Effects of ifosfamide and cisplatin exposure combined with a climate change scenario on the transcriptome responses of the mussel Mytilus galloprovincialis

Coastal ecosystems are currently exposed to pollutants and climate change. Namely, the increasing consumption of antineoplastics drugs and their potential release to aquatic ecosystems are raising concerns. Nevertheless, information regarding the toxicity of these drugs towards non-target species is scarce, especially considering climate change scenarios. Ifosfamide (IF) and cisplatin (CDDP) are among the antineoplastics already detected in aquatic compartments and due to their mode of action (MoA) can negatively affect aquatic organisms. This study evaluates the transcription of 16 selected target genes related to the MoA of IF and CDDP in Mytilus galloprovincialis gills exposed to environmentally relevant and toxicological meaningful concentrations (IF - 10, 100, 500 ng/L; CDDP - 10, 100, 1000 ng/L), under an actual (17 °C) and predicted warming scenario (21 °C). Results showed an upregulation of the cyp4y1 gene when exposed to the highest concentrations of IF, regardless of the temperature. Both drugs upregulated genes related to DNA damage and apoptosis (p53, caspase 8 and gadd45), especially at warmer conditions. Increased temperature also downregulated genes related to stress and immune responses (krs and mydd88). Therefore, the present results showed that antineoplastic drugs at low concentrations upregulated mussel gene signalling related to their MoA and warmer temperatures modulated those effects.

Biomonitoring of potentially toxic elements through oysters (Saccostrea palmula and Crassostrea corteziensis) from coastal lagoons of Southeast Gulf of California, Mexico: health risk assessment

The coastal lagoons of the Gulf of California support important traditional fisheries and mollusc cultures (generally oysters) and receive important volumes of agricultural, industrial and urban effluents, consumption of the oysters could pose risk to human health. The concentrations of arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), and zinc (Zn) in the oysters Saccostrea palmula and Crassostrea corteziensis, from four coastal lagoons (Altata, AL; Macapule, ML; Navachiste, NL; El Colorado, ECL) in the Southeast Gulf of California, were seasonally evaluated (summer 2019-spring 2020). The order of magnitude of potentially toxic elements concentrations in the soft tissue in both oyster species and at all sites was Zn > Fe > Cu > As > Cd > Pb. Cadmium, Cu, Pb, and Zn exceeded the maximum permissible limits in more than one sampling site. The highest concentrations (mg kg^-1, wet weight) of As (4.2 ± 1.1, spring) and Cd (3.3 ± 0.7, autumn) were registered in S. palmula et al. and NL sampling sites, respectively. Crassostrea corteziensis presented higher levels of Cu (40.5 ± 6.7, spring), Pb (2.0 ± 0.4, spring), and Zn (96.9 ± 20.4, spring) in ECL and Fe (62.2 ± 25.4, autumn) in ML. The hazard quotient (HQ) values exceeded the safe level of 1 for Cd in S. palmula and C. corteziensis in NL for children (~ 16 kg weight). In addition, in children, the hazard index (HI) values in both species of oysters ranged from 0.7 to 2.1 and 0.6 to 1.9, respectively. On the other hand, the intake of the studied elements through the consumption of oysters would not induce adverse effects to human health (men and women weighing 70 and 60 kg, respectively); HQ and HI values were < 1.

Mussel antiviral transcriptome response and elimination of viral haemorrhagic septicaemia virus (VHSV)

As filter-feeding bivalves, mussels have been traditionally studied as possible vectors of different bacterial or viral pathogens. The absence of a known viral pathogen in these bivalves makes it particularly interesting to study the interaction of the mussel innate immune system with a virus of interest. In the present work, mussels were challenged with viral haemorrhagic septicaemia virus (VHSV), which is a pathogen in several fish species. The viral load was eliminated after 24 h and mussels evidenced antiviral activity towards VHSV, demonstrating that the virus was recognized and eliminated by the immune system of the host and confirming that mussels are not VHSV vectors in the marine environment. The transcriptome activating the antiviral response was studied, revealing the involvement of cytoplasmic viral sensors with the subsequent activation of the JAK-STAT pathway and several downstream antiviral effectors. The inflammatory response was inhibited with the profound downregulation of MyD88, shifting the immune balance towards antiviral functions. High modulation of retrotransposon activity was observed, revealing a mechanism that facilitates the antiviral response and that had not been previously observed in these species. The expression of several inhibitors of apoptosis and apoptosis-promoting genes was modulated, although clear inhibition of apoptosis in bivalves after severe viral infection and subsequent disease was not observed in this study. Finally, the modulated expression of several long noncoding RNAs that were correlated with genes involved in the immune response was detected.

