High sensitivity of embryo-larval stage of the Mediterranean mussel, Mytilus galloprovincialis to metal pollution in combination with temperature increase

Transcriptomic profiling of the thermal tolerance in two subspecies of the bay scallop Argopecten irradians

The bay scallop is a eurythermal species with high economic value and now represents the most cultured bivalve species in China. Two subspecies of the bay scallop, the northern subspecies Argopecten irradians irradians Korean population (KK) and the southern subspecies Argopecten irradians concentricus (MM), exhibited distinct adaptations to heat stress. However, the molecular mechanism of heat resistance of the two subspecies remains unclear. In this study, we compared the transcriptomic responses of the two subspecies to heat stress and identified the involved differentially expressed genes (DEGs) and pathways. More DEGs were found in the KK than in the MM when exposed to high temperatures, indicating elevated sensitivity to thermal stress in the KK. Enrichment analysis suggests that KK scallops may respond to heat stress more swiftly by regulating GTPase activity. Meanwhile, MM scallops exhibited higher resistance to heat stress mainly by effective activation of their antioxidant system. Chaperone proteins may play different roles in responses to heat stress in the two subspecies. In both subspecies, the expression levels of antioxidants such as GST were significantly increased; the glycolysis process regulated by PC and PCK1 was greatly intensified; and both apoptotic and anti-apoptotic systems were significantly activated. The pathways related to protein translation and hydrolysis, oxidoreductase activity, organic acid metabolism, and cell apoptosis may also play pivotal roles in the responses to heat stress. The results of this study may provide a theoretical basis for marker-assisted breeding of heat-resistant strains.

Comparative study of integrated bio-responses in deep-sea and nearshore mussels upon abiotic condition changes: Insight into distinct regulation and adaptation

Deep-sea mussels, one of the dominant species in most deep-sea ecosystems, have long been used as model organisms to investigate the adaptations and symbiotic relationships of deep-sea macrofauna under laboratory conditions due to their ability to survive under atmospheric pressure. However, the impact of additional abiotic conditions beyond pressure, such as temperature and light, on their physiological characteristics remains unknown. In this study, deep-sea mussels (Gigantidas platifrons) from cold seep of the South China Sea, along with nearshore mussels (Mytilus coruscus) from the East China Sea, were reared in unfavorable abiotic conditions for up to 8 days. Integrated biochemical indexes including antioxidant defense, immune ability and energy metabolism were investigated in the gill and digestive gland, while cytotoxicity was determined in hemocytes of both types of mussels. The results revealed mild bio-responses in two types of mussels in the laboratory, represented by the effective antioxidant defense with constant total antioxidant capability level and malondialdehyde content. There were also disparate adaptations in deep-sea and nearshore mussels. In deep-sea mussels, significantly increased immune response and energy reservation were observed in gills, together with the elevated cytotoxicity in hemocytes, implying the more severe biological adaptation was required, mainly due to the symbiotic bacteria loss under laboratory conditions. On the contrary, insignificant biological responses were exhibited in nearshore mussels except for the increased energy consumption, indicating the trade-off strategy to use more energy to deal with potential stress. Overall, this comparative study highlights the basal bio-responses of deep-sea and nearshore mussels out of their native environments, providing evidence that short-term culture of both mussels under easily achievable laboratory conditions would not dramatically alter their biological status. This finding will assist in broadening the application of deep-sea mussels as model organism in future research regardless of the specialized research equipment.

Unraveling the interplay between environmental microplastics and salinity stress on Mytilus galloprovincialis larval development: A holistic exploration

The rise of plastic production has triggered a surge in plastic waste, overwhelming marine ecosystems with microplastics. The effects of climate change, notably changing salinity, have shaped the dynamics of coastal lagoons. Thus, understanding the combined impact of these phenomena on marine organisms becomes increasingly crucial. To address these knowledge gaps, we investigated for the first time the interactive effects of environmental microplastics (EMPs) and increased salinity on the early development of Mytilus galloprovincialis larvae. Morphological assessments using the larval embryotoxicity test revealed larval anomalies and developmental arrests induced by EMPs and increased salinity. Transcriptomic analyses targeting 12 genes involved in oxidative stress, apoptosis, DNA repair, shell formation, and stress proteins were conducted on D-larvae uncovered the potential effects of EMPs on shell biomineralization, highlighting the role of Histidine Rich Glycoproteine (HRG) and tubulin as crucial adaptive mechanisms in Mytilus sp. in response to environmental shifts. Furthermore, we explored oxidative stress and neurotoxicity using biochemical assays. Our findings revealed a potential interaction between EMPs and increased salinity, impacting multiple physiological processes in mussel larvae. Our data contribute to understanding the cumulative effects of emerging anthropogenic pollutants and environmental stressors, emphasizing the need for a holistic approach to assessing their impact on marine ecosystems.

