First measurements of the scope for growth (SFG) in mussels from a large scale survey in the North-Atlantic Spanish coast

Nano-titanium dioxide exacerbates the harmful effects of perfluorooctanoic acid on the health of mussels

Exposing marine organisms to contemporary contaminants, such as perfluorooctanoic acid (PFOA) and nano-titanium dioxide (nano-TiO2), can induce multifaceted physiological consequences. Our investigation centered on the responses of the mussel, Mytilus coruscus, to these agents. We discerned pronounced disruptions in gill filament connections, pivotal structures for aquatic respiration, suggesting compromised oxygen uptake capabilities. Concurrently, the respiratory rate exhibited a marked decline, indicating a respiratory distress. Furthermore, the mussels' clearance rate, a metric of their filtration efficacy, diminished, suggesting the potential for bioaccumulation of deleterious substances. Notably, the co-exposure of PFOA and nano-TiO2 exhibits interactive effects on the physiological performance of the mussels. The mussels' digestive performance waned in the face of heightened PFOA and nano-TiO2 concentrations, possibly hampering nutrient assimilation and energy accrual. This was mirrored in the noticeable contraction of their energy budget, suggesting long-term growth repercussions. Additionally, the dysregulation of the gut microbiota and the reduction in its diversity further confirm alterations in intestinal homeostasis, subsequently impacting its physiological functions and health. Collectively, these findings underscore the perils posed by escalated PFOA and nano-TiO2 levels to marine mussels, accentuating the need for a deeper understanding of nanoparticle-pollutant synergies in marine ecosystems.

Ocean acidification impact on the uptake of trace elements by mussels and their biochemical effects

This study delves into the intricate interplay between ocean acidification (OA), metal bioaccumulation, and cellular responses using mussels (Mytilus galloprovincialis) as bioindicators. For this purpose, environmentally realistic concentrations of isotopically labelled metals (Cd, Cu, Ag, Ce) were added to investigate whether the OA increase would modify metal bioaccumulation and induce adverse effects at the cellular level. The study reveals that while certain elements like Cd and Ag might remain unaffected by OA, the bioavailability of Cu and Ce could potentially escalate, leading to amplified accumulation in marine organisms. The present findings highlight a significant rise in Ce concentrations within different mussel organs under elevated pCO2 conditions, accompanied by an increased isotopic fractionation of Ce (140/142Ce), suggesting a heightened potential for metal accumulation under OA. The results suggested that OA influenced metal accumulation in the gills of mussels. Conversely, metal accumulation in the digestive gland was unaffected by OA. The exposure to both trace metals and OA affects the biochemical responses of M. galloprovincialis, leading to increased metabolic capacity, changes in energy reserves, and alterations in oxidative stress markers, but the specific effects on other biomarkers (e.g., lipid peroxidation, some enzymatic responses or acetylcholinesterase activity) were not uniform, suggesting complex interactions between the stressors and the biochemical pathways in the mussels.

Pearl Farming Micro-Nanoplastics Affect Oyster Physiology and Pearl Quality

Pearl farming is crucial for the economy of French Polynesia. However, rearing structures contribute significantly to plastic waste, and the widespread contamination of pearl farming lagoons by microplastics has raised concerns about risks to the pearl industry. This study aimed to evaluate the effects of micro-nanoplastics (MNPs, 0.4-200 μm) on the pearl oyster (Pinctada margaritifera) over a 5-month pearl production cycle by closely mimicking ecological scenarios. MNPs were produced from weathered plastic pearl farming gear and tested at environmentally relevant concentrations (0.025 and 1 μg L-1) to decipher biological and functional responses through integrative approaches. The significant findings highlighted the impacts of MNPs on oyster physiology and pearl quality, even at remarkably low concentrations. Exposure to MNPs induced changes in energy metabolism, predominantly driven by reduced assimilation efficiency of microalgae, leading to an alteration in gene expression patterns. A distinct gene expression module exhibited a strong correlation with physiological parameters affected by MNP conditions, identifying key genes as potential environmental indicators of nutritional-MNP stress in cultured oysters. The alteration in pearl biomineralization, evidenced by thinner aragonite crystals and the presence of abnormal biomineral concretions, known as keshi pearls, raises concerns about the potential long-term impact on the Polynesian pearl industry.

Scope for growth and dietary needs of Mediteranean Pinnids maintained in captivity

Background

The measurement of the energy available for growth (scope of growth, SFG) can be used in bivalves to make a long-term prediction in a short-term experiment of the condition of the individual. In order to tackle the best conditions for captive maintenance of Mediterranean Pinnids, a SFG study was conducted using Pinna rudis as a model species. Three diets were examined to test the viability of live microalgae and commercial products: i) a control diet using 100% of live microalgae based on the species Isochrysis galbana (t-ISO), ii) a 100% of commercial microalgae diet based on the product Shellfish Diet 1800®, and iii) a 50/50% mix diet of I. galbana (t-ISO) and Shellfish Diet 1800®.

Results

SFG results showed significant differences among diets in the physiological functions measured and suggested lower acceptability and digestibility of the commercial product. Negative SFG values were obtained for the commercial diet which indicates that it should be rejected for both Pinnid maintenance. The mixed diet showed improved physiological performance compared to the commercial diet, resulting in a higher SFG that had no significant differences with the control diet. However, in the long-term, the lower digestibility of the mixed diet compared to the control diet could lead to a deterioration of individuals’ conditions and should be considered cautiously.

Conclusions

This work represents the first case study of SFG in Pinna spp. and provides fundamental data on dietary needs for the critically endangered species, P. nobilis.

