Marine environments that are subjected to seasonal changes are increasingly exposed to various factors, such as water pollution, climate change, coastal development, and human impacts. Therefore, this study examined seasonal changes in the main physicochemical parameters of seawater around Dangli Island, Langkawi, Malaysia to better understand the environmental conditions that affect the local marine ecosystem. This study examined seasonal variations in the main physicochemical parameters of seawater such as salinity, temperature, conductivity, pH, dissolved oxygen (DO), Total Ammoniacal Nitrogen (TAN), and Orthophosphate (PO₄³⁻) between twelve monitoring stations D1–D12 around Dangli Island during the Southwest and Northwest Monsoons. The results showed a significant difference between the Southwest Monsoon (SWM) season, which exhibited higher salinity up to 31.16 ppt, temperature up to 30.62°C, and conductivity, while the Northwest Monsoon (NEM) was recorded with cooler temperatures as low as 28.73°C and a slight increase in dissolved oxygen in some areas. This phenomenon causes the ocean to absorb CO₂ and control ocean acidification. Warmer waters during NEM can reduce CO₂ solubility, while cooler, oxygen-rich SWM conditions increase CO₂ uptake, potentially increasing acidification. By studying and understanding how these seasonal conditions affect ocean chemistry, it can help assess the long-term impacts of climate change on the marine environment of Dangli Island and allow us to prepare early conservation strategies for the future. These factors can be influenced by seasonal variations and upwelling phenomena. Two-way ANOVA results demonstrated that all physicochemical parameters have no significant difference between sampling stations (p > 0.05). In addition, there have high significant differences between monsoon seasons (p < 0.05) except for conductivity and DO level. The variations in the physicochemical properties of seawater around Dangli Island reveal the influences of rainfall, river discharges, and upwelling phenomenon on stratification shifts that show the differences in the distribution of seawater physicochemical parameters. These findings also provide valuable insights and help to conserve the marine environment, offering a basis for future research and environmental management strategies around Dangli Island.
Continue reading ‘The spatial and temporal variability physicochemical seawater parameter in Dangli Island of Langkawi, Malaysia’Posts Tagged 'Indian'
The spatial and temporal variability physicochemical seawater parameter in Dangli Island of Langkawi, Malaysia
Published 28 September 2026 Science ClosedTags: chemistry, field, Indian
Aragonite saturation state indicates emerging ocean acidification hotspots in the Gulf of Mannar and Palk Bay along the southeast coast of India
Published 23 September 2026 Science ClosedTags: biogeochemistry, chemistry, field, Indian
The impact of ocean acidification (OA) on seawater carbonate chemistry, particularly on the aragonite saturation state (Ωarag), is inadequately understood in the Gulf of Mannar (GoM) and Palk Bay (PB). In this study, we analyzed the spatial and temporal variability of Ωarag to pinpoint potential ocean acidification hotspots within these two ecologically critical coastal habitats along the southeastern coast of India. A pilot study was conducted over 24 locations during 2023–2024. The findings reveal that PB had a higher mean pH (8.33 ± 0.06) than GoM (8.08 ± 0.02). In GoM, Ωarag values were lower, at 2.82 ± 0.20, indicating that calcification conditions were not adequate. In PB, it reached 3.22 ± 0.57, which means that conditions for calcifying organisms were favourable. Seasonal variability in Ωarag was primarily controlled by pH, carbonate ion concentration, pCO2, and monsoonal hydrographic processes Seasonal patterns corroborated that these conditions were modulated by both anthropogenic activities and natural processes. During the Northeast and Southwest monsoons, there were significant drops in Ωarag that matched changes in important biogeochemical indices. Overall, these results reveal that PB experiences greater variability in Seawater carbonate chemistry, while GoM exhibits relatively stable but slightly lower carbonate saturation. Pearson correlation and Structural Equation Modelling further demonstrated that pH and carbonate ion concentration positively influenced Ωarag, whereas pCO2 and Revelle factor showed negative relationships. The findings enunciate that GoM is more vulnerable to ocean acidification than PB and emphasize the value of Ωarag as a sensitive indicator for detecting emerging acidification hotspots in coastal waters. It also emphasizes the importance of regular monitoring of OA parameters in these regions to protect these critical ecosystems and their associated services.
Continue reading ‘Aragonite saturation state indicates emerging ocean acidification hotspots in the Gulf of Mannar and Palk Bay along the southeast coast of India’Impact of ocean acidification on coastal copepod Pseudodiaptomus serricaudatus: implications for futuristic coastal dynamics
Published 21 September 2026 Science ClosedTags: biological response, crustaceans, Indian, laboratory, mortality, reproduction, zooplankton
Highlights
- Impact of ocean acidification on coastal copepods is proportional to its intensity.
