Cerastoderma Edule Research Articles

Exploring aquaculture related traits of the grooved carpet shell (Ruditapes decussatus) in relation to other bivalve species using Dynamic Energy Budget theory

To assess the potential of the grooved carpet shell (Ruditapes decussatus) for aquaculture in Europe, we used Dynamic Energy Budget (DEB) theory to perform extensive parametrization on the species and compared its energy allocation strategy with those of commonly farmed bivalve species: mussels (Mytilus edulis and Mytilus galloprovincialis), oysters (Ostrea edulis and Magallana gigas), the common cockle (Cerastoderma edule), and great scallop (Pecten maximus). The comparison was based on DEB primary parameters relevant to aquaculture production, such as maximum assimilation rate and kappa, which represents the fraction of energy allocated to maintenance and growth, and compound parameters like the von Bertalanffy growth coefficient and maximum storage density. Furthermore, we evaluated the production efficiency at the population level, which represents the ratio of assimilated energy converted into biomass. Our results revealed notable differences in energy utilization strategies among species. However, uncertainties in parameter estimation and environmental factors challenge the direct translation of these parameters to real-world aquaculture, therefore our interpretation focuses on how these parameters might influence a species’ potential for aquaculture. The grooved carpet shell exhibits a balanced energy allocation strategy with a low growth coefficient and low maintenance costs, leading to high production efficiency. Similarly, the common mussel focuses on growth with significant biomass investment over reproduction, while the Pacific oyster and Mediterranean mussel prioritize reproductive development. The flat oyster and scallop demonstrate rapid growth at the cost of the low production efficiencies. The grooved carpet shell and mussels face constraints such as limited reserves, making them comparatively more susceptible to low food quality and quantity. In contrast, high storage densities in species like the common cockle, scallop, and Pacific oyster suggest resilience to fluctuating food conditions. These findings, along with both agreements and discrepancies with existing literature, highlight the need for further experimental research to refine DEB parameters and enhance their application in aquaculture. Overall, the DEB framework proves effective for exploring aquaculture traits across species and underscores the need for additional work on temperature-related processes, life-history events, and morphological variation.

Multispecies macrozoobenthic seasonal bioturbation effect on sediment erodibility

Bioturbation in estuarine environments describes all sediment reworking processes implied in sediment transport. However, modelling at large spatial and temporal scales remains a challenge because of the need to consider the fauna at the community level, and because animal behaviour is highly seasonal with non-linear effects of macrofauna functional trait interactions. Bioturbation processes can be linked to the activity of organisms, based on the principle of energy ecology, linking the metabolic rate to the erodibility of a sediment colonised by benthic fauna. This study investigates this postulate by evaluating the erodibility parameters of a sediment subjected to: i) the bioturbation under seasonal temperature variations; ii) the synergistic bioturbation of different species. The experimental design consisted of: i) three temperature levels (winter, spring and summer), ii) three types of species duos (Cerastoderma edule and Macoma balthica; Scrobicularia plana and Hediste diversicolor; Corophium volutator and Peringia ulvae) at 4 different relative densities. Two successive experiments were carried out on the same individuals: measurement of oxygen consumption of fauna then measurement of the erodibility of the colonised sediment in a flume. The oxygen consumption confirmed that the metabolic rate is a good model of the fauna respiration, regardless of species. The erosion results indicated that the metabolic rate in the case of the fluff layer resuspension is an interesting descriptor for 1) the assessment of the bioturbation under variable temperatures and 2) the integration of the two different bioturbator species that could co-occur in the same habitat. In contrast, the effect of bioturbation on the mass sediment erosion threshold cannot be easily modelled by using the metabolic rate and the classification in functional groups is required. Bioturbation models of the fluff layer using metabolic rate is a promising tool for modelling the effects of faunal communities on sediment transport at the scale of an estuary and over the long term, even projected in the context of global warming.