Antioxidant capacity and carbon-based scope for growth of brackish water clams Corbicula japonica under the combined effects of natural and anthropogenic factors

Changes in natural estuarine environment and anthropogenic disturbances are becoming significant threats to organisms, particularly bivalves. A deeper understanding of the relationship between biochemical- and individual-level responses is necessary to assess the combined effects of natural and anthropogenic factors on bivalves. To the best of our knowledge, this is the first study where the oxygen radical absorbance capacity (ORAC) and carbon-based scope for growth (C-SFG) were applied as biomarkers to evaluate the response of the brackish water clam Corbicula japonica to four spatiotemporally varying environmental factors. High water temperature and food availability supported C-SFG while high salinity inhibited it. Most of wastewater (WW) treatments resulted in negative C-SFG values because of a reduced clearance rate and increased excretion rate. In particular, high food availability with WW treatment resulted in the lowest C-SFG value of -114 μg C·ind^-1 h^-1. The ORAC was activated in response to high salinity with WW treatment (p < 0.05). To ascertain the combined effects of the natural and anthropogenic factors, principal component and cluster analyses were performed on the ORAC and C-SFG data. Anthropogenic WW was found to have different effects on the physiological and biochemical biomarkers according to the natural conditions. A roughly negative correlation was observed between ORAC and C-SFG because activation of the antioxidant capacity can influence the growth potential of the clams through the additional use of available metabolic energy. However, some exceptions were observed where both the ORAC and C-SFG values were either high or low, which could be because the C-SFG response varies depending on different metabolic behaviors even when the ORAC response remains the same. These results indicate that the biochemical-level response (i.e., ORAC) of C. japonica can be interpreted using individual-level response (i.e., C-SFG), but careful attention must be given to over- or underestimation.

Microplastics can aggravate the impact of ocean acidification on the health of mussels: Insights from physiological performance, immunity and byssus properties

Ocean acidification may increase the risk of disease outbreaks that would challenge the future persistence of marine organisms if their immune system and capacity to produce vital structures for survival (e.g., byssus threads produced by bivalves) are compromised by acidified seawater. These potential adverse effects may be exacerbated by microplastic pollution, which is forecast to co-occur with ocean acidification in the future. Thus, we evaluated the impact of ocean acidification and microplastics on the health of a mussel species (Mytilus coruscus) by assessing its physiological performance, immunity and byssus properties. We found that ocean acidification and microplastics not only reduced hemocyte concentration and viability due to elevated oxidative stress, but also undermined phagocytic activity of hemocytes due to lowered energy budget of mussels, which was in turn caused by the reduced feeding performance and energy assimilation. Byssus quality (strength and extensibility) and production were also reduced by ocean acidification and microplastics. To increase the chance of survival with these stressors, the mussels prioritized the synthesis of some byssus proteins (Mfp-4 and Mfp-5) to help maintain adhesion to substrata. Nevertheless, our findings suggest that co-occurrence of ocean acidification and microplastic pollution would increase the susceptibility of bivalves to infectious diseases and dislodgement risk, thereby threatening their survival and undermining their ecological contributions to the community.

Comparative role of microplastics and microalgae as vectors for chlorpyrifos bioacumulation and related physiological and immune effects in mussels

Microplastics (MP) are contaminants of concern per se, and also by their capacity to sorb dissolved chemicals from seawater, acting as vehicles for their transfer into marine organisms. Still, the role of MP as vehicles for contaminants and their associated toxicological effects have been poorly investigated. In this work we have compared the role of MP (high density polyethylene, HDPE, ≤22 μm) and of natural organic particles (microalgae, MA) as vehicle for chlorpyrifos (CPF), one of the most common pesticides found in river and coastal waters. We have compared the capacity of MP and MA to carry CPF. Then, the mussel Mytilus galloprovincialis has been exposed for 21 days to dissolved CPF, and to the same amount of CPF loaded onto MP and MA. The concentration of CPF in mussel' tissues and several physiological, energetics and immune parameters have been analyzed after 7 and 21 days of exposure. Results showed similar CPF accumulation in mussel exposed to MP and to MA spiked with CPF. This revealed that MP acted as vector for CPF in a similar way (or even to a lesser extent) than MA. After 21 days of exposure mussels exposed to MP spiked with CPF displayed similar or more pronounced biological effects than mussels exposed to dissolved CPF or to MA loaded with CPF. This suggested that the combined "particle" and "organic contaminant" effect produced an alteration on the biological responses greater than that produced by each stressor alone, although this was evident only after 3 weeks of exposure.

Bioenergetics in environmental adaptation and stress tolerance of aquatic ectotherms: linking physiology and ecology in a multi-stressor landscape

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior and ecology. Metabolic rates define the physiological and life-history performance of an organism, have direct implications for Darwinian fitness, and affect ecologically relevant traits such as the trophic relationships, productivity and ecosystem engineering functions. Natural environmental variability and anthropogenic changes expose aquatic ectotherms to multiple stressors that can strongly affect their energy metabolism and thereby modify the energy fluxes within an organism and in the ecosystem. This Review focuses on the role of bioenergetic disturbances and metabolic adjustments in responses to multiple stressors (especially the general cellular stress response), provides examples of the effects of multiple stressors on energy intake, assimilation, conversion and expenditure, and discusses the conceptual and quantitative approaches to identify and mechanistically explain the energy trade-offs in multiple stressor scenarios, and link the cellular and organismal bioenergetics with fitness, productivity and/or ecological functions of aquatic ectotherms.

