Mollusc Species Research Articles

Multi-scale influences on Escherichia coli concentrations in shellfish: from catchment to estuary.

Sustainability of bivalve shellfish farming relies on clean coastal waters, however, high levels of faecal indicator organisms (FIOs, e.g. Escherichia coli) in shellfish results in temporary closure of shellfish harvesting beds to protect human health, but with economic consequences for the shellfish industry. Active Management Systems which can predict FIO contamination may help reduce shellfishery closures. This study evaluated predictors of E. coli concentrations in two shellfish species, the blue mussel (Mytilus edulis) and the Pacific oyster (Crassostrea gigas), at different spatial and temporal scales, within 12 estuaries in England and Wales. We aimed to: (i) identify consistent catchment-scale or within-estuary predictors of elevated E. coli levels in shellfish, (ii) evaluate whether high river flows associated with rainfall events were a significant predictor of shellfish E. coli concentrations, and the time lag between these events and E. coli accumulation, and (iii) whether operation of Combined Sewer Overflows (CSO) is associated with higher E. coli concentrations in shellfish. A cross-catchment analysis gave a good predictive model for contamination management (R2 = 0.514), with positive relationships between E. coli concentrations and river flow (p=0.001), turbidity (p=0.002) and nitrate (p=0.042). No effect was observed for catchment area, the number of point source discharges, or agricultural land use type. 64% of all shellfish beds showed a significant relationship between E. coli and river flow, with typical lag-times of 1-3 days. Detailed analysis of the Conwy estuary indicated that E. coli counts were consistently higher when the CSO had been active the previous week. In conclusion, we demonstrate that real-time river flow and water quality data may be used to predict potential risk of E. coli contamination in shellfish at the catchment level, however, further refinement (coupling to fine-scale hydrodynamic models) is needed to make accurate predictions for individual shellfish beds within estuaries.

Long-term variations in the diet composition of Atlantic wolffish, Anarhichas lupus marisalbi (Zoarcoidei: Anarhichadidae), in Kandalaksha Bay, White Sea

Understanding the diet variability of the White Sea wolffish, Anarhichas lupus marisalbi Barsukov, 1956, is essential for explaining its population dynamics and variations in its life cycle. This study examined the food spectrum of wolffish from the coastal waters of Chupa Inlet (Kandalaksha Bay, White Sea) and analyzed interannual and seasonal changes in the species composition of its diet. During the summer period, wolffish feeds on a variety of macrobenthic organisms in its feeding grounds, particularly molluscs, echinoderms, crustaceans, and ascidians. The diet was predominantly composed of bivalves and gastropods, with Buccinum undatum Linnaeus, 1758 and Serripes groenlandicus (Mohr, 1786) being the most important prey species. Statistical analysis of multi-year diet data from 2001 to 2023 revealed interannual variations in the frequency of occurrence of key food organisms in wolffish stomachs. The results showed that in the early 2000s, the role of epibenthic crustaceans Hyas araneus (Linnaeus, 1758) and Pagurus pubescens Krøyer, 1838 in the wolffish diet was significantly greater compared to other years of the study. The dietary importance of the bivalve S. groenlandicus increased gradually and statistically significantly during the observation period, while Buccinum undatum dominated the wolffish diet throughout the entire study period. Overall, three species (B. undatum, S. groenlandicus, and Mytilus edulis Linnaeus, 1758) accounted for a significant portion of the wolffish diet during 2001–2023. In some years, other mollusc species, as well as crustaceans and the ascidian Styela rustica Linnaeus, 1767, were also included in the group of important prey items. The feeding intensity of wolffish in Chupa Inlet showed interannual variability. Throughout the observation period, certain years were identified as having the greatest frequency of fish with empty stomachs. Female wolffish showed a seasonal pattern in the frequency of occurrence of individuals with empty stomachs: the highest occurrence of such fish was observed during the spawning period of wolffish, in late July to early August. No significant seasonal changes in the frequency of occurrence of individuals with empty stomachs were found in males.

Detecting Perkinsus-like organisms and Perkinsus marinus (Myzozoa: Perkinsidae) within new bivalve hosts in the southeastern Gulf of California.

