Seawater Acidification Reduced the Resistance of Crassostrea gigas to Vibrio splendidus Challenge: An Energy Metabolism Perspective

Sub-acute exposure of sea urchin (Strongylocentrotus intermedius) to environmentally relevant concentrations of PFOA and GenX influences gonadal development

Perfluorooctanoic acid (PFOA) and its substitute, hexafluoropropylene oxide dimer acid (GenX), are widely used perfluorinated compounds (PFCs) that pose significant risks to marine ecosystems. However, the specific impacts of these contaminants on marine invertebrates, particularly echinoderms, remain poorly understood. Strongylocentrotus intermedius, a globally significant benthic aquacultural species, may be potentially affected by PFCs. This study aimed to assess the reproductive toxicity of PFOA and GenX in S. intermedius. After exposing S. intermedius to either PFOA or GenX for 7 or 14 days, it was observed that even at environmentally relevant concentrations (2 μg/L), both compounds inhibited normal growth and gonadal development in S. intermedius, with effects becoming more pronounced over time. Further analysis revealed that prolonged exposure to PFCs resulted in a significant reduction in energy reserves (glycogen, lipids, and proteins) and caused abnormal changes in metabolic enzyme activities, with PFOA exhibiting more pronounced effects compared to GenX. At the genetic level, the expression of genes related to gonadal development initially increased and then decreased as the concentrations of the compounds rose. Additionally, integrated biomarker response analysis indicated that PFOA had greater reproductive toxicity than GenX, in terms of both concentration and exposure duration. These results provided a preliminary evaluation of the impact of PFCs on marine invertebrates, offering a foundation for further research into their ecological risks and contributing to the development of more comprehensive environmental risk assessments for these contaminants.

Effects of single or combined exposure to tralopyril and ocean acidification on energy metabolism response and sex development in Pacific oysters (Crassostrea gigas)

The combined effects of the novel antifouling biocide tralopyril (TP) nitrile and ocean acidification (OA) on marine organisms are still not well understood, despite the increasing attention given to the toxic effects of emerging pollutants and OA on marine organisms in recent years. In this study, Crassostrea gigas (C. gigas) was exposed to TP, OA, and a combination of TP and OA for 21 days with a 14-day depuration. This study investigated the inter-tissue variability in energy metabolism responses and the impacts on gonadal development in C. gigas under both single and combined exposures to TP and OA. The results indicate that TP exposure and OA resulted in up-regulation of energy metabolism genes in the C. gigas, with tissues exhibiting enhanced aerobic metabolism. Furthermore, OA influences the sex determination of C. gigas, promoting the development of female individuals. Moreover, following depuration, C. gigas is able to restore normal energy metabolism and sexual development through the accumulation of suitable energy reserves. This study provides a valuable reference for the environmental and ecological risk assessment of TP, addressing the research gap in understanding the combined toxicity of TP and OA on aquatic organisms.

To live or die: "Fine-tuning" adaptation revealed by systemic analyses in symbiotic bathymodiolin mussels from diverse deep-sea extreme ecosystems

Hydrothermal vents (HVs) and cold seeps (CSs) are typical deep-sea extreme ecosystems with their own geochemical characteristics to supply the unique living conditions for local communities. Once HVs or CSs stop emission, the dramatic environmental change would pose survival risks to deep-sea organisms. Up to now, limited knowledge has been available to understand the biological responses and adaptive strategy to the extreme environments and their transition from active to extinct stage, mainly due to the technical difficulties and lack of representative organisms. In this study, bathymodiolin mussels, the dominant and successful species surviving in diverse deep-sea extreme ecosystems, were collected from active and extinct HVs (Southwest Indian Ocean) or CSs (South China Sea) via two individual cruises. The transcriptomic analysis and determination of multiple biological indexes in stress defense and metabolic systems were conducted in both gills and digestive glands of mussels, together with the metagenomic analysis of symbionts in mussels. The results revealed the ecosystem- and tissue-specific transcriptional regulation in mussels, addressing the autologous adaptations in antioxidant defense, energy utilization and key compounds (i.e. sulfur) metabolism. In detail, the successful antioxidant defense contributed to conquering the oxidative stress induced during the unavoidable metabolism of xenobiotics commonly existing in the extreme ecosystems; changes in metabolic rate functioned to handle toxic matters in different surroundings; upregulated gene expression of sulfide:quinone oxidoreductase indicated an active sulfide detoxification in mussels from HVs and active stage of HVs & CSs. Coordinately, a heterologous adaptation, characterized by the functional compensation between symbionts and mussels in energy utilization, sulfur and carbon metabolism, was also evidenced by the bacterial metagenomic analysis. Taken together, a new insight was proposed that symbiotic bathymodiolin mussels would develop a "finetuning" strategy combining the autologous and heterologous regulations to fulfill the efficient and effective adaptations for successful survival.