Impact of elevated temperature on physiological energetics of Penaeus monodon post larvae: A mesocosm study

Global climate change induced warming has profound repercussion on physiological performances of marine animals. The Indian Sundarban is one of the best nursery grounds for various shrimp populations which need estuarine realm to complete their bipartite life cycle. From last couple of decades, a clear indication of temperature escalation has been identified in Sundarban. In the present study, we have assessed the physiological energetics of Penaeus monodon post larvae from Indian Sundarban under different temperatures, 28 °C (annual average habitat temperature) and elevated temperatures 30 °C, 32 °C, 34 °C in a month long mesocosm experiment. Significant alterations were observed in growth performances as well as physiological energetics. The length, weight, survival percentages, ingestion rates were reduced, howbeit respiration and ammonia excretion rate had been increased in elevated temperature treatments culminating in a negative Scope for Growth. PERMANOVA results showed a significant (p ≤ 0.05) variation in different physiological performances of shrimp post larvae both in different temperature treatments and days of exposure. The present results clearly highlighted the detrimental effect of elevated temperature on physiological energetics of shrimp larvae that might potentially reduce shrimp population and affect the coastal fishery.

Proteomic analysis and biochemical alterations in marine mussel gills after exposure to the organophosphate flame retardant TDCPP

Organophosphate flame retardants (OPFRs) are (re-)emergent environmental pollutants increasingly being used because of the restriction of other flame retardants. The chlorinated OPFR, tris(1,3-dichloro-2-propyl) phosphate (TDCPP) is among those of highest environmental concern, but its potential effects in the marine environment have rarely been investigated. We exposed a widely used sentinel marine mussel species, Mytilus galloprovincialis, to 10 μg L^-1 of TDCPP during 28 days and studied: (i) the kinetics of bioaccumulation and elimination of the compound, (ii) the effect on two molecular biomarkers, glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities, and (iii) proteomic alterations in the gills, following an isobaric labeling quantitative shotgun proteomic approach, at two exposure times (7 and 28 days). Uptake and elimination of TDCPP by mussels were very fast, and the bioconcentration factor of this compound in mussels was 147 L kg_ww^-1, confirming that this compound is not very bioaccumulative, as predicted by its chemical properties. GST activity was not affected by TDCPP exposure, but AChE activity was inhibited by TDCPP at both 7 and 28 days of exposure. Proteomic analysis revealed subtle effects of TDCPP in mussel gills, since few proteins (less than 2 % of the analysed proteome) were significantly affected by TDCPP, and effect sizes were low. The most relevant effects detected were the up-regulation of epimerase family protein SDR39U1, an enzyme that could be involved in detoxification processes, at both exposure times, and the down-regulation of receptor-type tyrosine-protein phosphatase N2-like (PTPRN2) after 7 days of exposure, which is involved in neurotransmitter secretion and might be related to the neurotoxicity described for this compound. Exposure time rather than TDCPP exposure was the most important driver of protein abundance changes, with 33 % of the proteome being affected by this factor, suggesting that stress caused by laboratory conditions could be an important confounding factor that needs to be controlled in similar ecotoxicology studies. Proteomic data are available via ProteomeXchange with identifier PXD019720.

No evidence that vitellogenin protein expression is induced in marine mussels after exposure to an estrogenic chemical

A wide variety of endocrine disrupting chemicals reach the marine environment and can cause harmful effects in different marine organisms. Vitellogenin (Vtg), the egg-yolk precursor, is a commonly used endocrine disruption biomarker in fish and more recently in marine invertebrates under the assumption of high expected similarities in the endocrine system of vertebrates and invertebrates. However, this assumption has been recently questioned. The results from previous studies focused on bivalve molluscs showed that Vtg induction could be misleading because of the use of either non-robust or indirect techniques to measure Vtg. In this study, mussels (Mytilus galloprovincialis) were exposed to either 10 or 100 ng/L of the synthetic hormone 17α-ethinylestradiol (EE2) at different exposure times (4 and 24 days) and under different feeding regimes (representing different energy balances), and Vtg levels in both male and female mussel gonads were quantified by label free shotgun LC-MS/MS proteomic analysis. Vtg protein was not detected in male gonads. In female gonads, Vtg levels were not significantly affected by EE2 at any exposure time or EE2 concentration tested, whereas a significant correlation was found between the degree of maturation of the gonad and Vtg levels in females. Results obtained in the present study critically question the use of Vtg as a biomarker of endocrine disruption in marine mussels, and show that the degree of maturation of the gonad can be an important confounding factor in the attempts to evaluate estrogenic effects through Vtg measurement in mussel gonads.

Feeding regimes modulate biomarkers responsiveness in mussels treated with diclofenac

This study investigated the role of the feeding regime on cellular (lysosomal membrane impairment), oxidative (superoxides and nitric oxides generation, as well as lipid peroxidation) and genotoxic (nuclear abnormalities) biomarkers measured in hemocytes of mussels Mytilus galloprovincialis treated with diclofenac (DCF). Specifically, unfed mussels, or mussels fed ad libitum with algal species Tisochrysis lutea or Tetraselmis suecica (Tiso/DCF- and Tetra/DCF- treated mussels, respectively) were exposed to DCF (20 μgL^-1) for 4 days. The results showed that biomarkers' responsiveness against DCF, were more pronounced in unfed and Tetra/DCF-, rather than Tiso/DCF- treated mussel hemocytes, thus revealing food deprivation, changes in mussel feeding/filtration rate and digestion processes, as potent factors of mussels' immune efficiency and response against DCF. Those findings could provide valuable data for the optimization of mussels' feeding regime during laboratory studies, in order to assess reliably the effects of emerging contaminants on non-target sentinel organisms, such as mussels.