Shipping can be achieved but cargo arrives with damage - titanium dioxide nanoparticles affect the DNA of Pacific oyster sperm

Titanium dioxide nanoparticles (TiO₂ NP) were reported to be reprotoxic in humans and fish. However, the effects of these NP on the reproduction of marine bivalves, namely oysters, remain unknown. Thus, a short-term (1 h) direct exposure of sperm of the Pacific oyster (Crassostrea gigas) to two TiO₂ NP concentrations (1 and 10 mg.L-1) was performed, and sperm motility, antioxidant responses, and DNA integrity were evaluated. Although no changes occurred in sperm motility and the activities of the antioxidants, the genetic damage indicator increased at both concentrations, demonstrating that TiO₂ NP affects the DNA integrity of oyster sperm. Although DNA transfer can happen, it does not fulfill its biological mission since the transferred DNA is not intact and may compromise the reproduction and recruitment of the oysters. This vulnerability of C. gigas sperm towards TiO₂ NP highlights the importance of studying the effects of NPs exposure to broadcast spawners.

Binational survey using Mytilus galloprovincialis as a bioindicator of microplastic pollution: Insights into chemical analysis and potential risk on humans

Microplastic (MP) contamination in edible mussels has raised concerns due to their potential risk to human health. Aiming to provide valuable insights regarding the occurrence, physicochemical characteristics, and human health implications of MP contamination, in the present study, two nationwide surveys of MP contamination in mussels (Mytilus galloprovincialis) were conducted in Morocco and Tunisia. The results indicated that MP frequency ranged from 79 % to 100 % in all the analyzed samples. The highest MP density was detected in mussels from Morocco (gills "GI": 1.88 MPs/g ww^-1; digestive glands "DG": 0.92 MPs/g ww^-1) compared to mussels of Tunisia (GI: 1.47 MPs g^{- 1}; DG: 0.79 MPs g^{- 1}). No significant differences in MP density were found between the two organs (GI and DG) for both countries. MPs were predominantly blue and black fibers, and smaller than 1000 μm. Seven polymeric types were identified, of which PET, PP, and PE were the most abundant, accounting for >87 % of all samples. Scanning Electron Microscopy (SEM) coupled with Energy dispersive X-ray (EDX) showed that most MPs have noticeable signs of weathering and inorganic components on their surface. The highest MP daily intake was found in children, while the lowest was estimated in women and men. Moreover, the annual dietary exposure of MPs through mussel consumption was estimated to be 1262.17 MPs/year in Morocco and 78.18 MPs/year in Tunisia. The potential risk assessment of MPs in mussels based on the polymer hazard index (PHI) was estimated in the high-risk levels, implying that MPs may pose health risks to humans. Overall, this research suggests that the consumption of mussels represents a considerable MP exposure route for the Moroccan and Tunisian populations.

Impacts of freshwater mussels on planktonic communities and water quality

Live Freshwater Mussels (FMs) have remarkable characteristics to support other species and the ecosystem. The objective of the study was to identify the planktonic composition; dye absorbance by living FMs; analyze the water quality indicators; and determine the heavy metals from FMs of different rivers in Bangladesh. In order to assess the planktonic composition, planktons were collected from the experimental ponds and then identified under the microscope. Methyl blue (MB) and methyl red (MR) dye absorbance were assessed using live FMs. After co-cultivating Silver barb (Barbonymus gonionotus) with FMs, water quality indicators (including pH, DO, hardness, total dissolved solids, ammonia, nitrite, and nitrate) were recorded. For determining heavy metals (Cu, Cr, Cd, Pb, Zn), mussels (Lamellidens marginalis) samples were collected from different rivers of Bangladesh. The findings of the study showed that the planktons were significantly (p < 0.01) greater in the 'Fish' group, compared to the 'Mussels' and 'Mussels + Fish' groups. Also, the MB and MR dye absorption were significantly higher (p < 0.01) in mussels, indicating that live FMs can accumulate hazardous dyes. Furthermore, the hardness value in the 'Mussels' and 'Mussels + Fish' groups were significantly (p < 0.01) greater than in the 'Fish' group. In addition, the values of nitrite and nitrate in the 'Fish' group were also significantly (p < 0.05) greater than those in the 'Mussels + Fish' group. The heavy metals content in the mussels of the Buriganga river was significantly (p < 0.05) higher compared to the mussels of the Rupsha and Brahmaputra rivers. This study revealed that the live FMs have the profound potential to consume plankton, absorb hazardous wastewater dyes, and maintain good water quality which may serve as the ecological indicators in freshwater environment.

