Ruditapes Decussatus Research Articles

Assessment of Risks Associated with Extreme Climate Events in Small-Scale Bivalve Fisheries: Conceptual Maps for Decision-Making Based on a Review of Recent Studies

Extreme climate events, such as heatwaves and torrential rain, affect the physiology and functioning of marine species, especially in estuarine habitats, producing severe ecological and socioeconomic impacts when the affected species support important fisheries, such as artisanal shellfisheries. Studies of the impact of sudden decreases in salinity and increases in temperature were reviewed with the aim of producing comprehensive conceptual maps to aid the management of fisheries of the native clams Ruditapes decussatus and Venerupis corrugata, the introduced Ruditapes philippinarum, and the cockle Cerastoderma edule in Galicia (NW Spain). The maps show the effects on mortality, scope for growth, ability to burrow, changes in gonad development or predation risk. While V. corrugata will generally be more affected by low salinity (5 to 15) or high temperature (30 °C) during only two tidal cycles, C. edule populations may recover. Both species are also expected to become more vulnerable to predators. The clams R. philippinarum and R. decussatus will be more resistant, unless extreme events occur after massive spawning episodes; however, the presence of the intertidal seagrass Zostera noltei may buffer the negative effects of high sediment temperature on the growth of some species, such as R. decussatus. Finally, recommendations for assessing climate risk and designing management actions for shellfisheries are given.

Transcriptional Profiling of Populations in the Clam Ruditapes decussatus Suggests Genetically Determined Differentiation in Gene Expression along Parallel Temperature Gradients and between Races of the Atlantic Ocean and West Mediterranean Sea

Ongoing ocean warming due to climate change poses new challenges for marine life and its exploitation. We have used transcriptomics to find genetically based responses to increased temperature in natural populations of the marine clam Ruditapes decussatus, which lives along parallel thermal gradients in southern Europe. Clams of the Atlantic and West Mediterranean races were collected in northern (cool) and a southern (warm) localities. The animals were kept in running seawater in the warm, southern Atlantic locality for a 15-week period. During this period, water temperature was raised to typical southern European summer values. After this period, an expression profile was obtained for a total of 34 clams and 11,025 probes by means of an oligonucleotide microarray. We found distinct transcriptional patterns for each population based on a total of 552 differentially expressed genes (DEGs), indicating innate differences which probably have a genetic basis. Race and latitude contributed significantly to gene expression differences, with very different sets of DEGs. A gene ontology analysis showed that races differed mainly in the genes involved in ribosomal function and protein biosynthesis, while genes related to glutathione metabolism and ATP synthesis in the mitochondria were the most outstanding with respect to north/south transcriptional differences.

Possible Interaction between ZnS Nanoparticles and Phosphonates on Mediterranean Clams Ruditapes decussatus.

This study aims to evaluate the toxicity of ZnS nanoparticles (ZnS NP50 = 50 µg/L and ZnS NP100 = 100 µg/L) and diethyl (3-cyano-1-hydroxy-2-methyl-1-phenylpropyl)phosphonate or P (P50 = 50 µg/L and P100 = 100 µg/L) in the clams Ruditapes decussatus using chemical and biochemical approaches. The results demonstrated that clams accumulate ZnS NPs and other metallic elements following exposure. Moreover, ZnS NPs and P separately lead to ROS overproduction, while a mixture of both contaminants has no effect. In addition, data showed that exposure to P100 resulted in increased levels of oxidative stress enzyme activities catalase (CAT) in the gills and digestive glands. A similar trend was also observed in the digestive glands of clams treated with ZnS100. In contrast, CAT activity was decreased in the gills at the same concentration. Exposure to ZnS100 and P100 separately leads to a decrease in acetylcholinesterase (AChE) levels in both gills and digestive glands. Thus, AChE and CAT after co-exposure to an environmental mixture of nanoparticles (ZnS100) and phosphonate (P100) did not show any differences between treated and non-treated clams. The outcome of this work certifies the use of biomarkers and chemical assay when estimating the effects of phosphonate and nanoparticles as part of an ecotoxicological assessment program. An exceptional focus was given to the interaction between ZnS NPs and P. The antioxidant activity of P has been demonstrated to have an additive effect on metal accumulation and antagonistic agents against oxidative stress in clams treated with ZnS NPs.