Assessing the impact of lanthanum on the bivalve Corbicula fluminea in the Rhine River

Anthropogenic lanthanum predominantly derived from a point source has become an emerging contaminant in the Rhine River, but little is known about its ecotoxicological consequences on bivalve mollusks. A fundamental requirement of aquatic invertebrate adaptation and survival in stressful habitats is the maintenance of energy homeostasis. As such, the present study tested the impact of four dissolved La concentrations (0, 50, 100 and 200 μM) on the energy balance of the bivalve Corbicula fluminea in the Rhine River. Bivalves were collected at four sampling sites which were contaminated by La to different degrees, thereby allowing to understand the degree of their potential acclimation. With increasing exposure dose, shell and somatic growth (the most energetically expensive biological processes) decreased significantly in clams inhabited the control (uncontaminated) habitat; while less pronounced impacts were evident in all three contaminated sites. In particular, the latter showed virtually unaffected energy (glycogen and protein) reserves. An elucidation of shifts in the organismal energy budget may shed light on such improvement of growth performance. Irrespective of sampling sites, short-term exposure to La caused significant increases of oxygen consumption and ammonia excretion, indicating that the clams promoted their energy metabolism and thereby allocated more energy to essential physiological processes. Noteworthily, the clams originating from contaminated sites displayed virtually unaffected clearance rate, thereby being able to partially fulfill the increased energy demand and eventually alleviating the La-induced physiological interference. Taken together, findings of the present study demonstrate that whether, and to what extent, C. fluminea is able to sustain its energy homeostasis play a central role in the phenotypic plasticity and/or genetic adaptation in the face of anthropogenic La contamination in the Rhine River.

Microplastics Affect Energy Balance and Gametogenesis in the Pearl Oyster Pinctada margaritifera

Plastic pollution in the environment is increasing at global scale. Microplastics (MP) are derived from degradation of larger plastic items or directly produced in microparticles form (< 5 mm). Plastics, widely used in structures and equipment of pearl farming, are a source of pollution to the detriment of the lagoon ecosystem. To evaluate the impact of MP on the physiology of Pinctada margaritifera, a species of ecological and commercial interests, adult oysters were exposed to polystyrene microbeads (micro-PS of 6 and 10 μm) for 2 months. Three concentrations, 0.25, 2.5, and 25 μg L^-1, and a control were tested. Ingestion and respiration rate and assimilation efficiency were monitored on a metabolic measurement system to determine the individual energy balance (Scope For Growth, SFG). Effects on reproduction were also assessed. The assimilation efficiency decreased significantly according to micro-PS concentration. The SFG was significantly impacted by a dose-dependent decrease from 0.25 μg L^-1 ( p < 0.0001), and a negative SFG was measured in oysters exposed to 25 μg L^-1. Gonads may have provided the missing energy to maintain animals' metabolism through the production of metabolites derived from germ cells phagocytosis. This study shows that micro-PS significantly impact the assimilation efficiency and more broadly the energy balance of P. margaritifera, with negative repercussions on reproduction.

Interactive effects of nutrition, reproductive state and pollution on molecular stress responses of mussels, Mytilus galloprovincialis Lamarck, 1819

Marine bivalves including mussels Mytilus galloprovincialis are commonly used as sentinels for pollution monitoring and ecosystem health assessment in the coastal zones. Use of biomarkers to assess the pollution effects assumes that the effects of pollutants on the biomarkers exceed the natural background variability; yet this assumption has rarely been tested. We exposed mussels at different reproductive stages and nutritive states to two concentrations of a polycyclic aromatic hydrocarbon (fluoranthene, 3 and 60 μg L^-1) for three weeks. Expression levels of the molecular biomarkers related to the detoxification and general stress response [cytochrome P450 oxidase (CYP450), glutathione S-transferases (GST-α; GST-S1; GST-S2), the multixenobiotic resistance protein P-glycoprotein (PgP), metallothioneins (MT10 and MT20), heat shock proteins (HSP22, HSP70-2; HSP70-3; HSP70-4), as well as mRNA expression of two reproduction-related genes, vitellogenin (Vitel) and vitelline coat lysin M7 (VCLM7)] were measured. The mussels' nutrition and reproductive state affected the baseline mRNA levels of molecular biomarkers and modulated the transcriptional responses of biomarker genes to the pollutant exposure. Thus, mussel physiological state could act as a confounding factor in the evaluation of the response of pollution through molecular biomarkers. The biomarker baseline levels must be determined across a range of physiological states to enable the use of biomarkers in monitoring programs.

Blue mussels (Mytilus edulis spp.) as sentinel organisms in coastal pollution monitoring: A review

The blue mussel (Mytilus spp.) is widely used as a bioindicator for monitoring of coastal water pollution (mussel watch programs). Herein we provide a review of this study field with emphasis on: the suitability of Mytilus spp. as environmental sentinels; uptake and bioaccumulation patterns of key pollutant classes; the use of Mytilus spp. in mussel watch programs; recent trends in Norwegian mussel monitoring; environmental quality standards and background concentrations of key contaminants; pollutant effect biomarkers; confounding factors; particulate contaminants (microplastics, engineered nanomaterials); climate change; harmonization of monitoring procedures; and the use of deployed mussels (transplant caging) in pollution monitoring. Lastly, the overall state of the art of blue mussel pollution monitoring is discussed and some important issues for future research and development are highlighted.

