Wedge Clam Research Articles

Microsatellite variation in Donax trunculus from the Iberian Peninsula, with particular attention to Galician estuaries (NW Spain)

Genetic variation and population structure information is essential for conservation and stock management policies. The wedge clam Donax trunculus is an important fishing resource in the Iberian Peninsula and in some areas, such as the northwestern Spain, wild stocks have decreased greatly. Despite this, information is mainly from the southwestern Atlantic to the northwestern Mediterranean of the Iberian Peninsula. In this study, fifteen microsatellite loci were examined at 17 localities along the Iberian Peninsula to characterize its genetic diversity and population structure. Particular attention was paid to the northwestern Atlantic area, and to test if the pattern previously described for this species is confirmed when localities distributed across the Atlantic coast are included and different microsatellite markers are used. All localities displayed similar allelic richness values and heterozygosity levels but when genetic diversity levels were compared among groups of localities, tests were significant and samples from the northwestern area (Galicia) showed the lowest values. The analysis of population structure indicated that localities from the Atlantic coast are genetically homogeneous although some samples showed significant pairwise Fst values. These values were low and Bayesian analysis of genetic differentiation did not show a consistent structure along the Atlantic coast of the Iberian Peninsula. However, Atlantic samples were genetically different from those located in Mediterranean coast, which may be explained by the existence of the Almeria-Oran front. Moreover, Fuengirola, locality situated in the Alboran Sea between the Strait of Gibraltar and Mediterranean Sea, showed significant differences from all remaining localities included in the study. Overall, the data showed the existence of genetic homogeneity along the Atlantic coast of the Iberian Peninsula and support the three management units (Atlantic Ocean, the Alboran Sea and the northwestern Mediterranean) previously described in this species. Reduced diversity in the northwestern Spain samples could be related to the exploitation of this resource.

Pea-crab (Pinnotheres sp.) as commensal inside the shells of edible wedge clams and their predators along southwest coast of India

Pea-crab (Pinnotheres sp.) as commensal inside the shells of edible wedge clams and their predators along southwest coast of India

Population and production parameters of the wedge clam Donax trunculus (Linnaeus, 1758) in intertidal areas on the southwest Spanish coast: Considerations in relation to protected areas

The main objectives of this study were (i) to provide an updated age-length key for D. trunculus from Atlantic waters, and (ii) to evaluate population dynamics, the timing of recruitment and production parameters of the wedge clam Donax trunculus in two moderately exposed sandy beaches (the protected area of Doñana National Park and the tourist destination of Isla Canela) along the littoral of Huelva (SW Spain). First an in-depth analysis of the shell and updated estimation of growth parameters of the intertidal D. trunculus population were performed between January 2014 and July 2015 using two different methods i) thin-layer cross section (TL) (ii) length-frequency distributions (LFD). Von Bertalanffy growth functions provided an asymptotic length of 46mm (LFD) and 46.7mm (TL) and growth constants of 0.48 (LFD) and 0.47yr−1 (TL) in Doñana beach. In addition, several deformities as well as signs of shell repair were observed. Population dynamics analyses through length-frequency distribution clarified the timing of recruitment (February–March and July). The mean annual biomass (B¯) of intertidal populations of D. trunculus ranged between 3.03 (Doñana) and 3.31g ash-free dry mass (AFDW) m−2yr−1 (Isla Canela). Individual production showed the highest value at 27mm length (0.117gAFDWm−2yr−1) and annual production (P) ranged between 3.40 (Doñana) and 4.91g (Isla Canela), resulting in renewal rate (P/B¯) values between 1.03 and 1.61, respectively. The present results, together with information on environmental parameters, revealed clear differences in population dynamics and production between beaches related to the presence or absence of a protection figure.

Null alleles are ubiquitous at microsatellite loci in the Wedge Clam (Donax trunculus).