Do the individual and population-level traits of Donax trunculus reflect the effects of metal contamination in aquatic environments?

Heavy metals are considered a major threat to aquatic ecosystems, due to their ability to penetrate and accumulate through the food chain, putting marine organisms and the ecosystem at risk. This research presents a case study of the Taghazout coast, located in the central Atlantic of Morocco, which has become the focal point of various development projects, including the Taghazout Bay tourist resort. The study aimed to gain a deeper understanding of the harmful effects of these metals on the reproductive cycle and population dynamics of the bivalve Donax trunculus. The assessment of cadmium (Cd), lead (Pb), and copper (Cu) levels in D. trunculus bivalves and sediment at the research location provides evidence of exposure to these metal sources by these bivalves. The analysis of the reproductive cycle revealed a balanced sex ratio of males to females. The Sexual Maturity Index (SMI) and Condition Index (CI) of the bivalves were found to be significantly influenced by trace elements Pb and Cu, as well as environmental factors like temperature, dissolved oxygen, and salinity. The maturity stages of the gonads were classified into five stages: undifferentiated, developing, mature, spawning, and spent. Two spawning periods were observed aligning with the population dynamics study that identified a bimodal recruitment (early autumn and spring) in D. trunculus. The population was found to have 11 size cohorts, with a maximum length of 37.96 cm, a yearly growth rate of 1.93 cm, and a short lifespan of 1.5 years. The high mortality rate of 3.30 per year was attributed to the presence of trace elements in Taghazout coast. These findings shed light on heavy metal's impact on the population of D. trunculus, revealing that a sole emphasis on its physiological or cellular effects may overlook its larger impact.

Effects of Inorganic and Organic Pollutants on the Biomarkers' Response of Cerastoderma edule under Temperature Scenarios

Currently, there is increased chemical pollution, and climate change is a major concern to scientific, political and social communities globally. Marine systems are very susceptible to changes, and considering the ecological and economic roles of bivalve species, like Cerastoderma edule, studies evaluating the effects of both stressors are of great importance. This study intends to (a) determine the toxicity of copper (Cu) and oxyfluorfen at the lethal level, considering the temperature; (b) assess the changes in the antioxidant defence enzymes as a consequence of the simultaneous exposure to chemical and warming pressures; and (c) determine if lipid peroxidation (LPO) and neurotoxic effects occur after the exposure to chemical and temperature stressors. C. edule was exposed to Cu and oxyfluorfen at different temperatures (15 °C, 20 °C and 25 °C) for 96 h. The ecotoxicological results reveal a higher tolerance of C. edule to oxyfluorfen than to Cu, regardless of the temperature. The antioxidant defence system revealed efficiency in fighting the chemicals' action, with no significant changes in the thiobarbituric reactive species (TBARS) levels to 15 °C and 20 °C. However, a significant inhibition of acetylcholinesterase (AChE) was observed on the organisms exposed to oxyfluorfen at 20 °C, as well as a decreasing trend on the ones exposed to Cu at this temperature. Moreover, the catalase (CAT) showed a significant increase in the organisms exposed to the two highest concentrations of Cu at 15 °C and in the ones exposed to the highest concentration of oxyfluorfen at 20 °C. Looking at the temperature as a single stressor, the organisms exposed to 25 °C revealed a significant increase in the TBARS level, suggesting potential LPO and explaining the great mortality at this condition.

Hot and heavy: Responses of ragworms (Hediste diversicolor) to copper-spiked sediments and elevated temperature

Sediment contamination and seawater warming are two major stressors to macrobenthos in estuaries. However, little is known about their combined effects on infaunal organisms. Here we investigated the responses of an estuarine polychaete Hediste diversicolor to metal-contaminated sediment and increased temperature. Ragworms were exposed to sediments spiked with 10 and 20 mg kg^-1 of copper at 12 and 20 °C for three weeks. No considerable changes were observed in the expression of genes related to copper homeostasis and in the accumulation of oxidative stress damage. Dicarbonyl stress was attenuated by warming exposure. Whole-body energy reserves in the form of carbohydrates, lipids and proteins were little affected, but the energy consumption rate increased with copper exposure and elevated temperature indicating higher basal maintenance costs of ragworms. The combined effects of copper and warming exposures were mostly additive, with copper being a weak stressor and warming a more potent stressor. These results were replicable, as confirmed by two independent experiments of similar settings conducted at two different months of the year. This study suggests the higher sensitivity of energy-related biomarkers and the need to search for more conserved molecular markers of metal exposure in H. diversicolor.

