Posts Tagged 'salinity'

Triple threat: ocean acidification, warming, and hyposalinity synergistically weaken shell integrity in a Mediterranean calcifying mollusk

Published 30 January 2026 Science Closed
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Highlights

  • OA, OW, and hyposalinity drive skeletal and mineralogical responses in a Mediterranean clam.
  • Combined stress makes shells less dense, more porous, and more fracture-prone.
  • Microstructural changes reveal early calcification impairments under triple stress.
  • Triple-stressor synergy compromises shell integrity and threatens fishery species resilience.

Abstract

Anthropogenic climate change is rapidly altering marine environments primarily through ocean warming, acidification, and hyposalinity, posing significant challenges for marine calcifying organisms. This study investigated the short-term effects of these stressors on the Mediterranean bivalve Chamelea gallina, a key fishery species in the Adriatic Sea, by integrating skeletal, mechanical, and mineralogical responses. Adult clams of commercial size were exposed for 21 days to eight experimental treatments manipulating two levels of temperature (18 °C vs. 22 °C), pH (8.0 vs. 7.9), and salinity (35 vs. 32), chosen to reproduce near-future climate projections and the freshwater-driven variability typical of the Adriatic Sea. Despite the short exposure duration, the combined exposure to low pH, high temperature, and reduced salinity weakens the shell of Chamelea gallina at multiple levels, compromising shell integrity, by making shells less dense, more porous, more fragile, and more susceptible to fracture, and increasing mortality. Microstructural analysis revealed smaller aragonite crystallites and lower calcium content, indicative of early impairments in the calcification process. The study highlights the occurrence of synergistic effects among stressors and reveals the vulnerability of Chamelea gallina to near-future ocean conditions, with potential cascading consequences for ecosystem functioning and fishery sustainability, given the species’ key ecological role and commercial relevance in the Adriatic Sea.

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Combined effects of ocean acidification, warming, and salinity on the fertilization success in an Arctic population of sea urchins

Published 9 January 2026 Science Closed
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Anthropogenic stressors, including ocean acidification (OA), ocean warming (OW), and salinity changes, are rapidly altering marine ecosystems, with Arctic regions being particularly vulnerable. This study investigates the combined effects of these stressors on the fertilization success of the green sea urchin (Strongylocentrotus droebachiensis) from Kongsfjorden, Svalbard. We exposed gametes to various levels of pH, temperature, and salinity to assess their individual and combined impacts on fertilization performance. Our results show that temperature and pH significantly influenced fertilization success, with temperature having the strongest effect, while salinity had no significant impact. A significant statistical interaction between temperature and pH indicated that warming enhanced fertilization more effectively at higher pH levels, while low pH suppressed this increase. To compare the relative influence of each stressor, we used a conceptual model based on standardized slopes, which supported temperature as the dominant driver, followed by pH. These findings highlight the importance of considering the effects of combined stressors when assessing marine organism responses to climate change, especially in polar ecosystems. Our study underscores the need for further research into the mechanisms driving these combined effects, given that Arctic ecosystems face accelerated environmental changes.

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Impact of climate change driven freshening, warming, and ocean acidification on the cellular metabolism of Atlantic cod (Gadus morhua)

Published 27 October 2025 Science Closed
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Climate change is causing increasing sea surface temperature, ocean acidification and, in near shore waters, freshening. We investigated the metabolic effects of all three and their combination in Atlantic cod from the Skagerrak (eastern North Sea) by measuring concentration changes of a wide range of metabolites involved in energy production in the liver and muscles. Liver metabolism was more strongly affected than muscle, reflecting its central regulatory role. Most amino acid concentrations declined in both tissues across all treatments, and metabolomic pathway analysis revealed significant enrichment in ten metabolic pathways. This suggests enhanced amino acid metabolism in a climate change future. Warming and ocean acidification induced increased liver concentrations of lactate, glucose and fructose 1,6-bisphosphate indicating that gluconeogenesis will increase to meet increased production of enzymes to counter future stress. The molar contribution of glutamine to the total change in liver amino acids constituted 49%, 16% and 29% under warming, ocean acidification and their combination accentuating its importance in energy production also under future climate change. We observed contrasting responses in AMP, ADP, and NAD+ concentrations between warming and acidification suggesting possible antagonistic effects. Our findings demonstrate significant and complex metabolic responses to future climate stress in Atlantic cod in northern European waters.