Interactive effects of multiple antibiotic residues and ocean acidification on physiology and metabolome of the bay scallops Argopecten irradians irradians

Coastal areas are confronted with compounding threats arising from both climatic and non-climatic stressors. Antibiotic pollution and ocean acidification are two prevalently concurrent environmental stressors. Yet their interactive effects on marine biota have not been investigated adequately and the compound hazard remain obscure. In this study, bay scallops Argopecten irradians irradians were exposed to multiple antibiotics (sulfamethoxazole, tetracycline, oxytetracycline, norfloxacin, and erythromycin, each at a concentration of 1 μg/L) combined with/without acidic seawater (pH 7.6) for 35 days. The single and interactive effects of the two stressors on A. irradians irradians were determined from multidimensional bio-responses, including energetic physiological traits as well as the molecular underpinning (metabolome and expressions of key genes). Results showed that multiple antibiotics predominantly enhanced the process of DNA repair and replication via disturbing the purine metabolism pathway. This alternation is perhaps to cope with the DNA damage induced by oxidative stress. Ocean acidification mainly disrupted energy metabolism and ammonia metabolism of the scallops, as evidenced by the increased ammonia excretion rate, the decreased O:N ratio, and perturbations in amino acid metabolism pathways. Moreover, the antagonistic effects of multiple antibiotics and ocean acidification caused alternations in the relative abundance of neurotransmitter and gene expression of neurotransmitter receptors, which may lead to neurological disorders in scallops. Overall, the revealed alternations in physiological traits, metabolites and gene expressions provide insightful information for the health status of bivalves in a natural environmental condition under the climate change scenarios.

Effect of seawater acidification on physiological and energy metabolism responses of the common Cockle (Anadara antiquata) of Gazi Bay, Kenya

Ocean acidification (OA) is becoming a potential threat to marine organisms, especially in calcifying marine invertebrates. So far, along the Kenya Coast, there has been little research on the impact of OA on cockle (Anadara antiquata), particularly on their physiological impacts induced by exposure to acidified seawater. Hence, this study aimed to investigate the physiological and biochemical responses of Anadara antiquata under present and future predicted seawater pH. In this study, the Anadara antiquata was exposed to three pH treatments (pH 7.90, 7.60, and 7.30) for 8 weeks to mimic future OA and to understand the physiological and biochemical effects on the organisms. Condition index, energy reserves (glycogen and protein), and cellular damage (e.g., lipid peroxidation level) were measured. Condition index (CI) showed no significant difference at different pH treatments (pH 7.90, 7.60, and 7.30), whereas the survival Anadara antiquata was slightly reduced after 8 weeks of exposure to pH 7.30. Glycogen and protein content were not affected at reduced pH (7.60 and 7.30). However, after 8 weeks of exposure to pH 7.60 and 7.30, Anadara antiquata showed a slight decrease in lipid peroxidation, an indication of cellular damage. The physiological and biochemical parameters analyzed (glycogen and protein content; lipid peroxidation levels) showed useful biomarkers to assess ocean acidification impacts in cockle.

Changes in Hemolymph Microbiota of Chinese Mitten Crab (Eriocheir sinensis) in Response to Aeromonas hydrophila or Staphylococcus aureus Infection

