Mya Arenaria Research Articles

Distribution, stocks, and age structure of the invader Mya arenaria before and after mass mortalities in the Black Sea

The distribution, stocks, and age structure of the invader soft-shell clam Mya arenaria populations before and after the mass mortalities in the northwestern Black Sea have been studied from 1967 to 1987. At the prolonged influence of mortalities from 1973 to 1985, the number of age classes decreased from six in the period before the mortalities to three in 1985. The restoration of the stocks of Mya arenaria and the possibility of fishing these mollusks after the improvement of the ecological state in this part of the sea are predicted.

Distinctly variable mudscapes: Distribution gradients of intertidal macrofauna across the Dutch Wadden Sea

The Wadden Sea is a shallow coastal region, with a large area of sedimentary tidal flats that extends from The Netherlands to Denmark and has been declared a site of international importance in the Dutch and German parts (Ramsar status and UNESCO World Heritage Site). Benthic macrofauna are central to the ecosystem functioning of this area, as they recycle nutrients, decompose organic matter and are an important food source for many secondary consumers, like fish and waterbirds. Due to the environmental gradients characteristic of estuarine systems, it is expected that changes in assemblage composition will be observed across the physical and environmental gradients of the Wadden Sea. First, we explored the spatial variation in assemblage composition of benthic macrofauna across the intertidal part of the Dutch Wadden Sea using 3years of biomass data. Then, we identified the relative importance of six environmental variables for explaining and predicting changes in assemblage composition across the intertidal areas of the Wadden Sea using generalised dissimilarity modelling (GDM). In accordance with the environmental gradients across this system, the biomass contributed by a few common species differed from west to east and were distinct in the Dollard. In the west, bivalves Mya arenaria, Cerastoderma edule and Ensis directus contributed a relatively large and equal share of the total biomass, whereas C. edule contributed the sole largest share of the total biomass towards the east. The polychaete Alitta succinea became a large share of the total biomass in the upper Ems and in the Dollard estuary, but contributed little elsewhere. Similar to the observed differences in species composition, the spatial patterns in assemblage composition, as predicted by the GDM models, identified the Dollard as distinct and that the prevalence of assemblage types in the west differed to the east. Median grain size, followed by microphytobenthic biomass, and exposure time were the most important variables describing differences in assemblage composition. That the Wadden Sea forms a heterogeneous landscape where assemblage composition varies across multiple gradients has repercussions for management and monitoring.

Strong population differentiation of softshell clams (Mya arenaria) sampled across seven biogeographic marine ecoregions: possible selection and isolation by distance

Twenty-two Mya arenaria samples spanning seven marine ecoregions mostly situated in the Cold Temperate Northwest Atlantic (CTNA) biogeographic province were collected between 2001 and 2010 and genotyped at seven highly polymorphic microsatellite loci to test for population differentiation. Results showed strong regional differentiation with six genetic clusters: (1) Northern Gulf of St. Lawrence (GSL), (2) Magdalen Archipelago, (3) Southern GSL, (4) Lower Atlantic Canada, (5) US Coasts and (6) Northern Europe. Population structure was supported no matter the statistical approach and generally does not reflect the geographical limits of marine ecoregions. A latitudinal cline in allelic richness provides evidence for a northward post-glacial expansion range for this species. While geographical distance explains the genetic variation detected in southern CTNA, increased heterogeneity observed in northern CTNA can be explained by isolation by distance, marine landscaping and presumable selective processes acting at the Mar5 locus. Exclusion of Mar5 from analyses resulted in the detection of three genetic clusters instead of six.

A candidate reference material ‘Mya arenaria’ for the monitoring of butyltin compounds in mollusks in the marine environment

Most analytical techniques used for the speciation analysis of butyltin compounds in biological tissues usually contain multiple procedures (e. g., extraction, derivatization, separation, preconcentration, determination) which may increase the risk of systematic errors. The use of reference materials (RM) makes it possible to correct most of these errors and improve the validity of quality control. In this study, a new candidate RM for butyltin compounds in mollusks was developed. It was prepared with a mollusk 'Mya arenaria' directly bought from the market. The preparation of this candidate RM, the homogeneity and stability studies, the value assignment and the evaluation of uncertainty were described. The certified values of 0.33 +/- 0.08, 0.62 +/- 0.09, 2.64 +/- 0.20 mu g Sn g(-1) (based on dry mass) for monobutyltin (MBT, [Sn(C4H9)(3+)]), dibutyltin (DBT, [Sn(C4H9)(2)(2+)]) and tributyltin (TBT, [Sn(C4H9)(3)(+)]) respectively have been assigned by inter-laboratory comparison. This work will be of great support to the monitoring of butyltin compounds in biota, as well as meeting the need for implementing international treaties in China.

