The reduced sulfate input diminished total alkalinity (TA) generation relative to dissolved inorganic carbon (DIC). The stoichiometric shift of TA:DIC ratio could further contribute to acidification in adjacent coastal waters. Additionally, the S-mediated regulation of N partitioning appears to be nitrate-dependent: under nitrate limitation, higher sulfate favored N retention; conversely, with enriched nitrate, it potentially favored N removal. Integrating the coupling effect of salinity on interaction between N, C and S cycles, our study demonstrates that coastal water freshening may weaken wetlands’ ability to remove N and preserve C.

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Ocean acidification, more than warming or heatwaves, constrains shoaling behaviour in a range-extending fish through habitat simplification

Published 18 May 2026 Science Closed
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  1. Social context is a critical yet underexplored determinant of behavioural resilience to climate change. Group living can buffer individuals against environmental stress through enhanced vigilance, reduced predation risk and improved foraging efficiency.
  2. However, whether these behavioural expressions persist under chronic (warming, acidification) and acute (marine heatwaves) climate stressors remains unclear. Using natural climate analogues spanning present-day, ocean warming and combined warming–acidification reefs, we quantified how shoal size influences behavioural expression in a range-extending reef fish (Pomacentrus coelestis).
  3. Across all climate conditions, fish in larger shoals consistently exhibited higher foraging and activity levels and reduced risk-avoidance behaviours, whereas direct effects of warming, acidification and heatwaves on behaviour were negligible.
  4. In contrast, ocean acidification most likely constrained collective behaviour indirectly by simplifying benthic habitats, where fish densities were 84% lower than at the warming reef, resulting in shoals that were up to 79% smaller than the Warming and Control reefs.
  5. Combined, our data suggest that shoal size mediates behavioural expression between foraging and predator avoidance and that acidification-driven habitat simplification can alter behavioural expression indirectly by reducing fish densities and the formation of large shoals.
  6. We conclude that climate change can indirectly modify behavioural expression in shoal-forming fishes through habitat-driven erosion of social structure.
Continue reading ‘Ocean acidification, more than warming or heatwaves, constrains shoaling behaviour in a range-extending fish through habitat simplification’

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

Published 14 May 2026 Science Closed
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Highlights

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

Abstract

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

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

Published 13 May 2026 Science Closed
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Highlights

1.Predator cues can significantly induce byssal secretion in Mytilus coruscus.

2.Ocean acidification inhibits the anti-predatory responses of Mytilus coruscus.

3.Microplastics exerts sublethal effects on the byssus of Mytilus coruscus.

4.The presence of predators amplifies the mild disturbances caused by ocean acidification and microplastics.

5.The combined stress shows a synergistic inhibitory trend on the anti-predatory capability of Mytilus coruscus.

Abstract

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

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Coccolithophore genetic diversity, morphology, and contribution to particulate inorganic carbon production in Western North American coastal waters

Published 27 April 2026 Science Closed
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Coccolithophores, as calcifying phytoplankton, play a critical role in the global carbon cycle by producing calcium carbonate (CaCO3) in the ocean through their calcitic coccoliths. Here we examine Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related species abundance and genetic diversity along the West Coast of North America from samples taken on the 2021 NOAA West Coast Ocean Acidification (WCOA21) cruise, along the margin from British Columbia, Canada, to San Diego, California, USA. Significant carbonate chemistry gradients were observed across 17 transects, mostly in the onshore-offshore and north-to-south direction. Abundance and morphometrics of Gephyrocapsa spp. was evaluated using real-time PCR of mitochondrial cytochrome c oxidase subunit 3 ( cox3 ) gene and by microscopy. Variation in PIC concentrations, G. huxleyi and related species abundance, and coccosphere thickness were found to be associated with the gradients in carbonate chemistry and nutrient concentrations (phosphate, nitrate, nitrite, ammonium) across stations sampled during the cruise. We identified 5 unique amplicon sequence variants (ASVs) of Gephyrocapsa spp. cox3 that systematically varied in relative abundance across the California Current System. Southern California locations had greater diversity in cox3 sequences than northerly locations. These analyses represent baselines for evaluation of the impacts of future environmental changes in coastal waters along this productive upwelling regime.