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Ocean acidification interacts with low salinity and phosphorus limitation to modulate growth, photosynthesis, and physiology of mass-cultivated Gracilariopsis lemaneiformis

Published 4 August 2025 Science Closed
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Due to the effective removal of phosphorus during eutrophication control and intensive macroalgal cultivation, phosphorus limitation in coastal waters is normalized. As an economic macroalga cultivated on a large scale in production, Gracilariopsis lemaneiformis is also inevitably influenced by the combination of phosphorus limitation, ocean acidification caused by the increase of dissolved CO2 concentration and salinity decrease as a consequence of rainfall. In this study, G. lemaneiformis was cultured for 15 days under two pCO2 levels (LC: 400 μatm, HC: 1000 μatm), two salinities (LS: 22, HS: 30) and two phosphorus concentrations (LP: 0.1 μmol L−1, HP: 10.1 μmol L−1) to study the growth and photophysiology responses of this macroalga to the coupling of phosphorus limitation, ocean acidification and low salinity. Lower phosphorus (LP) treatment substantially reduced multiple parameters compared to higher phosphorus (HP) condition, including relative growth rate (RGR), photosynthetic rate, chlorophyll fluorescence parameters, and the contents of pigments, soluble protein, and soluble carbohydrate. Elevated CO₂ (HC) exposure induced a significant reduction in algal RGR under LP condition, while demonstrating no statistically significant impact on RGR under HP condition. Furthermore, HC treatment significantly inhibited carotenoid biosynthesis under LP condition. Notably, lower salinity (LS) stimulation significantly enhanced RGR in the ambient CO₂ (LC) group, but this promotive effect was completely negated under HC condition. These findings demonstrated that phosphorus limitation had an adverse outcome on algal growth, and phosphorus limitation exacerbated the adverse effect of ocean acidification on its growth. Moreover, the promotion effect of low salinity on algal growth could be neutralized by ocean acidification. This study provided important information about the influence of environmental changes on the photophysiological characteristics of G. lemaneiformis and new breeding directions for large-scale cultivation of coastal economic macroalgae.

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Physiological and growth responses of Black Sea salmon (Salmo labrax) to long-term salinity and high carbon dioxide stress

Published 16 July 2025 Science Closed
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Black Sea salmon (Salmo labrax), an anadromous salmonid species of regional importance, is increasingly considered for aquaculture in the Black Sea. This study investigates the physiological and growth responses of Black Sea salmon to seawater transfer, with a particular focus on carbon dioxide (CO₂) stress. The experiment began on 5 July 2022 with 720 fish (76.68±15.34 g) reared under semi-controlled conditions using a freshwater recirculating aquaculture system (RAS). On 12 October 2022, a group of fish was transferred to Black Sea water (18 ppt), and a subgroup was exposed to elevated CO₂ (1000 µatm pCO₂) until the end of the trial on 7 March 2023. Exposure to carbon dioxide showed negligible or minimal effects on seawater adaptation and growth. In contrast, physiological markers such as gill Na⁺/K⁺-ATPase (NKA) activity and the expression of nkaα1a, nkaα1b, and nkcc1a genes, along with growth metrics—including specific growth rate (SGR), condition factor (K value), and liver gene expression of igf-I, igfbp1b, ghr1, and ctsl—indicated that the fish were not physiologically prepared for seawater transfer in autumn. These findings suggest that the commonly practiced autumn sea transfer in the region may lead to suppressed growth and suboptimal performance. The results emphasize the importance of aligning seawater transfer with the smoltification window to support fish health and optimize aquaculture outcomes in Black Sea salmon farming.