Transcriptome analysis of neoplastic hemocytes in soft-shell clams Mya arenaria: Focus on cell cycle molecular mechanism

In North America, a high mortality of soft-shell clams Mya arenaria was found to be related to the disease known as disseminated neoplasia (DN). Disseminated neoplasia is commonly recognized as a tetraploid disorder related to a disruption of the cell cycle. However, the molecular mechanisms by which hemocytes of clams are transformed in the course of DN remain by far unknown. This study aims at identifying the transcripts related to DN in soft shell clams’ hemocytes using next generation of sequencing (Illumina HiSeq2000). This study mainly focuses on transcripts and molecular mechanisms involved in cell cycle. Using Illumina next generation of sequencing, more than 95,399,159 reads count with an average length of 45 bp was generated from three groups of hemocytes: (1) a healthy group with less than 10% of tetraploid cells; (2) an intermediate group with tetraploid hemocytes ranging between 10% and 50% and (3) a diseased group with more than 50% of tetraploid cells. After the reads were cleaned by removing the adapters, de novo assembly was performed on the sequences and more than 73,696 contigs were generated with a mean contig length estimated at 585 bp ranging from 189 bp to 14,773 bp. Once a Blastx search against NCBI Non Redundant database was performed and the duplicates removed, 18,378 annotated sequences matched known sequences, 3078 were hypothetical and 9002 were uncharacterized sequences. Fifty percent and 41% of known sequences match sequences from Mollusca and Gastropoda respectively. Among the bivalvia, 33%, 17%, 17% and 15% of the contigs match sequences from Ostreoida, Veneroida, Pectinoida and Mytiloida respectively. Gene ontology analysis showed that metabolic, cellular, transport, cell communication and cell cycle represent 33%, 15%, 9%, 8.5% and 7% respectively of the total biological process. Approximately 70% of the component process is related to intracellular process and 15% is linked to protein and ribonucleoprotein complex. Catalytic activities and binding molecular processes represent 39% and 33% of the total molecular functions. Interestingly, nucleic acid binding represents more than 18% of the total protein class. Transcripts involved in the molecular mechanisms of cell cycle are discussed providing new avenues for future investigations.

Comparative Study of the Accumulation of Ni in Different Tissues of Mussels and Soft Clams

Two bivalves, the mussel Mytilus galloprovincialis, and the soft clam Callista chione were exposed to various Ni concentrations for a total period of 20 days, and then a depuration period of 10 days followed. Nickel accumulation in gills, mantle and the remaining body of the animals was measured after 5, 10, 15 and 20 days of exposure to Ni-contaminated seawater. The two organisms showed different behavior regarding Ni accumulation in all three tissues examined. In all concentrations, Ni accumulation increased with time in all three tissues of Mytilus galloprovincialis with gills being the most effective accumulator per dry mass. On the other hand, Callista chione showed an initial response to Ni contamination the first 5 days, followed by stabilization or even a slight decrease of Ni accumulation.