Shellfish-algal systems as important components of fisheries carbon sinks: Their contribution and response to climate change

In the context of global climate change, ocean acidification and warming are becoming increasingly serious. Adding carbon sinks in the ocean is an important part of efforts to mitigate climate change. Many researchers have proposed the concept of a fisheries carbon sink. Shellfish-algal systems are among the most important components of fisheries carbon sinks, but there has been limited research on the impact of climate change on shellfish-algal carbon sequestration systems. This review assesses the impact of global climate change on shellfish-algal carbon sequestration systems and provides a rough estimate of the global shellfish-algal carbon sink capacity. This review evaluates the impact of global climate change on shellfish-algal carbon sequestration systems. We review relevant studies that have examined the effects of climate change on such systems from multiple levels, perspectives, and species. There is an urgent need for more realistic and comprehensive studies given expectations about the future climate. Such studies should provide a better understanding of the mechanisms by which the carbon cycle function of marine biological carbon pumps may be affected in realistic future environmental conditions and the patterns of interaction between climate change and ocean carbon sinks.

Impacts of exhaust gas cleaning systems (EGCS) discharge waters on planktonic biological indicators

Exhaust Gas Cleaning Systems (EGCS), operating in open-loop mode, continuously release acidic effluents (scrubber waters) to marine waters. Furthermore, scrubber waters contain high concentrations of metals, polycyclic aromatic hydrocarbons (PAHs), and alkylated PAHs, potentially affecting the plankton in the receiving waters. Toxicity tests evidenced significant impairments in planktonic indicators after acute, early-life stage, and long-term exposures to scrubber water produced by a vessel operating with high sulphur fuel. Acute effects on bacterial bioluminescence (Aliivibrio fischeri), algal growth (Phaeodactylum tricornutum, Dunaliella tertiolecta), and copepod survival (Acartia tonsa) were evident at 10 % and 20 % scrubber water, while larval development in mussels (Mytilus galloprovincialis) showed a 50 % reduction at ∼5 % scrubber water. Conversely, larval development and reproductive success of A. tonsa were severely affected at scrubber water concentrations ≤1.1 %, indicating the risk of severe impacts on copepod populations which in turn may result in impairment of the whole food web.

Can temperature influence the impacts induced in Mytilus galloprovincialis by neodymium? Comparison between exposure and recovery periods

Climate change-associated factors and pollutants, such as rare earth elements (REEs), have been identified as contributors to environmental changes. However, the toxicity resulting from the combination of these stressors has received little attention. Neodymium (Nd) is a REE that has been widely used, and this study aimed to evaluate the responses of Mytilus galloprovincialis to Nd exposure (10 µg/L), under actual (17 °C) and predicted warming conditions (21 °C), after fourteen days of exposure followed by fourteen days of recovery (without Nd), analyzing Nd accumulation, histopathological and biochemical alterations. The results showed that increased temperature and Nd exposure caused histopathological injuries in the gills. Contaminated mussels at 17 °C showed cellular damage, while at 21 °C, mussels were able to avoid cellular damage. After the recovery period, no improvements in gill's status were found and cellular damage was still present, highlighting the impacts caused by previous exposure to Nd.

The effect of ocean warming on accumulation and cellular responsiveness to cobalt in Mytilus galloprovincialis

Cobalt (Co) is among the hazardous substances identified in aquatic environments. Industrialization and population growth have also contributed to climate change, namely in what concerns ocean temperature rise. The aim of the present study was to evaluate the influence of temperature rise on the impacts caused by Co on Mytilus galloprovincialis. To this end, mussels were exposed for 28 days to 17 °C and 21 °C, without and with 200 μg L^-1 of Co. Results showed no significant differences in Co bioaccumulation by the organisms between temperatures. A significant interaction between temperature and Co contamination was observed in terms of oxidative damage, detoxification capacity, and neurotoxicity, with a synergistic effect particularly evident in terms of biotransformation enzymes' activity. The obtained results point out that population survival and distribution may be limited in the long term, highlighting the need for future research on the combined effects of both stressors.

Metal contamination and heat stress impair swimming behavior and acetylcholinesterase activity in embryo-larval stages of the Mediterranean mussel, Mytilus galloprovincialis

Behavioral parameters are increasingly considered sensitive and early bioindicators of toxicity in aquatic organisms. A video-tracking tool was specifically developed to monitor the swimming behaviour of D-larvae of the Mediterranean mussel, Mytilus galloprovincialis, in controlled laboratory conditions. Both maximum and average swimming speeds and trajectories were recorded. We then investigated the impact of copper and silver with or without a moderate rise of temperature on swimming behavior and acetylcholinesterase (AChE) activity of mussel D-larvae and the possible mechanistic link between both biological responses. Our results showed that copper and/or silver exposure, as well as temperature increase, disrupts the swimming behavior of mussel larvae which could compromise their dispersal and survival. In addition, the combined effect of temperature and metals significantly (p < 0.05) increased AChE activity in mussel larvae. Pearson's correlation analysis was performed and results showed that the AChE activity is positively correlated with maximum speeds (r = 0.71, p < 0.01). This study demonstrates the value of behavioral analyzes of aquatic invertebrates as a sensitive and integrate marker of the effects of stressors.