Using shell shape analysis based on landmarks to trace the geographical origin of the common cockle (Cerastoderma edule)

Determining the geographical origin of seafood is crucial for regulators and fishing industries who seek to prevent commercial fraud, enforce food safety regulations, and encourage high standards in sustainable fisheries management. The cockle, Cerastoderma edule (Linnaeus 1768), is a key species in estuarine ecosystems and is harvested all over Europe. Therefore, traceability tools using quick and inexpensive techniques to identify the origin of this bivalve are of paramount importance to support law enforcement. In this work, we explore the potential of using Geometric Morphometric (GM) methods to identify the geographical origin of cockle specimens. This method is based on landmarks identified in the shell to trace the origin of specimens obtained in nearby aquatic systems (from <35 km to <250 km distance). Specimens were collected in five aquatic systems (Ria de Aveiro, the Tagus and Sado estuaries, and the Albufeira and Óbidos coastal lagoons) in Portugal. Shells were digitalized and 16 landmarks were identified in each right valve and analyzed using Generalized Procrustes Superimposition. The discriminating power for traceability of 12 statistical and machine learning methods was assessed based on the corresponding shape variables, using R and Python (Linear Discriminant Analysis (LDA), Canonical Variable Analysis (CVA), Principal Component Analysis (PCA), Between-Group PCA (bgPCA), Partial Least Squares Discriminant (PLSD), Classification Regression Tree (CRT), Logistic Regression (LR), Random Forest (RF), Gradient Boosting (GB), K Nearest Neighbors (KNN), Support Vector Machines (SVM), Extending Gradient Boosting (XGBoost) and Neural Networks (NNET). LDA, CVA, SVM, and NNET demonstrated greater accuracy and a F1-score >80%, even with a small and unbalanced sample size. The highest percentage of correctly assigned individuals was obtained in the Tagus estuary (mean 89%) and in the Albufeira lagoon (mean 93%), which were also the systems with more specimens measured (174 and 59 respectively), whereas the worst results were obtained in the Sado estuary (50%, 56 specimens). In the Albufeira coastal lagoon, the best classification methods reached 100% correct classifications. It further highlights the importance of establishing statistical standards, such as the ones developed in the current work, to evaluate different methods, as small changes in the procedure may cause substantial differences in the results and conclusions. The revision of previous works (presented as a table) showed often >90% of correct classification in both bivalves and gastropods, highlighting the potential of the techniques for other mollusks. Our results support the use of GM based on landmarks as a reliable tool for bivalve's traceability, since it is a quick, simple and inexpensive approach. Further research should extend these findings to other species and other shape analysis techniques.

Assessment of sustainable baits for passive fishing gears through automatic fish behavior recognition

Low-impact fishing gear, such as fish pots, could help reduce human’s impact on coastal marine ecosystems in fisheries but catch rates remain low and the harvest of resources used for baiting increases their environmental cost. Using black seabreams (Spondyliosoma cantharus) as target species in the Bay of Biscay, we developed and assessed the efficiency of biodegradable biopolymer-based baits (hereafter bio-baits) made of cockles (Cerastoderma edule) and different biopolymer concentrations. Through a suite of deep and machine learning models, we automatized both the tracking and behavior classification of seabreams based on quantitative metrics describing fish motion. The models were used to predict the interest behavior of seabream towards the bait over 127 h of video. All behavior predictions categorized as interested to the bait were validated, highlighting that bio-baits have a much weaker attractive power than natural bait yet with higher activity after 4 h once natural baits have been consumed. We also show that even with imperfect tracking models, fine behavioral information can be robustly extracted from video footage through classical machine learning methods, dramatically lifting the constraints related to monitoring fish behavior. This work therefore offers new perspectives both for the improvement of bio-baits and automatic fish behavior recognition.

Partitioning of metals in the tissues and cytosolic fraction of Cerastoderma edule

The concentrations of Cd, Cu and Zn have been determined in the tissues and the cytosolic fraction of the common cockle, Cerastoderma edule, collected from sediments in the Tamar, Plym and Avon estuaries (South West, England). Metal concentrations in the tissues of C. edule from the Avon were lower than those from the Tamar and Plym, except for Cu in the digestive gland. Significant statistical relationships were only obtained between the total sedimentary metal concentrations and Cd in the body of C. edule and Cu in the digestive gland. The cytosolic fraction was extracted from each of the tissues and separated for protein analysis thereby allowing determination of the metal contents in high molecular weight (HMW) compounds, metallothionein-like proteins (MTLP) and very low molecular weight (VLMW) compounds. The digestive glands of C. edule from the Avon had relatively low concentrations of MTLP, whereas MTLP concentrations in the digestive gland of cockles from the Tamar and Plym were higher. The cytosolic fraction of C. edule had relatively low total Cd and Cu concentrations associated with MTLP, whereas Zn was preferentially associated with the HMW and the VLMW components. The results are relevant to metal distributions in C. edule and the role of cytosols in the management of metals by C. edule and other invertebrates.