Mollusc collection and Holocene palaeogeographical evolution in a southwestern iberian estuary: Statistical analysis of the early Holocene Cañada Honda shell midden (SW Spain)

The malacological analysis of the Cañada Honda shell midden (Tinto-Odiel estuary, SW Spain) has allowed an approximation of the palaeo biodiversity of this sector during the Mesolithic. During this period, the progressive marine transgression caused the flooding of this estuary, coinciding with an initial intensive capture of the bivalves Lutraria and Ruditapes decussatus in the northern and southern sector of this site, respectively. In a second phase, Ruditapes decussatus was the main collected species in all sectors. This last period coincided with some diversification in catches, still dominated by Ruditapes decussatus but with significant proportions of Cerastoderma edule. This stage witnessed a progressive sedimentary filling of the estuary and the creation of marshes and barrier islands. The almost total fragmentation of the specimens would imply that the surface of this shell midden was exposed for a long time while in use. In addition, an occasional charring of some molluscs has been detected. The main molluscs of this site are also the most abundant in other later shell middens (∼cal 5.2–4 kyr BP), indicating an important perpetuation of the collecting and/or eating habits in this environment. All the species determined in them are also currently found in this estuary and its surroundings, where they are also captured.

Effects of Carbon Nanoparticles and Chromium Combined Exposure in Native (Ruditapes decussatus) and Invasive (Ruditapes philippinarum) Clams.

Studies have described the occurrence of nanoparticles (NPs) in aquatic ecosystems, with particular attention to the widely commercialized carbon nanotubes (CNTs). Their presence in the environment raises concerns, especially regarding their toxicity when co-occurring with other pollutants such as metals. In the present study, changes to the metabolic capacity, oxidative, and neurologic status were evaluated in the presence of carboxylated multi-walled CNTs and chromium (Cr(III)) using two of the most ecologically and economically relevant filter feeder organisms: the clam species Ruditapes decussatus and R. philippinarum. Results indicated that although Cr, either alone or in combination with CNTs, was found in a similar concentration level in both species, a species-specific Cr accumulation was observed, with higher values in R. decussatus in comparison with R. philippinarum. Inhibition of antioxidant defenses and neurotoxic effects were detected only in R. philippinarum. The interaction between contaminants seems to have no effect in terms of antioxidant enzyme activities and neuro status. Nevertheless, synergistic activation of responses to both contaminants may have altered the metabolic capacity of bivalves, particularly evident in R. decussatus. While both clams are tolerant to both contaminants (alone and together), they showed a relevant accumulation capacity, which may represent a possible contaminant transfer to humans.

Are clam-seagrass interactions affected by heatwaves during emersion?

The increased frequency of heatwaves expected in the context of global warming will affect socio-ecological systems such as shellfish beds at intertidal seagrass meadows. A mesocosm experiment was performed to assess the effects of a simulated atmospheric heatwave during low tide on the bioturbation indicators and growth of the commercial juvenile native Ruditapes decussatus and the introduced clam R. philippinarum, and on their interactions with the seagrass Zostera noltei. Under the heatwave, heat dissipation at 5 cm depth was significantly greater in the sediments below Z. noltei than below bare sand, the photosynthetic efficiency (Fv/Fm) of Z. noltei decreased and the clams tended to grow less. Furthermore, after the heatwave clams below bare sand tended to burrow deeper than those below Z. noltei, indicating that seagrass provided a refuge for clams. Ruditapes philippinarum grew less, and did not burrow as deeply as R. decussatus, which may imply greater vulnerability to desiccation and heat at low tide. The particle displacement coefficient (PDC) of R. philippinarum indicated lower bioturbation values in Z. noltei than in bare sand and was a suitable bioturbation indicator for juvenile Ruditapes spp. clams. In Z. noltei coexisting with R. philippinarum, the Fv/Fm values were higher than without clams after a recovery period, which may be linked to the assimilation of phosphate excreted by the clams and suggests a facilitative interaction. No such interaction was observed with R. deccusatus, probably because of its deeper burrowing depth. The findings suggest reciprocal facilitative interactions between R. philippinarum and Z. noltei and the potential contribution of Z. noltei to the sustainability of clams under global warming scenarios, which may support management actions aimed at enhancing the coexistence between shellfishing activities and seagrass conservation.