Increasing arsenic accumulation as an implication of climate change: a case study using red algae

Climate change due to an increasing concentration of carbon dioxide in the atmosphere is a global issue. It can impact aquatic environments by affecting water flow, pollutant transformation and migration, and other toxicant-related effects. We assessed the interactive effects of temperature warming and pH changes on variations in accumulation of total arsenic (As_T) in the red alga Sarcodia suae at different levels of arsenite (As_III). Result showed that As_T variations in the alga were moderated by significant joint effects of warming temperature and/or increasing pH levels and their interactions with increasing As_III concentrations. Our study suggests possible deleterious impacts on macroalgal populations due to toxicological effects associated with prevailing environmental conditions. Therefore, improved pollution management, climate change adaptation, and mitigation strategies are needed to deal with current environmental issues and As aggravation.

Rehabilitation of Mytilus edulis larvae abnormalities induced by K2Cr2O7 in short-term experiments

Mytilus edulis embryo-larval development is often used as a bioassay to evaluate the negative impact of contaminants and environmental conditions. The toxicity criteria used in most protocols is the proportions of normal and abnormal larvae. The variety of abnormalities were described and classified, but further development of abnormal larvae remains obscure. This study aimed to reveal the possibility of correction of the morphological abnormalities after short-term exposure (48 h) in a variety of K₂Cr₂O₇ concentrations. For this purpose, abnormal larvae, which developed under the negative influence of the series of K₂Cr₂O₇ concentrations were transferred into clean seawater and studied after further 24 and 48 h. The obtained data, concerning changes in larval morphology, growth and survival rates during washing show that the abnormal larvae have enough capability to recover the normal D-shell structure. Moreover, restoration of the D-shell is possible even after exposure with concentration of the toxicant higher than the average effective one. The present research also pointed out that the development of larval shell (even abnormal one) is positively correlated with ability of the larvae to reconstruct D-shell and their survival rate. High mortality during washing occurs only at toxicant concentrations when no shell was formed within 48 h. Thus, the existence of the shell after 48 h exposure in the toxicant could indicate reversibility of the negative impact and help to distinguish the delay in development from its arrest.

Natural distribution of pure and hybrid Mytilus sp. along the south Mediterranean and North-east Atlantic coasts and sensitivity of D-larvae stages to temperature increases and metal pollution

The distribution of the Mediterranean mussel Mytilus galloprovincialis extends more and more northwards in the Atlantic. Crossings are frequently observed with the blue mussel Mytilus edulis along the French and English coasts. The aim of this study is firstlyto identify the co-presence of M. galloprovincialis, M. edulis, and their hybrids in different sites of the Mediterranean and Atlantic coasts, and to provide insights for the thermal tolerance and toxicant susceptibility of Mytilus edulis, Mytilus galloprovincialis and their hybrids. Mussels were collected from the shore at 20 sampling sitesin Europe and Tunisia and identified using Me 15/16 primers targeting the adhesive protein gene sequence. Samples were screened for the presence of Mytilus edulis, Mytilus galloprovincialis, and hybrids alleles using PCR. To get more information on hybrids sensitivities to temperature and metals, freshly fertilized eggs of the two species and their hybrids were reared at four temperatures 18, 20, 22, and 24 °C and exposed to concentrations of Cu, Ag, and a mixture of both metals. Arrests of development and malformations were recorded after 48 h of exposure. The genotypic identification of the two species on 20 sites of the Mediterranean and Atlantic coasts carried out during this study confirms the presence of pure and hybrid species of mussel. Our results highlighted that hybrid larvae from a female of M. galloprovincialis are significantly more tolerant to temperature increases than pure larvae of M. galloprovincialis and pure and hybrid larvae of M. edulis. No significant interspecies-differences of sensitivity were noted for metal exposure alone. However, a co-exposure of larvae to both metal and high temperature highlighted the higher tolerance of hybrid larvae from a female of M. galloprovincialis to both stresses. The overall results could allow the prediction of the future evolution of mussel populations facing environmental changes.

Toxic impacts of rutile titanium dioxide in Mytilus galloprovincialis exposed to warming conditions

Climate change is leading to a gradual increase in the ocean temperature, which can cause physiological and biochemical impairments in aquatic organisms. Along with the environmental changes, the presence of emerging pollutants such as titanium dioxide (TiO₂) in marine coastal systems has also been a topic of concern, especially considering the interactive effects that both factors may present to inhabiting organisms. In the present study, it has been assessed the effects of the presence in water of particles of rutile, the most common polymorph of TiO₂, in Mytilus galloprovincialis, under actual and predicted warming conditions. Organisms were exposed to different concentrations of rutile (0, 5, 50, 100 μg/L) at control (18 ± 1.0 °C) and increased (22 ± 1.0 °C) temperatures. Histopathological and biochemical changes were evaluated in mussels after 28 days of exposure. Histopathological examination revealed similar alterations on mussels' gills and digestive glands with increasing rutile concentrations at both temperatures. Biochemical markers showed that contaminated mussels have an unchanged metabolic capacity at 18 °C, which increased at 22 °C. Although antioxidant defences were activated in contaminated organisms at 22 °C, cellular damage was still observed. Overall, our findings showed that histopathological impacts occurred after rutile exposure regardless of the temperature, while biochemical alterations were only significantly noticeable when temperature was enhanced to 22 °C. Thus, this study demonstrated that temperature rise may significantly enhance the sensitivity of bivalves towards emerging pollutants.