- Projected low pH significantly increases Pseudodiaptomus serricaudatus mortality.
- Lower pH reduces overall population density and alters life-stage composition.
- Predicted acidification delays larval development in P. serricaudatus.
Abstract
Anthropogenic ocean acidification, driven by increased atmospheric CO2 absorption by seawater, poses significant threats to marine ecosystems, particularly in coastal environments, where pH reductions are expected to be more severe than in the open ocean. Copepods represent a critical link between primary producers and higher trophic levels in the classical marine food chain. However, their responses to the rapid decline in seawater pH expected by the century’s end remain poorly constrained—especially in dynamic coastal regions. The current study quantifies how near-future pH scenarios affect the survival and population dynamics of the Pseudodiaptomus serricaudatus, a perennial coastal and estuarine copepod of the West Coast of India. Adult copepods of this species were incubated at four target pH levels (8.10, 7.81, 7.51, 7.04) using an automated CO2-bubbling system to assess mortality and population dynamics. Mortality was evaluated every three days up to day 10; population stage composition was recorded on day 15. Mortality remained 23% at pH 8.1 (representing open-ocean conditions) but rose to 30% at pH 7.81 (present-day coastal average), 47% at pH 7.51 (projected late-21st-century coastal value), and 77% at pH 7.04 (extreme 23rd-century scenario). Population data revealed declines across life stages and copepodite-to-nauplius (Ct/N) ratio at lower pH values, indicating impaired development. Any potential impact of ocean acidification on copepods could affect the fisheries sector, as these copepods are the chief food source for mackerel, an economically important fish in the region. The critical pH threshold for P. serricaudatus appeared to lie between 7.51 and 7.81, corresponding closely to current coastal conditions and near-future projections. These findings suggest that coastal copepod populations may already be experiencing sublethal stress, with potential demographic collapse occurring within decades rather than by the end of the century.
Comparative responses of coastal Arabian sea plankton to different ocean acidification simulation methods
Published 16 September 2026 Science ClosedTags: abundance, biological response, BRcommunity, community composition, Indian, laboratory, otherprocess, phytoplankton, prokaryotes, zooplankton
Ocean acidification (OA) is expected to alter marine phytoplankton communities by modifying seawater carbonate chemistry, with important implications for marine food webs and biogeochemical cycling. In this study, we tested the hypothesis that comparable pH reductions achieved through different acidification methods generate distinct carbonate chemistry conditions and consequently different biological responses. A 5-day microcosm experiment was conducted using natural phytoplankton assemblages collected from the coastal Eastern Arabian Sea. OA was simulated by HCl addition (acid), CO2 enrichment (CO2), and acid–base manipulation. Changes in carbonate chemistry, nutrients, phytoplankton community composition, pigments, bacteria, microzooplankton, and organic carbon pools were monitored. As expected, the three manipulation methods produced significantly different carbonate chemistry conditions despite comparable pH reductions. Repeated-measures ANOVA and Tukey’s post hoc analyses confirmed significant treatment effects for pH, pCO2, DIC, HCO3−, CO32−, and total alkalinity. By Day 5, CO2 enrichment significantly increased total phytoplankton abundance and promoted microplankton dominance, driven by bloom-like proliferation of Thalassiosira sp., whereas picoplankton declined significantly. Conversely, pennate diatoms, cyanobacteria, dinoflagellates, and coccolithophores exhibited weak or negative responses. Concurrent changes in phosphate, nitrite, autotrophic bacteria, and microzooplankton indicated that nutrient availability, microbial recycling, and grazing interacted with carbonate chemistry to regulate phytoplankton succession. Our findings demonstrate that phytoplankton responses in the oligotrophic Eastern Arabian Sea are governed by the combined effects of carbonate chemistry, nutrient dynamics, and ecological interactions rather than pH alone.