Using a weight of evidence approach to identify sources of microbiological contamination in a shellfish-growing area with "Restricted" classification

Shellfish-growing areas in rural catchments are occasionally affected by elevated faecal contamination from diffuse sources and may be subject to frequent harvest closures/classification downgrades. We combined traditional risk management methods based on sanitary surveys and monitoring of Escherichia coli in seawater and shellfish with faecal source tracking, bacterial source apportionment, and hydrometeorological modelling to determine the causes of elevated E. coli concentrations contributing to harvest closures in Papanui Inlet (Aotearoa New Zealand). These multiple lines of evidence were used to inform a weight of evidence assessment of bacterial contamination in the inlet. Ruminant livestock was estimated to contribute 80% of the faecal coliform loading. Concentrations of E. coli in seawater were low (≤ 87 MPN 100 ml^-1) whilst concentrations in tuaki/cockles/little neck clams (Austrovenus stutchburyi) occasionally exceeded the "Approved" classification limit (230 MPN 100 g^-1). The most frequent positive genetic markers in seawater were the seagull (Catellicoccus marimammalium) (54% of seawater samples), and in shellfish, the bovine and seagull markers (both 12.5% of shellfish samples). Solar radiation was negatively correlated with E. coli in tuaki. We found that the growing area is affected by faecal inputs from animal and, to a lesser extent, human (septic tank discharges) sources which elevate contamination to levels detectable in tuaki but not in seawater, particularly in the summer months. The innovative approach can enhance the management of shellfish-growing areas affected by intermittent contamination and enables more targeted action to reduce pollution to improve shellfish water quality.

Identifying freshwater priority areas for cross-taxa interactions

Information about biotic interactions (e.g. competition, predation, parasitism, diseases, mutualism, allelopathy) is fundamental to better understand species distribution and abundance, ecosystem functioning, and ultimately guide conservation efforts. However, conservation planning often overlooks these important interactions. Here, we aim to demonstrate a new framework to include biotic interactions into Marxan. For that, we use freshwater mussels and fish interaction (as mussels rely on fishes to complete their life cycle) in the Douro River basin (Iberian Peninsula) as a case study. While doing that, we also test the importance of including biotic interactions into conservation planning exercises, by running spatial prioritisation analysis considering either: 1) only the target species (freshwater mussels); 2) freshwater mussels and their obligatory hosts (freshwater fishes); 3) freshwater mussels, fishes and their interactions. With this framework we found that biotic interactions tend to be underrepresented when the data on both freshwater mussels and fishes is not simultaneously included in the spatial prioritisation. Overall, the priority areas selected across all scenarios are mostly located in the western part of the Douro River basin, where most freshwater mussels and fishes still occur. Given the low overlap of priority areas identified here and the current Natura 2000 network, our approach may be useful for establishing (or enlarging) protected areas, especially in light of the EU Biodiversity Strategy for 2030. Also, this work may provide guidance for future habitat restoration and management of main threats to freshwater biodiversity.

Azaspiracid accumulation in Japanese coastal bivalves and ascidians fed with Azadinium poporum producing azaspiracid-2 as the dominant toxin component

The filter-feeding bivalves often accumulate marine toxins by feeding on toxic dinoflagellates that produce marine toxins. Azaspiracids (AZAs) are a group of lipophilic polyether toxins which have been detected in a variety of organisms in many countries. In our present study, accumulation kinetics and toxin distributions in the tissues of seven bivalve species and ascidians relevant to Japanese coastal waters were investigated by experimentally feeding a toxic dinoflagellate Azadinium poporum, which produces azaspiracid-2 (AZA2) as the dominant toxin component. All bivalve species and ascidians investigated in this study had the capability to accumulate AZA2 and no metabolites of AZA2 were detected in the bivalves and the ascidians. Japanese short-neck clams, Japanese oysters, Pacific oysters and ascidians accumulated AZA2 with the highest concentrations on the hepatopancreas, whereas the highest concentrations of AZA2 were found on the gills in surf clams and horse clams. Hard clams and cockles accumulated high levels of AZA2 in both the hepatopancreas and the gills. As far as we know, this is the first report describing detailed tissue distribution of AZAs in several bivalve species other than mussels (M. edulis) and scallops (P. maximus). Variation of accumulation rates of AZA2 in Japanese short-neck clams on different cell densities or temperatures were observed.