Perkinsus marinus, a parasite myzozoa native from the Atlantic Ocean, has spread across various bivalve species in the Pacific Ocean. In the Gulf of California, clams like Larkinia grandis and Leukoma grata have become a secondary fishery, experiencing demand. During annual sampling (August 2017 - July 2018, n = 30/month), the Ray's fluid thioglycollate medium (RFTM) revealed presumptive hypnospores of Perkinsus sp. in L. grandis, with a low parasite prevalence (4.16%) and density (≤ 3.14 hypnospores g-1 tissue). From summer 2020 to summer 2021, P. marinus was seasonally identified in L. grata via staining and PCR tests, showing mean prevalence and density of 48.33% and 48 hypnospores g-1 tissue, respectively. The infection level was light in both clams. This parasite's presence in these new hosts within the southeastern Gulf of California confirms its ability to expand into non-native places, signaling a need for intervention strategies in managing and transporting mollusk species within the region.

MolluscDB 2.0: a comprehensive functional and evolutionary genomics database for over 1400 molluscan species.

Mollusca represents the second-largest animal phylum but remains less explored genomically. The increase in high-quality genomes and diverse functional genomic data holds great promise for advancing our understanding of molluscan biology and evolution. To address the opportunities and challenges facing the molluscan research community in managing vast multi-omics resources, we developed MolluscDB 2.0 (http://mgbase.qnlm.ac), which integrates extensive functional genomic data and offers user-friendly tools for multilevel integrative and comparative analyses. MolluscDB 2.0 covers 1450 species across all eight molluscan classes and compiles ∼4200 datasets, making it the most comprehensive multi-omics resource for molluscs to date. MolluscDB 2.0 expands the layers of multi-omics data, including genomes, bulk transcriptomes, single-cell transcriptomes, proteomes, epigenomes and metagenomes. MolluscDB 2.0 also more than doubles the number of functional modules and analytical tools, updating 14 original modules and introducing 20 new, specialized modules. Overall, MolluscDB 2.0 provides highly valuable, open-access multi-omics platform for the molluscan research community, expediting scientific discoveries and deepening our understanding of molluscan biology and evolution.

Assessment of Heavy Metal (Zinc, Copper, Lead and Cadmium) Contamination in Common Edible Shellfish Species of the Hooghly River and Sunderbans, India

The content of four heavy metals (Zinc, Copper, Lead and Cadmium) in muscles of three shell fish species - prawns -Penaeus monodon and Penaeus indicus and crabs-Scylla serrata, the most prime shellfish food resources of human in the domestic and international market were studied at four stations in the estuarine belt near Bay-of-Bengal which receives wastes of various types from industries and various anthropogenic activities. The samples were digested by acid digestion. The metal contents were quantified using an AAS (Atomic absorption spectrophotometer). The distribution of trace metals accumulated in the muscle tissues of the above mentioned species was in the order- Zn > Cu> Pb> Cd. In the present study, levels of Zinc in the shell fishes ranged from 07.44±0.65 to 128.10 ±2.96 ; Cu ranged from 5 ±0.15 to 99.14 ±1.31; Pb varied from 1.67± 0.14 to 23.99 ± 0.79 and Cd ranged from 1.29± 0.35 to 7.09 ± 0.80.The concentration of the four metals exhibited spatial variation as station 1 >station 2 > station 3 > station 4, which could be a reflection of different bioavailability of metal concentrations in the water body at different stations. The results obtained showed that the metal concentrations in most of the cases were above the threshold value recommended by WHO. Metals such as Cu, Zn, Pb, Cd, can affect various aquatic organisms as well as human being either directly or indirectly as they can enter into the food chain and may be biomagnified at higher trophic levels which is one of the top concerns for human health. Essential heavy metals such as Zinc and Copper are relatively less harmful at low concentration while non-essential metals such as Cd and Pb are highly toxic even at low concentrations.