Continue reading ‘Comparative responses of coastal Arabian sea plankton to different ocean acidification simulation methods’Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean
Published 17 August 2026 Science ClosedTags: biological response, community composition, Indian, laboratory, otherprocess, photosynthesis, physiology, phytoplankton
Phytoplankton and microzooplankton (MZP) are key components of marine food webs, driving carbon transfer through the microbial loop. Short-term laboratory microcosm bottle incubations using seawater from the Bay of Bengal (BoB) and Arabian Sea (AS) in 2022 examined the effects of reduced pH. Phytoplankton biomass (Chl-a) remained stable or increased by up to 12% under low pH, suggesting reduced grazing or improved prey quality. MZP diversity (Shannon index, H′) showed basin-specific responses. In the BoB (Exps. 1–2), H′ ranged 2.00–3.70 with high evenness (J′ = 0.93–1.00) and slight declines under medium acidification (ΔpH = 0.2). In contrast, the AS (Exps. 3–4) showed wider variability (H′ = 0.00–3.63) and greater sensitivity, with sharp diversity losses under stronger acidification (ΔpH = 0.4). AS assemblages showed pronounced richness declines (D′ = 2.85–0.00), whereas BoB communities remained stable. Regional and pH-related differences were linked to shifts in ciliates and dinoflagellates. Autotrophic bacteria sustained under low pH, while heterotrophic bacteria increased later, indicating altered microbial-loop functioning. Overall, pH, chlorophyll-a, and heterotrophic bacteria structured the community, accounting for > 65% of the variation. Thus, short-term acidification reshapes MZP assemblages and may modify trophic interactions across the northern Indian Ocean.
Continue reading ‘Short-term pH variability reshapes phytoplankton and microzooplankton communities in the northern Indian Ocean’Giant kelp-associated variation in coastal seawater chemistry across contrasting sites in Chile and Tasmania
Published 13 August 2026 Science ClosedTags: algae, chemistry, field, Indian, South Pacific
Background and Aims
Widespread shifts in seawater chemistry are occurring across spatial and temporal scales, with important consequences for coastal ecosystems. Giant kelp (Macrocystis pyrifera) forests elevate seawater pH and dissolved oxygen (DO) through photosynthesis, potentially providing short-term refugia from ocean acidification and deoxygenation. However, whether these effects persist across contrasting environmental settings remains unclear. Here, we assess how biological and oceanographic conditions regulate giant kelp-mediated modification of seawater chemistry across multiple sites.
Methodology
Hourly measurements of seawater pH, DO and temperature were collected during spring–summer 2022–23 using paired deployments inside and outside giant kelp forests at one site in central Chile and four sites in Tasmania, Australia. The influence of giant kelp density was also evaluated at two sites in southern Chile and three sites in Tasmania. An upwelling index was calculated for the central Chile site to assess the influence of regional oceanographic forcing on kelp-associated seawater chemistry patterns.
Key Results
Hourly pH and DO were higher inside giant kelp forests than outside at the central Chile site and at one Tasmanian site. At these locations, stronger daytime pH–DO relationships indicated that photosynthetic carbon uptake exceeded night-time respiration, generating a net positive metabolic signal. In Tasmania, giant kelp density was positively associated with hourly pH and DO, whereas no such relationship was detected in southern Chile. At the central Chile site, kelp-associated effects intensified during a strong upwelling event, reducing the severity of low pH and DO conditions.
Conclusions
Giant kelp forests can locally buffer short-term fluctuations in seawater pH and DO, but this capacity is highly site-dependent and influenced by giant kelp density and environmental conditions. Overall, our findings suggest that continued loss of giant kelp forests in Tasmania may reduce their potential to provide short-term refugia, while in Chile the strength of kelp-mediated seawater chemistry modification is likely to remain strongly influenced by variability in upwelling and freshwater inputs.
Continue reading ‘Giant kelp-associated variation in coastal seawater chemistry across contrasting sites in Chile and Tasmania’Tracing the imprints of dual stressors: eco-physiological and genotoxic insights from Mystus gulio under acidification and warming scenario
Published 10 August 2026 Science ClosedTags: biological response, fish, Indian, individualmodeling, laboratory, modeling, molecular biology, physiology, reproduction
Global warming has caused a rise in ocean temperature and acidification, which collectively wreak havoc on marine animals. However, the combined ramifications of these stressors on energy metabolism, oxidative balance, and DNA integrity remain inadequately studied in teleosts. The present study aims to unravel the combined effects of warming (34°C) and acidification (pH 7.7) on energetic balance, antioxidant defense, and DNA stability in Mystus gulio at two intervals (15th and 45th day). Furthermore, the Effect Addition model was used to disentangle potential additive or non-additive effects of the combined stressors. Elevated temperature and acidification induced a marked energetic imbalance, as mirrored by suppressed ingestion and absorption rates, reduced scope for growth, and elevated excretion. Oxidative stress biomarkers revealed significant upregulation of SOD, CAT, and GST under combined treatment, which ultimately led to augmented lipid peroxidation. Genotoxic assessment delineated progressive upsurges in tail DNA (%) and olive tail moment, indicating compromised genomic stability. The integrated biomarker response consisted of six parameters, RR, ER, SOD, CAT, GST, and LPO, further corroborating that elevated temperature, alone and in combination with acidification, posed the highest cumulative physiological burden. Furthermore, the model assessment indicated that the interaction between warming and acidification varied among different biomarkers. Collectively, these findings corroborate that concurrent thermal and low pH perturbations destabilise physiological processes, oxidative instability, and DNA damage, which may undermine growth potential and jeopardise population structure and destabilise trophic relationships. The present study provides a mechanistic understanding of the impacts of multiple stressors and offers a robust integrative framework to predict fish vulnerability under future climate-driven oceanic vicissitudes.