Transcriptomic response to GnRH down regulation by RNA interference in clam Ruditapes philippinarum, suggest possible role in reproductive function

Gonadotropin-releasing hormone (GnRH) plays a key role in the control of the reproductive axis in vertebrates, however, little is known about its function in reproductive endocrine regulation in molluscs. In the present study, RNA-seq was used to construct transcriptomes of Ruditapes philippinarum testis and ovaries of control and GnRH suppressed individuals using RNA interference. GnRH suppression caused 112 and 169 enriched KEGG pathways in testis and ovary, with 92 pathways in common in both comparisons. The most enriched KEGG pathways occurred in the "Oxidative phosphorylation", "Dorso-ventral axis formation", "Thyroid hormone synthesis" and "Oxytocin signaling pathway" etc. A total of 1838 genes in testis and 358 genes in ovaries were detected differentially expressed in GnRH suppressed clams. Among the differentially expressed genes, a suit of genes related to regulation of steroid hormones synthesis and gonadal development, were found in both ovary and testis with RNAi of GnRH. These results suggest that GnRH may play an important role in reproductive function in bivalves. This study provides a preliminary basis for studying the function and regulatory mechanism of GnRH in bivalves.

Quantification of insecticides in commercial seafood sold in East Asian markets: risk assessment for consumers

The extraction of 21 insecticides and 5 metabolites was performed using an optimized and validated QuEChERS protocol that was further used for the quantification (GC-MS/MS) in several seafood matrices (crustaceans, bivalves, and fish-mudskippers). Seven species, acquired from Hong Kong and Macao wet markets (a region so far poorly monitored), were selected based on their commercial importance in the Indo-Pacific region, market abundance, and affordable price. Among them, mussels from Hong Kong, together with mudskippers from Macao, presented the highest insecticide concentrations (median values of 30.33 and 23.90 ng/g WW, respectively). Residual levels of fenobucarb, DDTs, HCHs, and heptachlors were above the established threshold (10 ng/g WW) for human consumption according to the European and Chinese legislations: for example, in fish-mudskippers, DDTs, fenobucarb, and heptachlors (5-, 20- and tenfold, respectively), and in bivalves, HCHs (fourfold) had higher levels than the threshold. Risk assessment revealed potential human health effects (e.g., neurotoxicity), especially through fish and bivalve consumption (non-carcinogenic risk; ΣHQ_LT > 1), and a potential concern of lifetime cancer risk development through the consumption of fish, bivalves, and crustaceans collected from these markets (carcinogenic risk; ΣTCR > 10^-4). Since these results indicate polluted regions, where the seafood is collected/produced, a strict monitoring framework should be implemented in those areas to improve food quality and safety of seafood products.

Effects of temperature, salinity, and food availability on shell growth rates of the Yesso scallop

Shell growth rates in relationship to seasonal changes of environmental factors were studied in a wild population of the Yesso scallop Mizuhopecten yessoensis inhabiting Amur Bay (Peter the Great Bay, Sea of Japan, Russia). It was found that food availability is not a limiting factor for the scallop growth in the study area. A phytoplankton biomass of 3.5-6.0 g m^-3 provided high scallop growth rates. The largest daily shell increments were observed with a phytoplankton biomass of about 6 g m^-3. With a decrease in the phytoplankton biomass to <2 g m^-3, as well as with an increase to >11 g m^-3, the daily shell increments reduced. It appeared that the main exogenous factors causing the seasonal variations in the scallop growth rates are the water temperature, which was too high in July and August (>18 °C) and too low in November-April (<4 °C), and the water salinity, which was too low (<30‰) for this stenohaline species in summer. The relationship of the daily shell increment in Yesso scallop with the water temperature can be described by a dome-shaped curve. The largest increments were observed at 8-16 °C. The dependence of the daily shell increments on the water salinity was also best described by a dome-shaped curve, showing the optimal range of 32.5-33.5‰. The revealed relationships, approximated by dome-shaped curves, evidently indicate that both insufficient and excessive effect of the factor negatively affects scallop growth. A suggestion was made to describe the result of the combined impact of several environmental factors on the daily shell increment as a multiplication of the functions of its dependence on each of the factors.

The environmental remediation capacity of Ulva lactuca: the potential of macroalgae to reduce the threats caused by Titanium in marine invertebrate species

As a result of the wide use of Titanium (Ti) compounds in various products, Ti and Ti nanoparticles (nTi) are released into aquatic environments, inducing varying degrees of toxicity on aquatic fauna. Ulva lactuca, green macroalgae commonly found in coastal areas, has been extensively studied due to its worldwide distribution and capacity to accumulate trace elements under toxic conditions, which makes it a good universal sorbent. The present study aimed to establish the remediation properties of U. lactuca by evaluating the toxicity of Ti and nTi in bivalves, in the presence and absence of algae. Using the bivalve species Mytilus galloprovincialis, Ti toxicity was evaluated by assessing changes in mussel's metabolic capacity and oxidative status. Results evidenced cellular damage in M. galloprovincialis exposed to Ti and nTi. This was a result of the inactivation of antioxidant defences. The presence of U. lactuca limited cellular damage, however, this was not a result of the previously demonstrated bioremediation capacity, as no accumulation of Ti was verified in algal tissues. As a metabolic depression was verified for mussels exposed to Ti/nTi in the presence of algae, we hypothesise that U. lactuca may have been responsible for changes to the water quality which induced this response.

