Relationship between bioenergetics responses and organic pollutants in the giant mussel, Choromytilus chorus (Mollusca: Mytilidae)

Transcriptome profiling of the early developmental stages in the giant mussel Choromytilus chorus exposed to delousing drugs

The giant mussel Choromytilus chorus is a marine bivalve commonly collected in central - southern Chile from fishery zones shared with the salmon industry. These economically relevant areas are also affected by the use of pesticides for controlling sea lice infestations in salmon aquaculture. Their main target is the sea louse Caligus rogercresseyi. However, other than some physiological impacts, the molecular effects of delousing drugs in non-target species such as C. chorus remain largely understudied. This study aimed to explore the transcriptome modulation of Trochophore and D larvae stages of C. chorus after exposure to azamethiphos and deltamethrin drugs. Herein, RNA-seq analyses and mRNA-lncRNAs molecular interactions were obtained. The most significant changes were found between different larval development stages exposed to delousing drugs. Notably, significant transcriptional variations were correlated with the drug concentrations tested. The biological processes involved in the development, such as cell movement and transcriptional activity, were mainly affected. Long non-coding RNAs (lncRNAs) were also identified in this species, and the transcription activity showed similar patterns with coding mRNAs. Most of the significantly expressed lncRNAs were associated with genes annotated to matrix metalloproteinases, collagenases, and transcription factors. This study suggests that exposure to azamethiphos or deltamethrin drugs can modulate the transcriptome signatures related to the early development of the giant mussel C. chorus.

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.

ZnO nanoparticles alter redox metabolism of Limnoperna fortunei

Nanoparticles such as zinc oxide nanoparticles (ZnO-NP) that are incorporated in consumer and industrial products have caused concern about their potential ecotoxicological impact when released into the environment. Bivalve mollusks are susceptible targets for nanoparticle toxicity since nanomaterials can enter the cells by endocytosis mechanisms. The aim of this study was to evaluate the influence of ZnO-NP on the redox metabolism in Limnoperna fortunei and the DNA damage after exposure to ZnO-NP. Adult bivalves were incubated with 1-, 10-, and 50-μg mL^-1 ZnO-NP for 2, 4, and 24 h. Ionic Zn release, enzymatic and non-enzymatic antioxidant activity, oxidative damage, and DNA damage were evaluated. Oxidative damage to proteins and lipids were observed after 4-h exposure and returned to baseline levels after 24 h. Superoxide dismutase levels decreased after 4-h exposure and increased after 24 h. No significant alteration was observed in the catalase activity or even DNA double-strand cleavage. The dissociation of ZnO may occur after 24 h, releasing ionic zinc (Zn²⁺) by hydrolysis, which was confirmed by the increase in the ionic Zn concentration following 24-h exposure. In conclusion, ZnO-NP were able to induce oxidative stress in exposed golden mussels. The golden mussel can modulate its own antioxidant defenses in response to oxidative stress and seems to be able to hydrolyze the nanoparticles and consequently, release Zn²⁺ into the cellular compartment.

Minimal impact at current environmental concentrations of microplastics on energy balance and physiological rates of the giant mussel Choromytilus chorus

Microplastic particles (MP) uptake by marine organisms is a phenomenon of global concern. Nevertheless, there is scarce evidence about the impacts of MP on the energy balance of marine invertebrates. We evaluated the mid-term effect of the microplastic ingestion at the current higher environmental concentrations in the ocean on the energy balance of the giant mussel Choromytilus chorus. We exposed juvenile mussels to three concentrations of microplastics (0, 100, and 1000 particles L^-1) and evaluated the effect on physiology after 40 days. The impacts of MP on the ecophysiological traits of the mussels were minimum at all the studied concentrations. At intermediate concentrations of MP, Scope for Growth (SFG) had little impact. Other relevant key life-history and physiological processes, such as size and metabolism, were not affected by microplastics. However, individuals treated with MP presented histopathological differences compared to control group, which could result in adverse health effects for mussels.