Recent studies have reported an unusually high frequency of nonamplifying alleles at microsatellite loci in bivalves. Null alleles have been associated with heterozygous deficits in many studies. While several studies have tested for its presence using different analytical tools, few have empirically tested for its consequences in estimating population structure and differentiation. We characterised 16 newly developed microsatellite loci and show that null alleles are ubiquitous in the wedge clam, Donax trunculus. We carried out several tests to demonstrate that the large heterozygous deficits observed in the newly characterised loci were most likely due to null alleles. We tested the robustness of microsatellite genotyping for population assignment by showing that well-recognised biogeographic regions of the south Atlantic and south Mediterranean coast of Spain harbour genetically different populations.

Implications for management and conservation of the population genetic structure of the wedge clam Donax trunculus across two biogeographic boundaries.

In a resource management perspective, the understanding of the relative influence of the physical factors on species connectivity remains a major challenge and is also of great ecological and conservation biology interest. Despite the overfishing threat on the wedge clam Donax trunculus in Europe, relatively little information is known about its population genetic structure and connectivity and their consequences on conservation policies. We employed 16 microsatellite loci to characterise the genetic diversity and population structure of D. trunculus. A total of 514 samples from seven different localities along the Atlantic-Mediterranean transition, from the Atlantic (Gulf of Cádiz) to the north-western Mediterranean were genotyped. The analysis of the population genetic structure displayed a clear distinction along the Atlantic-Mediterranean transition with different clusters in the Atlantic Ocean, the Alboran Sea and the northwestern Mediterranean. Consequently, we recommend that these three areas should be considered as different management units. We showed that all populations seem to be at high long-term risk of extinction with the exception of the protected Doñana National Park population which still seems to have evolutionary potential. Therefore, our results emphasized the necessity of protection of this economic resource and the validity of molecular tools to evaluate the population dynamics.

Discard analysis and damage assessment in the wedge clam mechanized dredging fisheries of the northern Alboran Sea (W Mediterranean Sea)

The composition and structure of discard, as well as the damage caused to target and non-target species, was analyzed in 95 commercial fishing hauls carried out between March 2013 and March 2014 by the mechanized dredging fleet targeting wedge clam (Donax trunculus) in the northern Alboran Sea (southern Spain). A large proportion of the catch (ca. 42% weight) is discarded, mainly wedge clam undersized individuals and non-commercial molluscs, decapods and echinoderms. Total discards within the study period showed a high species richness, with a total of 84 taxa discarded, and biomasses ranging from 337.1 to 8532.5g haul−1 (1579.9±157.9g haul−1, mean±SE), with maxima in spring. The composition, structure and biomass of discards displayed significant differences among study sites due to differences in the benthic communities of the fishing grounds. Individuals displaying intermediate (intermediate survival chance) and severe (low survival chance) damage in the discard displayed higher values when gravel and bioclastic material was more abundant in the catch. Overall, 15% of the discarded individuals displayed any type of damage, from which 12% were severely damaged, and with Echinoderms displaying the highest mean proportion of damaged individuals (79.5±2.9% of individuals). The target species displayed a high proportion of undamaged individuals to fishing impacts, which may represent an important factor for the maintenance of populations of this commercial species on the fishing grounds.

Population dynamics and secondary production of Donax trunculus (Mollusca, Bivalvia) in the Gulf of Annaba (Northeast Algeria)