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Salinity-dependent effects of seawater acidification on growth, photosynthetic physiology and biochemistry of the invasive macroalga Codium fragile

Published 25 March 2025 Science Closed
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Highlights

  • Decreased and increased salinity adversely affect the growth and photosynthetic physiology of Codium fragile under ambient pCO2 conditions.
  • Ocean acidification could help Codium fragile to encounter moderate salinity stress by up-regulating photosynthetic ability.
  • The deleterious effect of progressively decreased salinity on growth of Codium fragile was magnified when pCO2 increased.

Abstract

Ocean acidification (OA) and seawater salinity are two major environmental factors that influence the growth and distribution of macroalgae in coastal ecosystems. To investigate the effects of OA and salinity on the invasive macroalga Codium fragile, the growth, Chlorophyll a fluorescence, and biochemical compositions (pigment and soluble carbohydrate contents, the superoxide dismutase (SOD) activity, and malondialdehyde (MDA) contents) were studied after exposure to two pCO2 levels (400 ppmv, LC; and 1000 ppmv, HC) and four salinity regimes (high salinity, 40 psu; control salinity, 30 psu; medium salinity, 20 psu; low salinity, 10 psu). The results showed that, except for SOD activity at 20 psu, the growth, maximum and effective quantum yield of PSII, and maximum relative electron transport, pigment and soluble carbohydrate contents, SOD activity, and the MDA content were adversely impacted by both hypo- and hypersaline under LC conditions. Similarly, under HC conditions, the growth, photosynthetic physiology and biochemistry were negatively impacted by low salinity, while high salinity enhanced pigment contents and chlorophyll fluorescence parameters but inhibited SOD activity and MDA contents. Furthermore, higher pCO2 significantly promoted growth, pigment contents, and photosynthetic performance at 20 and 40 psu, while it amplified the depression in growth at 10 psu. These findings suggest that OA may enhance the potential invasive ability and salinity tolerance of C. fragile under medium hyposaline and hypersaline conditions by alleviating the negative effects of salinity stress on growth, photosynthesis, and pigments synthesis. However, it may also synergistically reduce algal growth at further reduced salinity. These data collected herein are valuable for understanding C. fragile cultivation and predicting its future distribution in response to changing ocean conditions.

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Between shells and seas: effects of ocean acidification on calcification and osmoregulation in yellow clam (Amarilladesma mactroides)

Published 14 March 2025 Science Closed
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Highlights

  • Decline in ocean pH due to increased CO2 is threatening the physiology of marine organisms.
  • Yellow clams (Amarilladesma mactroides) were exposed to ocean acidification and hypersaline stress for 96 hours to assess biomarkers of calcification and osmotic balance.
  • OA reduced Ca2+-ATPase activity in the mantle, damaging mineralized structures.
  • Elevated salinity increases carbonic anhydrase and Na+/K+-ATPase activity in the gills.
  • Increased carbonic anhydrase activity in the mantle may help maintain acid-base balance in the species.

Abstract

The decline in ocean pH due to rising CO2 levels is a critical factor impacting marine ecosystems. Ocean acidification (OA) is expected to negatively affect various organisms, particularly those with mineralized structures. While the effects of OA on the calcification of shells and exoskeletons are documented, the impact on homeostatic processes, such as osmoregulation, is less understood. Osmoregulation is vital for maintaining water and salt balance within marine organisms, crucial for their survival and physiological functions. Acidification may alter ion exchange mechanisms, affecting the regulation of ions. In this study, we evaluated the effects of intermediate OA (pH 7.6) with or without hypersaline stress (35‰) on calcification and osmotic balance biomarkers in the bivalve Amarilladesma mactroides after 96 hours of acute exposure. We found that pH did not affect hemolymph osmolality or extracellular Ca2+ concentration. However, OA impaired the bivalve’s ability to maintain its mineralized structures by decreasing Ca2+-ATPase enzyme activity in the mantle. The increase in carbonic anhydrase activity indicated a specific response to maintain acid-base balance in the tissue, i.e., compensating for the effects of acidification by neutralizing CO2 accumulation and stabilizing internal pH. In the gills, both enzymes showed increased performance under higher salinity and reduced pH. Exposure to less alkaline pH inhibited carbonic anhydrase and Na+/K+-ATPase activity, potentially affecting the regulation of essential inorganic osmolytes.