The Role of Temperature on the Impact of Remediated Water towards Marine Organisms

Marine organisms are frequently exposed to pollutants, including trace metals, derived from natural and anthropogenic activities. In order to prevent environmental pollution, different approaches have been applied to remove pollutants from waste water and avoid their discharge into aquatic systems. However, organisms in their natural aquatic environments are also exposed to physico-chemical changes derived from climate change-related factors, including temperature increase. According to recent studies, warming has a negative impact on marine wildlife, with known effects on organisms physiological and biochemical performance. Recently, a material based on graphene oxide (GO) functionalized with polyethyleneimine (PEI) proved to be effective in the remediation of mercury (Hg) contaminated water. Nevertheless, no information is available on the toxic impacts of such remediated water towards aquatic systems, neither under actual nor predicted temperature conditions. For this, the present study assessed the toxicity of seawater, previously contaminated with Hg and remediated by GO-PEI, using the clam species Ruditapes philippinarum exposed to actual and a predicted temperature conditions. The results obtained demonstrated that seawater contaminated with Hg and/or Hg+GO-PEI induced higher toxicity in clams exposed to 17 and 22 °C compared to organisms exposed to remediated seawater at the same temperatures. Moreover, similar histological and biochemical results were observed between organisms exposed to control and remediated seawater, independently of the temperatures (17 and 21 °C), highlighting the potential use of GO-PEI to remediate Hg from seawater without significant toxicity issues to the selected marine species.

Molecular mechanisms underlying the effects of temperature increase on Mytilus sp. and their hybrids at early larval stages

The present work aims to investigate the effects of water temperature increase on Mytilus galloprovincilis and Mytilus edulis pure larvae (PG, PE) and their hybrids (HFG, HFE). D-larvae were maintained at 18 °C or exposed to a higher temperature of 22 °C for 48 h. Initially, Embryotoxicity test was evaluated. Second, a transcriptomic analysis using a recently developed microarray platform was applied to determine the main biological processes involved in early life stages responses to temperature increase. Finally, an immunofluorescence investigation was performed to bridge the gap between transcriptomic regulation and the real changes at cellular/tissue levels. Embryotoxicity test revealed a higher sensitivity of M. edulis (PE) D-larvae as well as hybrids from females M. edulis (HFE) to temperature increase, with the highest rate of larval malformations. Transcriptomic results indicated a lack of an adequate heat shock protein (Hsp) response in PE and HFE larvae (the high expression was observed in PG larvae); the differential expression of gene involved in translation, energy metabolism and oxidative stress response may contribute to explain the observed complex alterations in the studied conditions. As revealed by immunohistochemistry, cytoskeleton proteins changes associated with a drastic decrease of Histidine-Rich Glycoprotein (HRG) may elucidate the larval abnormalities in shell development observed for PE and HFE larvae. Overall, the results indicate that each type of pure larva (PG and PE) and their respective female hybrid (HFG and HFE) react similarly to the temperature increase. Our data should be carefully considered in view of the water temperature increase in marine ecosystems and especially for the mussel's species in confluence zones.

Embryo bioassays with aquatic animals for toxicity testing and hazard assessment of emerging pollutants: A review

This review article gathers the available information on the use of embryo-tests as high-throughput tools for toxicity screening, hazard assessment and prioritization of new and existing chemical compounds. The approach is contextualized considering the new legal trends for animal experimentation, fostering the 3R policy, with reduction of experimental animals, addressing the potential of embryo-tests as high-throughput toxicity screening and prioritizing tools. Further, the current test guidelines, such as the ones provided by OECD and EPA, focus mainly in a limited number of animal lineages, particularly vertebrates and arthropods. To extrapolate hazard assessment to the ecosystem scale, a larger diversity of taxa should be tested. The use of new experimental animal models in toxicity testing, from a representative set of taxa, was thoroughly revised and discussed in this review. Here, we critically review current tools and the main advantages and drawbacks of different animal models and set researcher priorities.

