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Microplastic content (MPs) in mussels (Mytilus spp.) from two areas of the north coast of Spain was measured for the first time. Additionally, a comparison of microplastic levels observed in mussels digested with nitric acid and with potassium hydroxide was carried out. The average microplastic concentration in mussels digested with nitric acid was significantly lower than that observed in mussels digested with potassium hydroxide (p < 0.05). The average concentration of microplastics in mussels from the Cantabrian Sea (2.55±2.80 MPs g–1 WW) was slightly higher than that in mussels from the Ria of Vigo (1.59±1.28 MPs g–1 WW). Both in the Ria of Vigo and in the Cantabrian Sea the observed pattern of pollution was fitted to the one expected. Consequently, mussels have been confirmed as suitable sentinel organisms for microplastic pollution.

Tetrodotoxins (TTXs) are traditionally associated with the occurrence of tropical Pufferfish Poisoning. In recent years, however, TTXs have been identified in European bivalve mollusc shellfish, resulting in the need to assess prevalence and risk to shellfish consumers. Following the previous identification of TTXs in shellfish from southern England, this study was designed to assess the wider prevalence of TTXs in shellfish from around the coast of the UK. Samples were collected between 2014 and 2016 and subjected to analysis using HILIC-MS/MS. Results showed the continued presence of toxins in shellfish harvested along the coast of southern England, with the maximum concentration of total TTXs reaching 253 µg/kg. TTX accumulation was detected in Pacific oysters (Crassostrea gigas), native oysters (Ostrea edulis) common mussels (Mytilus edulis) and hard clams (Mercenaria mercenaria), but not found in cockles (Cerastoderma edule), razors (Ensis species) or scallops (Pecten maximus). Whilst the highest concentrations were quantified in samples harvested during the warmer summer months, TTXs were still evident during the winter. An assessment of the potential causative factors did not reveal any links with the phytoplankton species Prorocentrum cordatum, instead highlighting a greater level of risk in areas of shallow, estuarine waters with temperatures above 15 °C.

Freshwater pearl mussels (Margartifera margaritifera L.) are among the most critically threatened freshwater bivalves worldwide. The pearl mussel simultaneously fulfils criteria of indicator, flagship, keystone and umbrella species and can thus be considered an ideal target species for the process conservation of aquatic ecosystem functioning. The development of conservation strategies for freshwater pearl mussels and for other bivalve species faces many challenges, including the selection of priority populations for conservation and strategic decisions on habitat restoration and/or captive breeding. This article summarises the current information about the species' systematics and phylogeny, its distribution and status as well as about its life history strategy and genetic population structure. Based on this information, integrative conservation strategies for freshwater mollusc species which combine genetic and ecological information are discussed. Holistic conservation strategies for pearl mussels require the integration of Conservation Genetics and Conservation Ecology actions at various spatial scales, from the individual and population level to global biodiversity conservation strategies. The availability of high resolution genetic markers for the species and the knowledge of the critical stages in the life cycle, particularly of the most sensitive post-parasitic phase, are important prerequisites for conservation. Effective adaptive conservation management also requires an evaluation of previous actions and management decisions. As with other freshwater bivalves, an integrative conservation approach that identifies and sustains ecological processes and evolutionary lineages is urgently needed to protect and manage freshwater pearl mussel diversity. Such research is important for the conservation of free-living populations, as well as for artificial culturing and breeding techniques, which have recently been or which are currently being established for freshwater pearl mussels in several countries.