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Nonlinear responses of phytoplankton size, diversity, and chlorophyll a to environmental forcing along the Yellow Sea

Published 20 April 2026 Science Closed
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Highlights

  • Miniaturization coincides with reduced species diversity and elevated chlorophyll a.
  • Declining pH and reduced dissolved inorganic nitrogen are key drivers for smaller cells.
  • Salinity, dissolved oxygen and cooling jointly reshape phytoplankton community structure.

Abstract

Phytoplankton are tiny drifting photosynthetic organisms that support marine food webs and help control the global carbon cycle. However, it remains unclear how ongoing environmental changes are altering their cell size, species diversity, and chlorophyll a concentration in coastal seas. In this study, we investigated changes in phytoplankton cell size, species diversity, and chlorophyll a concentration along the Yellow Sea coast of China from 2021 to 2024, based on fourteen research cruises conducted at twenty-six coastal stations. We then employed statistical models to explore how individual and combined environmental factors were related to those biological features. We observed a clear shift to predominance of smaller cells, a reduction in species diversity, and an increase in chlorophyll a concentration. pH and reduced dissolved inorganic nitrogen were strongly associated with smaller cell size, while higher salinity and higher oxygen were associated with lower diversity. Lower surface water temperature and higher dissolved oxygen were associated with higher chlorophyll a concentrations. Overall, our findings suggest that interacting changes in pH, nutrient supply, temperature, salinity, and oxygen are associated with a simpler phytoplankton community structure, smaller mean cell size, and higher biomass levels in the Yellow Sea coastal region, with potential consequences for local food webs and carbon cycling.

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Effects of ocean acidification on the growth, shell integrity, and vulnerability to thermal stress and predation in Pacific oysters (Magallana gigas), and bay mussels (Mytilus spp.)

Published 17 April 2026 Science Closed
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The ocean is absorbing approximately one third of the anthropogenic carbon dioxide (CO₂) emissions to the atmosphere. As a result, the pH of the ocean is declining steadily, a phenomenon known as ocean acidification (OA). This decline in pH and the associated reductions in calcium carbonate saturation states of the water can have widespread consequences for marine life, particularly to calcifying organisms. In this thesis, I aim to understand the effects of OA on the growth, shell integrity, and susceptibility to secondary stressors like heatwaves or predation, of two important shellfish species in British Columbia, Pacific oysters (Magallana gigas) and bay mussels (Mytilus spp.). I also aim to identify potential tipping points beyond which the biological responses of these shellfish to OA rapidly become more pronounced. I reared oysters and mussels in experimental mesocosms, in four pCO₂ treatments for eight-weeks to determine growth. I subsequently exposed these OA-acclimated animals to a secondary stressor by simulating heatwave conditions to assess thermal tolerance, and by introducing a predatory sea star to assess vulnerability to predation. Finally, shell condition was visually assessed, and shells were mechanically crushed to determine integrity. I found that OA decreased the growth of both oysters and mussels. No tipping point was observed for oyster growth, but reduced growth only emerged at the highest levels of OA in mussels. Sensitivity to atmospheric warming was not increased after exposure to acidic conditions for either species, although oysters had a considerably higher thermal tolerance than mussels. Mussel vulnerability to predation did increase, although the relationship was complex and depended on predator size. OA negatively affected shell strength, and possible tipping points emerged for this response metric in both species. Overall, OA was shown to negatively affect both species, but patterns of effect and the presence of potential tipping points depended on the species and the response metric. Understanding how these ecologically and commercially important bivalves are responding to OA is important for understanding how changing ocean chemistry will affect marine ecosystems, and to inform aquaculture managers on mitigation strategies.

Continue reading ‘Effects of ocean acidification on the growth, shell integrity, and vulnerability to thermal stress and predation in Pacific oysters (Magallana gigas), and bay mussels (Mytilus spp.)’