Global genome-wide patterns of genetic diversity and population structure in Coryphaena hippurus
Published 10 August 2026 Science ClosedTags: biological response, fish, Indian, laboratory, Mediterranean, molecular biology, North Atlantic, North Pacific, physiology
Highlights
- Genome-wide SNPs reveal four discrete populations across ocean basins.
- Mediterranean population forms a deeply divergent and isolated lineage.
- Nuclear SNPs detect Pacific–Atlantic.
- Environmental gradients (salinity, phosphate, pH, light) shape genomic structure.
- Genetic connectivity varies within basins, revealing hidden substructure.
Abstract
The origin and maintenance of marine biodiversity remain poorly understood, particularly in highly connected oceanic environments where extensive dispersal is expected to limit population differentiation. Evolutionary processes driving population divergence or speciation frequently depend on a proper knowledge of species’ life history and its interaction with major environmental variables. Using a genome-wide approach, we investigated the global population structure of the cosmopolitan pelagic fish Coryphaena hippurus Linnaeus, 1758, generating a dataset of 8.7 million SNPs and complete mitochondrial genomes.
Our results reveal, for the first time, four genetically differentiated populations, corresponding to major oceanic basins: Atlantic, Pacific, Indian and Mediterranean Sea. The Mediterranean population exhibited a distinct genomic signature, likely resulting from historical isolation and restricted contemporary exchange through the strait of Gibraltar. Despite this structure, genome-wide analyses uncovered extensive signals of historical connectivity among basins. D-statistics and f4-ratio tests detected significant excess allele sharing, particularly between Indo-Pacific and Atlantic populations, while phylogenetic network reconstruction in TreeMix supported multiple migration events, highlighting the role of ancestral gene flow in shaping global genetic patterns.
At finer scales, a limited but significant intra-oceanic structure was detected within both Atlantic and Pacific basins. Seascape genomic analyses revealed that environmental gradients such as salinity, phosphate concentration, light availability (PAR, Kd), and pH are significantly associated with genomic variation, suggesting that ecological factors contribute to population differentiation across heterogeneous marine environments.
Localized biogeochemistry and seasonality govern carbonate chemistry in estuarine mangrove ecosystems
Published 3 August 2026 Science ClosedTags: biogeochemistry, chemistry, field, Indian
Sundarbans, the world’s largest contiguous mangrove ecosystem and representing shallow coastal Bay of Bengal of the Northern Ocean, faces dynamic climate variations, including ocean acidification. To delineate ocean acidification from natural pH variations, it is crucial to perform long-term measurements of multiple carbonate chemistry parameters such as pH, total alkalinity (TA), and dissolved nutrients, among others. In the present study, surface water carbonate chemistry parameters, including TA, pH, and dissolved nutrients (o-phosphate and silicate), were analysed monthly between 2014 and 2022 in three pre-defined stations, namely Stn1, Stn2, and Stn3, part of Sundarbans Biological Observatory Time Series (SBOTS) located in Sagar Island, the largest island of the Indian Sundarbans. The observed deviation from the linear TA-Salinity curve in the studied sites of SBOTS showed the influence of freshwater in modulating TA. Generalized Additive Model (GAM) revealed substantial seasonal variability in the controls on TA. During monsoon, salinity was a dominant driver of carbonate chemistry, consistent with enhanced freshwater discharge. In contrast, during the post-monsoon season, primary productivity as indicated by the relationship with Chla, dissolved silicate, was found to exert a stronger influence on TA variability. Multilinear regression (MLR) analysis of calculated pCO2 further supported these seasonal trends. Overall, the findings highlight the importance of season-specific assessments, highlighting the critical role of freshwater discharge in shaping estuarine carbonate dynamics. These insights are vital for predicting the vulnerability and response of mangrove estuaries under future climate change scenarios.