Search for new biomarkers of tolerance to Perkinsus olseni parasite infection in Ruditapes decussatus clams

The grooved carpet shell (Ruditapes decussatus) is a clam species with high economic and social importance in several European and Mediterranean countries. Production of this species suffered a decline caused by biotic (parasite infection) and abiotic factors (environmental factors, stress, poor management methods and intensive culture of the introduced species Ruditapes philippinarum). The protozoan parasite Perkinsus olseni is also responsible for the decline of production, being nowadays one of the major issues for clam culture. Molecular biomarkers that might represent tolerance of R. decussatus to P. olseni have already been uncovered, shedding light in a possible production improvement by selecting those clams with a strongest immune response.In the present study, new tolerance biomarkers to P. olseni infection in R. decussatus were identified. The haemolymph proteomic profiles of naturally non/low-infected (tolerant) and highly-infected (susceptible) clams by the parasite across several heavy affected areas of Europe were characterized through a shotgun proteomics approach. Also, the mechanisms that might be involved in the responses against the disease in chronic infections were explored. Proteins related to energy restoration and balance, metabolic regulation, energy accumulation, ROS production, lysosomal activity, amino acid synthesis, proteolytic activity, iron regulation, iron withholding, and immune response modulation were significantly regulated in susceptible clams. In the tolerant group, proteins related to phagocytosis regulation, control of cell growth and proliferation, gonadal maturation, regulation of apoptosis, growth modulation, response to oxidative stress, iron regulation, shell development and metabolic regulation were significantly expressed.In summary, the protein expression profile of tolerant individuals suggests that an efficient pathogen elimination mechanism coupled to a better metabolic regulation leads to a tolerance to the parasite infection by limiting the spread through the tissues.

Effect of the alveolate parasite Perkinsus olseni infection on sexual maturation and spawning efficiency of the clam Ruditapes decussatus.

The effect of Perkinsus olseni infection on the reproduction ability of clams has been underestimated so far. Although some studies found evidence of reduction of egg production and delay in gonad maturation after infection, the total effect of the infection is still unclear. In this study, Ruditapes decussatus clams from a naïve population were injected with two different doses of P. olseni parasites, a low dose leading to a light infection and a high dose leading to a heavy infection. Clams were maintained during 2 months for maturation, and at the end of the experiment, the spawning was induced, the number of larvae release and mortality were evaluated. During the maturation period, infection level, gonadal stage, condition index, gross biochemical composition and oxidative status of progenitors were evaluated at days 0, 30 and 60 post-injection. The effects of P. olseni infection on clams showed alterations on biochemical parameters, namely lipid peroxidation, a significant mortality and a delayed gonad maturation, with a greater effect in the highly infected individuals. The reproductive capacity of the clams was impaired in both infected groups showing a lower production and a higher mortality rate of larvae. Finally, this study indicates that the production of natural beds with a high prevalence of P. olseni could be compromised by a deregulation of the natural reproduction cycle and a decrease in larvae production by infected animals, probably due to a combination of lower egg production and lower lipid reserves in larvae from infected clams.

Effects of an Endocrine Disruptor Triclosan on Ruditapes decussatus: Multimarker and Histological Approaches.

The aim of this work was to study the ecotoxicological effects of an endocrine disruptor triclosan on the clam Ruditapes decussatus. The bivalves were exposed to three concentrations of this biocide (C1 = 100 ng/L, C2 = 200 ng/L and C3 = 500 ng/L) for three and seven days. The impact was assessed at the gills and digestive glands, through activities of an antioxidant defense biomarker (Gluthatione S-Transferase, GST), a damage biomarker (Malondialdehyde, MDA), and a neurotoxicity biomarker (Acetylcholinesterase, AChE). Furthermore, histological traits were approached in different organs to evaluate any possible alteration induced by triclosan. It appears from this study that both gills and digestive glands responded discernibly to triclosan and effects were concentration-dependent. The stressed clams showed a significant increase in their GST and MDA activities in gills and digestive glands compared to controls for both time slots considered. In turn, the AChE activity was clearly inhibited in both organs in a time dependent way. The histological study made it possible to observe several structural pathologies caused by triclosan in the gills and the digestive gland. These alterations consisted mainly of inflammatory reactions, malformations of the lamellae and fusion of the gill filaments, degeneration of the connective tissue, and the erosion of the gill cilia with the appearance of certain severe alterations (cell necrosis and apoptosis), which can thus cause a malfunction of the gills and eventually lead to a reduction in oxygen consumption and a disruption of the osmoregulation for bivalves. Alterations in the digestive gland have also been detected, mainly by epithelial alterations, thinning of the tubules, and alteration of the basal cell membrane which can impair the ability of clams to absorb food. At germinal cells, several damages were observed in the oocytes which probably disturbed the reproductive function and the fertility of the clams. The damages observed in female gonads were caused by the cytolysis of a large number of oocytes through autophagy and necrosis at 200 ng triclosan/L. Moreover, at 500 ng triclosan/L, hemocytic infiltration was observed in acini and apoptotic bodies reflected in the fragmentation of more than 90% of oocytes.