Synergistic effects of ocean acidification and thermal stress on shell biomineralization and parasitism in the white clam Leukoma asperrima (Bivalvia: Veneridae)

Published 17 April 2026 Science Closed
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Ocean acidification (OA) and global warming are fundamentally altering the biomineralization processes of calcifying marine organisms. This study evaluates shell malformations and parasitism in the white clam Leukoma asperrima at Bique Beach, Panama, from December 2024 to November 2025. Environmental parameters (pH, temperature) were monitored monthly across two sampling stations (n=1100). Results indicate that 13.6% of the population exhibited shell malformations, and 6.3% were parasitized by the pea crab Pinnotheres pisum. A strong positive correlation was found between pH and healthy individuals (r=0.97, p<0.001), whereas critical pH levels (min. 5.75) were associated with increased shell fragility and dissolution. Despite thermal tolerance observed up to 35.7°C, the synergistic effect of OA and local stressors compromises the structural integrity of L. asperrima, threatening the sustainability of this socio-economic resource in the Tropical Eastern Pacific.

Continue reading ‘Synergistic effects of ocean acidification and thermal stress on shell biomineralization and parasitism in the white clam Leukoma asperrima (Bivalvia: Veneridae)’

Future projections of compound events around the Main Hawaiian Islands

Published 15 April 2026 Science Closed
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The consequences of overlapping environmental stressors — referred to as compound events — may be more harmful to marine ecosystems than as individual stressors. Using recently conducted submesoscale-permitting future projections for the Main Hawaiian Islands, we present the first assessment of future compound events for Hawaiian waters. Our analysis focuses on surface and sub-surface heat-stress, ocean acidification, and low-oxygen events and is based on three different greenhouse gas emission scenarios. We show that a large fraction of ocean around Hawai‘i will be subject to compound events in the near future. However, the projected event characteristics such as duration and intensity vary substantially across the region suggesting that potential ecosystem impacts may differ over short distances. Our results reveal that these spatial differences are mainly driven by considerably different magnitudes of natural variability in ocean physics and chemistry across the domain driven by mesoscale processes, while anthropogenic trends exhibit only minor spatial differences. Our analysis demonstrates that small-scale tidal variability can significantly mitigate compound events in near-shore regions including some designated Marine Protected Areas. Overall, our findings highlight the need for high-resolution numerical models as well as for an extended observation network for robust future projections of local extreme events.

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NOAA PMEL scientists provide analysis and expertise for 2026 California Coast and Ocean Assessment report

Published 14 April 2026 Web sites and blogs Closed
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California’s 2026 Coast and Ocean Assessment was released in March by the California Ocean Protection Council (OPC), in partnership with the California Ocean Science Trust. This coast and ocean assessment is the result of the work of more than 120 scientific experts from academic institutions, state and federal agencies including NOAA, NGOs, and Tribes.

The report features the OA (ocean acidification) indicators analysis from NOAA PMEL Carbon Program scientists Adrienne Sutton and Simone Alin (starting on page 85). NOAA OAP (Ocean Acidification Program) funded coastal time-series moorings provided the foundation for the annual “trend” analysis and indicator development, led by Adrienne Sutton. Simone Alin, a long-time co-lead of WCOA cruises, served as West Coast OA subject matter expert.

NOAA teams were key to the development of the assessment report. OAP provided long-term coastal monitoring and data management, with significant partnership and synergy from the Global Ocean Monitoring and Observing (GOMO) Program-funded observation and data analysis efforts throughout the global ocean. Pacific Marine Environmental Laboratory (PMEL) supports lead researchers/primary investigators to engage with diverse coastal ocean interest holders, including fishery and water quality managers like the consortium of West Coast managers who requested the assessments in this report.

The 2026 report was initiated three years ago to codevelop ocean health indicators that could be used by the multiple California State agencies, non-governmental organizations, and tribal groups. These indicators provide the state with unified, comparable status and trend information, enabling better cross-organization collaboration.

Continue reading ‘NOAA PMEL scientists provide analysis and expertise for 2026 California Coast and Ocean Assessment report’

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