Shotgun Proteomics Analysis Discards Alkali Labile Phosphate as a Reliable Method To Assess Vitellogenin Levels in Mytilus galloprovincialis

Vitellogenin, the egg yolk precursor, is a well-known biomarker of endocrine disruption in oviparous vertebrates. In invertebrates, such as bivalves, it has been used in the last 10 years for the same purpose, despite the limited knowledge of invertebrate endocrinology. In bivalves, vitellogenin levels are usually estimated using an indirect technique, alkali labile phosphate (ALP), that assumes that vitellogenin is the most abundant phosphorylated protein in the analyzed tissue. In this study, we applied shotgun proteomics for the identification and quantification of vitellogenin in marine mussel gonads and compared the results with those obtained with the ALP method. The proteomic analysis revealed that vitellogenin is only detected in female gonads with expression levels that are rather variable among female mussels at different stages of gonad development. ALP analysis, on the contrary, detected similar amounts of phosphorylated proteins regardless of sex or gonad development stage. These results show evidence that the ALP method is not providing reliable information about Vtg levels, at least in marine mussel gonads. ALP is not a good proxy to assess Vtg levels in marine mussels, and careful verification of the adequacy of the procedure should be done before ALP is further assumed as a proxy of Vtg in other bivalve mollusks.

Biomarkers of general stress in mussels as common indicators for marine biomonitoring programmes in Europe: The ICON experience

This study investigated whether general stress biomarkers in mussels can be applied as common first-tier biomarkers in regional biomonitoring programmes in the North Sea (including Iceland) and western Mediterranean Sea. Stress on Stress (SoS) and lysosomal membrane stability (LMS) biomarkers were analysed in resident mussels (Mytilus sp.) from 8 coastal sites and in transplanted mussels (Mytilus galloprovincialis) from two Spanish Mediterranean coastal sites. The assessment of results, as input to pollution monitoring strategies, was performed jointly for LMS and SoS data from the two regions. Contaminant body burden of the mussels was compared with biomarker results. The results demonstrated that these two general and non-expensive stress biomarkers in mussel can be applied throughout European waters, providing a cost-effective and harmonised approach to screen contaminant-related biological effects within the framework of wide-scale pollution biomonitoring programmes, such as that proposed by the European Union, i.e. the Marine Strategy Framework Directive.

Assessing environmental quality status by integrating chemical and biological effect data: The Cartagena coastal zone as a case

Cartagena coastal zone (W Mediterranean) was chosen for a practical case study to investigate the suitability of an integrated indicator framework for marine monitoring and assessment of chemicals and their effects, which was developed by ICES and OSPAR. Red mullet (Mullus barbatus) and the Mediterranean mussel (Mytilus galloprovincialis) were selected as target species. Concentrations of contaminants in sediment and biota, and contaminant-related biomarkers were analysed. To assess environmental quality in the Cartagena coastal zone with respect to chemical pollution, data were assessed using available assessment criteria, and then integrated for different environmental matrices. A qualitative scoring method was used to rank the overall assessments into selected categories and to evaluate the confidence level of the final integrated assessment. The ICES/OSPAR integrated assessment framework, originally designed for the North Atlantic, was found to be applicable for Mediterranean species and environmental matrices. Further development of assessment criteria of chemical and biological parameters in sediments and target species from the Mediterranean will, however, be required before this framework can be fully applied for determining Good Environmental Status (GES) of the Marine Strategy Framework Directive in these regions.

Differences in the accumulation and tissue distribution of Pb, Cd, and Cu in Mediterranean mussels (Mytilus galloprovincialis) exposed to single, binary, and ternary metal mixtures

Heavy metals often accumulate in complex mixtures in the environment and are currently a source of concern in many marine ecosystems. Pb, Cd, and Cu are regarded as priority hazardous metals due to their great persistence, bioaccumulation, and toxicity. The aim of the present study was to investigate the tissue accumulation and distribution of these heavy metals in Mediterranean mussels (Mytilus galloprovincialis) exposed to binary and ternary mixtures of metals as opposed to only single exposures. Heavy metal concentrations in the digestive gland, gills, and the other soft tissues were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the distribution of each metal was analyzed according to compartments. The concentrations of Pb, Cd, and Cu increased significantly in the group exposed to the ternary mixture; however, there was no common response pattern to exposure in single and binary mixtures. Above all, the metals concentrated in the digestive gland, although the percentages of each element varied between compartments and varied between tissues according to the treatment.

CO2-induced pH reduction increases physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus

The increasing usage of nanoparticles has caused their considerable release into the aquatic environment. Meanwhile, anthropogenic CO₂ emissions have caused a reduction of seawater pH. However, their combined effects on marine species have not been experimentally evaluated. This study estimated the physiological toxicity of nano-TiO₂ in the mussel Mytilus coruscus under high pCO₂ (2500-2600 μatm). We found that respiration rate (RR), food absorption efficiency (AE), clearance rate (CR), scope for growth (SFG) and O:N ratio were significantly reduced by nano-TiO₂, whereas faecal organic weight rate and ammonia excretion rate (ER) were increased under nano-TiO₂ conditions. High pCO₂ exerted lower effects on CR, RR, ER and O:N ratio than nano-TiO₂. Despite this, significant interactions of CO₂-induced pH change and nano-TiO₂ were found in RR, ER and O:N ratio. PCA showed close relationships among most test parameters, i.e., RR, CR, AE, SFG and O:N ratio. The normal physiological responses were strongly correlated to a positive SFG with normal pH and no/low nano-TiO₂ conditions. Our results indicate that physiological functions of M. coruscus are more severely impaired by the combination of nano-TiO₂ and high pCO₂.