Sclerochronological and geochemical study of the carpet shell Ruditapes decussatus in archaeological contexts: A potential tool for season of collection and coastal paleo-temperature

Specimens of the carpet shell Ruditapes decussatus from the Mesolithic shell midden (6th millennium BC) of Beg-an-Dorchenn (Brittany, France) were studied in order to assess their period of collection as well as provide some insight on Paleo-temperature reconstructions. Cross sectioned shells display very clear growth structures allowing an assessment of a growth rhythm of 2 increments per lunar day. From this temporal framework, daily growth increments and winter annual growth breaks were characterized. Our results show the R. decussatus shells were typically collected in the early spring period. Chemical analyses of shell carbonates were also performed to assess a preliminary range of potential sea temperature data from oxygen isotopes values (δ18Oshell). δ18Oshell shows seasonal variations but do not record the whole seasonal temperature range as R. decussatus have a growth break during winter. However, results show predicted SSTs within the range of expected values. Thus, R. decussatus is particularly suited for paleo-environmental reconstructions at high temporal resolution such as seasonal timescales. Additional sclerochronological and chemical research on additional carpet shells and also other mollusk species from Beg-an-Dorchenn or other Mesolithic shell middens along the European Atlantic coast should be considered. Such studies will contribute to the understanding of the seasonal occupation patterns of the last hunter-gatherers of the European Atlantic coast as well as the climate variability at the Mesolithic-Neolithic transition.

Physiological Responses of the Bivalves Mytilus galloprovincialis and Ruditapes decussatus Following Exposure to Phenanthrene: Toxicokinetics, Dynamics and Biomarkers Study.

The aim of the current study was to assess the multifaceted effects of the polycylic aromatic hydrocarbon phenanthrene, mainly used in the colouring, explosive, and pharmaceutical industries, on the physiology of two bivalve species with economic value as seafood, namely, the Mediterranean mussel Mytilus galloprovincyalis and the European clam Ruditapes decussatus. The current study assessed how the phenanthrene affected several biomarkers and biometric endpoints in both bivalves, based on an in vivo experiment in silico approach. The bivalves were exposed during four time slots (i.e., 7, 15, 21, and 28 days) to two concentrations of phenanthrene in water (50 µg/L and 100 µg/L). For the clam R. decussatus, an additional contamination of sediment was applied due their typical benthic lifestyle (50 µg/kg and 100 µg/kg). The phenanthrene significantly reduced the ability of bivalves to tolerate desiccation and their Median Lethal Time, and also inhibited the activity of the enzyme acetylcholinesterase in a time-dependent manner. The activity of catalase indicated that bivalves also experienced oxidative stress during the first 21 days of the experiment. The significant decline in catalase activity observed during the last week of the experiment for the mussel M. galloprovincyalis supported a depletion of enzymes caused by the phenanthrene. The phenanthrene has also toxicokinetic and toxicodynamic properties, as assessed by the in silico approach. Overall, the results obtained suggest that the bivalves Ruditapes decussatus and M. galloprovincyalis can be used as a sentinel species in monitoring studies to assess the environmental impact of phenanthene in marine ecosystems. The significance of our findings is based on the fact that in ecotoxicology, little is known about the chronic effects, the simultaneous use of multiple species as bioindicators, and the interactions molecular modelling.