Assessing Microplastic Contamination in Shellfish: Insights from Pantai Remis Kuala Selangor, Strait of Malacca, Malaysia

Introduction: Microplastic (MP) contamination poses a global environmental threat, affecting terrestrial and marine ecosystems, and human health. This study investigates the presence, density, and composition of MPs in three commercially important shellfish species, oriental angel wing clam (Pholas orientalis), bamboo clam (Ensis leei), and blood cockles (Tegillarca granosa) at Pantai Remis Jeram, Kuala Selangor. Methods: Microplastics in shellfish were quantitatively analyzed for their abundance, colour, size, shape, and composition using microscopic techniques and micro-Fourier Transform Infrared (FTIR). Standard experimental protocols were followed. Statistical analysis of the data was performed using SPSS to identify correlations between these parameters. Results and Discussion: Our findings reveal a significant presence of MP particles in shellfish with T. granosa exhibiting the highest density (2.417 particles/cm³) compared to E. leei (0.721 particles/cm³) and P. orientalis (1.449 particles/cm³). Fibers and fragments were the dominant MP morphotypes, primarily in black color. P. orientalis and T. granosa contained a majority of MPs within the 1 - 5 mm size range, totalling 41 and 56 particles, respectively. Shellfish samples contain polymers of cellulase acetate and polyethylene terephthalate, indicating possible origins from plastic bottles and textile fibres. A statistically significant difference in the mean MP densities in the different species of shellfish was found by one-way ANOVA analysis (p = 0.042, p < 0.05). Conclusion: This study provides relevant data on MP pollution in commercially significant shellfish species. To effectively mitigate this environmental concern and comprehend the long-term ecological ramifications of MP intake by shellfish, more research is required.

Nematicidal Potentiality of Four Marine Molluscans' Defensive Secretions From the Red Sea Against Syphacia obvelata (Nematoda: Oxyuridae) In Vitro.

The continuous requirement to substitute safe and affordable alternatives for helminth medications, as well as address the resistance of some used drug classes, introduced bioactive products derived from marine animals into the field of competition; however, almost all the previous research only focused on their impact on bacterial and protozoal infection. In the present work, we investigated the potential in vitro nematocidal effect of the aqueous extract of defense secretions for four species of marine mollusks: two cephalopods, namely the cuttlefish Sepia pharaonis and the common Octopus Octopus vulagris and two gastropods, the sea hare Aplysia argus and the sea slug Berthillina citrina, against the adult murine pinworm Syphacia obvelata. Data showed dose and time efficacy in all examined extracts. The sea slug's skin acid secretion has the highest impact, causing death in the cultivated worms, followed by the ink of the sea hare, the common octopus and the cuttlefish, where LC90 after 10 h of exposure were 250, 290, 316, and 391 µg/mL, respectively. Comparatively with the control and albendazole-treated groups, the skin acid secretion of the sea slug caused the highest levels of the antioxidant enzymes SOD, Cat and GSH-PX; however, albendazole prompted the highest level of GSH-PX enzyme in all experimental groups.

The Ability of Gastropods of Lake Baikal to the Feeding and Excretion of Microplastic Particles with Different Morphological Structures

Studies of the pollution of Lake Baikal with microplastic particles have been started quite recently. Almost all research is focused on the assessment of surface water pollution, while the impact of microplastics on Baikal organisms remains unexplored. We conducted a laboratory experiment involving three species of gastropod mollusks, the Palearctic Lymnaea stagnalis (L., 1758) and Radix auricularia (L., 1758), as well as the Baikal endemic Benedictia baicalensis (Gerstfeldt, 1859). Two types of microplastics were used in the experiment: fragments of polystyrene and polyester fibers, prepared independently in the laboratory. These plastic particles, along with the food mixture, were placed in aquariums with mollusks. In total, as a result of the experiment, 386 preparations with mollusk excrement were obtained, of which 144 preparations were for the Radix auricularia species, 176 for the Lymnaea stagnalis species, and 67 for the Benedictia baicalensis species, the experiment with the latter species was carried out only with microplastic fragments. All preparations were analyzed according to the degree of fluorescence. The data were statistically processed using Spearman’s rank correlation coefficient. The data obtained allowed us to conclude that gastropods of these species are able to absorb microplastic particles and remove them from the body. However, the rate of removal of microplastic particles from the body of a mollusk is species-specific, and also directly depends on the morphological structure of microplastic particles.