Effect of diet quality on mussel biomarker responses to pollutants

The effect of the quality of two microalgal species on select biological and biochemical responses used as indicators of pollution were assessed. Mussels were conditioned for 6 weeks with the diatom Chaetoceros neogracile and the dinoflagellate Heterocapsa triquetra, chosen for being two clearly different types of primary production quality that differ in both biometric and biochemical characteristics. After dietary conditioning, the mussels were exposed to a polycyclic aromatic hydrocarbon, fluoranthene (FLU), for 1 week followed by 1 week of depuration. Results showed higher FLU accumulation in mussels fed on C. neogracile compared to those fed on H. triquetra. Concomitantly, a greater impact of this toxicant was observed in the biomarker responses of mussels fed on C. neogracile. These mussels showed an increase in the percentage of dead hemocytes, an activation of phagocytosis and ROS production of hemocytes after exposure. Some enzymatic activities also increased upon FLU exposure (superoxide dismutase -SOD-, catalase -CAT-, and glutathione reductases -GR-) and after depuration (glutathione-s-transferase -GST-). Results suggest that FLU exposure as well as food quality influence biomarker responses, with higher values of SOD, CAT and GR in non-exposed mussels fed on C. neogracile. In addition, upon exposure to the same FLU concentration, GR response varied according to dietary conditioning, suggesting that diet could act as a confounding factor in biomarker responses to pollution. Consequently, trophic conditions should be considered in marine pollution monitoring programs for a better interpretation of biomarker responses.

Effect of mussel reproductive status on biomarker responses to PAHs: Implications for large-scale monitoring programs

Biomarkers are useful tools to assess biological effects of pollutants and have been extensively used in monitoring programs to determine ecosystem health. In these programs, a wide range of environmental conditions are covered and sometimes, obtained data are difficult to interpret because of natural variables are affecting biomarker responses. Among these variables, musseĺs reproductive status has been considered one of the most changing variables between sites in a monitoring survey. Thus, the main aim of this work was to identify the effect that mussel reproductive status has on biomarker responses. For that purpose, mussels sampled at two periods in the reproductive cycle (reproductive and resting stages) were conditioned to the same laboratory conditions and exposed to fluoranthene (FLU) for three weeks. Studied biomarkers covering a wide range of organism responses were included: bioaccumulation, physiological rates (clearance rate -CR-, absorption efficiency -AE-, respiration rate -RR- and their integration in the scope for growth -SFG-), antioxidant enzyme activities (superoxide-dismutase -SOD-, catalase -CAT-, glutathione reductase -GR-, glutathione peroxidase -GPx-, glutathione-S-tranferase -GST-) and biochemical damage responses (lipid membrane peroxidation -LPO-). The results obtained evidenced that the levels of the biomarkers studied (RR, SOD, CAT and GPx) were higher at reproductive than at resting stage. On the other hand, the effect of toxicant was observed in SFG, CAT and GPx but this effect was only detected during the resting period. Moreover, there was a deterioration of mussel gonadal tissue with FLU exposure during reproductive stage. FLU accumulation in mussel tissues was also dependent of the reproductive status with higher internal concentrations during resting than reproductive period. In conclusion, there was a strong effect of reproductive status on studied biomarkers which seems to mask the effect of FLU at reproductive stage. The present study evidences the need to include the measurement of mussel biological status in marine pollution monitoring programs for a correct interpretation of biomarker data.

Combined effects of short-term exposure to elevated CO2 and decreased O2 on the physiology and energy budget of the thick shell mussel Mytilus coruscus

Hypoxia and ocean acidification are two consequences of anthropogenic activities. These global trends occur on top of natural variability. In environments such as estuarine areas, short-term acute pH and O2 fluctuations are occurring simultaneously. The present study tested the combined effects of short-term seawater acidification and hypoxia on the physiology and energy budget of the thick shell mussel Mytilus coruscus. Mussels were exposed for 72 h to six combined treatments with three pH levels (8.1, 7.7 and 7.3) and two dissolved oxygen (DO) levels (2 mg L(-1), 6 mg L(-1)). Clearance rate (CR), food absorption efficiency (AE), respiration rate (RR), ammonium excretion rate (ER), O:N ratio and scope for growth (SFG) were significantly reduced, and faecal organic dry weight ratio (E) was significantly increased at low DO. Low pH did not lead to a reduced SFG. Interactive effects of pH and DO were observed for CR, E and RR. Principal component analysis (PCA) revealed positive relationships among most physiological indicators, especially between SFG and CR under normal DO conditions. These results demonstrate that Mytilus coruscus was sensitive to short-term (72 h) exposure to decreased O2 especially if combined with decreased pH levels. In conclusion, the short-term oxygen and pH variation significantly induced physiological changes of mussels with some interactive effects.

Esterase activity (EA), total oxidant status (TOS) and total antioxidant capacity (TAC) in gills of Mytilus galloprovincialis exposed to pollutants: Analytical validation and effects evaluation by single and mixed heavy metal exposure

The aims of the present study were to optimize and validate methods for esterase activity (EA), total oxidant status (TOS) and total antioxidant capacity (TAC) determination in mussel' gills, and to establish the relationships between these biomarkers and Pb, Cd and Cu pollution, in single form and ternary mixture. Two different buffers for sample homogenization, the need of ultracentrifugation, and analytical validation were evaluated. Coefficients of variation, when buffer without additives and ultracentrifugation were used, were <15%, and recovery were 97%-109% in all cases. The EA response tends to decrease with treatments, TOS decreased significantly in Cd and ternary groups, while TAC tended to increase in treatments with Pb, Cd and ternary groups. In conclusion, the methods for EA, TOS and TAC measurements in gills of mussel were precise and accurate and could be interesting resources in biomonitoring programmes.