Contaminant exposure and ecotoxicological impacts in estuaries

Estuaries are highly dynamic geohydrological systems that form a transition zone between continental rivers and marine environments. They are subjected to many influences such as tides, waves, and influx/efflux of saline water and freshwater. The dynamic mixing of these types of waters provides nutrients in surface waters and sediments making estuaries among the most productive habitats of coastlines. Organisms dwelling in these environments are thus subjected to many combined stresses (salinities, tides and temperature fluctuations) and are particularly at risks to the influence of anthropogenic activity leading to pollution, climate changes and habitats perturbations. Hence, estuaries are area of choice to study the cumulative impacts of pollution in transition zones. A “sustainable partnership” was set up by a France– Quebec initiative in 2003 with the goal to promote and disseminate studies on the wide range of biological responses from organisms exposed to pollution gradients in estuaries of the Atlantic Ocean. This network combines stakeholders involved in both research, teaching, conservation, and protection activities pertaining to science of estuarine ecotoxicology. The success of this endeavor resided on the comparative examination of the impacts of pollution in estuaries from both the Canadian and European coastlines using similar species some cases and focusing on common objectives on either side of the Atlantic in France and Canada (Quebec). The EXECO International Consortium (contaminant exposure and ecotoxicological effects along continental–coastal continuums: http://wwz.ifremer.fr/pollution/Collaborations/GDR-IEXECO ) launched in 2009 has consolidated this important undertaking by combining the actions of two strategic networks: the Canadian (Quebec) CIRE network (Inter-Institutional Ecotoxicology Research Center: http://www.ecotox.uquebec.ca/programmes/htm) and French IMOPHYS network (Integration of Molecular and Physiological Responses to Chemical Contaminants in the Coastal Environment). This special edition on the impacts of pollution in estuarine organisms features a series of articles on work conducted on either side of the Atlantic in the common purpose to gain a better understanding on ecotoxicological effects of anthropogenic activities along the estuarine continuum. These studies featured a blend of both laboratory and field studies at different levels of biological organization and trophic levels. The studies on regulation and adaptation mechanisms were conducted on a molecular basis, e.g., DNA and immune defense alterations, the alteration of physiological functions such as reproduction, and the epidemiological study of chemical contaminant-related tumors. Many papers are based on fish (Platichthys flesus, Microgadus tomcod, Scophtalmus maximus, Limanda limanda, Alosa alosa, Liza ramada), which possess a strong metabolic capacity but the reader will also find papers on bivalve mollusks: the Mytilus edulis mussel and soft shell clam Mya arenaria. Responsible editor: Philippe Garrigues

Palynological study of a Mi'kmaw shell midden, Northeast Nova Scotia, Canada

Before now, no palynological studies were made on shell midden deposits in Nova Scotia, despite a long history of archaeological research. A test study of samples taken from the shell midden at Maligomish (Indian Island) on the Northumberland Strait was conducted to determine if sufficient pollen, fern and moss spores, and other non-pollen palynomorphs (NPP's, including fungal remains, algal spores) could be recovered to allow interpretation of environmental conditions at the time of deposition. Several pollen processing methods were tested: sieving and swirling, chemical treatment with cold HCl, 5% KOH and brief exposure to 5% NH4OH, and treatment with acetolysis solution. We recovered variable amounts of pollen, spores and NPP's from samples taken at 3–5 cm, 5–15 cm and 15–25 cm below surface. Abundant microcharcoal fragments prevented effective use of the swirling technique, but sufficient palynomorphs were recovered by chemical treatments to allow assessment of down-section changes in assemblages. Three radiocarbon ages from Mya arenaria and Crassostrea sp., and measurements of sediment grain size, moisture, organic and inorganic carbon, provide a framework for analysing palynological assemblage changes and context for interpreting differential palynomorph preservation. Despite some oxidation and microbial degradation of palynomorphs in the time interval (ca. 380–1600 cal yr BP), the midden assemblages correlate with pollen zones from marine and lake core sites within ca. 50 km of Maligomish. Shifts in abundances of algal spores, testate amoebae and aquatic plant pollen also indicate changes in depositional conditions during the time of midden use. The study provides the first reference for archaeologists attempting to use palynology for analysis of samples from Nova Scotian shell-bearing contexts.

Selective initiation and transmission of disseminated neoplasia in the soft shell clam Mya arenaria dependent on natural disease prevalence and animal size