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Transcriptome‐to‐phenome response of larval Eastern oysters under multiple drivers of aragonite undersaturation

Published 19 February 2025 Science Closed
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Understanding how interactive environmental challenges affect marine species is critical to long‐term ecological and economic stability under global change. Marine calcifiers are thought to be vulnerable to ocean acidification (OA; elevated pCO2); active dissolution of aragonite (Ωar) is associated with disrupted development, survivorship, and gene expression in bivalve larvae, resulting in an early life‐stage bottleneck. Dynamic carbonate chemistry in coastal systems emphasizes the importance of multiple stressors, e.g., warming and low salinity events may change organismal responses relative to OA alone. We exposed Eastern oyster larvae ( Crassostrea virginica ) to a full‐factorial experimental design using two temperatures (23°C and 27°C), salinities (17 and 27), and pCO2 levels (~700 μatm and 1850 μatm pCO2), resulting in Ωar conditions 0.3–1.7. Ωar reduced by low salinity, elevated pCO2, and low temperature, each slowed early development and reduced survival. Low salinity × elevated pCO2 was linked to severe Ωar undersaturation (< 0.5) that suppressed expression of bicarbonate transport, biomineralization and augmented expression for ciliary locomotion, proteostasis, and histone modifiers. In isolation and under moderate Ωar intensity (0.5 < Ωar < 1), larvae increased transcription for osmoregulatory activity and endocytosis under low salinity, and suppressed transcription for iron metabolism under elevated pCO2. Although shell growth and survival were affected by Ωar undersaturation, gene expression patterns of D‐stage oyster larvae and oyster juveniles suggests tolerance to dynamic estuarine environments. Genes and expression patterns that confer survival of postmetamorphosed oysters can improve our understanding of environmental‐organismal interactions and improve breeding programs enabling sustainable production.

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Thalassia hemprichii may benefit from ocean acidification and slightly increased salinity in the future

Published 13 February 2025 Science Closed
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Highlights

  • Thalassia hemprichii highly adapted to acidified environments.
  • The effect of elevated salinity on the physiology and growth of Thalassia hemprichii is not linearly.
  • Ocean acidification could further enhance the resilience of Thalassia hemprichii to high salinity.
  • Both acidification and slight salinity increased the photosynthetic activity of Thalassia hemprichii.

Abstract

Since the industrial revolution, the direct impacts of elevated CO2 concentrations, such as ocean acidification, and indirect impacts, such as extreme drought events, have synergistically influenced coastal ecosystems, including seagrass meadow. Consequently, investigating the individual and combined effects of ocean acidification and extreme drought-induced increased salinity on seagrasses is crucial for enhancing the management and monitoring of these ecosystems. This study used a two-factor crossover indoor simulation experiment to thoroughly examine the effects of seawater acidification at pH 7.7 and elevated salinity levels at 43‰ and 51‰ on the physiological responses and growth status of the dominant tropical seagrass species Thalassia hemprichii. The results indicated that seawater acidification at pH 7.7 significantly enhanced the growth rate and photosynthetic activity of T. hemprichii across all salinity levels. A salinity of 43‰ activated certain antioxidant enzymes without inducing severe osmotic stress in T. hemprichii and positively influenced leaf photosynthetic activity, with a 15.6% increase in growth rate compared to the CK group. The extreme salinity of 51‰ imposed osmotic stress, leading to increase in reactive oxygen species and decreased photosynthetic activity and a 52% decrease in growth rate compared to seagrasses in the CK group. Under future scenarios of ocean acidification and frequent extreme droughts, T. hemprichii inhabiting enclosed marine environments may exhibit greater adaptability and secure an ecologically competitive edge. Our findings underscore the importance of conserving declining meadows, forecasting the ecological trajectory of these ecosystems, and managing salinity in lagoons for the well-being of seagrass ecosystems.