Physiological and gene expression responses of the mussel Mytilus galloprovincialis to low pH and low dissolved oxygen

The prevalence and frequency of hypoxia events have increased worldwide over the past decade as a consequence of global climate change and coastal biological oxygen depletions. On the other hand, anthropogenic emissions of CO₂ and consequent accumulation in the sea surface result in a perturbation of the seawater carbonate system, including a decrease in pH, known as ocean acidification. While the effect of decreases in pH and dissolved oxygen (DO) concentration is better understood, their combined effects are still poorly resolved. Here, we exposed adult mussels (Mytilus galloprovincialis) to two pHs (8.27 and 7.63) and DO concentrations (7.65 and 2.75 mg L^-1) over 17 days in a full-factorial design. These levels correspond to extremes of the present natural variability and are relevant in the context of ocean acidification and hypoxia. No mortality was observed during the experiment. However, sublethal effects were observed for clearance and oxygen consumption rates, as well as total haemocytes count and haemocytes viability and gene expression in mussels exposed to the combination of low pH and low DO. Respiration and excretion rates were not significantly impacted by low pH and DO, alone or in combination. Overall, low pH alone led to a decrease in all tested physiological parameters while low DO alone led to a decline in clearance rate, haemocyte parameters and an increase in carbohydrate content. Both parameters led to up- or down-regulation of most of the selected genes. Not surprisingly, the combined effect of low pH and low DO could not be predicted by a simple arithmetic additive response at the effect level, highlighting more complex and non-linear effects.

A review of freshwater benthic clams (Corbicula fluminea): Accumulation capacity, underlying physiological mechanisms and environmental applications

Asian clams (Corbicula fluminea) have been extensively applied in biomonitoring and other environmental fields based on their high enrichment capacity and rapid response to pollutants. This review first summarizes the kinetic process of metals and organic pollutants enriched by C. fluminea and discusses the environmental behavior and application. The accumulation ability of Cu, Zn, and Mn were significantly higher than that of other metals, which were attributed to their high uptake rate constant and low elimination rate constant. The visceral mass was found to be the major burden tissue. However, large knowledge gaps existed regarding the accumulation capacity of C. fluminea for organic pollutants and nanoparticles. Moreover, physiological mechanisms underlying the accumulation of environmental pollutants were proposed. C. fluminea can improve the niche of benthic algae by ingesting pelagic algae, mitigating water eutrophication. It can also remove pathogens and parasites based on the biological assimilation of nonspecific immunity, interrupting disease transmission. The novel insight into the application of C. fluminea in wastewater treatment further broadens the range of pest management strategies and offers the feasibility of blocking the spread of invasive bivalves.

Radiological dose and associated risk due to 210Po in commercial inter-tidal bivalves of southwest (Arabian Sea) coast of India

The activity concentration of ²¹⁰Po was determined in edible tissues of commercial bivalves on the southwest coast of India. The ²¹⁰Po activity ranged from 38.3 ± 6.9 Bq kg^-1 to 91.2 ± 18.6 Bq kg^-1. The annual committed effective dose (ACED) and lifetime carcinogenic risk (LCR) were calculated for different age groups to determine the potential health risk associated with bivalve consumption. The average ACED ranged from 81.5 to 194.1 μSv y^-1, with the 10th and 95th percentiles being 68 and 261 μSv y^-1, respectively. Lifelong mortality risk (LMTR) values ranged from 1.2 × 10^-3 to 2.9 × 10^-3, while lifetime morbidity risk (LMBR) values ranged from 1.9 × 10^-6 to 4.9 × 10^-6. The effective dose was found to be within the UNSCEAR limits.