Peculiarities of the Species Composition, Abundance and Biotope Distribution of Mollusks Fam. Sphaeriidae in Rivers with a Many Lakes in the Catchment Area (by the Example of Water Courses of the Onega Lake Basin)

Using the example of the rivers of the Onega Lake basin, the species composition of mollusks of the Sphaeriidae family, their abundance, biomass, and contribution to benthic communities in rivers with many lakes in the catchment areas were analyzed. Patterns of spatial distribution of species across biotopes and gradients of environmental variables were traced. 26 species of mollusks of this family were identified, among them European-Siberian species predominate. Most of the species of mollusks of the family Sphaeriidae found by us have wide ecological ranges and are found in water bodies of various types. It was found that the contribution of Sphaeriidae to the species richness and functioning of aquatic communities in rivers in the conditions of branched lake-river systems (Lake Onega basin) exceeds the values usual for rivers with a small number of lakes in the catchment area. Using the ANOSIM and PERMANOVA methods, it was proved that the species composition of rocky rapids and riffles, sandy rifts and soft bottom soils is different. Using the IndVal test, seven species were shown to have a statistically significant association with one of these biotopes, and four of them, with rocky bottoms of river rapids and riffles. Using the NMDS method, it was shown that the greatest changes in the species composition of representatives of Sphaeriidae are observed when environmental conditions change from small streams with slow current and brown water to large rivers with fast current and clear water.

Skerki Bank (Strait of Sicily) is a hotspot of molluscan biodiversity: multiple new records for Tunisian waters and description of three new species

Sea bottom sampling of the Skerki Bank in the Strait of Sicily updates the census of marine molluscs inhabiting a biogeographically key sector of the Mediterranean Basin. One single dredge haul at 112-m depth yielded 110 molluscan species belonging to Gastropoda, Bivalvia, and Scaphopoda, of which 41 are new records for Tunisian jurisdictional waters, including three gastropod species new to science. Nearly all the species are shared with the fauna inhabiting the adjacent Italian waters, and most of them are reported also from Malta. We stress that sites characterized by a relevant species richness, diagnosed by hosting more than 100 species, inclusive of rare taxa, are important areas for conservation in need of adequate management.

Uptake, Efflux, and Sequestration of Mercury in the Asian Clam, Corbicula fluminea, at Environmentally Relevant Concentrations, and the Implications for Mercury Remediation

(1) Mercury (Hg) is a persistent, ubiquitous contaminant that readily biomagnifies into higher trophic level species in aquatic environments across the globe. It is crucial to understand the movement of environmentally relevant concentrations of Hg in impacted freshwater streams to minimize risks to ecological and human health. (2) The bioconcentration kinetics of aqueous Hg exposure (20, 100, and 200 ng/L) in the invasive Asian Clam, Corbicula fluminea, were measured. A toxicokinetic model, the first parameterized for Hg accumulation in freshwater clams, was developed to estimate uptake and efflux parameters and compared to previous parameter values estimated for other mollusk species. (3) Results demonstrated that even at low Hg concentrations, Corbicula record signals of contamination through bioconcentration, and both direct measurement and toxicokinetic models demonstrate large Hg bioconcentration factors (as high as 1.34 × 105 mL/g dry tissue), similar to partitioning coefficients seen in engineered Hg sorbents. (4) Our study found that Corbicula accumulated Hg at aqueous concentrations relevant to impacted streams, but well below regulatory drinking water limits, demonstrating their utility as a sensitive sentinel species and potential bioremediator.

Vertebrate endocrine disruptors induce sex-reversal in blue mussels

Mollusks are the second most diverse animal phylum, yet little is known about their endocrinology or how they respond to endocrine disrupting compound (EDC) pollution. Characteristic effects of endocrine disruption are reproductive impairment, skewed sex ratios, development of opposite sex characteristics, and population decline. However, whether classical vertebrate EDCs, such as steroid hormone-like chemicals and inhibitors of steroidogenesis, exert effects on mollusks is controversial. In the blue mussel, Mytilus edulis, EDC exposure is correlated with feminized sex ratios in wild and laboratory mussels, but sex reversal has not been confirmed. Here, we describe a non-destructive qPCR assay to identify the sex of M. edulis allowing identification of males and females prior to experimentation. We exposed male mussels to 17α-ethinylestradiol and female mussels to ketoconazole, EDCs that mimic vertebrate steroid hormones or inhibit their biosynthesis. Both chemicals changed the sex of individual mussels, interfered with gonadal development, and disrupted gene expression of the sex differentiation pathway. Impacts from ketoconazole treatment, including changes in steroid levels, confirmed a role for steroidogenesis and steroid-like hormones in mollusk endocrinology. The present study expands the possibilities for laboratory and field monitoring of mollusk species and provides key insights into endocrine disruption and sexual differentiation in bivalves.