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Combined effects of pCO2 and salinity on the silicification of estuarine diatoms

Published 8 January 2025 Science Closed
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Highlights

  • Low salinity enhanced the weakening of silicification by ocean acidification (OA).
  • OA and salinity influenced the quality of diatom frustules and cell size.
  • OA could affect estuarine diatoms’ competitiveness in future environment.

Abstract

Understanding the combined effects of seawater acidification and salinity is crucial for assessing the adaptation of estuarine organisms to climate change. This study examined the physiological and nanostructural responses of two coastal diatoms, Thalassiosira pseudonana and Thalassiosira weissflogii, under different pCO2 and salinity conditions. Our results indicated that high pCO2 and low salinity decreased the biogenic silica and chlorophyll contents in both species. The weakly condensed silicon increased alongside the decrease in biogenic silica under high pCO2 conditions, with this trend being further amplified in low salinity environments. Meanwhile, the biochemical compositions and nanostructure of the diatom frustules were significantly altered by the lower salinity, leading to reduced cell size and porosity. These changes to diatom physiology and morphology may affect the diatoms’ capacity to defend against predators and viruses. This study highlights the chemical and morphological changes occurring in diatom cell walls in future acidic estuarine waters.

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Energy budget as a tool to assess the effects of environmental stressors: a study on whiteleg shrimp (Penaeus vannamei) exposed to variations in salinity and ocean acidification

Published 10 October 2024 Science Closed
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Our goal was to use the energy budget as a tool to evaluate the effects of salinity (20, 25, 30, 35 or 40‰) and ocean acidification (pH 8.0 or 7.3) in Penaeus vannamei. We assessed the energy budget a range of physiological processes (ingestion, defecation, growth, metabolism, excretion, energy substrate, hepatosomatic index, and osmoregulation). In general, salinity had an accentuated effect than pH, as it altered nearly all physiological parameters, including the energy channeled into growth (up to −56%). Reduced pH also affected the energy budget: increased energy lost in feces (25 and 40‰: +21% and 13%, respectively), excretion (25‰: +55%), and metabolism (20‰: +58%). Furthermore, acidified pH increased oxygen consumption by 60%, which may be related to higher energy expenditure. In conclusion, the energy budget can be a valuable tool for assessing the impacts of environmental stressors and the salinity has an accentuated effect than the ocean acidification predicted.

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High light intensity and CO2 enrichment synergistically mitigated the stress caused by low salinity in Pyropia yezoensis

Published 7 August 2024 Science Closed
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Macroalgae, playing a crucial role in coastal marine ecosystems, are subject to multiple environmental challenges due to tidal and seasonal alterations. In this work, we investigated the physiological responses of Pyropia yezoensis to ocean acidification (ambient CO2 (AC: 400 μatm) and elevated CO2 (HC: 1000 μatm)) under changing salinity (20, 30 psu) and light intensities (50, 100 μmol photons m−2 s−1) by measuring the growth, pigment content, chlorophyll fluorescence, and soluble sugar content. The key results are the following: (1) P. yezoensis exhibited better growth under normal salinity (30 psu) compared to hyposaline conditions (20 psu). (2) Intermediate light intensity increased phycoerythrin content, ultimately enhancing thalli growth without significant changes to the contents of chlorophyll a and carotenoids. (3) Ocean acidification alleviated hyposaline stress by enhancing pigment production in P. yezoensis only at a salinity of 20 psu, highlighting the complex interplay of these environmental factors. These findings indicate that higher light intensities and elevated pCO2 levels could mitigate the stress caused by low salinity.