Abstract The invasive bivalve mollusk Limnoperna fortunei (Dunker 1857), commonly known as the “golden mussel”, was recently recorded in the Amazon region, in August 2023 on the Tocantins River (State of Pará). Native to Southeast Asia, L. fortunei has been present in Brazilian waters since the 1990s and, due to its biological and ecological characteristics, found an environment favorable to its proliferation in the country. Numerous records of the species and the significant environmental and economic impacts it causes are well-documented in the scientific literature. Here, we present the first qualitative and quantitative data on the bioinvasion of L. fortunei in the Brazilian Amazon region. Sampling was conducted in October 2024 in three sites at the Pedral do Lourenço, a rock formation in the Tocantins River located between the municipalities of Marabá and Tucuruí (State of Pará). The specimens exhibited an average total length of 12.22±4.19 mm, with average population density of mussels found of 11,940 ind.m2, with sizes between 1.92 mm and 22.10 mm, with records reaching 15,849 ind.m2. This study represents the first preliminary data on the population structure of L. fortunei for the Amazon region. The results suggest a recent settlement in the Tocantins River, with evidence of at least one reproductive cycle already completed. Monitoring a broader area of the Tocantins River and its tributaries will provide a better diagnosis of the invasion. Resumo O molusco bivalve invasor Limnoperna fortunei (Dunker 1857), conhecido popularmente por “mexilhão-dourado”, recentemente foi registrado na região Amazônica, em agosto de 2023 no rio Tocantins (Estado do Pará). Nativo do sudeste asiático, L. fortunei está presente em águas brasileiras desde a década de 1990 e, devido suas características biológicas e ecológicas, encontrou no país um ambiente favorável à sua proliferação. Diversos registros da espécie são documentados na literatura científica, assim como os inúmeros impactos ambientais e econômicos causados por esse invasor. Aqui, apresentamos os primeiros dados quali-quantitativos da bioinvasão de L. fortunei para a região Amazônica brasileira. A amostragem ocorreu outubro de 2024 em três pontos sobre o Pedral do Lourenço, que é uma formação rochosa disposta no rio Tocantins situada entre os municípios de Marabá e Tucuruí (Estado do Pará). Encontrou-se um comprimento médio de 12,22±4,19 mm de comprimento total, variando de 1,92 mm e o máximo de 22,10 mm, com densidade populacional média de 11.940 ind.m2 e máxima de 15.849 ind.m2. Este é o primeiro estudo contendo dados preliminares da estrutura populacional de L. fortunei para a região amazônica. Os resultados indicam um assentamento recente no Rio Tocantins, com indícios de ao menos um ciclo de reprodução já efetuado. Um monitoramento em uma ampla área do rio Tocantins e seus afluentes, possibilitará um melhor diagnóstico da invasão.

The thick-shelled clam Meretrix morphina, previously referred to as Meretrix meretrix, now occurs in the west Indian Ocean region, along the eastern seaboard of Africa, from the Red Sea to the Mlalazi Estuary, close to the Tugela River. Its presence in South Africa is only of recent recording. Meretrix morphina was detected for the first time in Lake St Lucia in 2000. The population declined and was not detected from 2005 until 2011, most likely as a result of a severe drought that resulted in widespread desiccation and hypersalinity in the lake. The system then experienced increased freshwater input resulting in lower salinities from 2011 until 2014, during which time M. morphina reappeared and their population gradually increased. In 2015, M. morphina became abundant in St Lucia, attaining unprecedented densities of 447 ind./m 2 . Biomass, expressed as a fresh weight, varied in the different basins of St Lucia, ranging from 195 g/m 2 at Lister’s Point to 1909.8 g/m 2 at Catalina Bay. However, in 2016, when drought conditions returned,M. morphina disappeared. This species appears to thrive under brackish salinities and high temperatures. It is able to establish large populations with high biomass and can become dominant. However, M. morphina is sensitive to desiccation and hypersaline conditions. This clam has substantial commercial value and is exploited along the African east coast, particularly in Mozambique. In future, it may feature more prominently in South African estuaries. However, the ecology of M. morphina is still largely unknown. Significance: • First record of population irruption of M. morphina in South Africa. • Report on the largely unknown ecology of a commercially valuable bivalve. • Update on the taxonomy and poleward spread of M. morphina.

Tetrodotoxins (TTX) are a potent group of natural neurotoxins putatively produced by symbiotic microorganisms and affecting the aquatic environment. These neurotoxins have been recently found in some species of bivalves and gastropods along the European Coasts (Greece, UK, and The Netherlands) linked to the presence of high concentrations of Vibrio, in particular Vibrio parahaemolyticus. This study is focused on the evaluation of the presence of Vibrio species and TTX in bivalves (mussels, oysters, cockles, clams, scallops, and razor clams) from Galician Rias (northwest of Spain). The detection and isolation of the major Vibrio spp. and other enterobacterial populations have been carried out with the aim of screening for the presence of the pathways genes, poliketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) possibly involved in the biosynthesis of these toxins. Samples containing Vibrio spp. were analyzed by biochemical (API20E-galery) and genetic tests (PCR-RT). These samples were then screened for TTX toxicity by a neuroblastoma cell-based assay (N2a) and the presence of TTX was further confirmed by LC-MS/MS. TTX was detected in two infaunal samples. This is the first confirmation of the presence of TTX in bivalve molluscs from the Galician Rias.