The Chinese mitten crab (Eriocheir sinensis) has significant economic potential in both the Chinese domestic and global markets. The hemolymph microbiota is known to play a critical role in regulating physiological and biochemical functions in crustaceans. However, the study of the hemolymph microbiota of E. sinensis in response to infections has not been undertaken. In this study, changes in the composition and function of the hemolymph microbiota in E. sinensis infected with either Staphylococcus aureus (Sa) or Aeromonas hydrophila (Ah) were investigated using 16S rRNA sequencing, with a phosphate buffer saline (PBS) injection serving as the control. Results showed that the dominant hemolymph microbiota of E. sinensis were Proteobacteria, Bacteroidota, and Firmicutes. The relative abundance of the phyla Firmicutes, Bdellovibrionota, and Myxococcota was significantly reduced in both Sa and Ah groups compared to the PBS group. At the genus level, compared to the PBS group, a significant increase in the abundance of Flavobacterium and Aeromonas was found in both Ah and Sa groups. The analysis of the functional profile showed that pathways related to 'cell growth and death', 'metabolism of terpenoids and polyketides', 'cancers', 'lipid metabolism', 'neurodegenerative diseases', 'metabolism of other amino acids', 'xenobiotics biodegradation and metabolism', and 'circulatory system and endocrine system' were predominant in the Ah group. Meanwhile, pathways related to 'metabolism or genetic information progressing', such as 'translation', 'metabolic diseases', and 'cellular processes and signaling', were enriched in the Sa group. This study revealed the effects of pathogens (S. aureus or A. hydrophila) on the maintenance of the hemolymph microbiota in E. sinensis. It shed light on the mechanisms employed by the hemolymph microbiota of E. sinensis under pathogen stimulation.

Effect of heat and hypoxia stress on mitochondrion and energy metabolism in the gill of hard clam

Aquatic animals suffer from heat and hypoxia stress more frequently due to global climate change and other anthropogenic activities. Heat and hypoxia stress can significantly affect mitochondrial function and energy metabolism. Here, the response and adaptation characteristics of mitochondria and energy metabolism in the gill of the hard clam Mercenaria mercenaria under heat (35 °C), hypoxia (0.2 mg/L), and heat plus hypoxia stress (35 °C, 0.2 mg/L) after 48 h exposure were investigated. Mitochondrial membrane potentials were depolarized under environmental stress. Mitochondrial fusion, fission and mitophagy played a key role in maintain mitochondrion function. The AMPK subunits showed different expression under environmental stress. Acceleration of enzyme activities (phosphofructokinase, pyruvate kinase and lactic dehydrogenase) and accumulation of anaerobic metabolites in glycolysis and TCA cycle implied that the anaerobic metabolism might play a key role in providing energy. Accumulation of amino acids might help to increase tolerance under heat and heat combined hypoxia stress. In addition, urea cycle played a key role in amino acid metabolism to prevent ammonia/nitrogen toxicity. This study improved our understanding of the mitochondrial and energy metabolism responses of marine bivalves exposed to environmental stress.

Gut Microbiota Mediates Skin Ulceration Syndrome Outbreak by Readjusting Lipid Metabolism in Apostichopus japonicus

The intestinal tract is the most important location for symbiotes and pathogens, and the microbiota plays a crucial role in affecting the health of the gut and other host organs. Dysbacteriosis in the intestinal system has been proven to be significant in skin ulceration syndrome (SUS) in sea cucumbers. This study investigates whether the gut microbiota and lipid metabolites are relevant to the initiation and progression of SUS in a Vibrio-splendidus-infected sea cucumber model. The tight junction genes were downregulated and the inflammatory factor gene transcriptions were upregulated after V. splendidus infection in the intestinal tissue of the sea cucumber. V. splendidus infection modulated the gut microbiota by interacting with Psychromonas macrocephali, Propionigenium maris, Bacillus cereus, Lutibacter flavus, and Hoeflea halophila. Meanwhile, the metabolites of the long-chain fatty acids in the intestinal tissue, including triglycerides (TG), phosphatidylethanolamines (PE), and phosphatidylglycerols (PG), were altered after V. splendidus infection. V. splendidus engaged in positive interactions with PG and PE and negative interactions with specific TG. These results related to gut microbiota and metabolites can offer practical assistance in the identification of the inflammatory mechanisms related to SUS, and this study may serve as a reference for predicting the disease.

Identification, characterization and expression analyses of PC4 genes in Yesso scallop (Patinopecten yessoensis) reveal functional differentiations in response to ocean acidification