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Physiological responses of Atlantic cod to climate change indicate that coastal ecotypes may be better adapted to tolerate ocean stressors

Published 7 June 2024 Science Closed
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Healthy ecosystems and species have some degree of resilience to changing conditions, however as the frequency and severity of environmental changes increase, resilience may be diminished or lost. In Sweden, one example of a species with reduced resilience is the Atlantic cod (Gadus morhua). This species has been subjected to overfishing, and with additional pressures such as habitat degradation and changing environmental conditions there has been little to no recovery, despite more than a decade of management actions. Given the historical ecological, economical, and cultural significance of cod, it is important to understand how Atlantic cod respond to global climate change to recover and sustainably manage this species in the future. A multi-stressor experiment was conducted to evaluate physiological responses of juvenile cod exposed to warming, ocean acidification, and freshening, changes expected to occur in their nursery habitat. The response to single drivers showed variable effects related to fish biometrics and increased levels of oxidative stress dependent parameters. Importantly, two separate responses were seen within a single treatment for the multi-stressor and freshening groups. These within-treatment differences were correlated to genotype, with the offshore ecotype having a heightened stress response compared to the coastal ecotype, which may be better adapted to tolerate future changes. These results demonstrate that, while Atlantic cod have some tolerance for future changes, ecotypes respond differently, and cumulative effects of multiple stressors may lead to deleterious effects for this important species.

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Ocean acidification and desalination increase the growth and photosynthesis of the diatom Skeletonema costatum isolated from the coastal water of the Yellow Sea

Published 5 April 2024 Science Closed
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Highlights

  • This study aims to investigate the combined effects of pH (400 μatm and 1000 μatm), temperature (10 °C, 20 °C), and salinity (20 psu, 30 psu) on the diatom S. costatum.
  • In this study, we investigated the effects of ocean acidification and seawater desalination on Skeletonema costatum in varying seasonal temperatures.
  • We found that ocean acidification and seawater desalination promoted the growth of S. costatum under the simulated conditions.

Abstract

Global climate changes induce substantial alterations in the marine system, including ocean acidification (OA), desalination and warming of surface seawater. Here, we examined the combined effects of OA and reduced salinity under different temperatures on the growth and photosynthesis of the diatom Skeletonema costatum. After having been acclimated to 2 CO2 concentrations (400 μatm, 1000 μatm) and 2 salinity levels (20 psu, 30 psu) at temperature levels of 10 °C and 20 °C, the diatom showed enhanced growth rate at the lowered salinity and elevated pCO2 irrespective of the temperature. The OA treatment increased the net photosynthetic rate and biogenic silica (Bsi) contents. Increasing the temperature from 10 to 20 °C raised the net photosynthetic rate by over twofold. The elevated pCO2 increased the net and gross photosynthetic rates by 20%–40% and by 16%–32%, respectively, with the higher enhancement observed at the higher levels of salinity and temperature. Our results imply that OA and desalination along with warming to the levels tested can enhance S. costatum‘s competitiveness in coastal phytoplankton communities under influence of future climate changes.

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Recent developments in ionophore-based potentiometric electrochemical sensors for oceanic carbonate detection

Published 18 March 2024 Science Closed
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The increasing level of atmospheric carbon dioxide (CO2) driven by human activities contributes to the global concern of climate change. A consequence of these circumstances is ocean acidification, which reduces seawater pH. The increasing absorption of atmospheric CO2 into the ocean decreases the concentration of carbonate ions and causes the sea to become more acidic, severely harming marine species. This harm to marine life has created the need for in situ carbonate sensing and monitoring to understand how marine ecosystems respond to pH reduction. Over the past few decades, many sensors with different compositions and structures have been developed to detect carbonate in seawater and other aquatic environments to simulate oceanic conditions. This review summarizes the recent developments in carbonate ionophores, a key component in carbonate electrochemical sensors, and compares the reported performance of these sensors through various parameters (e.g., sensitivity, response time, lifetime, testing media, and measuring range). Current challenges within the development of carbonate ionophores and sensors and possibilities for future research are also discussed.