In recent field studies, suspected gymnophallid metacercariae were histologically located in the mantle of mussels from the Norwegian Sea. Mussels from the sites in which that infection was detected also presented abnormally high pearl numbers. It has been previously described that gymnophallid metacercariae could cause pearl formation processes in mussels, as a host reaction to encapsulate these metacercariae. Given the pathological host reaction these parasites elicit, a study was performed to identify gymnophallid metacercariae found in mussels collected from Tromsø at morphological and molecular level and to assess, by the use of molecular tools, the relationship between the parasite and the biological material inside the pearls. As a result, Gymnophallus bursicola metacercariae infecting Norwegian Mytilus edulis were identified according to morphological characters, along with the first 18S rDNA and COI sequences for this trematode species. In addition, parasite DNA from the core of the pearls was extracted and amplified for the first time, confirming the parasitological origin of these pearls. This procedure could allow identifying different parasitic organisms responsible for the generation of pearls in bivalves.

In 2015, tetrodotoxins (TTXs) were considered a potential threat in Europe since several studies had shown the presence of these toxins in European bivalve molluscs. In this study, we investigated the occurrence of TTXs in 127 bivalve samples (mussels and oysters) and in 66 gastropod samples (whelks) collected all along the French mainland coasts in 2017 and 2018. Analyses were carried out after optimization and in-house validation of a performing hydrophilic interaction liquid chromatography associated with tandem mass spectrometry (HILIC-MS/MS) method. The concentration set by European Food Safety Authority (EFSA) not expected to result in adverse effects (44 µg TTX equivalent/kg) was never exceeded, but TTX was detected in three mussel samples and one whelk sample (1.7–11.2 µg/kg). The tissue distribution of TTX in this whelk sample showed higher concentrations in the digestive gland, stomach and gonads (7.4 µg TTX/kg) than in the rest of the whelk tissues (below the limit of detection of 1.7 µg TTX/kg). This is the first study to report the detection of TTX in French molluscs.

A variety of bivalve mollusks (phylum Mollusca, class Bivalvia) constitute a prominent commodity in fisheries and aquacultures, but are also crucial in order to preserve our ecosystem’s complexity and function. Bivalve mollusks, such as clams, mussels, oysters and scallops, are relevant bred species, and their global farming maintains a high incremental annual growth rate, representing a considerable proportion of the overall fishery activities. Bivalve mollusks are filter feeders; therefore by filtering a great quantity of water, they may bioaccumulate in their tissues a high number of microorganisms that can be considered infectious for humans and higher vertebrates. Moreover, since some pathogens are also able to infect bivalve mollusks, they are a threat for the entire mollusk farming industry. In consideration of the leading role in aquaculture and the growing financial importance of bivalve farming, much interest has been recently devoted to investigate the pathogenesis of infectious diseases of these mollusks in order to be prepared for public health emergencies and to avoid dreadful income losses. Several bacterial and viral pathogens will be described herein. Despite the minor complexity of the organization of the immune system of bivalves, compared to mammalian immune systems, a precise description of the different mechanisms that induce its activation and functioning is still missing. In the present review, a substantial consideration will be devoted in outlining the immune responses of bivalves and their repertoire of immune cells. Finally, we will focus on the description of antimicrobial peptides that have been identified and characterized in bivalve mollusks. Their structural and antimicrobial features are also of great interest for the biotechnology sector as antimicrobial templates to combat the increasing antibiotic-resistance of different pathogenic bacteria that plague the human population all over the world.

Pharmaceuticals such as chlorpromazine (Cpz) are emerging aquatic pollutants with potential effects on non-target organisms. However, its effects on aquatic organisms remain limited and inconclusive. The aim of this study was to compare the responses to Cpz in marine and freshwater bivalve molluscs. Methods. Mytilus galloprovincialis and Unio tumidus were exposed to pM and nM concentrations of Cpz for 14 days and analysed 16 parameters, including cytotoxicity, oxidative/reductive stress responses, metallothionein concentration and biotransformation enzymes in the digestive gland. Results. In both species, Cpz increased EROD activity, possibly leading to the formation of reactive metabolites. Marine mussels exposed to Cpz I and II showed increased GST activity, suggesting detoxification, whereas freshwater mussels showed decreased GST activity, suggesting higher Cpz toxicity. Activation of the GTPase dynamin in U. tumidus exposed to Cpz I confirmed the effect of Cpz on endocytosis. Oxidative stress responses were observed in both species, with changes in oxidative/reductive stress responses, suggesting toxic effects of Cpz. GSH and metallothionein concentrations increased in all exposures, while the NADH/NAD+ ratio increased significantly in U. tumidus. Loss of lysosomal membrane stability was observed in all exposed groups, with CtD efflux detected only in mussels. Differences in caspase-3 activity were also observed between species. Conclusion. Cpz showed adverse effects on vertebrates at μM concentrations, while mussels were affected at pM to nM concentrations, indicating concentration-dependent interspecies effects. Stress responses were similar between species, suggesting that marine molluscs are a potential model for assessing the adverse effects of Cpz on higher vertebrates.