An Ecological Study of the Brown Garden snail Cornu aspersum (Müller, 1774) from selected habitats in Jadiriya in Baghdad vicinity.

The present study is considered a pioneer investigation that deal with the terrestrial brown garden snail Cornu aspersum (Müller), in Iraq. Cornu aspersum however is considered an exotic species in many parts of the world ,The species is most probably infiltrates with plants transferred from one place to another. The species has gained importance in many ways. Nutritionally, the species is consumed as food item in many countries, but in other cases it is considered as pest for the damage it causes when feeding on valuable plant shoots. It also has medical importance for its role and ability in healing wounds, burns and remedy of other skin problems. This snail species however may act as a vector for some parasitic nematodes that cause serious diseases. The species is also important in scientific research, usually referred to as ‘ecological indicator’ employed in environmental pollution problems such as the one caused by heavy metals. A great deal of research on this species has been carried out in different parts of the world, however, in Iraq, the scientific attention given to land snails in general and to Cornu aspersum in particular is rare and may be negligible in comparison with the research carried out on aquatic Mollusca species. A total of 1880 individuals of Cornu aspersum were collected from all sampling sites. The study was carried out for the period November 2007 to November 2008 on three sites within the Jadiriya district in Baghdad.. Growth, size classes and shell dimensions of Cornu aspersum populations, and their relationship with major environmental factors; ambient temperature; soil pH, moisture, texture; and the soil content of organic matter have been also investigated. Identification of the species was confirmed by the British Natural History Museum.The data were analyzed by means of standard statistical procedures.

"Groundbreaking study: Combined effect of marine heatwaves and polyethylene microplastics on Pacific oysters, Crassostrea gigas"

Microplastics (MPs) and rising marine seawater temperatures are one of the major environmental problems threatening the survival of marine organisms and biodiversity. However, interactions between such multiple stressors are virtually unexplored. This study aimed to assess the combined effect of two temperatures and polyethylene MPs on the Pacific oyster Crassostrea gigas, one of the most globalized mollusc species for aquaculture. Our work highlights the potential ecological risk posed by these two factors on marine bivalve molluscs. The experimental design was carried out following a 14-day exposure of oysters to environmental concentrations of polyethylene MPs (0.01 mg.L-1), and to two temperatures (15 °C and 22 °C). Sampling was performed on days 0, 7, and 14. The μ-FTIR analysis was applied to quantify MPs of interest and to check a potential environmental contamination. Tissue samples of digestive glands were collected from the oysters to evaluate the activity of biomarkers including superoxide dismutase, glutathione-s-transferase, malondialdehyde and laccase through protein levels. We note that the combination of MPs and high water temperature (HWT, 22 °C) had a significant impact both on the survival of animals and on stress markers, by modifying lipid peroxidation and immune responses. This original study gave the first innovative results on this topic and provides us with knowledge of the combined effects of MPs pollution and HWT (simulating marine heatwaves situation) on C. gigas. There remains a lack of information on the toxicity and the potential environmental hazard of plastics in the marine environment.

Under-documented micro species and the end of Carolinian endemism: bivalves of the Waccamaw Formation (basal Pleistocene, S.E. USA)