The population dynamics and secondary production of the wedge clam Donax trunculus were studied in the Gulf of Annaba (Northeast Algeria) monthly for one year at a site close to the Annaba port and the Seybouse river, affected by industrial and agricultural pollution (Sidi Salem), and at a site more distant from major pollution sources, but exploited by fishery (Echatt). The number of individuals (N) was lower at Sidi Salem (36–148 ind m-2) than at Echatt (63–272 ind m-2) in most sampling dates, while the biomass was more variable from one date to another, with no consistent pattern of differences between sites. The condition index (CI), although slightly higher at Sidi Salem than at Echatt, showed at both sites a major increase in March/April, June/July and October, reflecting two main periods of gonads development and increase in the level of stored reserves at the end of the reproductive period. Consistently, the recruitment of D. trunculus ran from April to October with a major peak of abundance in spring and a minor one in early fall. The maximum age of D. trunculus was 3 years and the growth rate was highest in the first year. Annual somatic production (P) was lower at Sidi Salem (0.773 g AFDM m-2 yr-1) than at Echatt (1.262 g AFDM m-2 yr-1), possibly reflecting a lower mean annual biomass at Sidi Salem (1.642 AFDM m-2) than at Echatt (3.046 AFDM m-2), while the annual P/B ratio was similar between the two sites (i.e. 0.471 and 0.414 yr-1, respectively). Lower N and P at Sidi Salem compared to Echatt are consistent with the proximity of Sidi Salem to the industrial port of Annaba and low hydrodynamic conditions which may favor the accumulation of pollutants, such as hydrocarbons. On the other hand, moderate secondary production of D. trunculus at Echatt compared to other Mediterranean sites may be due to excessive harvesting. We suggest that the low secondary production described in this study should be taken into account for the development of sustainable strategies of clam exploitation in the Gulf of Annaba. In particular, effort should be made to reduce land-based pollution and to regulate the collection of D. trunculus according to the life cycle and production potential of this species.

Timing variations and effects of size on the reproductive output of the wedge clam Donax trunculus (L. 1758) in the littoral of Huelva (SW Spain)

This study aimed to augment existing knowledge of the reproductive characteristics of Donax trunculus through analysis of timing variations and the influence of shell size on partial fecundity (PF) during the reproductive period. To achieve this objective, two reproductive timing characteristics were also studied: size at first maturity (SL50) and the reproductive cycle using histology and image analysis techniques. SL50 was 10.83 mm for females and 10.86 for males. Donax trunculus showed a continuous and simultaneous release of gametes and high oocyte regeneration ability during the reproductive period (from February to July). These reproductive characteristics impeded the estimation of total fecundity. However, throughout the reproductive period an increasing pattern of PF was observed followed by a significant drop at the end of the same period, which could be quantified (293,390 of vitellogenic and ripe oocytes). At the same time PF quantifications allowed for predicting and estimating the influence of shell length (SL) on the reproductive output as a function of oocyte typology (PF = 4.12 + 3.96 SL; r2 = 0.86; all types). Levels of prevalence of a digenetic trematode-like parasite with castrate ability fluctuated between 0–20% depending on the time of the year and sex. In addition, the possible consequences of two different scenarios of population size structure on the reproductive output were simulated, and highlighted how beach areas supporting high levels of anthropogenic pressure (Isla Canela) could compromise future recruitments, producing 84% less oocytes than a beach with a lower level of disturbance (Doñana).

Status of population dynamics of the Asian wedge clam,Donax scortum(Bivalvia: Donacidae): a first report from Asia

For the management of mollusc resources, knowledge of various population parameters and exploitation level of the population of wedge clams are needed. Population dynamics on wedge clam,Donax scortumis still unknown in Asia. FAO-ICLARM Stock Assessment Tools (commonly known as FiSAT) was used for calculating population parameters of this species. The specimens ofD. scortumwere collected from Padukere sandy beach at monthly intervals from February 2009 to January 2010. Asymptotic length (Lα) was 70.88 mm and growth coefficient (K) was estimated at 0.64 year−1. The sizes attained byD. scortumwere 33.51, 51.17, 60.49, 65.40, 67.99 and 69.36 mm at the end of first, second, third, fourth, fifth and sixth years of age, respectively. Density of clams ranged from 2 ind. m−2(June, July and August) to 8 ind. m−2(December). Biomass (total weight) of clams ranged between 10.084 g m−2(August) to 185.100 g m−2(December). Total mortality (Z) forD. scortumwas 3.20 year−1. Natural mortality (M) and fishing mortality (F) were 0.64 year−1and 2.56 year−1respectively. Exploitation level (E) was computed as 0.80, indicating that the fishery ofD. scortumin the coastal waters of Karnataka is overexploited.