Unravelling epigenetic mechanisms in Cerastoderma edule genome: a comparison of healthy and neoplastic cockles

Cancer is a multifaceted genetic disease characterized by the acquisition of several essential hallmarks. Notably, certain cancers exhibit horizontal transmissibility, observed across mammalian species and diverse bivalves, the latter referred to as hemic neoplasia. Within this complex landscape, epigenetic mechanisms such as histone modifications and cytosine methylation emerge as fundamental contributors to the pathogenesis of these transmissible cancers. Our study delves into the epigenetic landscape of Cerastoderma edule, focusing on whole-genome methylation and hydroxymethylation profiles in heathy specimens and transmissible neoplasias by means of Nanopore long-read sequencing. Our results unveiled a global hypomethylation in the neoplastic specimens compared to their healthy counterparts, emphasizing the role of DNA methylation in these tumorigenic processes. Furthermore, we verified that intragenic CpG methylation positively correlated with gene expression, emphasizing its role in modulating transcription in healthy and neoplastic cockles, as also highlighted by some up-methylated oncogenic genes. Hydroxymethylation levels were significantly more elevated in the neoplastic samples, particularly within satellites and complex repeats, likely related to structural functions. Additionally, our analysis also revealed distinct methylation and activity patterns in retrotransposons, providing additional insights into bivalve neoplastic processes. Altogether, these findings contribute to understanding the epigenetic dynamics of bivalve neoplasias and shed light on the roles of DNA methylation and hydroxymethylation in tumorigenesis. Understanding these epigenetic alterations holds promise for advancing our broader understanding of cancer epigenetics.

A new molecular method for fast differentiation of cockles Cerastoderma edule and Cerastoderma glaucum

Cerastoderma edule and C. glaucum are two species of cockles that co-exist in European waters. They are morphologically similar but exhibit remarkable differences in biological, ecological, and genetic aspects, as well as in resistance to parasites (e.g., Martellia cochilia) and in disease incidence (e.g., disseminated neoplasia). Moreover, they differ in their economic significance; while C. edule represents a highly valuable marine resource, C. glaucum is only marginally fished. The aim of this work was to develop a simple and fast method that, for the first time, uses the sequence of a mitochondrial gene for the molecular differentiation of the two cockle species. A total of 304 partial sequences of the cytochrome c oxidase subunit I (COI) gene, retrieved from the Nucleotide database, were used to design two sets of species-specific primers to generate PCR products of different sizes (322 bp in C. glaucum and 247 bp in C. edule). The discriminatory ability of the PCR assay was tested in cockles from the Spanish, French, and Italian coasts with successful differentiation in all cases. This novel molecular identification method requires minimal technical equipment and can be carried out in one working day. For its simplicity, it can be very useful for conservation and sustainable management of the two cockle species, facilitating the assessment of distribution, abundance and relative sensitivity to viruses, parasites and diseases.

Raised water temperature enhances benthopelagic links via intensified bioturbation and benthos-mediated nutrient cycling

Sediment reworking by benthic infauna, namely bioturbation, is of pivotal importance in expansive soft-sediment environments such as the Wadden Sea. Bioturbating fauna facilitate ecosystem functions such as bentho-pelagic coupling and sediment nutrient remineralization capacities. Yet, these benthic fauna are expected to be profoundly affected by current observed rising sea temperatures. In order to predict future changes in ecosystem functioning in soft-sediment environments like the Wadden Sea, knowledge on the underlying processes such as sediment reworking, is crucial. Here, we tested how temperature affects bioturbation and its associated ecosystem processes, such as benthic nutrient fluxes and sediment oxygen consumption, using luminophore tracers and sediment incubation cores. We used a controlled mesocosm experiment set-up with key Wadden Sea benthos species: the burrowing polychaetes Arenicola marina and Hediste diversicolor, the bivalve Cerastoderma edule, and the tube-building polychaete Lanice conchilega. The highest bioturbation rates were observed from A. marina, reaching up to 375 cm2yr−1; followed by H. diversicolor, with 124 cm2yr−1 being the peak bioturbation rate for the ragworm. Additionally, the sediment reworking activity of A. marina facilitated nearly double the amount of silicate efflux compared to any other species. Arenicola marina and H. diversicolor accordingly facilitated stronger nutrient effluxes under a warmer temperature than L. conchilega and C. edule. The oxygen uptake of A. marina and H. diversicolor within the sediment incubation cores was correspondingly enhanced with a higher temperature. Thus, increases in sea temperatures may initially be beneficial to ecosystem functioning in the Wadden Sea as faunal bioturbation is definitely expedited, leading to a tighter coupling between the sediment and overlying water column. The enhanced bioturbation activity, oxygen consumption, and facilitated nutrient effluxes from these invertebrates themselves, will aid in the ongoing high levels of primary productivity and organic matter production.