Compared responses to copper and increased temperatures of hybrid and pure offspring of two mussel species

This study investigates the combined effects of increased temperatures and copper on the early live stages of the Mediterranean mussel Mytilus galloprovincialis and the blue mussel Mytilus edulis as well as their hybrids. For this purpose, developmental abnormalities was measured after 48 h of exposure as well as a battery of oxidative stress markers such as, antioxidant enzyme activities, lipid peroxidation measured as malondialdehyde accumulation (MDA) and metallothionein contents (MT) and related gene expression pattern. Embryotoxicity and metal accumulation in tissues of mussel larvae exposed to a sublethal concentration of copper (10 μg/L) along with a slight temperature increase from 18 °C to22 °C were significantly increased after 48 h of exposure. Co-exposure to Cu and elevated temperatures significantly increased the antioxidant enzyme activities termed as, glutathione-S-transferase (GST), catalase (CAT), superoxide dismutase (SOD) and being maintained at 22 °C only in pure M. galloprovincialis (PG) larvae and female galloprovincialis x male edulis hybrid larvae (HFG). A significant decrease in mRNA abundance of cat, sod, gst gene transcription levels was showed in the same species. Furthermore, metallothionein accumulation increased significantly in PG D-larvae exposed to copper at 22 °C. The same pattern was observed in term of gene expression of MTs cognates (mt-10 and mt-20). Significant increase of MDA levels in pure M. edulis (PE) larvae and their female M. edulis x male M. galloprovincialis hybrid larvae (HFE) combined with a low MTs content were observed. Overall, this study provides clues about the relatively higher resistance and resilience of M. galloprovincialis species compared to M. edulis species under environmental pollution and future climate change scenarios.

Synergistic Effects of Climate Change and Marine Pollution: An Overlooked Interaction in Coastal and Estuarine Areas

Coastal areas have been increasingly affected by human activities, marine pollution and climate change are among the most important pressures affecting these environments. Human-induced pressures occur in a cumulative way and generate additive, antagonistic or synergistic effects. Knowledge on synergistic effects is crucial to coastal zone management, since they may imply a change in human uses of these systems, as well as dedicated action plans in order to reduce hazards and environmental risks. In this work, we provide an overview of the available literature on synergistic effects between climate change and chemical pollution, and discuss current knowledge, methodological approaches, and research gaps and needs. Interactions between these two pressures may be climate change dominant (climate change leads to an increase in contaminant exposure or toxicity) or contaminant-dominant (chemical exposure leads to an increase in climate change susceptibility), but the mechanistic drivers of such processes are not well known. Results from a few meta-analyses studies and reviews showed that synergistic interactions tend to be more frequent compared to additive and antagonistic ones. However, most of the studies are individual-based and assess the cumulative effects of a few contaminants individually in laboratory settings together with few climate variables, particularly temperature and pH. Nevertheless, a wide diversity of contaminants have already been individually tested, spanning from metals, persistent organic pollutants and, more recently, emergent pollutants. Population and community based approaches are less frequent but have generated very interesting and more holistic perspectives. Methodological approaches are quite diverse, from laboratory studies to mesocosm and field studies, or based on statistical or modelling tools, each with their own potential and limitations. More holistic comparisons integrating several pressures and their combinations and a multitude of habitats, taxa, life-stages, among others, are needed, as well as insights from meta-analyses and systematic reviews.

Moderate temperature elevation increase susceptibility of early-life stage of the Mediterranean mussel, Mytilus galloprovincialis to metal-induced genotoxicity

The present study aims to evaluate the effects of copper and silver alone or along with a moderate temperature increase on embryonic development, DNA integrity and target gene expression levels in early life stages of Mytilus galloprovincialis. For this purpose, upon fertilized embryos were exposed to a sub-lethal concentration of Cu (9.54 μg/L), Ag (2.55 μg/L) and to the mixture of the two metals (Cu (6.67 μg/L) + Ag (1.47 μg/L)) along with a temperature gradient (18, 20 and 22 °C). In all experiments, larvae were exposed to stressors for 48 h except for those designed to DNA damage analysis exposed only for 24 h (before shell formation).Our results showed a significant increase in the percentage of malformed D-larvae (p < 0.05) with increasing temperature and exposure to silver and copper alone or in a mixture. Moreover, metal toxicity increased significantly (p < 0.05) with the temperature rise. Genotoxicity was evaluated using classic and modified with Formamidopyrimidine DNA glycosylase (Fpg) Comet assay. Results suggest that co-exposure to metals and temperature significantly increased DNA damage on mussel larvae with a more accentuated oxidative damage. A significant transcription modulation was observed for genes involved in DNA repair and DNA replication (p53, DNA ligase II and topoisomerase II) when larvae are exposed to a single stressor. However, in the case of multiple stresses, caspase involved in the cell apoptosis pathway was overexpressed. Our study suggests that mussel larvae exposed to a moderate increase in temperature may have a compromised ability to defend against genotoxicity. This is particularly relevant in the context of global warming and thermal pollution.