Relationships between environmental factors and biological parameters of Asian wedge clam,Donax scortum, morphometric analysis, length-weight relationship and condition index: a first report in Asia

Wedge clam,Donax scortumoccurrence was studied from February 2009 to January 2010 in Padukere sandy beach, Karnataka (India). The following biological parameters were measured in 2367 individuals of the wedge clam,Donax scortum: length, breadth, width, total weight, shell weight, wet meat weight, dry meat weight and number of clams. The calculated linear equation of length-breadth and length-width relationships wereB= 3.5968 + 0.5421L andW= 0.8191 + 0.4345L respectively. The length-total weight, length-wet meat weight, length-dry meat weight and length-shell weight relationships were 0.0001414L3.0224,W= 0.0000037L3.5204,W= 0.0000011L3.4513and 0.0000852L2.9912respectively. The values of correlation coefficient for different shell dimensional relationships were very close to unity. It was clear from the study that the most ideal period for clam harvest was April, June and December, especially when condition index was maximum. Length showed a strong correlation with silt and clay. Dry meat weight was negatively correlated with air temperature. Shell weight showed positive correlation with length, breadth, width and dry meat weight, and abiotic parameters, silt and clay. Condition index was positively correlated with electrical conductivity, whereas it was negatively correlated with dissolved oxygen. It showed a strong positive correlation with salinity. Seasonal fluctuation of condition index inD. scortumwas probably related to reproductive activity. The harvesting of wedge clam could be carried out considering the maximum sustainable yield without over-exploitation

EDNA and specific primers for early detection of invasive species – A case study on the bivalve Rangia cuneata, currently spreading in Europe

Intense human activities facilitate the successful spread and establishment of non-indigenous aquatic organisms in marine and freshwater ecosystems. In some cases such intrusions result in noticeable and adverse changes in the recipient environments. In the Baltic Sea, the discovery and rapid initial spread of the North American wedge clam Rangia cuneata represents a new wave of invasion which may trigger unpredictable changes of the local benthic communities. In this study we present a species-specific DNA-based marker developed in silico and experimentally tested on environmental samples. Marker specificity and sensitivity were assessed in vitro from water samples containing different mixtures of the target species and other five bivalves currently present in the region: the native Cerastoderma glaucum, Macoma balthica and Mytilus trossulus, the invasive Dreissena polymorpha and the cryptogenic Mya arenaria. Cross-species amplification was not found in any case. The method allows to detecting at least 0.4 ng of R. cuneata DNA per μl, and 0.1 g of tissue per liter of water. Finally, the marker performance was assessed in water samples from the Baltic Sea and Vistula Lagoon. The coincidence between independent visual observations of R. cuneata and positive PCR amplification of the marker from the water samples confirmed the efficiency of this highly reproducible, fast, and technically easy method. R. cuneata traces can be detected from environmental DNA even when the population is sparse and small, enabling rapid management responses and allowing to track the invasion dynamics.

Water Content as a New Tool for Discrimination between some Shellfishes

Water Content as a New Tool for Discrimination between some Shellfishes

Profiles of paralytic shellfish toxins in bivalves of low and elevated toxicities following exposure to Gymnodinium catenatum blooms in Portuguese estuarine and coastal waters

Profiles of paralytic shellfish toxins (PSTs) were examined in 405 composite samples of Mytilus spp., Cerastoderma edule, Donax trunculus and Spisula solida collected between 2007 and 2012 from natural production areas in two estuaries (Aveiro and Mondego), two coastal lagoons (Óbidos and Formosa), and three open coastal areas (Aguda, Comporta and Culatra). Toxin concentrations were obtained from the biotoxin monitoring programme database. Episodes of PST toxicity in Portugal have been associated with Gymnodinium catenatum blooms. Toxin profiles for each species showed no trend over the surveyed years. In general, profiles differ only slightly among areas, except for Óbidos. However, toxin profiles in bivalves varied between low and elevated toxicities, corresponding to below and above the PST regulatory limit, respectively. The ratio R1=(C1+2):B1, which were the main toxins produced by G. catenatum cells, decreased considerably between elevated and low toxicity cockles, indicating the elimination of C1+2 or conversion of compounds into B1. R2=[(dcSTX)+(dcGTX2+3)]:[(C1+2)+(B1)], which represents the ratio of minor to major toxins in G. catenatum cells, increased substantially in wedge clams (D. trunculus) of low toxicity and less markedly in cockles (C. edule) and mussels (Mytilus spp.). These differences are interpreted as the predominance of a biotransformation phase after exposure to the algal bloom. The toxin profile of surf clams (S. solida) was dominated by decarbamoyl compounds, reflecting intense biotransformation during exposure to blooms. The higher ratio R2 in low toxicity samples suggests that elimination of the produced decarbamoyl toxins was slower than biotransformation.