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Biological and physiological responses of marine crabs to ocean acidification: a review

Published 14 February 2024 Science Closed
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Marine crabs play an integral role in the food chain and scavenge the debris in the ecosystem. Gradual increases in global atmospheric carbon dioxide cause ocean acidification (OA) and global warming that leads to severe consequences for marine organisms including crabs. Also, OA combined with other stressors like temperature, hypoxia, and heavy metals causes more severe adverse effects in marine crabs. The present review was made holistic discussion of information from 111 articles, of which 37 peer-reviewed original research papers reported on the effect of OA experiments and its combination with other stressors like heavy metals, temperature, and hypoxia on growth, survival, molting, chitin quality, food indices, tissue biochemical constituents, hemocytes population, and biomarker enzymes of marine crabs. Nevertheless, the available reports are still in the infancy of marine crabs, hence, this review depicts the possible gaps and future research needs on the impact of OA on marine crabs.

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Reviews and syntheses: The clam before the storm – a meta-analysis showing the effect of combined climate change stressors on bivalves

Published 6 February 2024 Science Closed
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The impacts of climate change on marine organisms have been increasingly documented in laboratory and experimental studies. However, the use of different taxonomic groupings and the assessment of a range of processes make identifying overall trends challenging. Meta-analysis has been used to determine general trends, but coarse taxonomic granularity may mask phylogenetically specific responses. Bivalve molluscs are a data-rich clade of ecologically and economically important calcifying marine taxa that allow for the assessment of species-specific vulnerability across developmental stages. Drawing on the large body of available literature, we conduct a meta-analysis of 203 unique experimental set-ups in order to examine how bivalve growth responds to increased water temperature, acidity, deoxygenation, and changes in salinity in 10 climate change stressor combinations. This is the most complete examination of bivalve responses to date and shows that anthropogenic climate change will disproportionally affect particular families, suggesting taxonomic differentiation in climate change response. Specifically, Mytilidae, Ostreidae, and Pectinidae (67 % of experiments) respond with negative effect sizes for all individual stressors, whereas responses in Pinnidae, Tellinidae, and Veneridae are more complex. Our analysis shows that earlier studies reporting negative impacts on bivalves are driven by only three or four well-studied, commercially important families. Despite the taxonomic differentiation, almost all drivers and their combinations have significant negative effects on growth. The synergistic impacts of deoxygenation, acidification, and temperature result in the largest negative effect size. Infaunal taxa, including Tellinidae and Veneridae, appear more resistant to warming and oxygen reduction than epifaunal or motile taxa, but this difference between the two taxa is also based on a small number of data points. The current focus of experimental set-ups on commercially important taxa and families within a small geographic range creates gaps in the understanding of global impacts on these economically important foundation organisms.

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High light intensity and CO2 enrichment synergistically mitigated the stress caused by low salinity in Pyropia yezoensis

Published 30 November 2023 Science Closed
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Macroalgae, playing a crucial role in coastal marine ecosystems, are subject to multiple environmental challenges due to tidal and seasonal alterations. In this work, we investigated the physiological responses of Pyropia yezoensis to ocean acidification (ambient CO2 (AC: 400 μatm) and elevated CO2 (HC: 1000 μatm)) under changing salinity (20, 30 psu) and light intensities (50, 100 μmol photons m−2 s−1) by measuring the growth, pigment content, chlorophyll fluorescence, and soluble sugar content. The key results are the following: (1) P. yezoensis exhibited better growth under normal salinity (30 psu) compared to hyposaline conditions (20 psu). (2) Intermediate light intensity increased phycoerythrin content, ultimately enhancing thalli growth without significant changes to the contents of chlorophyll a and carotenoids. (3) Ocean acidification alleviated hyposaline stress by enhancing pigment production in P. yezoensis only at a salinity of 20 psu, highlighting the complex interplay of these environmental factors. These findings indicate that higher light intensities and elevated pCO2 levels could mitigate the stress caused by low salinity.