ABSTRACT The Waccamaw Formation is a Gelasian (basal Pleistocene, 2.5–1.8 Ma) muddy shell-sand found in patches in southeastern North Carolina and northeastern South Carolina, USA. It has a diverse molluscan fauna but has never been monographed. Previous studies documented about 650 species of molluscs, including about 215 bivalves. Extensive sampling of three sites and examination of other unpublished collections has increased those figures to 1,250 and 335 species, respectively. In addition to numerous geographical and chronological range extensions, this study has also discovered 52 undescribed species of bivalves and 8 apparently undescribed genera of bivalves (two of those are extant and known from previous studies) and 9 families of bivalves new to the formation. Galeommatoidea has seen the greatest increase in documented diversity, going from 21 to 53 species known from the formation; the next most dramatic is Anomalodesmata, going from 14 to 32 species known to be present. The molluscan fauna of the Waccamaw Formation has a species richness more typical of tropical areas, but with a distinctive mix of subtropical shallow to mid-shelf taxa, and a few typically cold-water groups. The Recent fauna in the region with the most comparable average water temperature, South Carolina to northern Florida, has much lower diversity (about 775 species of molluscs, with about 280 of them bivalves) and lower endemism (almost no recent endemics) in a comparable amount of geographic area to the Waccamaw Formation deposits. A dramatic drop in typical winter water temperatures c. 1.8–1.7 Ma seems to be the most likely cause for these changes. Bivalve groups which have had the greatest drop in regional diversity are Noetiidae, Carditidae, Astartidae, Galeommatoidea, Ungulinidae and Pandoridae. Contrastingly, the local diversities of Arcidae, Mytiloidea, Lucinidae, Cardiidae and Pholadidae have all increased between the Gelasian and the recent, overwhelmingly through northwards range expansions.

Shell-bearing Bivalvia and Gastropoda from a rocky shore in the Central Caribbean of Colombia

This study documents the natural accumulation of mollusk shells on an elevated rocky shore carved into the calcareous rocks of the La Popa formation at Punta Roca (Atlántico), covering an estimated area of 0.35 km2. Hydrodynamic transport and differential exposure to environmental conditions are the primary factors contributing to shell deposition. A total of 58 mollusk species were identified, including 30 bivalves and 28 gastropods. The Veneridae was the most prominent, with the highest number of species (7) and shells comprising 64.22 % of the total. Key species contributing to the accumulation include the bivalves Anomalocardia cf. flexuosa, Polymesoda cf. arctata, Leukoma pectorina, Tivela mactroides, Crassostrea rhizophorae, and the gastropod Vitta virginea. These species are primarily characteristic of estuarine environments, with the exception of T. mactroides. Notably, the first recorded occurrence of the non-native gastropod Naria turdus (Cypraeidae) on the Colombian Caribbean coast was documented. The accumulations exhibit varying degrees of abrasion, fragmentation, encrustation, and bioerosion, with some shells appearing almost intact, indicating differences in origin and transport mechanisms. The extraction of shells for ornamental purposes poses a significant challenge to this natural accumulation.

Bioaccumulation of natural radionuclides in edible molluscs and associated risk from the Ashtamudi Estuary, situated in a high background natural radiation zone (HBNRA), Kerala, southwest coast of India

The study investigated various natural radionuclides, including 238U, 232Th, 210Po, and 210Pb, in edible molluscan species collected from different zones of the Ashtamudi estuary. Physicochemical and sedimentological factors played crucial roles in influencing the distribution of radionuclides in water and sediments. Notably, bivalve species, particularly those from the Cyrenidae family, exhibited significant bioaccumulation of 210Po (up to 432.8 Bq kg−1) and 210Pb (up to 121.3 Bq kg−1), with Zone VI recording the highest biological concentration factor (BCF) and biological sediment accumulation factor (BSAF). The calculated effective dose for humans consuming bivalve meat was moderate, falling above the lower end of the ICRP range of 1 mSv y−1 but well below the upper limit of 20 mSv y−1 for existing elevated radiation zones. The intake of radioactivity from some bivalves corresponded to a cancer risk of approximately 3.2 × 10−2 (total mortality + morbidity), exceeding the acceptable risk threshold reported by the USEPA. However, this level of exposure indicated that immediate action might not be necessary, especially if further dose reduction proved impractical, in line with the ICRP's approach to optimizing radiation protection.

A Study on the Availability of Finfish and Shellfish of Junput Mangrove, East Midnapore, West Bengal, India