Evaluation of antioxidant capacity and digestive enzyme activities in Mytilus galloprovincialis exposed to nanoplastics under different patterns of hypoxia

In the marine environment, plastic pollution may occur simultaneously with hypoxia. However, current ecological risk assessments of nanoplastics have rarely considered the impact of additional environmental factors, such as hypoxia. In this study, we investigated the effect of polystyrene nanospheres (PS-NPs) on the digestive performance (antioxidant system and digestive enzymes) of mussels Mytilus galloprovincialis under different patterns of hypoxia (normoxia, constant hypoxia, and fluctuating hypoxia). The result showed that PS-NPs caused oxidative damage in the digestive glands of mussels, while all patterns of hypoxia exacerbated this oxidative damage. Activities of four digestive enzymes (α-amylase, cellulase, trypsin, and lipase) were examined. Among these, the activity of the α-amylase was inhibited by PS-NPs, and the inhibition was aggravated by all the hypoxia patterns. The cellulase activity and trypsin activity was enhanced by PS-NPs, and the increase was further stimulated by hypoxia. Lipase activity was not affected by PS-NPs alone, but significant inhibition was detected after the coexposure to PS-NPs and hypoxia. Conclusively, the combined stress of hypoxia and nanoplastics can significantly affect the digestive performance of mussels and may alter the mussel nutrient uptake strategy. Our work has provided new insight into the ecological risk assessment of plastics under global climate change.

The longest-lived metazoan, Arctica islandica, exhibits high mitochondrial H2O2 removal capacities

A greater capacity of endogenous matrix antioxidants has recently been hypothesized to characterize mitochondria of long-lived species, curbing bursts of reactive oxygen species (ROS) generated in this organelle. Evidence for this has been obtained from studies comparing the long-lived naked mole rat to laboratory mice. We tested this hypothesis by comparing the longest-lived metazoan, the marine bivalve Arctica islandica (MLSP = 507 y), with shorter-lived and evolutionarily related species. We used a recently developed fluorescent technique to assess mantle and gill tissue mitochondria's capacity to consume hydrogen peroxide (H₂O₂) in multiple physiological states ex vivo. Depending on the type of respiratory substrate provided, mitochondria of Arctica islandica could consume between 3 and 14 times more H₂O₂ than shorter-lived species. These findings support the contention that a greater capacity for the elimination of ROS characterizes long-lived species, a novel property of mitochondria thus far demonstrated in two key biogerontological models from distant evolutionary lineages.

The forgotten ones of ports: The filter feeders at the heart of siltation processes

Siltation is a major concern in dynamic and complex ecosystems, such as ports. The mud must be regularly dredged to avoid disturbing the navigation channels. Sediments are carried by the waters entering the port and are partially trapped by harbour structures. Numerous studies have been conducted on the physical factors influencing siltation in port areas, whereas, few have focused on the role of biotic factors in mud formation. However, research in other contexts has shown that organisms that are abundant in pontoons, such as bivalves and tunicates, play an important role in this siltation process. All of these organisms belong to the filter feeder group. The sediments sucked in by the filter feeders are excreted in the form of faeces or mucus-bound pseudo-faeces. These waste materials, called bioproducts, settle efficiently and are involved in the composition of the mud. This study aimed to highlight the role of filter feeders in the siltation process in port areas and to determine the factors that influence the production of bioproducts by filter feeders. To investigate the role of filter feeders in the siltation processes, an experimental analysis was conducted in the largest marina in Europe (La Rochelle, France). It is divided into four basins with distinct filter feeder communities and environmental conditions, allowing for a detailed study of the environmental factors that influence the production of bioproducts. This analysis consisted of recovering and studying the bioproducts generated by the filter feeders using sediment traps fixed under pontoons. To explore the evolution of this biological production, 16 campaigns were conducted from January to March 2020 and May to July 2020. The total amount of dry matter produced was constant between seasons at approximately 130 g/m²/d; marina-wide, this amount represents a total daily production of 3.2 tons. However, the production amount varies spatially and temporally in relation to marine hydrodynamics and the organisms involved. Bioproduction was taxon-dependent: areas abundant in oysters and mussels were the areas with the most pronounced bioproduction, whereas there was no significant relationship between bioproduction and the presence of tunicates or scallops. If we consider bioproduction on a seasonal scale, we can see that the campaigns with the greatest production correspond to the periods when the sediment supply was the highest, i.e. when the tidal range was the highest. The quality of the bioproducts (organic matter content) differed between seasons, which can be explained by both environmental and metabolic changes. Understanding the role of filter feeders in siltation processes appears to be essential in port environments that need to be regularly dredged to ensure safe navigation.