Assessment of the distribution of Ruditapes spp. in northern Mediterranean sites using morphological and genetic data

ABSTRACT In the 1970s, Ruditapes philippinarum was introduced to France at Arcachon Bay for aquaculture. At present, in Europe, R. philippinarum is often found in place of the native species Ruditapes decussatus. The aim of this study is to evaluate the distribution of these two species along the northern Mediterranean coastline using morphological and morphometric analysis. The sampling period was between June and December 2018. Among the 11 French sites, only 2 contained R. philippinarum, whereas only the indigenous species was present at the other sites. Genetic analyses were used to confirm species identity and to confirm this distribution. A site in Italy, Pialassa Baiona, was also added to the sample. This analysis of Ruditapes from multiple French sites and one Italian site highlights species-level differences in shell morphology between R. decussatus and R. philippinarum. The intraspecific morphometric analysis showed the presence of different groups depending on spatial scales (i.e. at the large scale, between the Mediterranean Sea and the Atlantic, and on the small scale, that is within the Berre lagoon in France. No relationship between morphometric and genetic variation was found. This suggests that the differences in the shell shape of Ruditapes are driven by local environmental conditions.

Evaluation of the Ruditapes decussatus immune response after differential injected doses of Perkinsus olseni

Ruditapes decussatus is a highly appreciated clam species, with a high demand, especially in European countries. However, natural populations of this species have been affected by over-exploitation, abiotic factors and also by diseases mainly caused by bacteria, virus and protozoans. Within the latter group of pathogens, Perkinsus spp. has been attracting attention for causing relevant mortality rates on bivalves around the world. From all species of this genus, Perkinsus olseni is one of the most impactful for R. decussatus, as it may cause chronic infection with fatal consequences under adverse conditions. Therefore, in this study, naïve clams were injected with two doses of P. olseni in order to better understand the response of R. decussatus against this parasite. So, one of the main goals of this experiment was to evaluate the differential response of the clams at gene expression level after injection and also to monitor the possible mortalities related to parasite. Results indicated that the methods applied for injection and detection of parasite load are effective. Furthermore, altogether, R. decussatus gene expression studies indicate differences on expression of some of the addressed genes among distinct levels of infection over time, which require further studies to confirm if these genes could be used as molecular markers of P. olseni infection. According to the results obtained, Adiponectin-C1q seems to be a promising gene to be used as molecular marker of chronic infection in claḿs haemolymph.

Ecotoxicity of Copper(I) Chloride in Grooved Carpet Shell (Ruditapes decussatus).

Copper (Cu) is a ubiquitous trace element in the aquatic environment, and is usually found at low levels. Copper environmental concentrations can be altered as a result anthropogenic activities. Shellfish are useful bioindicators to ensure adequate environmental monitoring. Thus, the aim of the present study was as follows: (a) determine the LC50 of copper(I) chloride in grooved carpet shell (Ruditapes decussatus) collected in the Santa Gilla lagoon (Sardinia, Italy), and (b) analyze the antioxidant biomarkers in digestive gland and gills of same specimens exposed to different concentrations of the above-mentioned metal (0.045, 0.45, and 0.90 mg/L) for 96 h. A withdrawal period of 96 h was considered for the treated clam, carrying out the same biochemical analyses, superoxide dismutase (SOD), catalase (CAT), selenium-dependent glutathione peroxidase (Se-GPx), glutathione S-transferases (GSTs), and total glutathione (GSH+2GSSG) in the two tissues. Different time and dose responses of the antioxidant biomarkers were recorded in the digestive glands and gills. Oxidative stress biomarkers highlighted the ability of Cu to induce oxidative stress in R. decussatus. Clam, following the withdrawal period of 96 h, has not been able to achieve the control levels of all biochemical markers in the digestive gland and gills. R. decussatus can be a suitable model to assess the ecotoxicity of copper in aquatic ecosystems. These findings may advance knowledge on the role and the effects of copper on oxidative stress biomarkers in grooved carpet shell. The metal ecotoxicity response can be useful to perform accurate biomarker-based monitoring programs using this bivalve species.

Effects of short-term hyposalinity stress on four commercially important bivalves: A proteomic perspective