Toxicity of two pesticides in binary mixture on survival and enzymatic response of Cerastoderma edule – The warming influence

Pesticide application increased by about 1 million tonnes in the last 3 decades. Pesticides' overuse, coupled with the need for several pesticides to control different pests in the same crop, and its application many times per year, results in dangerous chemical cocktails that enter in aquatic systems, with impacts to the ecosystems and its communities. Climatic changes are currently another great concern, is predicted by the end of the 21st century, the earth's surface temperature will increase by about 4 °C. Bivalve species are reported as essential to the ecosystems' balance. However, they are also indicated as the organisms that will suffer the most serious effects of the temperature increase. So, this work intends to: a) verify the harm of the sub-lethal concentrations of two worldwide used pesticides, oxyfluorfen and copper (Cu), when combined, to Cerastoderma edule at 15 °C and 20 °C; b) assess the changes in the antioxidant defence system, the activity of the neurological enzyme acetylcholinesterase and the nutritive value of C. edule, after exposure to sub-lethal concentrations of oxyfluorfen and Cu, single and in the mixture, at 15 °C and 20 °C; c) observe the interaction between Cu and oxyfluorfen, considering the different biomarkers. Bivalves were exposed to oxyfluorfen and Cu, single and combined, for 96 h, at 15 °C and 20 °C. Results showed lethal effects to the organisms exposed at 20 °C when exposed to the highest binary mixture concentrations. Biochemical effects were observed on the organisms exposed to 15 °C, despite not observing any lethal effects. Briefly, there was a reported increase in oxidative stress and a decrease in protein content, regardless of the increase in the activity of antioxidant enzymes. These results suggest the potentially dangerous effects of the chemicals' mixture combined with the temperature, on this species and its consumers, impacting the trophic chain, and consequently, the community structure and function.

A cockle-induced bioturbation model and its impact on sediment erodibility: A meta-analysis

Modelling the dynamics of an estuary and the evolution of its morphology requires a process-based description not only of the physical processes, but also of the influence of benthic fauna on sediment characteristics at ecosystem scale. A meta-analysis was tested as an approach for modelling the effect of bioturbation exerted by the cockle Cerastoderma edule on sediment erodibility. Six different erosion flume datasets were collected to ensure a broad range of experimental conditions including bed shear stress, population characteristics, and sediment composition. First, a model was built to describe the biogenic fluff layer created by C. edule activity in relation to (i) bioturbation activity using the population metabolic rate [mW·m−2] as a proxy for faunal metabolic energy, and (ii) the silt content [%] of the sediment. Second, different erosion models were compared by testing parameterization steps incorporating both erosion of the fluff layer and/or mass erosion of the sediment bed. Structural differences in the flumes and in the preparation of samples in the six different datasets makes it difficult to propose a single model that satisfactorily simulates all the data and encompasses both types of subsequent erosion, that of the fluff layer and that of the underlying consolidated bed. However, a generic model is proposed for the surficial fluff layer erosion covering a moderate range of bed shear stress (<1 Pa). This study shows that including several datasets covering a wide range of environmental conditions is a key to the robustness of this model, and that new insights can be gained by integrating the complexity of sediment features. We expect that this two-part model can be used in broad contexts in terms of cockle populations, estuarine habitats, and climatic conditions and can combined with various hydro-morpho-sedimentary models that include these biological effects.