Transcriptional coactivator p15 (PC4), considered a multifunctional chromosome associated protein, is actively involved in transcription regulation, DNA replication, damage repair and chromosome formation. Although studies have reported significant effects of PC4 in most vertebrates and some invertebrates, the complete PC4 gene members are less systematically identified and characterized in scallops. In this study, seven PC4 genes (PyPC4s) were identified in the Yesso scallop Patinopecten yessoensis using whole-genome scanning via bioinformatic analyses. Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of the seven genes. Expression profiles of PyPC4s were further investigated in embryos/larvae at all developmental stages, healthy adult tissues, and mantles that were exposed to low pH stress (pH 6.5 and 7.5) with different time durations (3, 6, 12 and 24 h). Spatiotemporal expression patterns indicated the functional roles of PyPC4s at all development stages and in healthy adult tissues, with PY-3235.33 demonstrating remarkably high constitutive expressions. Expression regulations (up- and down-regulation) of PyPC4s under low pH stress levels demonstrated a time-dependent pattern with functional complementation and/or enhancement, revealing that PyPC4s exhibited differentiated functions in response to ocean acidification (OA). Collectively, our data offer a novel perspective stating that low pH is a potential inducer leading to functional differentiation of PyPC4s in scallops. The results provide preliminary information on the versatile roles of PC4(s) in bivalves in response to OA.

Cellular level response of the bivalve Limecola balthica to seawater acidification due to potential CO2 leakage from a sub-seabed storage site in the southern Baltic Sea: TiTank experiment at representative hydrostatic pressure

Understanding of biological responses of marine fauna to seawater acidification due to potential CO₂ leakage from sub-seabed storage sites has improved recently, providing support to CCS environmental risk assessment. Physiological responses of benthic organisms to ambient hypercapnia have been previously investigated but rarely at the cellular level, particularly in areas of less common geochemical and ecological conditions such as brackish water and/or reduced oxygen levels. In this study, CO₂-related responses of oxygen-dependent, antioxidant and detoxification systems as well as markers of neurotoxicity and acid-base balance in the Baltic clam Limecola balthica from the Baltic Sea were quantified in 50-day experiments. Experimental conditions included CO₂ addition producing pH levels of 7.7, 7.0 and 6.3, respectively and hydrostatic pressure 900 kPa, simulating realistic seawater acidities following a CO₂ seepage accident at the potential CO₂-storage site in the Baltic. Reduced pH interfered with most biomarkers studied, and modifications to lactate dehydrogenase and malate dehydrogenase indicate that aerobiosis was a dominant energy production pathway. Hypercapnic stress was most evident in bivalves exposed to moderately acidic seawater environment (pH 7.0), showing a decrease of glutathione peroxidase activity, activation of catalase and suppression of glutathione S-transferase activity likely in response to enhanced free radical production. The clams subjected to pH 7.0 also demonstrated acetylcholinesterase activation that might be linked to prolonged impact of contaminants released from sediment. The most acidified conditions (pH 6.3) stimulated glutathione and malondialdehyde concentration in the bivalve tissue suggesting potential cell damage. Temporal variations of most biomarkers imply that after a 10-to-15-day initial phase of an acute disturbance, the metabolic and antioxidant defence systems recovered their capacities.

A proteomic analysis of the effect of ocean acidification on the haemocyte proteome of the South African abalone Haliotis midae

As a result of increasing CO₂ emissions and the prevalence of global climate change, ocean acidification (OA) is becoming more pervasive, affecting many trophic levels, particularly those that rely on succinctly balanced ocean chemistry. This ultimately threatens community structures, as well as the future sustainability of the fishing/aquaculture industry. Understanding the molecular stress response of key organisms will aid in predicting their future survivability under changing environmental conditions. This study sought to elucidate the molecular stress response of the South African abalone, Haliotis midae, an understudied organism with high economic value, utilising a high throughput iTRAQ-based proteomics methodology. Adult abalone were exposed to control (pH 7.9) and experimental (pH 7.5) conditions for 12, 72 and 168 h, following which protein was isolated from sampled haemocytes and subsequently processed. iTRAQ-labelled peptides were analysed using mass spectrometry, while an array of bioinformatics tools was utilised for analysing the proteomic data. COG analysis identified "Cytoskeleton", "Translation, ribosomal structure and biogenesis", "Post-translational modification, protein turnover, chaperones", and "Intracellular trafficking, secretion and vesicular transport" to be the most enriched functional classes, while statistical analysis identified a total of 33 up-regulated and 23 down-regulated effectors of OA stress in abalone. Several of the up-regulated proteins that were identified function in central metabolism (ENO1, PGK, DUOX1, GPD2), the stress/immune response (CAMKI, HSPA5/GRP78, MAPKI), and cytoskeleton, protein sorting and signal transduction (IQGAP1, MYO9B, TLN1, RDX, TCP-1/CCT, SNX6, CHMP1a, VPS13a). Protein-protein interactions were predicted using STRING DB, Cytoscape and Ingenuity Pathway Analysis, providing a model of the effects of OA on the H. midae haemocyte proteome. The data indicated that H. midae underwent a metabolic shift under OA conditions to utilize more energy-efficient mechanisms of ATP generation, while attempts at restoring haemocyte stabilisation and homeostasis were reflected by up-regulation of oxidative stress and cytoskeletal proteins. Our results support other molluscan studies that report a complex array of overlapping functions of both the stress and immune response systems. This interplay of the mounted stress and immune response is maintained and observed through the up-regulation of proteins involved in protein synthesis and turnover, as well as intracellular signalling and transport. The data presented in this study highlight the value of employing sensitive and robust -omics technologies for assessing the effects of changing environmental conditions on marine organisms.