In vivo exposure of marine mussels to carbamazepine and 10-hydroxy-10,11-dihydro-carbamazepine: Bioconcentration and metabolization

Aquatic organisms are exposed to pharmaceuticals present in natural waters, but few data are available on the accumulation of these substances in such organisms. The present study evaluated the in vivo bioconcentration of two anticonvulsants--carbamazepine (CBZ) and 10-hydroxy-10,11-dihydro-carbamazepine (10 OH)--in marine mussels (Mytilus galloprovincialis) exposed to nominal 10 μg L(-1) concentrations for one week. The bioconcentration factors (BCFs) were 3.9 and 4.5 L kg(-1) dry weight (dw) for CBZ and 10 OH, respectively. CBZ accumulation reached an average tissue concentration of 29.3 ± 4.8 ng g(-1) dw, and 10 OH accumulated up to 40.9 ± 4.6 ng g(-1) dw in tissues within one week, showing first-order kinetics. BCF obtained with linear QSAR models correctly estimated the CBZ bioconcentration and overestimated the 10 OH bioconcentration to some extent. The detection of two metabolites (carbamazepine-10,11-epoxide and acridine) among the five sought suggested an active metabolism for CBZ. In contrast, none of the 10 OH metabolites were detected in mussels exposed to 10 OH. CBZ showed higher accumulation in the digestive gland, where some relevant metabolites were detected, than in other studied tissues. The implication of those findings on field biomonitoring is discussed.

Effect of nutritive status on Mytilus galloprovincialis pollution biomarkers: Implications for large-scale monitoring programs

Biomarkers have been extensively used in monitoring programs with the aim of assessing the biological effects of pollutants on marine organisms and determining environmental status. Data obtained from these programs are sometimes difficult to interpret due to the large amount of natural variables affecting biological processes, which could act as confounding factors on biomarker responses. The main aim of this work was to identify the effect of one of these variables, the food availability, and consequently, the mussel nutritive status, on biomarker responses. For that purpose, mussels (Mytilus galloprovincialis) were conditioned to three different food rations for 2 months in order to create three mussel nutritive statuses and afterwards, each status was exposed to three nominal concentrations of fluoranthene (FLU) for 3 weeks. A battery of biomarkers was considered in this study to cover a wide range of organism responses, both physiological (scope for growth - SFG) and biochemical (superoxide dismutase - SOD, catalase - CAT, glutathione reductase - GR, glutathione peroxidase - GPx, glutathione-S-transferase - GST and phenoloxidase - PO activities, and lipid membrane peroxidation - LPO). The results obtained, evidenced that most of the studied biomarkers (SFG, SOD, CAT, GPx, and PO) were strongly affected by mussel nutritive status, showing higher values at lower status, whereas the effect of toxicant was not always evident, masked by the nutritive status effect. This paper demonstrates that toxicants are not the only source of variability modulating pollution biomarkers, and confirms nutritive status as a major factor altering biochemical and physiological biomarkers.

Physiological energetics of the thick shell mussel Mytilus coruscus exposed to seawater acidification and thermal stress

Anthropogenic CO₂ emissions have caused seawater temperature elevation and ocean acidification. In view of both phenomena are occurring simultaneously, their combined effects on marine species must be experimentally evaluated. The purpose of this study was to estimate the combined effects of seawater acidification and temperature increase on the energy budget of the thick shell mussel Mytilus coruscus. Juvenile mussels were exposed to six combined treatments with three pH levels (8.1, 7.7 and 7.3)×two temperatures (25 °C and 30 °C) for 14 d. We found that clearance rates (CRs), food absorption efficiencies (AEs), respiration rates (RRs), ammonium excretion rates (ER), scope for growth (SFG) and O:N ratios were significantly reduced by elevated temperature sometimes during the whole experiments. Low pH showed significant negative effects on RR and ER, and significantly increased O:N ratios, but showed almost no effects on CR, AE and SFG of M. coruscus. Nevertheless, their interactive effects were observed in RR, ER and O:N ratios. PCA revealed positive relationships among most physiological indicators, especially between SFG and CR under normal temperatures compared to high temperatures. PCA also showed that the high RR was closely correlated to an increasing ER with increasing pH levels. These results suggest that physiological energetics of juvenile M. coruscus are able to acclimate to CO2 acidification with a little physiological effect, but not increased temperatures. Therefore, the negative effects of a temperature increase could potentially impact the ecophysiological responses of M. coruscus and have significant ecological consequences, mainly in those habitats where this species is dominant in terms of abundance and biomass.

Influence of mussel biological variability on pollution biomarkers

This study deals with the identification and characterization of biological variables that may affect some of the biological responses used as pollution biomarkers. With this aim, during the 2012 mussel survey of the Spanish Marine Pollution monitoring program (SMP), at the North-Atlantic coast, several quantitative and qualitative biological variables were measured (corporal and shell indices, gonadal development and reserves composition). Studied biomarkers were antioxidant enzymatic activities (CAT, GST, GR), lipid peroxidation (LPO) and the physiological rates integrated in the SFG biomarker (CR, AE, RR). Site pollution was considered as the chemical concentration in the whole tissues of mussels. A great geographical variability was observed for the biological variables, which was mainly linked to the differences in food availability along the studied region. An inverse relationship between antioxidant enzymes and the nutritional status of the organism was evidenced, whereas LPO was positively related to nutritional status and, therefore, with higher metabolic costs, with their associated ROS generation. Mussel condition was also inversely related to CR, and therefore to SFG, suggesting that mussels keep an "ecological memory" from the habitat where they have been collected. No overall relationship was observed between pollution and biomarkers, but a significant overall effect of biological variables on both biochemical and physiological biomarkers was evidenced. It was concluded that when a wide range of certain environmental factors, as food availability, coexist in the same monitoring program, it determines a great variability in mussel populations which mask the effect of contaminants on biomarkers.