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Atlantic-origin water extension into the Pacific Arctic induced an anomalous biogeochemical event

Published 15 November 2023 Science Closed
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The Arctic Ocean is facing dramatic environmental and ecosystem changes. In this context, an international multiship survey project was undertaken in 2020 to obtain current baseline data. During the survey, unusually low dissolved oxygen and acidified water were found in a high-seas fishable area of the western (Pacific-side) Arctic Ocean. Herein, we show that the Beaufort Gyre shrinks to the east of an ocean ridge and forms a front between the water within the gyre and the water from the eastern (Atlantic-side) Arctic. That phenomenon triggers a frontal northward flow along the ocean ridge. This flow likely transports the low oxygen and acidified water toward the high-seas fishable area; similar biogeochemical properties had previously been observed only on the shelf-slope north of the East Siberian Sea.

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Fig. 1: Schematic of the Arctic Ocean circulation and the study area with hydrographic stations.

a, b Maps of the Arctic Ocean and the study area. In a, yellow, blue, and red arrows represent flows from the shelf-slope at the north of the East Siberian Sea (ESS), and from the Pacific and Atlantic oceans in 2017–2020. Ocean circulation and water masses are abbreviated as follows: Beaufort Gyre (BG), Transpolar Drift (TPD), Pacific Water (PW), Lower Halocline Water (LHW), and Atlantic Water (AW). Geographical locations are abbreviated as follows: Canada Basin (CB), Chukchi Plateau (CP), Mendeleyev Ridge (MR), Makarov Basin (MB), and Lomonosov Ridge (LR). In b red, green, and blue dots denote the hydrographic stations conducted by the Research Vessel (R/V) Araon (Korea), R/V Mirai (Japan), and Canadian Coast Guard Ship Louis S. St-Laurent (Canada), under the 2020 Synoptic Arctic Survey project. Black dots indicate other hydrographic stations between 2002 and 2019 listed in Supplementary Table 1.

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Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)

Published 30 August 2023 Science Closed
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Highlights

  • Salinity and pH tolerance ranges were identified for Mactra chinensis Philippi juveniles in laboratory tests.
  • Survival rates were significantly reduced at extreme pH and salinity.
  • Low pH and salinity induced oxidative stress, decreasing antioxidant enzyme activities.

Abstract

The study investigated the impact of salinity and pH changes on the survival, growth, and antioxidant enzyme activity in Mactra chinensis Philippi (1.00 ± 0.10 cm shell length, 0.75±0.04 cm shell height), a marine clam species. Juveniles were exposed to various pH levels (5.4 – 9.6) and salinities (5 – 35 psu) for up to 20 days at 19 ± 0.5 ˚C. The individual effect of salinity and pH on juveniles were evaluated under pH 8.0 and salinity 30 psu, respectively. The results indicated that the highest survival rates were observed at pH 8.0 (85%, salinity = 30 psu) and salinity 30 psu (95%, pH = 8.0). The survival rates were significantly reduced at extreme pH (≤ 7.2; ≥ 8.4) and salinities (≤ 15; 35 psu). Additionally, oxidative stress was observed in clams exposed to low pH and salinity as indicated by the decreased activities of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). Notably, no significant difference in relative growth rates was observed between salinity 25 and 30 psu, between pH 7.8/8.4 and pH 8.0. Our results provide information on potential impact of pH and salinity changes on economically important bivalve species and may be used to optimize pH and salinity in aquaculture.

Continue reading ‘Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)’

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