Continue reading ‘Localized biogeochemistry and seasonality govern carbonate chemistry in estuarine mangrove ecosystems’Freshwater forcing along the Indian Coastal Seas: impacts on productivity and acidification
Published 31 July 2026 Science ClosedTags: biological response, Indian, phytoplankton
Freshwater fluxes from precipitation and river runoff play a critical role in modulating upper-ocean stratification, nutrient availability, and biogeochemical processes in the coastal waters of the Indian subcontinent. The formation of the barrier layer thickness (BLT) links freshwater input to vertical mixing, influencing both productivity and carbonate chemistry. High-resolution (5 km) MITgcm-BLINGv2 simulations are conducted for the Arabian Sea (AS) and the Bay of Bengal (BoB), and sensitivity experiments are performed to represent reduced and increased freshwater perturbations. We analyzed seasonal variability of buoyancy frequency (N2), mixed layer depth (MLD), net primary productivity (NPP), pH, and phytoplankton biomass across five coastal regions. Reduced freshwater scenarios weakened or eliminated BLT, leading to deeper MLD and N2 maxima, with subsurface nutrient-rich waters entrained upward. This enhanced nutrient availability increased NPP in the coastal regions. However, the upward transport of subsurface carbon also lowered surface pH by 0.03, indicating a trade-off between biological enhancement and increased surface acidification. In the increased freshwater scenario, the BLT strengthened, the MLD shoaled, and NPP decreased, while surface pH increased due to reduced vertical carbon exchange. Interestingly, stratification deepening under reduced freshwater input is more pronounced in the southeastern AS than in the BoB, contrasting conventional understanding. Vertical phytoplankton responses are consistent with these trends, with small and large phytoplankton biomass increasing under weaker BLT and decreasing under enhanced BLT. Freshwater-driven BLT modulation drives a complex interplay between carbon uptake and export along Indian coastal waters. These findings emphasize the importance of accurately representing freshwater fluxes in biogeochemical models to capture regional ecosystem responses.
Continue reading ‘Freshwater forcing along the Indian Coastal Seas: impacts on productivity and acidification’Interplay between nutrient limitation and ocean acidification: plankton community shifts in the oligotrophic western Bay of Bengal
Published 30 July 2026 Science ClosedTags: biological response, community composition, Indian, morphology, multiple factors, nutrients, otherprocess, phytoplankton
Highlights
- Nutrient limits the phytoplankton growth in the Bay of Bengal due to stratification.
- Picoplankton dominated the phytoplankton community in the Bay.
- An increase in phytoplankton biomass was observed in response to ocean acidification (OA) in nutrient-rich regions.
- Decrease in phytoplankton biomass, bacteria and microzooplankton abundance was found in the nutrient-poor regions.
- Nutrient limitation overshadow the ocean acidification impact in the Bay of Bengal.
Abstract
The perennial rise in atmospheric carbon dioxide (CO2) from anthropogenic activities increased oceanic carbon uptake, thereby lowering seawater pH. Rapid ocean acidification (OA) by 2 to 3 times than other regions of the same latitudinal belts was reported in the Bay of Bengal (BoB) due to the deposition of atmospheric pollutants, in addition to the dissolution of atmospheric CO2. Therefore, the impact of OA on phytoplankton composition is hypothesized to be greater in the BoB than elsewhere in the globe. On the other hand, the BoB experiences intense oligotrophic conditions due to strong stratification driven by nutrient-poor freshwater discharge from major rivers, which is the primary bottleneck for phytoplankton growth, rather than carbon. It is hypothesized that nutrient limitation may overshadow OA’s impact on plankton in the BoB. To test this hypothesis, six microcosm experiments were conducted in the western BoB between 13 and 20°N with different nutrient levels in the surface waters. The pH of the surface water was adjusted by 0.2 units below the ambient pH using CO2 gas bubbling to simulate the projected OA scenario for the year 2100. Following pH adjustment, incubations were carried out for three days. Picoplankton dominated the phytoplankton community (∼96%) at all stations, with prochlorophytes as the dominant group. Among the phytoplankton, procholorophytes, diatoms, and prymeniophytes increased due to OA across all stations, while other groups of phytoplankton were declined. The increase in phytoplankton biomass was observed in the nutrient-rich stations, while a decrease in phytoplankton biomass, bacteria and microzooplankton abundance was found in the nutrient-poor stations, suggesting that nutrient availability dominated over the OA. Under a business-as-usual scenario, an increase in stratification due to melting Himalayan glaciers is projected, leading to strong stratification and reduced nutrient inputs through vertical mixing in the future in the BoB. Under such a scenario, nutrient limitation may possibly overshadow the OA impact in the future, despite a rapid decline in pH driven by increased CO2 dissolution and deposition of atmospheric pollutants.