The current situation and potential effects of climate change on the microbial load of marine bivalves of the Greek coastlines: an integrative review

Global warming affects the aquatic ecosystems, accelerating pathogenic microorganisms' and toxic microalgae's growth and spread in marine habitats, and in bivalve molluscs. New parasite invasions are directly linked to oceanic warming. Consumption of pathogen-infected molluscs impacts human health at different rates, depending, inter alia, on the bacteria taxa. It is therefore necessary to monitor microbiological and chemical contamination of food. Many global cases of poisoning from bivalve consumption can be traced back to Mediterranean regions. This article aims to examine the marine bivalve's infestation rate within the scope of climate change, as well as to evaluate the risk posed by climate change to bivalve welfare and public health. Biological and climatic data literature review was performed from international scientific sources, Greek authorities and State organizations. Focusing on Greek aquaculture and bivalve fisheries, high-risk index pathogenic parasites and microalgae were observed during summer months, particularly in Thermaikos Gulf. Considering the climate models that predict further temperature increases, it seems that marine organisms will be subjected in the long term to higher temperatures. Due to the positive linkage between temperature and microbial load, the marine areas most affected by this phenomenon are characterized as 'high risk' for consumer health.

Contrasting Immunomodulatory Effects of Probiotic and Pathogenic Bacteria on Eastern Oyster, Crassostrea Virginica, Larvae

Several Vibrio spp. cause acute and severe mortality events in hatcheries where larvae of bivalve mollusks are reared, potentially leading to subsequent shortage of bivalve seed for the grow-out industry. In particular, strains of Vibrio coralliilyticus have been identified as a major cause of disease in Pacific, Crassostrea gigas, and eastern, C. virginica, oyster hatcheries in the United States of America. Probiotic bacteria are an inexpensive, practical, and natural method of disease control. Previous research shows that pretreatment of larval oysters with probiotic bacteria Bacillus pumilus RI06-95 (RI) and Phaeobacter inhibens S4 (S4) significantly decreases mortality caused by experimental challenge with the bacterial pathogen V. coralliilyticus RE22 (RE22). This study aims to characterize the immune response of 6-10-day-old eastern oyster larvae to experimental challenge with pathogen V. coralliilyticus RE22 and probionts RI and S4. Treatments included (a) pathogen and probiont exposure at a concentration of 5 × 10⁴ CFU per mL (~2500 bacterial cells per larva) for a duration of 6 h, (b) probiont exposure at the same concentration for a duration of 24 h, and (c) probiont RI daily treatment of larvae in the hatchery for 4, 11, and 15 days. Differential gene expression analysis compared pathogen or probiotic-treated transcriptomes to unexposed controls. Probiotic and pathogen treatment led to upregulation of transcripts coding for several immune pattern recognition receptors (PRRs) involved in environmental sensing and detection of microbes in oyster larvae. Larval oyster responses to pathogen RE22 suggested suppression of expression of genes in immune signaling pathways (myd88, tak1, nkap), failure in upregulation of immune effector genes, high metabolic demand, and oxidative stress that potentially contributed to mortality. On the other hand, the transcriptomic response to probiotic bacteria RI and S4 suggested activation of immune signaling pathways and expression of immune effectors (e.g., Cv-spi2, mucins and perforin-2). These key features of the host immune response to probiotic bacteria were shared despite the length of probiotic exposure, probiotic species, and the type of environment in which exposures were conducted. This study suggests that pre-exposure of eastern oyster larvae to probiotics for 6-24 h prior to pathogenic challenge leads to a robust and effective immune response that may contribute to protecting larvae from subsequent challenge with V. coralliilyticus RE22. This research provides new insights into host-microbe interactions in larval oysters that could be applied in the management of vibriosis in bivalve hatcheries.