Long-term survey discloses a shift in the dynamics pattern of an emerging disease of cockles Cerastoderma edule, marteiliosis, and raises hypothesis to explain it

Drivers of marine disease outbreaks are poorly understood in spite of their growing impact. We present here results from a unique case study examining how cockles Cerastoderma edule have responded to the introduction of the novel protistan Marteilia cochillia, which led in 2012 to cockle fishery collapse in Galician rias. Based on intensive survey for eight years (2011-2019) of two affected shellfish beds, inner and outer in the Ría de Arousa, involving monthly evaluation of cockle health status and estimation of mortality, detailed information is provided of the declining impact of marteiliosis over a wild cockle population with evidence suggesting its increasing resistance. Disease dynamics involved an annual “breaking wave” of prevalence and subsequent cockle mass mortality, causing the nearly extinction of every recruited cohort. A shift in this pattern, from a severe epidemic towards an endemic profile was observed in the inner shellfish bed since the cohort recruited in 2016, suggesting the hypothesis of increasing marteiliosis resistance through natural selection. Risk factors that may contribute to trigger marteiliosis outbreaks were analysed. Host age and sex did not influence susceptibility to marteiliosis. No clear relationships between environmental conditions (temperature, salinity and upwelling index) or cockle density and disease dynamics were found. Spatial differences in disease dynamics could be due to differences in the abundance of infective stages hypothetically linked to spatial differences in the population dynamics of a putative planktonic intermediate host. All these findings have potential implications for the management of diseased populations.

BivalveNet: A hybrid deep neural network for common cockle (Cerastoderma edule) geographical traceability based on shell image analysis

Bivalve traceability is a major concern. It is of utmost importance to develop tools that allow providing important information to the consumer, not only on the origin of the product but also on its sustainability and safety, due to the harvest restrictions imposed by regulatory entities. This study evaluated the application of computer vision machine learning technologies for efficiently discriminating cockle harvesting origin based on shell geometric and morphometric analysis, improving the traceability methodologies in these organisms, and highlighting the potential of these low-cost techniques as a reliable traceability tool. Thirty Cerastoderma edule samples were collected along the five locations in Atlantic West and South Portuguese coast with individual images processed using lazysnapping segmentation, spectro-textural-morphological phenotype extraction, and feature selection through hybrid Principal Component Analysis and Neighborhood Component Analysis which resulted in R, a*, b*, entropy, and diameter. Three approaches of traceability models were developed and tested: pre-trained networks (EfficientNet-Bo, ResNet101, MobileNetV2, InceptionV3) with numerical inputs (Approach 1), image-based pre-trained networks (Approach 2), and hybrid deep neural networks of Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU), and Bidirectional LSTM (BiLSTM) (Approach 3). Based on the test results, Approach 3 with GRU-LSTM-BiLSTM sequence exhibited the highest accuracy (96.91%) and sensitivity (96%) among the other thirteen machine learning models, hence, named as BivalveNet. Comparing the attained accuracy from the BivalveNet to other mollusc traceability studies, it was observed that an efficiency close to the attained using standard destructive, time-consuming, and expensive techniques, making BivalveNet a highly advantageous approach for common cockle geographical traceability studies, available for application to other bivalve species.

A common garden experiment supports a genetic component underlying the increased resilience of common cockle (Cerastoderma edule) to the parasite Marteilia cochillia.

The common cockle is a valuable bivalve species inhabiting the Atlantic European coasts. The parasite Marteilia cochillia has devastated cockle beds in the southern Galician (NW Spain) rias since 2012. Previous data suggested that cockles from Ría de Arousa acquired some resilience to this parasite through natural selection after consecutive annual marteiliosis outbreaks and candidate markers associated with marteiliosis resilience were identified using population genomics and transcriptomics approaches. Here, a common garden experiment was performed using a naïve stock (from Ría de Muros-Noia) and an affected stock (from Ría de Arousa) to test this hypothesis. Breeders from both stocks were used to produce seed cohorts at hatchery, which were pre-grown in a raft (outdoor nursery stage) and deployed in two shellfish beds affected by marteiliosis in Ría de Arousa (growing-out stage). In both beds, the naïve stock showed high marteiliosis prevalence and was fully depleted in a short period, while the affected stock barely showed evidence of marteiliosis. A set of 45 SNPs putatively associated with marteiliosis resilience were fitted for MassARRAY genotyping to check their role in the differential resilience detected between both stocks. Though no significant differentiation was found between the naïve and the affected stocks with neutral markers, 28 SNPs showed significant divergence between them, suggesting that these SNPs were involved in directional selection during eight generations (to the most) of marteiliosis pressure (long-term selection). Furthermore, signals of selection were also detected in the naïve stock along the marteiliosis outbreak in the growing-out stage (short-term selection) and six SNPs, all shared with the long-term evaluation, showed consistent signals of differentiation according to the infection severity. Some of these SNPs were located within immune genes pertaining to families such as proteasome, ubiquitin, tumor necrosis factor, and glutathione S-transferase. These resilience-associated markers will be useful to recover cockle production in Galicia.