Continue reading ‘Interplay between nutrient limitation and ocean acidification: plankton community shifts in the oligotrophic western Bay of Bengal’A satellite-derived re-analysis of surface-ocean pH variability in the coastal waters of India
Published 22 July 2026 Science ClosedTags: chemistry, Indian
Monitoring pH variations in coastal waters is essential for maintaining marine life and developing strategies to combat ocean acidification caused by climate change. The present study examines pH changes on interannual and seasonal scales along the northwest (NW), southwest (SW), southeast (SE), and northeast (NE) coasts of India over 30 years (1993–2022) using satellite data. Results reveal a significant decline in pH levels (R 2 = 0.727) across Indian coastal waters, with notable regional differences. The northeastern coast showed the greatest pH stability and the smallest decrease (R 2 = 0.798), while the southwestern coast experienced the highest variability (R 2 = 0.490). These regional pH fluctuations suggest varying resilience to ocean acidification. The NE and SW coasts, with higher variability, may be more susceptible to environmental changes, underscoring the importance of targeted monitoring and mitigation measures. In contrast, the more stable trends along the SE and NW coasts present opportunities to explore long-term resilience mechanisms. Seasonal fluctuations were evident everywhere, with winter consistently showing higher pH values and monsoon seasons the lowest. Principal component analysis indicated that the first two components accounted for 85.7% of the variance, highlighting factors such as seasonal river inflows, biological activity, and monsoonal freshwater input. Overall, these findings emphasise the importance of region-specific coastal management strategies to address climate change impacts and human pressures, while also providing a baseline for tracking future ocean acidification trends and assessing their effects on marine biodiversity and ecosystem services.
Continue reading ‘A satellite-derived re-analysis of surface-ocean pH variability in the coastal waters of India’Acute low pH associated with coastal acidification is detrimental to larval development of the Cape urchin Parechinus angulosus
Published 26 June 2026 Science ClosedTags: biological response, BRcommunity, echinoderms, growth, Indian, laboratory, mortality, physiology, reproduction
Acidification in coastal habitats is increasing in duration and amplitude under the continued influence of ocean acidification and contributing coastal processes. The impacts of low pH conditions on calcifying organisms, especially echinoderms, is well established, with the early developmental stages being especially vulnerable. This is the first study to assess the impact of locally relevant coastal acidification scenarios on the early development of the Cape urchin Parechinus angulosus. Our findings suggest that the early larval stages of this species are unlikely to survive when exposed to low pH conditions, specifically during the onset of skeletogenesis. In our laboratory experiments, larvae that were exposed to the low pH treatment (pH 7.32) showed significantly reduced growth (GLMM, Time × Treatment interaction: β = −0.361 ± 0.019, z = −19.06, p < 0.001) and developmental regression compared with those from the control treatment (pH 7.95). Substantially slower growth rates were observed in the low pH treatment (length = 72.3 hpf0.18) compared with in the control treatment (length = 24.24 hpf0.54). There was also evidence of abnormal and delayed development and potential dissolution of skeletal structures under the low pH condition. However, fertilisation success and larval survival did not differ significantly between the experimental treatments, suggesting that developmental impacts of low pH over short durations, even though substantial, may be sublethal. The developmental impacts are likely to impair the transition of larvae to the adult stages, which may ultimately affect populations of this ecologically important species under future coastal acidification scenarios.
Continue reading ‘Acute low pH associated with coastal acidification is detrimental to larval development of the Cape urchin Parechinus angulosus’Identification of the source of carbonaceous aerosols using stable carbon and nitrogen isotopes and the implications of its deposition on the coastal ocean
Published 24 June 2026 Science ClosedTags: chemistry, Indian
Highlights
- Aerosols and their major sources are seasonally variable at Visakhapatnam.
- Total suspended matter was higher during winter than during summer.
- Biomass burning is a dominant source of aerosols during winter.
- Fossil fuel and coal combustion are the major sources during summer.