High-frequency sampling and piecewise models reshape dispersal kernels of a common reef coral

Models of dispersal potential are required to predict connectivity between populations of sessile organisms. However, to date, such models do not allow for time-varying rates of acquisition and loss of competence to settle and metamorphose, and permit only a limited range of possible survivorship curves. We collect high-resolution observations of coral larval survival and metamorphosis, and apply a piecewise modeling approach that incorporates a broad range of temporally varying rates of mortality and loss of competence. Our analysis identified marked changes in competence loss and mortality rates, the timing of which implicates developmental failure and depletion of energy reserves. Asymmetric demographic rates suggest more intermediate-range dispersal, less local retention, and less long-distance dispersal than predicted by previously employed non-piecewise models. Because vital rates are likely temporally asymmetric, at least for nonfeeding broadcast-spawned larvae, piecewise analysis of demographic rates will likely yield more reliable predictions of dispersal potential.

The impacts of warming on the toxicity of carbon nanotubes in mussels

With the increased production and research on nanoparticles, the presence of carbon nanotubes (CNTs) in aquatic systems is very likely to increase. Although it has been shown that CNTs may cause toxicity in marine organisms, to our knowledge, the possible impacts under global temperature increase is still unknown. For this reason, biochemical and physiological impacts induced in Mytilus galloprovincialis due to the presence of functionalized multi-walled CNTs (f-MWCNTs) and increased temperature were investigated in the present study. The mussels exposed to increased temperature alone presented higher metabolic capacity and expenditure of glycogen as an energy resource to fuel up defense mechanisms and thus preventing oxidative damage. Contrarily, organisms exposed to f-MWCNTs alone seemed not stressed enough to demonstrate differences in the metabolism capacity. Furthermore, f-MWCNTs seemed not able to significantly activate their antioxidant and biotransformation enzymes, which in turn may led to oxidative damage in the cells especially when organisms were exposed to a warmer temperature. In fact, at higher temperature, the antioxidant response of organisms exposed to f-MWCNTs was not effective and oxidative damage levels were observed. Nevertheless, no additive or synergetic effects were observed when mussels were exposed to both stressors simultaneously.

Comparative sensitivity of Crassostrea angulata and Crassostrea gigas embryo-larval development to As under varying salinity and temperature

Oysters are a diverse group of marine bivalves that inhabit coastal systems of the world's oceans, providing a variety of ecosystem services, and represent a major socioeconomic resource. However, oyster reefs have become inevitably impacted from habitat destruction, overfishing, pollution and disease outbreaks that have pushed these structures to the break of extinction. In addition, the increased frequency of climate change related events promise to further challenge oyster species survival worldwide. Oysters' early embryonic development is likely the most vulnerable stage to climate change related stressors (e.g. salinity and temperature shifts) as well as to pollutants (e.g. arsenic), and therefore can represent the most important bottleneck that define populations' survival in a changing environment. In light of this, the present study aimed to assess two important oyster species, Crassostrea angulata and Crassostrea gigas embryo-larval development, under combinations of salinity (20, 26 and 33), temperature (20, 24 and 28 °C) and arsenic (As) exposure (0, 30, 60, 120, 240, 480, 960 and 1920 μg. As L^-1), to infer on different oyster species capacity to cope with these environmental stressors under the eminent threat of climate change and increase of pollution worldwide. Results showed differences in each species range of salinity and temperature for successful embryonic development. For C angulata, embryo-larval development was successful at a narrower range of both salinity and temperature, compared to C. gigas. Overall, As induced higher toxicity to C. angulata embryos, with calculated EC50 values at least an order of magnitude lower than those calculated for C. gigas. The toxicity of As (measured as median effective concentration, EC50) showed to be influenced by both salinity and temperature in both species. Nonetheless, salinity had a greater influence on embryos' sensitivity to As. This pattern was mostly noticed for C. gigas, with lower salinity inducing higher sensitivity to As. Results were discussed considering the existing literature and suggest that C. angulata populations are likely to become more vulnerable under near future predictions for temperature rise, salinity shifts and pollution.

Ranked effects of heavy metals on marine bivalves in laboratory mesocosms: A meta-analysis

Bivalves are commonly used as biomonitors for heavy metal pollution in marine environments because they accumulate heavy metal ions quickly, are sessile, abundant, and widely dispersed, and adult mortality from contamination is rare. However, the breadth of experiments used to measure the effect of heavy metal contamination can obscure general trends. It is unclear which heavy metals cause the most severe effects, how severity varies with exposure concentration and duration, and whether effects vary with level of biological organization. I conducted a meta-analysis of 48 mesocosm studies on the effects of heavy metal ions - silver, cadmium, copper, mercury, lead, and zinc - on marine bivalves. The ordering of effect sizes was Pb > Hg > Cu > Zn > Cd > Ag. The significance and direction of concentration and duration as moderators depended on the metal and the biological level. Future studies should consider non-linear effects over time and concentration, and measure both bioaccumulation and effect of the metals being studies.