The fish species diversity is the most important indicator of health of aquatic environment. A good piscina ecosystem diversity illustrates the equable environment. The present study deals with the variety of fishes in the Junput mangrove area (Biramput to Haripur), East Midnapore district. The Junput mangrove area is located at the northern end of the Bay of Bengal (Latitude- 21°94'04.5"N Longitude- 87°26'59.5"E), West Bengal. The field study was taken for a season of two years and data are collected monthly basis were made from May 2022 to April 2024. The study results of the actual inquiry express the occurrence of 93 species (51 finfishes and 42 shellfishes). 51 finfishes belonging to 44 genera, 34 different family and 18 orders and 42 shellfishes belonging to 26 different genera, 15 different family and 03 orders. Among the rerecorded finfish species, 2 species were Vulnerable (VU), 01 species were Near Threatened (NT), 35 species were Least Concern (LC) while 06 species were Not Evaluated (NE), 07 species were Data Deficient (DD) with 44 genus, 18 orders and 34 families. In the case of recorded shellfish species, 33 species were Not Evaluated (NE), 06 species were Least Concern (LC) and 03 species were Data Deficient (DD) with 26 genus, 03 orders and 15 families. The number of species richness in the order Decapoda were dominated by 39 species followed by Perciformes with 08 species; Clupeiformes with 07 species; Tetradontiformes with 05 species; both Gobiformes and Anguilliformes with 04 species; both Acanthuriformes and Carangiformes with 03 species; Siluriformes, Spariformes, Pleuronectiformes, Mugilliformes, Scombriformes, Aulopiformes and Xiphosurida with 02 species; Myliobactiformes, Cypriniformes, Carcharniformes, Elopiformes, Beloniformes and Stomatopoda with 01 species. Out of 93 finfish and shellfish, 50 were carnivores, 39 were omnivores, and 02 were each herbivores and detritivores.

Understanding the role of microbes in health and disease of farmed aquatic organisms.

Aquaculture is critical to reduce protein deficiencies and supplement the world's demand for seafood. However, the culture environment predisposes farmed animals to infectious diseases. In particular, the high density of fish, crustacean, mollusk, sea cucumber or algal species allows for the rapid spread of infectious diseases resulting in devastating losses. Massive amounts of antibiotics have been used to sustain aquaculture production. This has led to the critical need to evaluate the impact of current control measures and optimize disease management schemes with an emphasis on global impact and sustainability. Furthermore, local and global changes have enhanced the pathogens' effects over aquaculture settings because increased temperature and pollution may trigger virulence genes and toxin production. Technological developments including biofloc technology, integrated multitrophic systems, recirculating aquaculture systems and probiotics have contributed to enhancing aquaculture sustainability and reducing the need for high loads of antibiotics and other chemicals. Furthermore, biotechnological tools (e.g., omics and cell biology) have shed light on cellular processes in the health and disease of reared organisms. Metagenomics is a reliable and relatively quick tool to identify microbial communities in aquaculture settings.

Two decades of data on the neurotoxic Gymnodinium catenatum dynamics and paralytic shellfish toxins contamination of molluscs in the southwestern Mediterranean: What have we learned?

Harmful algal blooms have been documented in the Moroccan Western Mediterranean region since 1993, primarily associated with the presence of paralytic shellfish toxins (PSTs) produced by the dinoflagellate Gymnodinium catenatum. The proliferation of this neurotoxic species has led to recurring bans on the harvesting of molluscs, resulting in significant socio-economic repercussions and threats to human health. In the present study, we examine the dynamics of G. catenatum and mollusc PST contamination patterns over a 20-year period (2002−2021) in two distinct marine ecosystems: M'diq Bay and the Oued Laou Estuary. For the PST contamination, we considered two commercially important shellfish species: the smooth clam, Callista Chione, and the cockle, Acanthocardia tuberculata. The highest G. catenatum abundances were consistently observed from November to February in both sites. Our data revealed inter-annual variations in G. catenatum abundance, peaking at 91,840 cells.L−1 in November 2011. PST contamination levels in A. tuberculata were significantly higher than those observed in C. chione. Furthermore, we identified a significant correlation (Pearson, P-value <0.05) between PST contamination of smooth clams and the abundance of G. catenatum. The contamination of A. tuberculata by PSTs reached very high levels, with up to 13,500 μg STX di-HCl eq. kg−1 of shellfish meat, exceeding the established safety thresholds by 16-fold. Additionally, there has been an increase in the prevalence and incidence of PSTs over the years. Notably, we observed a substantial increase in G. catenatum blooms and PST events in the Western Mediterranean during the last decade (2010−2021). The examined data suggest that rainfall could play a pivotal role in G. catenatum bloom dynamics by enriching marine waters with nutrients. The statistical model selection approaches indicated that nutrient concentrations (i.e., nitrate and phosphorus) were the most significant parameters for G. catenatum blooms in the studied area.