Metabolomics approach reveals disruption of metabolic pathways in the marine bivalve Mytilus galloprovincialis exposed to a WWTP effluent extract

Conventional wastewater treatment plants (WWTPs) discharge a highly diverse range of organic contaminants in aquatic environments, including marine waters. The health of marine ecosystems could be threatened by contaminants release. Environmental metabolomics can be helpful to assess the effects of multi-contamination on marine organisms without any a priori information since it is able to provide meaningful information on the biochemical response of organisms to a stress. The aim of the present study was to evaluate the potential of metabolomics to highlight key metabolites disrupted by a WWTP effluent extract exposure and then elucidate the biological effects of such exposure on Mediterranean mussels (Mytilus galloprovincialis). Exposed male mussels showed numerous metabolites altered in response to WWTP effluent exposure. The highlighted metabolites belong mainly to amino acids metabolism (e.g. tyrosine, phenylalanine, leucine, proline, etc.), neurohormones (dopamine and a serotonin metabolite), purine and pyrimidine metabolism (e.g. adenosine, adenine, guanine, uracil etc.), citric acid cycle intermediates (e.g. malate, fumarate), and a component involved in oxidative stress defense (oxidized glutathione). Modulation of these metabolites could reflect the alteration of several biological processes such as energy metabolism, DNA and RNA synthesis, immune system, osmoregulation, byssus formation and reproduction, which may lead to a negative impact of organism fitness. Our study provided further insight into the effects of WWTP effluents on marine organisms.

Incidence of morphometry variation, growth alteration, and reproduction performance of the annular sea bream (Diplodus annularis) as effective tools to assess marine contamination: how useful is a multi-biotimarkers approach?

A wide variety of contaminants in the aquatic environment causes several deleterious effects on aquatic organism traits ranging from molecular to individual and population levels. This in situ study investigated morphometry, growth performance, and reproduction success of a teleost fish, Diplodus annularis, from a polluted site "Sayada" and a reference site "Salakta" in the eastern Tunisian coastline. Morphometric indexes, generalized Procruste analysis, thin plate, and otolith contour methods were used to assess the pollution effects on morphological traits. The growth performance of fish from contaminated and control sites were studied using the Von Bertalanffy equation. Gonadosomatic (GSI) and Hepatosomatic (HSI) Indexes and absolute and relative fecundity were used to assess the impact of pollution on the reproduction success of this species. The obtained results showed that the fish of the contaminated zone had significant alteration of the morphology, slower growth, significant increase in the HSI, significant decrease in female GSI, and a decrease in absolute and relative fecundity compared to specimens from the unpolluted zone. Based on these results, the biological traits of Diplodus annularis can be used as biological biomarkers in the monitoring and protection programs of the marine contamination in the Mediterranean Sea.

Burrowing behavior and burrowing energetics of a bioindicator under human disturbance

Bioindicator species are extensively used for rapid assessment of ecological changes. Their use commonly focuses on changes in population abundance and individual sizes in response to environmental change. These numerical and demographic shifts likely have behavioral and physiological mechanistic drivers that, if understood, could provide additional insights into the use of these species as bioindicators of habitat health.The Atlantic ghost crab, Ocypode quadrata, is a global bioindicator species of human disturbance on sandy shores. Individual size and population abundance of O. quadrata decline dramatically at sites with human disturbance, and the causes of this phenomenon remain unclear.Here, we test the hypothesis that individual and population-level changes at disturbed sites reflect changes in burrowing behavior and energetics. Specifically, we examine whether or not the burrowing behavior (e.g., burrow fidelity and longevity) of O. quadrata changes because of human disturbance. We also examine energy required for burrowing by O. quadrata across different levels of human disturbance.We show that O. quadrata have the highest burrow fidelity and longevity at sites with low level of human impact, and weakest burrow fidelity and longevity at pristine sites. O. quadrata reduce the burrowing energy allocation by manipulating the burrow dimension and increasing the burrow longevity even under low levels of human disturbance.Overall, this study shows that human disturbances not only change the behavior of organisms, but also shift energetic balance. Our results support the use of a bioenergetic approach to better understand how human disturbances influence natural populations, and the specific use of this approach with this bioindicator species.