Baseline levels of metabolites in different tissues of mussel Mytilus galloprovincialis (Bivalvia: Mytilidae)

The Mediterranean mussel Mytilus galloprovincialis (Lamarck 1819) is a popular shellfish commonly included in human diet and is routinely used as bioindicator in environmental monitoring programmes worldwide. Recently, metabolomics has emerged as a powerful tool both in food research and ecotoxicology for monitoring mussels' freshness and assessing the effects of environmental changes. However, there is still a paucity of data on complete metabolic baseline of mussel tissues. To mitigate this knowledge gap, similarities and differences in metabolite profile of digestive gland (DG), gills (G), and posterior adductor muscle (PAM) of aquaculture-farmed M. galloprovincialis were herein investigated by a proton nuclear magnetic resonance (¹H NMR)-based metabolomic approach and discussed considering their physiological role. A total of 44 metabolites were identified in mussel tissues and grouped in amino acids, energy metabolites, osmolytes, neurotransmitters, nucleotides, alkaloids, and miscellaneous metabolites. A PCA showed that mussel tissues clustered separately from each other, suggesting a clear differentiation in their metabolic profiles. A Venn diagram revealed that mussel DG, G and PAM shared 27 (61.36%) common metabolites, though with different concentrations. Osmolytes were found to dominate the metabolome of all tissues. The DG exhibited higher level of glutathione and carbohydrates. The G showed greater level of osmolytes and the exclusive presence of neurotransmitters, namely acetylcholine and serotonin. In PAM higher levels of energetics-related metabolites were found. Overall, findings from this study are helpful for a better understanding of mussel tissue-specific physiological functions as well as for future NMR-based metabolomic investigations of marine mussel health and safety.

Risk assessment of bilge water discharges in two Baltic shipping lanes

Environmental concentrations and effects of bilge water contaminants in two Baltic Sea areas were estimated from modelling of discharge rates and analytical data on bilge water from seven ships. Biodegradation of bilge water oil was accounted for and annual water concentrations were estimated to peak in late spring, which coincides with the beginning of a period with extensive biological activities in the sea. Concentrations on bilge water metals were calculated both as water concentrations and as the annual contribution of metals to sediments. The predicted bilge water concentrations of oil and metal in the marine environment were estimated to be 4 to 8 orders of magnitude lower than reported toxic concentrations. However, available toxicity data are based on short term exposure and there is to date limited information on toxic effects of the small but chronically elevated contaminant concentrations derived from bilge water discharge and other operational shipping activities.

Combined effects of arsenic, salinity and temperature on Crassostrea gigas embryotoxicity

The combined effects of different salinity and temperature levels on the toxicity of Arsenic (As) were studied on the embryonic development of the oyster Crassostrea gigas. A standardized embryotoxicity test was performed to assess the interactive effects of these stressors, in a full factorial design experiment including a range of salinities (15, 19, 24, 28 and 32), temperatures (16, 20, 24, 28 and 32°C) and As concentrations (100, 300, 600, 1200, 2400µgL^-1). The embryotoxicity endpoint was about the determination of normal larvae development rates at various conditions, and median effect concentration (EC₅₀) determination for each As exposure condition. Results showed that toxicity induced by As was characterized by retardation of embryonic development observing toxic effects at lower concentrations than previously reported studies. The presence of As in seawater resulted in a narrower range of tolerance to both salinity and temperature. These findings bring new insights on the impacts of a common contaminant on an important shellfish species having a planktonic early life stage development, with potential implications for population survival and ecosystem functioning in a changing environment.

Laboratory simulation reveals significant impacts of ocean acidification on microbial community composition and host-pathogen interactions between the blood clam and Vibrio harveyi

It has been suggested that climate change may promote the outbreaks of diseases in the sea through altering the host susceptibility, the pathogen virulence, and the host-pathogen interaction. However, the impacts of ocean acidification (OA) on the pathogen components of bacterial community and the host-pathogen interaction of marine bivalves are still poorly understood. Therefore, 16S rRNA high-throughput sequencing and host-pathogen interaction analysis between blood clam (Tegillarca granosa) and Vibrio harveyi were conducted in the present study to gain a better understanding of the ecological impacts of ocean acidification. The results obtained revealed a significant impact of ocean acidification on the composition of microbial community at laboratory scale. Notably, the abundance of Vibrio, a major group of pathogens to many marine organisms, was significantly increased under ocean acidification condition. In addition, the survival rate and haemolytic activity of V. harveyi were significantly higher in the presence of haemolymph of OA treated T. granosa, indicating a compromised immunity of the clam and enhanced virulence of V. harveyi under future ocean acidification scenarios. Conclusively, the results obtained in this study suggest that future ocean acidification may increase the risk of Vibrio pathogen infection for marine bivalve species, such as blood clams.