Increased heavy rainfall can reduce salinity to values close to 0 in estuaries. Lethal and sublethal physiological and behavioural effects of decreases in salinity below ten have already been found to occur in the commercially important clam species Venerupis corrugata, Ruditapes decussatus and R. philippinarum and the cockle Cerastoderma edule, which generate an income of ∼74 million euros annually in Galicia (NW Spain). However, studies of the molecular response to hyposaline stress in bivalves are scarce. This ‘shotgun’ proteomics study evaluates changes in mantle-edge proteins subjected to short-term hyposaline episodes in two different months (March and May) during the gametogenic cycle. We found evidence that the mantle-edge proteome was more responsive to sampling time than to hyposalinity, strongly suggesting that reproductive stages condition the stress response. However, hyposalinity modulated proteome profiles in V. corrugata and C. edule in both months and R. philippinarum in May, involving proteins implicated in protein folding, redox homeostasis, detoxification, cytoskeleton modulation and the regulation of apoptotic, autophagic and lipid degradation pathways. However, proteins that are essential for an optimal osmotic stress response but which are highly energy demanding, such as chaperones, osmoprotectants and DNA repair factors, were found in small relative abundances. In both months in R. decussatus and in March in R. philippinarum, almost no differences between treatments were detected. Concordant trends in the relative abundance of stress response candidate proteins were also obtained in V. corrugata and C. edule in the different months, but not in Ruditapes spp., strongly suggesting that the osmotic stress response in bivalves is complex and possibly influenced by a combination of controlled (sampling time) and uncontrolled variables. In this paper, we report potential molecular targets for studying the response to osmotic stress, especially in the most osmosensitive native species C. edule and V. corrugata, and suggest factors to consider when searching for biomarkers of hyposaline stress in bivalves.

Comparative study of immunological biomarkers in the carpet shell clams (Ruditapes decussatus) from metal-contaminated sites in the South Lagoon of Tunis (Tunisia)

The South Lagoon of Tunis (Tunisia) is a Mediterranean lagoon adversely affected by industrial contaminants, harbour activity and untreated urban sewage. In this lagoon, the clam Ruditapes decussatus has been widely used as a biomonitor of seawater pollution through measurements of parameters related to oxidative stress and neurotoxicity. However, few studies have considered parameters of the immune system of this species in the South Lagoon of Tunis. Therefore, the aim of the present work was to evaluate several immune-related parameters in the cell-free haemolymph of carpet shell clams sampled during August and February from three polluted sites in the South Lagoon of Tunis (S1, S2 and S3) and one less polluted site as a reference site (RS) in order to identify suitable biomarkers for environmental quality assessments of this ecosystem. Concerning the immune-related parameters, seasonal factors modulated phenoloxidase, lysozyme, protease and esterase activity, with lower values measured for samples collected in August than for samples collected in February. In fact, bactericidal activity against two of the pathogenic bacteria tested and the activity of most immune-related enzymes were reduced in the cell-free haemolymph of clams collected from the most sampling sites in August compared to February one. In addition, values of abiotic parameters (temperature, salinity and pH) and metal (cadmium, copper, iron, lead and zinc) concentrations in the clams’ soft tissues, previously obtained and published by the authors, as well as the values of immune-related parameters were integrated using principal component analyses. Results indicated that the values of all measured immune-related parameters were negatively correlated with the temperature values and the variations most of these parameters highlighted that the chemical industrial area (S3) was the most impacted location within the South Lagoon of Tunis. The present study illustrates that the immune-related parameters measured in carpet shell clam cell-free haemolymph represent suitable biomarkers for environmental quality assessments because they provide effective seasonal and spatial discrimination.

Effects of warming on biological interactions between clams and the seagrass Zostera noltei: A case study using open top chambers

Bivalves and seagrasses can interact through diverse environmentally-modulated mechanisms. To assess the effects of climate warming on bivalve-seagrass interactions, we carried out a pioneering field experiment in which open top chambers (OTCs) were used to increase air and sediment temperature in a shellfish bed in NW Spain during two consecutive spring tides (16 days of exposure to OTCs). The temperature increase produced by OTCs was significant, as observed in the daily maximum and mean temperature and in degree hours, although the difference was greater in air and at the sediment surface (up to 8 °C and 3 °C, respectively) than at 5 cm depth (up to 1 °C). Warming was less acute in boxes with the seagrass Zostera noltei, which acted as a thermal buffer, reducing the mean temperature by 1 °C at the sediment surface in OTC boxes and control boxes (without OTCs). Although the short-term increase in temperature did not greatly affect physiological responses of Z. noltei, the carbohydrate reserves and nutrient content increased in the presence of clams. Growth of the native clam Ruditapes decussatus was significantly slower in OTC boxes with bare sediment, and the seagrass thus buffered the negative effect of warming on growth. The presence of Z. noltei may save clams from having to spend energy to burrow deeper to encounter cooler conditions, leaving more energy available for growth. Conversely, growth of the introduced clam R. philippinarum did not differ between habitats or treatments. Our findings confirm a two-way facilitative interaction that may be particularly important in relation to the resilience of both species in the current context of global warming.