Bacciger bacciger (Trematoda: Fellodistomidae) infection effects on wedge clam Donax trunculus condition.

Wedge clams Donax trunculus inhabit high-energy environments along sandy coasts of the northeastern Atlantic Ocean and the Mediterranean Sea. Two sites were sampled monthly, one in Morocco (Mehdia), where the density was normal, and one in France (Biscarosse), where the density was very low. We tested the hypothesis that the difference in density between the sites was related to infection by the trematode parasite Bacciger bacciger. Identity of both the parasite and the host were verified using anatomical and molecular criteria. Parasite prevalence (i.e. the percentage of parasitized clams) was almost 3 times higher at Biscarosse. At this site, overall prevalence reached 32% in July and was correlated with the migration of several individuals (with a prevalence of 88%) to the sediment surface. After this peak, prevalence decreased rapidly, suggesting death of parasitized clams. The deleterious effect of B. bacciger on wedge clams was also supported by our calculations indicating that the weight of the parasite made up to 56% of the total weight of the parasitized clams. However, condition indices of trematode-free clams were also lower in Biscarosse than in Mehdia or other sites, suggesting that other factors such as pollutants or microparasites (Microcytos sp.) may alter wedge clam population fitness in Biscarosse.

Depuration Times of Donax trunculus and Tapes decussatus.

The present study was performed to determine the depuration time and ability of Donax trunculus (Wedge Clam) and Tapes decussatus (Carpet Shell) contaminated with Escherichia coli, Salmonella enterica subsp. enterica serovar Typhimurium and Vibrio parahaemolyticus. Clams were contaminated with each bacterium at the level of 7.0 - 8.0 Log10 cfu/g. After contamination, clams were analyzed every 3 h in the first 24 h time period and every 6 h until the 72nd hour. During the depuration process of both clams, the level of bacteria decreased quickly to 40% of initial load in the first 12 h. The results of this study indicate that the depuration time of carpet shells for all bacteria is 66 h. The depuration process of the wedge clam was different from the carpet shell; S. typhimurium and E. coli can be depurated in 66 and 78 h, respectively, while V. parahaemolyticus was present after 72 h at the level of 1.7 Log10 cfu/g.

Characterization of nineteen microsatellite markers and development of multiplex PCRs for the wedge clam Donax trunculus (Mollusca: Bivalvia).

The wedge clam Donax trunculus is an Atlantic-Mediterranean warm-temperate species found from Senegal to the northern coast of France, including the Mediterranean and Black Sea. It is commercially exploited in several European countries and constitutes an important fishing resource due to its high economical value. To contribute to its conservation and management, nineteen microsatellite markers were isolated from two enriched genomic libraries. These loci were characterized in 30 clams from a single population from northwest Spain. The number of alleles per locus ranged from 2 to 17 and observed and expected heterozygosity varied from zero to 0.714 and from 0.078 to 0.950, respectively. Linkage disequilibrium was not detected and nine loci were in agreement with Hardy-Weinberg equilibrium. Fifteen polymorphic markers were arranged into three multiplex PCR sets to reduce both time and cost of microsatellite genotyping. This is the first time that polymorphic microsatellite markers have been reported for D. trunculus. These new markers provide a valuable resource for future population genetics studies and management and culture of this species.

Exposure to the Cyanotoxin Microcystin Arising from Interspecific Differences in Feeding Habits among Fish and Shellfish in the James River Estuary, Virginia.