Environmental cadmium exposure impacts physiological responses in Manila clams

The physiological responses of marine bivalves to chronic cadmium (Cd) exposure at sub-lethal concentrations have been well documented. As of now, few studies have examined the effect of Cd exposure and subsequent recovery period at environmentally realistic concentrations. In this study, environmentally, Cd exposures were performed to assess the physiological responses of the Manila clam Ruditapes philippinarum. The clams were exposed to waterborne Cd at two environmentally realistic concentrations (4 and 40 μg L(-1)) for 35 days and then allowed to recover for another 35 days. The accumulation and elimination of Cd in R. philippinarum were tissue-specific and dose- and time-dependent. Cd accumulation increased sharply in the digestive gland, and Cd elimination was rapid in the gill. Major physiological responses, including clearance rate, absorption efficiency, respiration rate, excretion rate, oxygen to nitrogen ratio, and scope for growth, were significantly affected by Cd exposure. Yet, the clams exposed to 4-μg L(-1) Cd were able to quickly recover their normal physiological processes and clearly exhibited catch-up growth once they were transferred to clean seawater. Hence, R. philippinarum can exhibit good physiological plasticity when confronted with moderately environmental Cd exposure. All physiological responses measured exhibited a highly significant and generally predictable correlation with tissue Cd concentration, which in turn, reflected environmentally realistic exposure conditions. Our results further confirm that the measurement of physiological responses is a sensitive method for assessing stress at environmentally realistic metal concentrations.

Combined use of chemical, biochemical and physiological variables in mussels for the assessment of marine pollution along the N-NW Spanish coast

This study undertakes an overall assessment of pollution in a large region (over 2500 km of coastline) of the N-NW Spanish coast, by combining the use of biochemical (AChE, GST, GPx) and physiological (SFG) responses to pollution, with chemical analyses in wild mussel populations (Mytilus galloprovincialis). The application of chemical analysis and biological techniques identified polluted sites and quantified the level of toxicity. High levels of pollutants were found in mussel populations located close to major cities and industrialized areas and, in general, average concentrations were higher in the Cantabrian than in the Iberian Atlantic coast. AChE activities ranged between 5.8 and 27.1 nmol/min/mg prot, showing inhibition in 12 sampling sites, according to available ecotoxicological criteria. GST activities ranged between 29.5 and 112.7 nmol/min/mg prot, and extreme variability was observed in GPx, showing activities between 2.6 and 64.5 nmol/min/mg prot. Regarding SFG, only 5 sites showed 'moderate stress' (SFG value below 20 J/g/h), and most sites presented a 'high potential growth' (>35 J/g/h) corresponding to a 'healthy state'. Multivariate statistical techniques applied to the chemical and biological data identified PCBs, organochlorine pesticides and BDEs as the main responsible of the observed toxicity. However, the alteration of biological responses caused by pollutants seems to be, in general, masked by biological variables, namely age and mussel condition, which have an effect on the mussels' response to pollutant exposure.

Impact assessment of agricultural inputs into a Mediterranean coastal lagoon (Mar Menor, SE Spain) on transplanted clams (Ruditapes decussatus) by biochemical and physiological responses

The Mar Menor is a coastal lagoon threatened by the development of intensive agriculture in the surrounding areas. Large amounts of pesticides from these areas are discharged into El Albujón, a permanent watercourse flowing into the lagoon. We have used a multi-biomarker approach to assess the biological effects of agricultural pollution on a bivalve species. Biomarkers indicative of neurotoxicity (acetylcholinesterase, AChE), oxidative stress (catalase, CAT; glutathione reductase, GR and lipid peroxidation, LPO), phase II biotransformation of xenobiotics (glutathione S-transferase, GST) and physiological stress (scope for growth, SFG) were measured in clams transplanted to four sites of the lagoon (two reference sites and two sites affected by the dispersion of the effluent of the El Albujón), for exposure periods of 7 and 22 days. The hazards of this effluent were also examined by simultaneously measuring up to 83 contaminants (pesticides, PCBs, PAHs and others) in samples of fresh water from the watercourse mouth and seawater from the deployed sites, as well as the bioaccumulation of organochlorinated compounds and PAHs in the transplanted animals. Biomarker responses showed marked differences between reference and affected sites after 7 and 22 days. However it was only after 22 days that principal component analysis (PCA) of the biomarker responses distinguished between clams deployed in sites affected by the dispersion of the effluent of the watercourse and those from the reference sites. The chemical analysis of water showed high concentrations of pesticides close to El Albujón watercourse mouth, with the greatest input flux corresponding to the organophosphate chlorpyrifos, followed by pendimethalin and naphthalene, and at lower levels acenaphthene, terbuthylazine-desethyl and chlorpyrifos-methyl. In this regard, PCA analysis showed that the biological effects of the mixture of pesticides in caged clams after 22 days were reduced levels of AchE and SFG and increased levels of GR and phase II GST activity. An integrated biomarker response index was calculated from the combination of these biomarkers, proving useful for the assessment of the impact of agricultural pollution in caged clams.