Somatic evolution of marine transmissible leukemias in the common cockle, Cerastoderma edule.

Transmissible cancers are malignant cell lineages that spread clonally between individuals. Several such cancers, termed bivalve transmissible neoplasia (BTN), induce leukemia-like disease in marine bivalves. This is the case of BTN lineages affecting the common cockle, Cerastoderma edule, which inhabits the Atlantic coasts of Europe and northwest Africa. To investigate the evolution of cockle BTN, we collected 6,854 cockles, diagnosed 390 BTN tumors, generated a reference genome and assessed genomic variation across 61 tumors. Our analyses confirmed the existence of two BTN lineages with hemocytic origins. Mitochondrial variation revealed mitochondrial capture and host co-infection events. Mutational analyses identified lineage-specific signatures, one of which likely reflects DNA alkylation. Cytogenetic and copy number analyses uncovered pervasive genomic instability, with whole-genome duplication, oncogene amplification and alkylation-repair suppression as likely drivers. Satellite DNA distributions suggested ancient clonal origins. Our study illuminates long-term cancer evolution under the sea and reveals tolerance of extreme instability in neoplastic genomes.

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

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

Effect of seawater acidification on physiological and energy metabolism responses of the common Cockle (Anadara antiquata) of Gazi Bay, Kenya

Ocean acidification (OA) is becoming a potential threat to marine organisms, especially in calcifying marine invertebrates. So far, along the Kenya Coast, there has been little research on the impact of OA on cockle (Anadara antiquata), particularly on their physiological impacts induced by exposure to acidified seawater. Hence, this study aimed to investigate the physiological and biochemical responses of Anadara antiquata under present and future predicted seawater pH. In this study, the Anadara antiquata was exposed to three pH treatments (pH 7.90, 7.60, and 7.30) for 8 weeks to mimic future OA and to understand the physiological and biochemical effects on the organisms. Condition index, energy reserves (glycogen and protein), and cellular damage (e.g., lipid peroxidation level) were measured. Condition index (CI) showed no significant difference at different pH treatments (pH 7.90, 7.60, and 7.30), whereas the survival Anadara antiquata was slightly reduced after 8 weeks of exposure to pH 7.30. Glycogen and protein content were not affected at reduced pH (7.60 and 7.30). However, after 8 weeks of exposure to pH 7.60 and 7.30, Anadara antiquata showed a slight decrease in lipid peroxidation, an indication of cellular damage. The physiological and biochemical parameters analyzed (glycogen and protein content; lipid peroxidation levels) showed useful biomarkers to assess ocean acidification impacts in cockle.

Exploring the feasibility of cryopreserving larvae of the common cockle (Cerastoderma edule) for hatchery production

The decline of natural populations of the common cockle (Cerastoderma edule) through the European coast is posing a threat to local small-scale fisheries. These declines are primarily attributed to the prevalence of several pathogens and the disseminated neoplasia in cockle populations. The institution of a biobank of cryopreserved larvae could enhance hatchery production and help the restocking. The present work aimed at the development of a cryopreservation protocol for larvae of the common cockle using the mollusk cryopreservation protocols designed in our laboratory. Toxicity bioassays and short-term cryopreservation experiments were performed for protocol optimization according with cellular tolerance. Once settled, the viability of cryopreserved larvae was studied long term. Toxicity tests evidenced high tolerance of larvae against detrimental effects of Cryoprotecting Agents (CPAs). Cryopreservation of 48 h-old D-larva showed a 100% survival when increasing the equilibrium time from 15 to 60 min and using Propylene-Glycol (PG) + 0.4 M Trehalose (TRE) in Filtered Sea Water (FSW) and 60 min of exposure to CPA solution before slow-cooling. However, when cryopreserving the older larvae, the variation in equilibrium times hardly showed any effect but 10% Ethylene-Glycol (EG) + 0.4 M TRE and 60 min of exposure yielded the best relative survivorship (100%). Cryopreservation caused a significant delay on the growth rate of the latest larval stage. However, cryopreserved larvae survived to day 4–6, while 30 ± 12.17% of control larvae developed into pediveliger stage, of which 50% settled and transformed into juvenile cockles. These results demonstrated the role of the cell-type specificity in cryopreservation and highlight the importance of studying potential long-term effects of this tool to ensure the viability of the protocols.