Species vulnerability under climate change: Study of two sea urchins at their distribution margin

In order to develop powerful predictions on the impact of climate change on marine organisms, it is critical to understand how abiotic drivers such as temperature can directly and indirectly affect marine organisms. Here, we evaluated and compared the physiological vulnerability of the leading-edge populations of two species of sea urchins Loxechinus albus and Pseudechinus magellanicus in response to predicted ocean warming and food limitation. After exposing sea urchins to a 60-day experimental period to contrasting temperature (1 °C, 7 °C and 14 °C corresponding respectively to the actual average summer temperature in Antarctica, the control treatment temperature and the predicted future temperature in the Strait of Magellan) and diet levels (ad libitum or food limitation), sea urchin stress tolerance was assessed. Sea urchins' physiology was measured at the organismal and sub-cellular level by studying the organisms energy balance (behavior, growth, gonad index, ingestion rate, O₂ uptake, energy reserves) and the expression of genes associated with aerobic metabolism. Our results showed that at their distribution edge, and despite their distinct geographical repartition, both species might be resilient to ocean warming. However, the combination of ocean warming and food limitation reduced the stress tolerance of sea urchins. In a warming ocean, another strategy could be to migrate toward the pole to a cooler environment but incubation at 1 °C resulted in a diminution of both species' aerobic scope. Overall, if these engineer species are unable to acclimate to food limitation under future climate, population fitness could be affected with ecological and economic consequences.

Diel-cycling seawater acidification and hypoxia impair the physiological and growth performance of marine mussels

Ocean acidification and hypoxia are concurrent in some coastal waters due to anthropogenic activities in the past decades. In the natural environment, pH and dissolved oxygen (DO) may fluctuate and follow diel-cycling patterns, but such effects on marine animals have not been comprehensively studied compared to their constant effects. In order to study the effects of diel-cycling seawater acidification and hypoxia on the fitness of marine bivalves, the thick shell mussels Mytilus coruscus were exposed to two constant levels of dissolved oxygen (2 mg/L, 8 mg/L) under two pH treatments (7.3, 8.1), as well as single diel fluctuating pH or DO, and the combined diel fluctuating of pH and DO for three weeks. The experimental results showed that constant acidification and hypoxia significantly reduced the extracellular pH (pH_e) and condition index (CI) of mussels, and significantly increased HCO₃^-, pCO₂ and standard metabolic rate (SMR). Diel fluctuating hypoxia and acidification also significantly reduced the pH_e and CI, and significantly increased pCO₂ and SMR, but had no significant effects on HCO₃^-. However, the diel-cycling acidification and hypoxia resulted in a higher CI compared to continuous exposure. In general, continuous and intermittent stress negatively impact the hemolymph and growth performance of mussels. However, mussels possess a little stronger resistance to diel-cycling seawater acidification and hypoxia than sustained stress.

Structure and functional analysis reveal an important regulated role of arginine kinase in Patinopecten yessoensis under low pH stress

Arginine kinase (AK), an important member of the phosphokinase family, is involved in temporal and spatial adenosine triphosphate (ATP) buffering systems. AK plays an important role in physiological function and metabolic regulations, in particular tissues with high and fluctuating energy demands. In present study, four AK genes were firstly identified from Yesso scallop (Patinopecten yessoensis) genome, respectively named PyAK1-4. PyAKs have highly conserved structures with a six-exon/five-exon structure, except for PyAK3. PyAK3 contains an unusual two-domain structure and a "bridge intron" between the two domains, which may originate from gene duplication and subsequent fusion. Phylogenetic analysis showed that all PyAKs belonged to an AK supercluster together with other AK proteins from Mollusca, Platyhelminthes, Arthropoda, and Nematode. A transcriptome database demonstrated that PyAK3 and PyAK4 were the main functional executors with high expression level during larval development and in adult tissues, while PyAK1 and PyAK2 were expressed at a low level. Furthermore, both PyAK2 and PyAK3 showed notably high expression in the male gonad, and PyAK4 was broadly expressed in almost all tissues with the highest level in striated muscle, indicating a tissue-specific expression pattern of PyAKs. In addition, quantitative real-time PCR results demonstrated that the expression of PyAK2, PyAK3 and PyAK4 were significantly upregulated in response to pH stress, especially in an extremely acidifying condition (pH 6.5), revealing the possible involvement of PyAKs in energetic homeostasis during environmental changes. Collectively, a comprehensive analysis of PyAKs was conducted in P. yessoensis. The diversity of PyAKs and their specific expression patterns promote a better understanding of energy metabolism in the growth, development and environmental response of P. yessoensis.