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.

Interactions between oil-spill pollutants and natural stressors can compound ecotoxicological effects

Coastal estuaries are among the most biologically productive habitats on earth, yet are at risk from human activities including marine oil spills. The 2010 Deepwater Horizon oil spill contaminated hundreds of kilometers of coastal habitat, particularly in Louisiana's delta. Coastal estuaries are naturally dynamic habitats where periodic and stochastic fluctuations, for example in temperature, salinity, nutrients, and hypoxia, are common. Such environmental variability regularly imposes suboptimal conditions for which resident species must continually compensate by drawing on diverse physiological abilities. However, exposures to oil, in addition to their direct toxic effects, may interfere with functions that normally enable physiological compensation for suboptimal conditions. This review summarizes the panoply of naturally-encountered stressors that may interact with oil, including salinity, hypoxia, pathogens, and competition, and the mechanisms that may underlie these interactions. Combined effects of these stressors can amplify the costs of oil-exposures to organisms in the real world, and contribute to impacts on fitness, populations, and communities, that may not have been predicted from direct toxicity of hydrocarbons alone. These interactions pose challenges for accurate and realistic assessment of risks and of actual damage. To meet these challenges, environmental scientists and managers must capitalize on the latest understanding of the complexities of chemical effects of natural stressors on organisms, and adopt integrative and holistic measures of effect from the molecular to whole-animal levels, in order to anticipate, characterize, diagnose, and solve, ecotoxicological problems.

Impact of medium-term exposure to elevated pCO(2) levels on the physiological energetics of the mussel Mytilus chilensis

This study evaluated the impact of medium-term exposure to elevated pCO(2) levels (750-1200 ppm) on the physiological processes of juvenile Mytilus chilensis mussels over a period of 70 d in a mesocosm system. Three equilibration tanks filled with filtered seawater were adjusted to three pCO(2) levels: ~380 (control), ~750 and ~1200 ppm by bubbling air or an air-CO(2) mixture through the water. For the control, atmospheric air (with aprox. 380 ppm CO(2)) was bubbled into the tank; for the 750 and 1200 ppm treatments, dry air and pure CO(2) were blended to each target concentration using mass flow controllers for air and CO(2). No impact on feeding activity was observed at the beginning of the experiment, but a significant reduction in clearance rate was observed after 35 d of exposure to highly acidified seawater. Absorption rate and absorption efficiency were reduced at high pCO(2) levels. In addition, oxygen uptake fell significantly under these conditions, indicating a metabolic depression. These physiological responses of the mussels resulted in a significant reduction of energy available for growth (scope for growth) with important consequences for the aquaculture of this species during medium-term exposure to acid conditions. The results of this study clearly indicate that high pCO(2) levels in the seawater have a negative effect on the health of M. chilensis. Therefore, the predicted acidification of seawater associated with global climate change could be harmful to this ecologically and commercially important mussel.

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

SFG and physiological rates were measured in wild mussels from the Spanish Marine Pollution monitoring program (SMP) in order to determine seawater quality. It consists of 41 stations, covering almost 2500 km of coast, making the SMP the widest-ranging monitoring network in the Iberian Peninsula's Atlantic region. Results of the 2007 and 2008 surveys when 39 sites were sampled: (20 in 2007 and 19 in 2008, being 8 sites sampled both years) were presented. Chemical analyses were carried out to determine the relationships between physiological rates and the accumulation of toxic compounds. Data presented are the first to become available on the use of SFG as a biomarker of the marine environment on a large spatial scale (>1000 km) along Spain's Atlantic seaboard. SFG values enable significant differences to be established between the areas sampled and between the two years surveyed. The integration of biological and chemical data suggests that certain organochlorine compounds, namely chlordanes and DDTs, may have a negative effect on SFG, although such an effect is of a lesser magnitude than that associated with certain biological parameters such as condition index and mussel age. These variables act as confounding factors when attempting to determine the effect of chemical compounds present in the marine environment on mussel SFG. Further research is therefore needed on the relation between these confounding factors and SFG in order to apply the relevant corrective strategies to enable this index to be used in monitoring programs. The effect of these confounding factors is more clearly revealed in studies that cover a wide-ranging spatial and time scale, such as those carried out within the SMP. These results do not invalidate the use of biological data in monitoring programs, but rather point to the need to analyze all the factors affecting each biological process.