Does global warming threaten small-scale bivalve fisheries in NW Spain?

Shellfisheries of the intertidal and shallow subtidal infaunal bivalves Ruditapes decussatus, Ruditapes philippinarum, Venerupis corrugata and Cerastoderma edule are of great socio-economic importance (in terms of landings) in Europe, specifically in the Galician Rías Baixas (NW Spain). However, ocean warming may threaten these fisheries by modifying the geographic distribution of the species and thus affecting productive areas. The present study analysed the impact of rising ocean temperature on the geographical distribution of the thermal comfort areas of these bivalves throughout the 21st century. The Delft3D model was used to downscale climate data from CORDEX and CMIP5 and was run for July and August in three future periods (2025–2049, 2050–2074 and 2075–2099) under the RCP8.5 scenario. The areas with optimal temperature conditions for shellfish harvesting located in the middle and outer parts of the rias may increase in the near future for R. decussatus, V. corrugata and C. edule and decrease in the far future for R. philippinarum. Moreover, shellfish beds located in the shallower areas of the inner parts of the Rías Baixas could be affected by increased water temperature, reducing the productive areas of the four species by the end of the century. The projected changes in thermal condition will probably lead to changes in shellfish harvesting modality (on foot or aboard vessels) with further socio-economic consequences.

SOME MORPHOLOGICAL TRAITS AND HEAVY METAL ACCUMULATION IN MUSCLE TISSUE OF Ruditapes decussatus (Linnaeus, 1758)

This study aimed to investigate some morphological features and heavy metal accumulation in muscle tissue of Ruditapes decussatus (Linnaeus, 1758) in the spring and autumn seasons of 2018 in the Yumurtalık Coastline of İskenderun Bay located in the northeastern Mediterranean Sea. To this end, shell length (SL), total weight (TW), shell height (SH), shell inflation (SI), shell weight (SW), roundness index (RI), cup index (CI) and total length-weight relationship (LWR) of Bivalvia and heavy metal accumulation in the muscle tissue of Bivalvia were measured for two seasons. Minimum and maximum values of SL, TW, SH, SI, SW, RI and CI were determined as 21.50-39.00 mm, 0.80-22.15 g, 10.50-28.70 mm, 9.11-20.90 mm, 3.08-4.66 g, 1.03-2.14 and 0.58-0.67 respectively. The relationship between total length and total weight of R. decussatus was calculated to be W=0.0052*SL2.54 for spring and W=0.0031*SL2.88 for autumn. The growth type of Bivalvia specimens was determined as isometric growth (2.971). Heavy metal accumulation in the muscle tissue in spring and autumn seasons was found as statistically significant only for zinc and copper in different seasons (P

The Impact of Climate Change on Bivalve Farming: Combined Effect of Temperature and Salinity on Survival and Feeding Behavior of Clams Ruditapes decussatus

European clam (Ruditapes decussatus) is one of the most relevant emergent bivalve species from the aquaculture sector in Europe with high economic value. Climate changes represent a potential limiting factor to this activity, directly interfering with the survival and behavior of bivalves. Severe fluctuations in temperature along with periods of heavy rainfall or periods of drought that significantly change the salinity can promote physiological stress in bivalves, resulting in changes in physiological and behavioral responses and, in extreme cases, leading to high mortalities. This study aimed to evaluate the combined effect of temperature and salinity on mortality and feeding behavior of R. decussatus. Juveniles and adults were exposed to combined ranges of temperature (5°C–35°C) and salinity (0–40). Mortality and feeding behavior were registered every 24 h of each 120-h trial. A control temperature range was set between 15°C and 23°C, where mortality and feeding behavior were considered as the normal scenario. Our data suggested salinity 15 as a “turning point,” a point from which occurred distinct patterns in mortality and feeding behavior. The results evidently indicate that abrupt reductions in salinity and sharp increases in temperature will lead to high mortality of R. decussatus. Juveniles were revealed to be more sensitive to the increase of temperature in a less saline environment, to suffer greater and faster mortalities, and to be more resistant to extremely high temperatures under more saline conditions. The high temperatures and sporadic heavy rainfall that are predicted to occur in the south of Europe due to climate changes will contribute to compromise the recruitment of European clam, thus threatening the production of this species and consequently impacting the economic sector.