Abstract
The continuous rise in anthropogenic aerosol emissions degrades ambient air quality, and their deposition onto the surface ocean alters chemical and biological characteristics. Identifying the sources of aerosols is crucial for taking appropriate measures to minimize their impacts. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) are promising tools for identifying sources of carbonaceous aerosols. The objective of this study is to identify the dominant sources of carbonaceous aerosols over an urban region using stable carbon (δ13C) and nitrogen (δ15N) isotope ratios, and to evaluate their potential influence on surface ocean acidification in the coastal Bay of Bengal. Aerosol samples were collected between March 2016 and February 2017 at a fortnightly interval, over an urban region, to examine the sources of carbonaceous aerosols and to evaluate the possible impacts on surface ocean acidification. Significantly high concentrations of total suspended particulates (TSP) during winter (112 ± 26 μg m−3) compared to summer (58.8 ± 8 μg m−3), associated with an insignificant seasonality in δ13CTC (−26.9‰ to −22.9‰), indicating ageing of organic aerosol through oxidation. In contrast, higher δ15NTN during winter (2.2‰ to 12.1‰; 5.4 ± 2.9‰) than summer (−12.9‰ to −1.8‰; −4.7 ± 3.3‰) indicate different sources. Based on source characteristics of δ13CTC, δ15NTN and the isotope mixing model, biomass burning and coal combustion are the major sources of carbonaceous aerosols during winter, whereas coal and fossil fuel burning contributed during summer. Since biomass burning contains higher concentrations of acidic aerosols, such as sulfates, and its deposition over the surface ocean results in higher level of pH levels compared to coal ashes. A higher decline in pH of the coastal waters during winter than summer was reported in the coastal Bay of Bengal. This study confirms that the deposition of higher sulphate and nitrates due to biomass burning in the Indo-Gangetic Plain (IGP) region is responsible for a greater decline in pH of the surface ocean during winter than summer. Taking appropriate measures to reduce biomass burning in the IGP region would decrease ocean acidification and allow the atmospheric CO2 sink into the coastal Bay of Bengal to achieve net zero carbon emissions in the future.
Continue reading ‘Identification of the source of carbonaceous aerosols using stable carbon and nitrogen isotopes and the implications of its deposition on the coastal ocean’Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification
Published 18 June 2026 Science ClosedTags: algae, annelids, biological response, BRcommunity, bryozoa, cnidaria, community composition, corals, crustaceans, echinoderms, fish, Indian, laboratory, mollusks, morphology, North Pacific, otherprocess, physiology, vents
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.
Continue reading ‘Marine invertebrates and fishes exhibit inconsistent body size responses to ocean acidification’Pteropod vulnerability to ocean acidification in the eastern Arabian Sea
Published 18 June 2026 Science ClosedTags: biological response, BRcommunity, Indian, laboratory, mollusks, zooplankton
Highlights
- First study on pteropod response to ocean acidification in the eastern Arabian Sea.
- High pteropod abundance during fall inter monsoon season due to food availability.
- pH in the Arabian Sea was low during south west monsoon with pHT upto 7.75
- Pteropod shell dissolution was observed under acidified conditions
- Protrusions through the pteropod shell were observed under acidified conditions
Abstract
The rapid rise in atmospheric CO2 and its subsequent uptake by the oceans has led to ocean acidification and other associated changes in the marine ecosystem. The recent reports of the shoaling of the aragonite saturation horizon in the northern Indian Ocean are particularly alarming, as they pose a serious threat to the survival of calcareous organisms. Pteropods, also known as sea-butterflies, are believed to be highly susceptible to ocean acidification due to their thin aragonite shell. In our study in the eastern Arabian Sea, we found low pH conditions with surface pHT as low as 7.751 during late South-west monsoon (SWM). The pteropod abundance is high during the fall inter-monsoon (FIM), suggesting that the system continues to sustain productivity even after the cessation of peak monsoon activity. This also implies that the food availability regulates pteropod abundance in the eastern Arabian Sea. As pteropods are key components of food sources for many marine species, such as fish, any changes in their abundance can have cascading effects on the marine food web. To show how pteropods will be affected in futuristic elevated CO2 conditions, a CO2 manipulation experiment was conducted in the eastern Arabian Sea during December 2024. Pteropods belonging to Creseis acicula from the eastern Arabian Sea were subjected to pHT = 7.470, and pCO2 = 1734 μatm under controlled conditions. Our findings suggest that acidification led to the dissolution of pteropod shells. Acidification also led to protrusion through the shells, and these protrusions varied in length up to 88 μm. These structural alterations represent an acute response of pteropod shells to reduced pH, highlighting their rapid vulnerability to acidification stress. These observed protrusions need to be assessed further to determine if they provide any competitive advantage in combating or minimizing the impact of ocean acidification.