The cyanotoxin, microcystin (MC), is known to accumulate in the tissues of diverse aquatic biota although factors influencing exposure, such as feeding habits and seasonal patterns in toxin production, are poorly known. We analyzed seasonal variation in the MC content of primary and secondary consumers, and used dietary analysis (gut contents and stable isotopes) to improve understanding of cyanotoxin transport in food webs. Periods of elevated toxin concentration were associated with peaks in the abundance of genes specific to Microcystis and MC toxin production (mcyD). Peak toxin levels in consumer tissues coincided with peak MC concentrations in seston. However, toxins in tissues persisted in overwintering populations suggesting that potential health impacts may not be limited to bloom periods. Interspecific differences in tissue MC concentrations were related to feeding habits and organic matter sources as pelagic fishes ingested a greater proportion of algae in their diet, which resulted in greater MC content in liver and muscle tissues. Sediments contained a greater proportion of allochthonous (terrestrial) organic matter and lower concentrations of MC, resulting in lower toxin concentrations among benthic detritivores. Among shellfish, the benthic suspension feeder Rangia cuneata (wedge clam) showed seasonal avoidance of toxin ingestion due to low feeding rates during periods of elevated MC. Among predators, adult Blue Catfish had low MC concentrations, whereas Blue Crabs exhibited high levels of MC in both muscle and viscera.

The alien gulf wedge clam (Rangia cuneata G. B. Sowerby I, 1831) (Mollusca: Bivalia: Mactridae) in the Polish part of the Vistula Lagoon (SE. Baltic)

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Postmonorchis sp. inq. (Digenea: Monorchiidae) metacercariae infecting natural beds of wedge clam Donax trunculus in Italy

The wedge clam Donax trunculus Linnaeus, 1758 is one of the most common bivalve molluscs inhabiting the sandy shores of the Mediterranean Sea and is considered an important commercial resource. In this study, we report the first molecular, morphological and histopathological descriptions of metacercariae from a trematode belonging to the genus Postmonorchis (Digenea: Monorchiidae) that infects D. trunculus in natural beds of the Italian Tyrrhenian coast (Campania, Lazio and Tuscany). Morphological analysis of the parasite revealed a combination of features that exist in the 3 previously identified species of Postmonorchis, viz. P. donacis, P. variabilis and P. orthopristis, with the addition of new, distinctive morphological characteristics. The pathogen exhibited a predilection for the gill; however, it was also present in the labial palp and mantle in addition to the gut, kidney epithelium and foot. The inflammatory response was characterised by either a focal or diffuse haemocyte infiltration followed by the formation of multiple, large multi-layered capsules associated with tissue destruction. The prevalence of the pathogen ranged from 75 to 100%, while the infection intensity fluctuated among the study areas. Further studies regarding the life cycle of this parasite and the identification of other larval and adult stages and their respective hosts may confirm the identification of a new species of Postmonorchis that infects wedge clams in Mediterranean waters. The study of the parasite is completed by molecular analysis of the ITS1 and ITS2 rDNA sequences.

Feeding ecology of Kelp Gulls (Larus dominicanus) in marine and limnetic environments

The diet of the Kelp Gull (Larus dominicanus) was investigated at the northern limit of its distribution along the South American Atlantic coast. We used two complementary methods, pellet analysis and stable isotope analysis (SIA), to describe and compare Kelp Gull feeding ecology in freshwater and marine environments. The assimilated diet over two different time scales was investigated via SIA of plasma and red blood cells, blood components with different turnover rates. Fish composed the bulk of the diet of Kelp Gulls in both marine (White Croaker Micropogonias furnieri and Banded Croaker Paralonchurus brasiliensis) and limnetic areas (Armoured Catfish Loricariidae and La Plata Croaker Pachyurus bonariensis), despite the importance of benthic prey from the intertidal zone in samples collected from the marine environment (Wedge Clam Donax hanleyanus and the Yellow Clam Mesodesma mactroides). The fish consumed by the gulls were common discards from fisheries in both environments, and marine bivalves were found at a high density at the marine beach. Diet varied between the different time scales analysed. Conventional diet data generally agreed with stable isotope model estimates, emphasising the importance of using complementary approaches in dietary studies.