Responses of digestive metabolism to marine heatwaves in pearl oysters

Marine heatwaves (MHWs) have increased in intensity and frequency in global oceans, causing deleterious effects on many marine organisms and ecosystems they support. Bivalves are among the most vulnerable taxonomic groups to intensifying MHWs, yet little is known about the underlying mechanisms. Here, we investigated the impact of MHWs on the digestive metabolism of pearl oysters (Pinctada maxima). Two moderate and severe scenarios of MHWs were performed by increasing seawater temperature respectively from 24 °C to 28 °C and 32 °C for 3 days. When subjected to MHWs and with increasing intensity, pearl oysters significantly enhanced their digestive enzymatic activities, such as lipase and amylase. LC-MS-based metabolomics revealed negative responses in the lipid metabolism (e.g., steroid biosynthesis, glycerophospholipid metabolism, and sphingolipid metabolism), the amino acid metabolism (e.g., glutamate, histidine, arginine, and proline), and the B-vitamins metabolism. These findings indicate that the digestive metabolism of marine bivalves can likely succumb to intensifying MHWs events.

Molecular characterization of Vasa homolog in the pen shell Atrina pectinata: cDNA cloning and expression analysis during gonadal development

Vasa is an ATP-dependent RNA helicase of the DEAD (Asp-Glu-Ala-Asp) box family and a representative component of the germ plasm. In this study, we cloned the full-length vasa homolog in the bivalve Atrina pectinata (psvasa), and performed phylogenetic analysis, mRNA expression analysis for tissue-specific distributions, and immunostaining analysis to reveal its histological localization. The sequence of psvasa was 3587 bp in length and contained a 5' untranslated region of 150 bp, an open reading frame of 2214 bp, and a 3' untranslated region of 1223 bp. The deduced amino acid sequence of psvasa was 737 amino acids long and contained evolutionarily conserved sequences reported in other animals. The mRNA expression analysis showed the highest expression levels in the gonads. Expression was especially high in the ovaries, followed by the testes. The immunostaining analysis showed Vasa-positive cells in the developing gonads, suggesting the presence of putative germ stem cells contributing to the supply of germ cells. Furthermore, characteristic Vasa signals were observed in the basophilic nuclei of the oocytes, suggesting that psvasa plays an important role in the progression of meiosis in oocytes.

Ecotoxicological effects of silver nanoparticles in marine mussels

As the production of silver nanoparticles (AgNPs) is becoming more prevalent, it is becoming increasingly necessary to understand the toxicological effects they can have on different ecosystems. In the marine bioindicator species M. galloprovincialis Lam we predicted toxicity and bioaccumulation of 5 nm alkane-coated and 50 nm uncoated silver nanoparticles (AgNPs) along with silver nitrate as a function of the actual dose level. We generated a time persistence model of silver in seawater and used the Area Under the Curve (AUC) as independent variable in the hazard assessment. This approach allowed us to evaluate unbiased ecotoxicological endpoints for acute (survival) and chronic toxicity (byssal adhesion). Logistic regression analysis rendered an overall LC50_96h values of 0.81 ± 0.07 mg h L^-1 irrespectively of the silver form. By contrast, for byssal adhesion regression analysis revealed a much higher toxicological potential of silver nitrate vs AgNPs with EC50_24h values respectively of 0.0024 ± 0.0009 vs 0.053 ± 0.016 and 0.063 (no computable error for 50 nm AgNP) mg h L^-1, undoubtedly confirming a prevalence of ionic silver effects over AgNPs. Bioaccumulation was more efficient for silver nitrate >5 nm AgNP >50 nm AgNP reflecting a parallel with the preferential uptake route / target organ. Finally, we derived Risk Quotient (RQs) for acute and chronic effects of nanosilver in shellfish and showed that the RQs are far from the Level of Concern (LoC) at current estimated environmental concentrations (EECs). This information can ultimately help researchers, policy makers, and industry professionals decide how to safely regulate and/or dispose of AgNPs.

Transcriptome analysis reveals the diverse response of pearl oyster Pinctada fucata martensii after different PAMP stimulation

Bivalves have evolved effective strategies to combat different pathogens in the environment. They rely on innate immunity to deal with the invasion of various bacteria, viruses, and other microorganisms. However, the molecular mechanisms underlying the responses remain largely unknown. Herein, we constructed 21 transcriptomes of the hemocytes after lipopolysaccharide (LPS), peptidoglycan (PGN) and polyinosinic-polycytidylic acid (poly(I:C)) stimulation to investigate the molecular mechanisms underlying adaptations and plastic responses to different pathogen-related molecular patterns (PAMPs) in pearl oyster Pinctada fucata martensii. Transcriptome analysis revealed 1986-3427 responsive genes enriched in the major immune and cell cycle-related pathways at different times after PAMP stimulation, and the expression patterns of genes under these pathways are complex and diverse. Moreover, "lysosomes" were enriched 6 h after LPS and PGN stimulation, while "peroxisomes" were only enriched in poly(I:C) group. These results suggest different response strategies of pearl oyster to different PAMPs. Furthermore, we identified 261 pattern-recognition receptors (PRRs) including 4 retinoic acid-inducible gene I-like receptors, 38 NOD-like receptors, 83 Toll-like receptors, and 136 C-type lectins in the genome of P. f. martensii. The diverse expression patterns of these PRRs after different PAMP stimulation indicated that pearl oyster evolved complex and specific recognition systems due to tandem repeat and diverse domain combination, which may help pearl oyster cope with the different pathogens in the environment. The present study improved our understanding of the molecular response of pearl oyster to different PAMP stimulation.