CO2-driven ocean acidification repressed the growth of adult sea urchin Strongylocentrotus intermedius by impairing intestine function

Strongylocentrotus intermedius cultured in the northern Yellow Sea in China was utilized to evaluate the effects of chronic CO₂-driven ocean acidification (OA) on adult sea urchins. Based on the projection of the Intergovernmental Panel on Climate Change (IPCC), present natural seawater conditions (pH_NBS = 8.10 ± 0.03) and three laboratory-controlled OA conditions (OA₁, ΔpH_NBS = - 0.3 units; OA₂, ΔpH_NBS = - 0.4 units; OA₃, ΔpH_NBS = - 0.5 units) were employed. After 60-day incubation, our results showed that (1) OA significantly repressed the growth of adult S. intermedius; (2) food consumption tended to be decreased with pH decline; (3) intestinal morphology was changed, and activities of intestinal cellulase and lipase were decreased under acidified conditions; (4) expression levels of two immune-related genes (SiTNF14 and SiTGF-β) were altered; (5) rate-limiting enzyme activities of the glycolytic pathway and tricarboxylic acid cycle (TAC) were changed in all OA treatments compared to those of controls.

Impact of Ocean Acidification on the Energy Metabolism and Antioxidant Responses of the Yesso Scallop (Patinopecten yessoensis)

Ocean acidification (OA), which is caused by increasing levels of dissolved CO2 in the ocean, is a major threat to marine ecosystems. Multiple lines of scientific evidence show that marine bivalves, including scallops, are vulnerable to OA due to their poor capacities to regulate extracellular ions and acid-based status. However, the physiological mechanisms of scallops responding to OA are not well understood. In this study, we evaluated the effects of 45 days of exposure to OA (pH 7.5) on the energy metabolism and antioxidant capability of Yesso scallops. Some biochemical markers related to energy metabolism (e.g., content of glycogen and ATP, activity of ATPase, lactate dehydrogenase, glutamate oxaloacetate transaminase, and glutamate-pyruvate transaminase), antioxidant capacity (e.g., reactive oxygen species level, activity of superoxide dismutase, and catalase) and cellular damage (e.g., lipid peroxidation level) were measured. Our results demonstrate that the effects of the reduced pH (7.5) on scallops are varied in different tissues. The energy reserves are mainly accumulated in the adductor muscle and hepatopancreas. Yesso scallops exhibit energy modulation by increasing lactate dehydrogenase activities to stimulate anaerobic metabolism. The highly active Na+/K+-ATPase and massive ATP consumption in the mantle and gill indicate that a large amount of energy was allocated for the ion regulation process to maintain the acid-base balance in the reduced-pH environment. Moreover, the increase in the reactive oxygen species level and the superoxide dismutase and catalase activities in the gill and adductor muscle, indicate that oxidative stress was induced after long-term exposure to the reduced-pH environment. Our findings indicate that the effects of OA are tissue-specific, and physiological homeostasis could be modulated through different mechanisms for Yesso scallops.

Field studies on the effects of Marteilia sp. on growth of mussel Mytilus galloprovincialis in Thermaikos Gulf

Global warming may accelerate growth and distribution of pathogens influencing aquatic organisms' diseases and human health. Despite the extensive research, the biology, cellular development and life cycle and of Marteilia sp. parasites as well as the influence of parasitic infection on the hosts are not fully understood. The aim of this study was to investigate the effect of Marteilia sp. prevalence and infection intensity on mussels' growth rate and morphometric characteristics under natural conditions in Thermaikos Gulf, a major bivalve production area in Greece, during a five-month growth period. The length, width, height and weight of the infected mussels were significantly lower compared to non-infected and the decrease was proportional to the intensity of mussel infection by the parasite. Moreover, the estimation of allometric relations between length, height, width and weight revealed significantly lower growth of mussel wet weight in relation to shell length for infected mussels compared to healthy ones. The negative effect of marteiliosis on the shell length growth rate of infected mussels was also confirmed by von Bertalanffy equations.