Continue reading ‘Pteropod vulnerability to ocean acidification in the eastern Arabian Sea’Temperature, but not acidification, influences the growth and lipid profile of juvenile sand whiting, Sillago ciliata (Cuvier 1829)
Published 18 June 2026 Science ClosedTags: biological response, fish, Indian, mesocosms, morphology, multiple factors, physiology, reproduction, temperature
Seafood provides an essential source of macro- and micronutrients for coastal communities worldwide. Climate change is a key threat to seafood security, altering the sizes, abundances, distributions, physiology and ecological interactions of fisheries species, and increasingly, there is evidence of impacts to seafood nutritional quality. In a 12-week mesocosm experiment, we tested the influence of projected ocean warming and acidification scenarios on the growth and lipid quality of juvenile sand whiting (Sillago ciliata), a popular fisheries species in eastern Australia. The growth of S. ciliata significantly increased (by 61% body weight) under elevated temperature (+3°C) but was not affected by acidification treatment levels. Lipidomic analysis revealed no influence of temperature or acidification on total lipid content or the composition and total proportions of lipid classes and subclasses. However, elevated temperatures significantly impacted the overall composition of fatty acids, including a shift toward higher saturation and a decline in important omega-3 fatty acids. Fish exposed to elevated temperature treatments had more saturated fatty acids than those at control temperatures, along with reduced levels of the valuable omega-3 eicosapentaenoic (C20:5) and docosahexaenoic (C22:6) fatty acids. Despite impacting fatty acid composition in S. ciliata, the increased growth of the juvenile whiting, if sustained into adulthood, under elevated temperatures, may help compensate for the overall availability of essential polyunsaturated fatty acids to support consumer nutritional requirements. These findings contribute to the growing body of evidence on variable climate resilience in nearshore species to future environmental conditions and the implications for the trophic transfer of nutrients in estuarine ecosystems.
Continue reading ‘Temperature, but not acidification, influences the growth and lipid profile of juvenile sand whiting, Sillago ciliata (Cuvier 1829)’Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island
Published 16 June 2026 Science ClosedTags: biogeochemistry, biological response, chemistry, cnidaria, community composition, corals, field, Indian, otherprocess, vents
Gas hydrates modulate methane and carbon dioxide benthic fluxes into the ocean and usually occur embedded in the sediment. Here we use acoustic surveys alongside optical and geochemical observations from remotely operated vehicles to show that CO2 hydrate mounds are forming directly on the seafloor atop a large liquid CO2 vent field offshore Mayotte Island. The venting, which initiated following volcanic activity in 2018, deleteriously impacts surrounding coral communities due to local acidification.
Continue reading ‘Large CO2 seeps and hydrate field on the seafloor offshore Mayotte Island’Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective
Published 28 May 2026 Science ClosedTags: field, Indian, modeling, regionalmodeling, salinity
This study comprehensively assesses the long-term variability of temperature, ocean acidity changes, and their implications on sound absorption and acoustic propagation in the Bay of Bengal. The analysis reveals a persistent warming trend in the Indian Ocean over the past 50 years, with a significant increase in temperature observed during the Sagar Maitri cruise in 2019. Thermal structure analysis using HadleySST EN4 data indicates warming in the upper 50m but a cooling trend in the 100-200m depth range. Oceanic Heat Content analysis highlights an increasing tendency of heat storage in the upper 50m, indicative of global warming.
In the context of surface ducted propagation, Sonic Layer Depth (SLD) and gradients in the Sound Speed Profile (SSP) were crucial factors influencing acoustic energy behavior. The study revealed a decreasing trend in in-layer gradient (Gr_SL) since 1990, intensifying after that period. The below-layer gradient (Gr_BL) also exhibited a decreasing trend, implying complex dynamics in the sonic layer with potential implications for sound propagation in the surface duct.
The investigation into pH changes spanning 65 years demonstrates a declining trend, particularly since the 1990s, attributed to increased atmospheric CO2 dissolution. The study linked this decrease to anthropogenic activities, aligning with global trends. The analysis of sound absorption illustrated a nonlinear relationship between absorption, frequency, and pH, emphasizing a significant impact of ocean acidification on sound absorption in the Bay of Bengal. The acoustic propagation modeling further highlighted a decrease in transmission loss with reducing pH, leading to increased sound travel and potentially noisier oceans. Salinity variations play a more significant role than temperature in influencing sound absorption.
Continue reading ‘Long term variability of temperature and pH in the Bay of Bengal: an investigation on acoustic perspective’