Responses of Mytilus galloprovincialis to challenge with environmental isolates of the potential emerging pathogen Malaciobacter marinus

Bacteria of the Arcobacter-like spp. represent emerging foodborne zoonotic pathogens in humans and animals. Their increasing presence in seafood, suggesting higher occurrence in seawater due to marine pollution, is raising some environmental concern. Although Arcobacter is frequently detected in diseased oysters and stressed bivalve species, no data are available so far on its potential pathogenicity or interactions with the immune system of the bivalve host. In this work, responses to challenge with two strains of Malaciobacter marinus IRTA-19-131 and IRTA-19-132, R1 and R2), isolated from adult Crassostrea gigas during a mortality event in 2019 in Spain, were investigated in the mussel Mytilus galloprovincialis. In vivo experiments were performed in larvae (48 h post-fertilization), and in adult mussels at 24 h post-injection, in order to evaluate the pathogenicity for early developmental stages, and the hemolymph immune responses, respectively. Both R1 and R2 were moderately pathogenic to early larvae, with significant decreases in the development of normal D-veligers from 10⁴ and 10³ CFU/mL, respectively. In adults, both strains decreased hemocyte lysosomal membrane stability (LMS), and stimulated extracellular defense responses (ROS production and lysozyme activity). The interactions between mussel hemocytes and M. marinus were investigated in in vitro short-term experiments (30-90 min) using the R1 strain (10⁶-10⁸ CFU/mL). R1 decreased LMS and induced lysosomal enlargement, but not cell detachment or death, and stimulated extracellular ROS production and lysozyme release, confirming in vivo data. Moreover, lysosomal internalization and degradation of bacteria were observed, together with changes in levels of activated mTor and LC3, indicating phagocytic activity. Overall, the results indicate the activation of both extracellular and intracellular immune defenses against M. marinus R1. Accordingly, these responses resulted in a significant hemolymph bactericidal activity, with a large contribution of hemolymph serum. The results represent the first data on the potential pathogenicity of Arcobacter isolated from a shellfish mortality to bivalve larvae and adults, and on their interactions with the immune system of the host.

Variations in the toxicity and condition index of five bivalve species throughout a red tide event caused by Alexandrium catenella: A field study

Harmful red tides in China have caused paralytic shellfish toxins (PSTs) pollution and led to severe socioeconomic effects in shellfish aquaculture. Although shellfish can survive harmful algal blooms, the effects on their Condition Index (CI) have been underestimated. This study sought to evaluate the effects of the profiles and levels of paralytic shellfish toxins on variations in the CI in bivalves under natural blooming conditions. We observed clear soft tissue lesions to varying degrees except in Mytilus galloprovincialis after toxin exposure. Among the five species of shellfish exposed in situ, only M. galloprovincialis accumulated PSTs content above the maximum permitted level (800 μg STX di-HCl eq./kg). The highest toxin content in all sample tissues was observed in Patinopecten yessoensis. Significant interspecies differences in PSTs accumulation among the five bivalve species were observed in the hepatopancreas. A total of nine PSTs components and four new C-11 hydroxyl metabolites (so-called M-toxins) toxins were detected, and detoxification diversity was observed among bivalves. We observed a higher proportion of M-toxin in early stages, and the proportions changed only slightly over time in M. galloprovincialis and Magallana gigas, thus accounting for the significantly higher metabolism rate. Notably, the CI in M. gigas and Argopecten irradians was positively correlated with lowest toxin accumulation of PSTs content, but significantly inhibited. In conclusion, our results revealed a significant inhibitory effect on the CI in shellfish, in a species specific manner, with distinct levels of inhibition correlated with different toxin metabolites. Our study revealed the toxin content of different bivalves exposed to a natural red tide environment and the consequent effects on growth, thus building a foundation for research on the mechanisms underlying the effects of PSTs on growth. These data establish the ecological and economic significance of the effects of harmful algal blooms on bivalves.