Energy homeostasis as an integrative tool for assessing limits of environmental stress tolerance in aquatic invertebrates

Energy balance is a fundamental requirement of stress adaptation and tolerance. We explore the links between metabolism, energy balance and stress tolerance using aquatic invertebrates as an example and demonstrate that using key parameters of energy balance (aerobic scope for growth, reproduction and activity; tissue energy status; metabolic rate depression; and compensatory onset of anaerobiosis) can assist in integrating the effects of multiple stressors and their interactions and in predicting the whole-organism and population-level consequences of environmental stress. We argue that limitations of both the amount of available energy and the rates of its acquisition and metabolic conversions result in trade-offs between basal maintenance of a stressed organism and energy costs of fitness-related functions such as reproduction, development and growth and can set limit to the tolerance of a broad range of environmental stressors. The degree of stress-induced disturbance of energy balance delineates transition from moderate stress compatible with population persistence (pejus range) to extreme stress where only time-limited existence is possible (pessimum range). It also determines the predominant adaptive strategy of metabolic responses (energy compensation vs. conservation) that allows an organism to survive the disturbance. We propose that energy-related biomarkers can be used to determine the conditions when these metabolic transitions occur and thus predict ecological consequences of stress exposures. Bioenergetic considerations can also provide common denominator for integrating stress responses and predicting tolerance limits under the environmentally realistic scenarios when multiple and often variable stressors act simultaneously on an organism. Determination of bioenergetic sustainability at the organism's level (or lack thereof) has practical implications. It can help identify the habitats and/or conditions where a population can survive (even if at the cost of reduced reproduction and growth) and those that are incapable of supporting viable populations. Such an approach will assist in explaining and predicting the species' distribution limits in the face of the environmental change and informing the conservation efforts and resource management practices.

Novel control and steady-state correction method for standard 28-day bioaccumulation tests using Nereis virens

Evaluation of dredged material for aquatic placement requires assessment of bioaccumulation potentials for benthic organisms using standardized laboratory bioaccumulation tests. Critical to the interpretation of these data is the assessment of steady state for bioaccumulated residues needed to generate biota sediment accumulation factors (BSAFs) and to address control correction of day 0 contaminant residues measured in bioassay organisms. This study applied a novel performance reference compound approach with a pulse-chase experimental design to investigate elimination of a series of isotopically labeled polychlorinated biphenyl ((13)C-PCBs) in the polychaete worm Nereis virens while simultaneously evaluating native PCB bioaccumulation from field-collected sediments. Results demonstrated that all (13)C-PCBs, with the exception of (13)C-PCB209 (> 80%), were eliminated by more than 90% after 28 d. The three sediment types yielded similar (13)C-PCB whole-body elimination rate constants (k(tot)) producing the following predictive equation: log k(tot)  =  - 0.09 × log K(OW)  - 0.45. The rapid loss of (13)C-PCBs from worms over the bioassay period indicated that control correction, by subtracting day 0 residues, would result in underestimates of bioavailable sediment residues. Significant uptake of native PCBs was observed only in the most contaminated sediment and proceeded according to kinetic model predictions with steady-state BSAFs ranging from 1 to 3 and peaking for congeners of log K(OW) between 6.2 and 6.5. The performance reference compound approach can provide novel information about chemical toxicokinetics and also serve as a quality check for the physiological performance of the bioassay organism during standardized bioaccumulation testing.

