Posts Tagged 'Black Sea'

Effect of experimental seawater acidification on the prooxidant-antioxidant system of the Pacific oyster Magallana gigas (Thunberg, 1793) under normoxic and hypoxic conditions

Published 8 January 2026 Science Closed
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Highlights

  • Lipid peroxidation in oyster gills was enhanced during exposure to acidification + hypoxia.
  • SOD and GPx activities changed in gills and hepatopancreas, while CAT activity unchanged in both.
  • Water acidification does not promote DNA strand breaks in hemocytes of M. gigas.
  • Acidification + hypoxia more severe damaging than acidification under normoxia.

Abstract

Bivalve mollusks, particularly the Pacific oyster (Magallana gigas), are both environmentally and commercially significant species that live in coastal waters and may be affected by global climate change factors including hypoxia and acidification. In this study, we investigated the impact of acidification in combination with normoxia and hypoxia on oxidative stress markers in the gills and hepatopancreas of M. gigas oysters. Oysters were collected from a shellfish farm and subjected to acidified conditions (pH 7.3 ± 0.05) in combination with either normoxic (8.0 ± 0.3 mg/L O2) or hypoxic (2.0 ± 0.3 mg/L O2) conditions for an 8-day period. Changes of DNA damage levels, reactive oxygen species (ROS) production in hemocytes, as well as antioxidant enzyme activities (catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx)) and lipid peroxidation in the gills and hepatopancreas were evaluated. Additionally, the mortality rate in experimental groups was monitored throughout the experiment. Our results showed that lipid peroxidation in gills was enhanced during prolonged acidification in combination with hypoxia (6–8 days). We observed rapid and consistent changes in SOD and GPx activity in gills and hepatopancreas. CAT activity remained stable in both tissues. The results of the study indicate that acidification was shown to induce oxidative stress in oysters. Combination of acidic environment to hypoxia had a more severe effect on oysters compared to acidification under normal oxygen conditions, leading to their death after 8 days of exposure.

Continue reading ‘Effect of experimental seawater acidification on the prooxidant-antioxidant system of the Pacific oyster Magallana gigas (Thunberg, 1793) under normoxic and hypoxic conditions’

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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Impacts of ocean acidification and hypoxia on cellular immunity, oxygen consumption and antioxidant status in Mediterranean mussel

Published 1 October 2024 Science Closed
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Highlights

  • Prolonged exposure to acidification can have negative effects on immunity and metabolism.
  • Acidification reduces ROS production by hemocytes during prolonged the exposure period.
  • Acidification combined with normoxia/hypoxia reduces the mussel’s respiratory rate.

Abstract

There is growing recognition that the hypoxic regions of the ocean are also becoming more acidic due to increasing levels of global carbon dioxide emissions. The impact of water acidification on marine life is largely unknown, as most previous studies have not taken into account the effects of hypoxia, which may affect how organisms respond to low pH levels. In this study, we experimentally examined the consequences of water acidification in combination with normoxic or hypoxic conditions on cellular immune parameters in Mediterranean mussels. We measured total hemocyte counts in hemolymph, the cellular composition of hemolymph, phagocytosis, reactive oxygen species (ROS) production. General response of the organism was evaluated on the basis of the activity of antioxidant enzymes in the hepatopancreas, as well as respiratory rates over an 8-day exposure period. The mussels were exposed to low pH conditions (7.3), either under normoxic conditions (dissolved oxygen concentration of 8 mg/L) or hypoxic conditions (dissolved oxygen concentration of 2 mg/L). The parameters were assessed at days 1, 3, 6, and 8 of the experiment. Experimental acidification under normoxic conditions reduced THC and ROS production by hemocytes during later stages of exposure, but phagocytic activity (PA) only decreased at day 3 and then recovered. Combined acidification and hypoxia suppressed PA in hemocytes at the beginning of exposure, while hemocyte ROS production and THC decreased by the end of the experiment. The hemolymph cellular composition and activity of antioxidant enzymes were unaffected by acidified conditions under different oxygen regimes, but mussel respiratory rate (RR) decreased with a more significant reduction in oxygen consumption under hypoxia. Mussels showed a relatively high tolerance to acidification in combination with various dissolved oxygen levels, although prolonged acidification exposure led to increased detrimental effects on immunity and metabolism.

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Metabolism variations in the bivalve mollusk Anadara kagoshimensis Tokunaga, 1906 (bivalvia: arcidae) under upwelling conditions in the Black Sea (experimental data)

Published 6 September 2024 Science Closed
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Studies of the energy metabolism in a bivalve mollusk, the ark clam Anadara kagoshimensis (Tokunaga, 1906), were carried out for the first time under experimental conditions simulating dynamic variations in the seawater characteristics at the stages of development and end of upwelling event in the Black Sea. It was shown that the level of energy metabolism of A. kagoshimensis, while being in the zone of upwelling formation, decreased, on average, by 5% per degree of temperature decrease. During the upwelling relaxation phase (14 → 26°C), the restoration of the respiration intensity parameters of the clam was slower than expected, with a temperature coefficient of Q10 = 1.31. The acidification of the seawater by 1.0 (up to рН 7.2), combined with a temperature decrease (26 → 20°C), aggravated the negative effect by 25–45%. It has been found that the clam A. kagoshimensis reduces energy expenditure by approximately 60% under upwelling conditions (cold stress and acidification). The consequences of the negative effect of a sharp temperature variation lead to a delay in the metabolism recovery to normal values.