Heterogeneous microgeographic genetic structure of the common cockle (Cerastoderma edule) in the Northeast Atlantic Ocean: biogeographic barriers and environmental factors.

Knowledge of genetic structure at the finest level is essential for the conservation of genetic resources. Despite no visible barriers limiting gene flow, significant genetic structure has been shown in marine species. The common cockle (Cerastoderma edule) is a bivalve of great commercial and ecological value inhabiting the Northeast Atlantic Ocean. Previous population genomics studies demonstrated significant structure both across the Northeast Atlantic, but also within small geographic areas, highlighting the need to investigate fine-scale structuring. Here, we analysed two geographic areas that could represent opposite models of structure for the species: (1) the SW British Isles region, highly fragmented due to biogeographic barriers, and (2) Galicia (NW Spain), a putative homogeneous region. A total of 9250 SNPs genotyped by 2b-RAD on 599 individuals from 22 natural beds were used for the analysis. The entire SNP dataset mostly confirmed previous observations related to genetic diversity and differentiation; however, neutral and divergent SNP outlier datasets enabled disentangling physical barriers from abiotic environmental factors structuring both regions. While Galicia showed a homogeneous structure, the SW British Isles region was split into four reliable genetic regions related to oceanographic features and abiotic factors, such as sea surface salinity and temperature. The information gathered supports specific management policies of cockle resources in SW British and Galician regions also considering their particular socio-economic characteristics; further, these new data will be added to those recently reported in the Northeast Atlantic to define sustainable management actions across the whole distribution range of the species.

Assessing the demographic connectivity of common cockles in a shallow estuary as a basis for fisheries management and stock protection efforts

Common cockle Cerastoderma edule populations in the Danish Limfjorden constitute an important ecosystem component and a valuable resource for fishermen and industries, providing a large proportion of cockle landings in both Denmark and the European Union. However, processes driving cockle recruitment and mortality are not well understood, and prevent sustainable fisheries management and species protection efforts. We report a thorough study of processes that are the main drivers of population recruitment, namely larval dispersal and settlement. Outputs from biophysical modelling of cockle larval dispersal, connectivity analysis and derived graph theory metrics were used to analyse potential demographic connectivity or isolation between known cockle populations and other parts of Limfjorden. The results show that the most productive and commercially important cockle beds are almost exclusively dependent on larval imports from unexploited spawning biomass elsewhere rather than on self-recruitment, allowing for exploitation levels that would be unsustainable otherwise. Other parts of Limfjorden are relatively isolated, relying mostly on self-recruitment. The results also show that in some areas where predicted larval settlement potentials are highest, the absence of a cockle population indicates that other factors, likely environmental, are more important. This study provides an example of contrasting population dynamics and connectivity, suggesting that the vulnerability of cockle populations to exploitation or natural mortality may be highly variable and interlinked. Ignoring processes affecting larval dispersal may jeopardise cockle populations and fisheries in Limfjorden. This study highlights the importance of understanding processes of marine connectivity for the protection of bivalve populations and sustainable fisheries management.

Microencapsulated Diets as an Alternative to Bivalve Feeding: Particle Size and Microalga Content Affect Feed Intake.

Bivalve mollusks represent a nutritious source with a low environmental impact; as a result, they are one of the most attractive aquaculture options. Advances in microencapsulation technology offer great potential to face key bivalve nutrition problems, and an alga-based microencapsulated diet can turn enriched bivalves into potential functional foods. The central goal of this study was the evaluation of food intake as a function of particle size and microalga content following the supply of four microencapsulated diets, incorporating as core material Nannochloropsis sp. or Tetraselmis sp. in 20 or 40 µm diameter pellets (diets N20, T20, N40, and T40, respectively) in five bivalve species (Magallana gigas, Solen marginatus, Ruditapes decussatus, Ruditapes philippinarum, and Cerastoderma edule). Overall, all tested diets were easily ingested, although food intake was higher for N20 (except for the S. marginatus, which showed a higher rate for the diet T40). Concerning a size-related analysis, C. edule and S. marginatus favored, respectively, smaller and bigger pellet-sized diets, with no signs of selectivity for microalga species. The diet T20 was the lesser ingested, except for C. edule. This knowledge enables a better selection of feed with appropriate and species-adjusted profiles, contributing to the optimization of microencapsulated diets for bivalve rearing and a better final product.