Integrated assessment of water quality of the Costa da Morte (Galicia, NW Spain) by means of mussel chemical, biochemical and physiological parameters

The aim of this study was to assess environmental quality at some of the sites most severely affected by the Prestige oil spill off 2 years after the spillage (April and November 2004). For this purpose analyses of polycyclic aromatic hydrocarbons (PAH) and several biochemical (antioxidant enzymes catalase, glutathione reductase, glutathione peroxidase, superoxide dismutase and DT-diaphorase and lipid peroxidation) and physiological [scope for growth (SFG)] biomarkers were determined on wild mussel populations (Mytilus galloprovincialis) collected at four points along the Costa da Morte and compared with those of a reference site not affected by the oil spill. Results showed that PAH contents had markedly decreased 17 months after the accident, although they were higher in April than in November, when they showed values similar to background levels reported for this area. Nevertheless, the predominance of chrysene on PAH profiles, similarly to findings obtained immediately after the spill, indicated the Prestige as their main source. In spite of the low PAH levels recorded, antioxidant activity levels (explained through the integrated antioxidant response-IAR) were higher in the Costa da Morte than at the reference site either in April and November. In April IAR seems to be related to PAH levels found 3 months after the accident (February 2003), suggesting the persistence in the environment of oxidative stress-producing components from the spill. However, evidence of oxidative stress was not reflected at physiological level by scope for growth, with only very slight differences being observed between values from the reference site and those from Costa da Morte sites. In conclusion, although 2 years after the spill PAHs bioaccumulated by mussels from the Costa da Morte had decreased to background levels, biochemical parameters showed signals of oxidative stress in mussels from this area. However, SFG reflected a good health status for the mussel populations studied and did not reveal evidence of physiological disturbance either 17 or 24 months after the Prestige spill.

Dynamic exposure of organisms and passive samplers to hydrophobic chemicals

An insight into the dynamic aspects of the accumulation process is essential for understanding bioaccumulation as well as effect studies of hydrophobic organic chemicals. This review presents an overview of kinetic studies with organisms (fish, bivalve, crustacean, insect, worm, algae, and protozoan) as well as passive samplers (solid and liquid phase microextraction, semipermeable membrane device, polymer sheet, solid-phase extraction, Chemcatcher, etc.) for the uptake of neutral nonpolar chemicals from the aqueous phase. Information about uptake rates, elimination rates, and 95% equilibration times was collected and analyzed with diffusion based models. The present literature review suggests that the surface to volume ratio appears to be a critical parameter for the uptake rate of the more hydrophobic chemicals both for samplers and organisms. In addition, as a very first approximation, the combination of the first-order kinetic model with the assumption that diffusion through the aqueous boundary layers is rate limiting, gives a reasonable description of the experimental kinetic data. In this way, the presented model might be used to estimate uptake and elimination rate constants of chemicals by organisms or passive samplers.

Bioenergetic responses in green lipped mussels (Perna viridis) as indicators of pollution stress in Xiamen coastal waters, China

Samples of green lipped mussels (Perna viridis) were collected from three sites (Huoshao, I'Maluan and Tong'an) around Xiamen coastal waters, where levels of various trace organic pollutants have been studied. Samples were also collected at a "cleaner" reference site near Dongshan Island for comparison. Clearance rate, absorption efficiency and oxygen consumption of the mussels were measured under controlled laboratory condition; organic pollutants in their tissues were also analyzed. Scope for growth (SFG) was employed as a general biomarker to evaluate the stress of pollutants. Specimens from Tong'an site had the lowest SFG values (1.14 J/h/g); while specimens from the I'Maluan site and Huoshao site had SFG values of 5.01 and 6.72 J/h/g, respectively. Specimens from Dongshan (reference site) had a relatively high SFG value of 10.96 J/h/g. There was a significant negative correlation between the SFG of the different populations of green lipped mussels and the concentration of DDT in their tissues.