Continue reading ‘Metabolism variations in the bivalve mollusk Anadara kagoshimensis Tokunaga, 1906 (bivalvia: arcidae) under upwelling conditions in the Black Sea (experimental data)’

How water acidification influences the organism antioxidant capacity and gill structure of Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) at normoxia and hypoxia

Published 24 June 2024 Science Closed
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Highlights

  • Mediterranean mussels demonstrate relative tolerance to water acidification and hypoxia.
  • Acidification combined with normoxia/hypoxia did not promote ROS formation and DNA damage in hemocytes.
  • The activity of SOD and CAT in gills was stable upon acidification and hypoxia.
  • Acidification combined with normoxia/hypoxia led to inflammation in gills and the morphological lesions of filaments

Abstract

The effect of water acidification in combination with normoxia or hypoxia on the antioxidant capacity and oxidative stress markers in gills and hemolymph of the Mediterranean mussel (Mytilus galloprovincialis), as well as on gill microstructure, has been evaluated through an in vivo experiment. Mussels were exposed to a low pH (7.3) under normal dissolved oxygen (DO) conditions (8 mg/L), and hypoxia (2 mg/L) for 8 days, and samples were collected on days 1, 3, 6, and 8 to evaluate dynamic changes of physiological responses. Cytoplasmic concentrations of reactive oxygen species (ROS) and levels of DNA damage were measured in hemocytes, while the activity of catalase (CAT) and superoxide dismutase (SOD) and histopathological changes were assessed in gills. The results revealed that while water acidification did not significantly affect the activity of SOD and CAT in gills under normoxic and hypoxic conditions, there was a trend towards suppression of CAT activity at the end of the experimental period (day 8). Similarly, we did not observe increased formation of ROS in hemocytes or changes in the levels of DNA damage during the experimental period. These results strongly suggest that the oxidative stress response system in mussels is relatively stable to experimental conditions of acidification and hypoxia. Experimental acidification under normoxia and hypoxia caused changes to the structure of the gills, leading to various histopathological alterations, including dilation, hemocyte infiltration into the hemal sinuses, intercellular edema, vacuolization of epithelial cells in gill filaments, lipofuscin accumulation, changes in the shape and adjacent gill filaments, hyperplasia, exfoliation of the epithelial layer, necrosis, swelling, and destruction of chitinous layers (chitinous rods). Most of these alterations were reversible, non-specific changes that represent a general inflammatory response and changes in the morphology of the gill filaments. The dynamics of histopathological alterations suggests an active adaptive response of gills to environmental stresses. Taken together, our data indicate that Mediterranean mussels have a relative tolerance to water acidification and hypoxia at tissue and cellular levels.

Continue reading ‘How water acidification influences the organism antioxidant capacity and gill structure of Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) at normoxia and hypoxia’

Energy metabolism of Mytilus galloprovincialis under low seawater pH (in Russian)

Published 25 September 2023 Science Closed
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The problem of acidification of the World Ocean and predicting the consequences for its inhabitants is becoming more and more relevant every year. The effect of short-term pH fluctuations in coastal ecosystems on the physiology of calcifying organisms—bivalves—remains poorly understood. The energy metabolism of the Black Sea mussel Mytilus galloprovincialis was investigated for the marine environment in a wide pH range, from 8.2 to 6.65. Lowering the pH to 7.0–7.5 led to a 20–25 % reduction in oxygen consumption by molluscs. At lower pH (6.54–6.7), aerobic respiration sharply decreased by 85–90 %, down to the minimum values (2.12–2.62 µgO2 /g dry/h), and the organisms transitioned to anaerobic metabolism. The metabolic response of the mussels subjected to short-term pH changes (8.2→6.65→7.2) has been investigated. The oxygen consumption of molluscs exposed at the same pH of 7.2 depended on the direction of the change in pH. Thus, in the case of pH 6.65→7.2, the respiration intensity was 30 % higher compared to the values obtained under the acidification pH 8.2→7.2. The Black Sea mussel M. galloprovincialis is shown to have the capacity for survival in the marine environment characterized by the rapid fluctuations in pH that occur during the upwelling events in the coastal areas of the Black Sea.

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Analysis of Black Sea ocean acidification

Published 1 November 2021 Science Closed
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Increasing anthropogenic CO2 concentration in the troposphere causes more uptake by oceans and results in ocean acidification. Albeit, food web in the ocean, marine animals and calcifying bioata are affected negatively. Some marine species might have the possibility of extinction and some may have evolved eventually due to ocean acidification. In this study, the acidification of Black Sea is analyzed based on the pH observations made between 1990 and 2014. Sea surface pH value is found to be decreased by 0,07 and increased by 0,104 between 1990-2004 and 2005-2014 respectively. The pH annual variations also compared analytically to the annual averages of air temperature and CO2 emissions of Turkey. Both the air temperature and CO2 emission is increasing either in 1990-2004 or 2005-2014, while the rate of increase in 2005-2014 is greater than in 1990-2004. The decreasing pH (which means acidification) in 1990-2004 is found to be the reason of this difference, because some CO2 is considered to be absorbed by Black Sea. In terms of climate change, it shows that this acidification is a little bit slowing down the temperature increase over the Black Sea region while CO2 and air temperature increasing rate is less between 1990-2004 (where surface pH of Black Sea decreases) than 2005-2014.

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