Disseminated neoplasia, a diffuse tumor of the hemolymph system, is one of the six most destructive diseases among bivalve mollusk populations, characterized by the development of abnormal, rounded blood cells that actively proliferate. Though the specific etiology of disseminated neoplasia in Mya arenaria remains undetermined, the involvement of viral pathogens and/or environmental pollutants has been suggested and considered. The current study used 5-bromodeoxyuridine (BrDU) known to induce the murine leukemia virus and filtered neoplastic hemolymph to initiate disseminated neoplasia in clams from different populations and size classes respectively. M. arenaria from three locations of different natural neoplasia occurrences were divided into a control and three experimental treatments and injected with 200μl of sterile filtered seawater or 50–200μg/ml BrDU respectively. In a concurrent experiment, animals from different size classes were injected with 2.5% total blood volume of 0.2μm filtered blood from a fully neoplastic animal. Animals were biopsied weekly and cell neoplasia development was counted and scored as 0–25, 26–50, 51–75 and 76–100% neoplastic hemocytes (stages 1–4) in 50μl samples. BrDU injection demonstrated that neoplasia development in M. arenaria was dose dependent on BrDU concentration. In addition, natural disease prevalence at the source location determined initiation of neoplasia induction, with animals from the area of the highest natural disease occurrence displaying fastest neoplasia development (p=0.0037). This could imply that depending on the natural disease occurrence, a potential infectious agent may remain dormant in normal (stage 1) individuals in higher concentrations until activated, i.e. through chemical injection or potentially stress. The size experiment demonstrated that only M. arenaria between 40 and 80mm developed 26–100% neoplastic hemocytes when injected with filtered neoplastic hemolymph, indicating that individuals smaller than 20mm or larger than 80mm were not or no longer susceptible to disease development. So far neoplasia studies have not considered natural disease prevalence or size involvement in neoplasia development and our results indicate that these should be future considerations in neoplasia examinations.

The presence of Mya arenaria in the Ria de Aveiro is the third confirmed record of this invasive clam on the Portuguese coast

The occurrence of the invasive clam Mya arenaria is confirmed in the Ria de Aveiro (northern Portugal). Some live specimens were collected from the mid-upper intertidal zone. The population density was low (about 0.15 ind m−2) and the individuals were large, of mean shell length 82.22 ± 14.85 mm. Large empty shells of M. arenaria, of mean shell length 85.32 ± 11.31 mm, were found in a life-like position, which indicates an episode of mass mortality in the sampling area and suggests that invasion by the clam in the Ria de Aveiro is not a recent event. Differences in the size-classes of empty shells of the invasive clam indicate that the clam is able to reproduce in this habitat. Occurrence of established populations of M. arenaria at different locations on the Portuguese coast, such as the Tagus estuary, the Lima estuary and the Ria de Aveiro, may be due to intentional introduction of M. arenaria in at least some cases.

Single Plex Branched DNA as an Alternative Assay to QuantifyP53-Like mRNA Levels in Softshell ClamMya arenariaHemocytes

Previous studies have shown that hemic neoplasia in softshell clams is related to the level of P53 -like mRNA in hemocytes. Traditionally, the p53-like mRNA level has been quantified using quantitative real-time RT-PCR (Q RT-PCR). However, this technique requires several steps that are sources of contamination and may result in a low accuracy of the analysis. The novel aspect of this study is that the p53-like mRNA level was quantified directly from a lysate of hemocytes without any RNA extraction or reverse transcription steps. This assay is based on branched DNA (bDNA) signal amplification technology and enables quantification of p53-like mRNA levels in as few as 2,500 hemocytes, with a coefficient of variation close to 6% (range, 2–12%). A significant correlation (R2= 0.99, P ≤0.01, n= 5) was found between the p53-like mRNA quantified directly from hemocytes without RNA extraction and from 1 µg total RNA extracted from hemocytes using the classic TRIzol protocol. To compare p53-like mRNA levels in hemocytes from diseased clams collected in North River (Prince Edward Island, Canada) and from healthy clams found in Havre aux Maisons at Magdalene Island (Quebec, Canada), the quantification of relative p53-like mRNA levels was performed using our single plex assay. Data showed a significantly (P ≤0.01, n= 5) high expression of p53-like in the hemocytes of clams collected from North River. Therefore, although Q RT-PCR remains the most widely used technique for the quantification of gene expression level, we believe that single plex using bDNA technology could represent a new generation of mRNA quantification tool, enabling a more efficient mollusc health management.

A kinetic approach to assess oxidative metabolism related features in the bivalve Mya arenaria

Electron paramagnetic resonance uses the resonant microwave radiation absorption of paramagnetic substances to detect highly reactive and, therefore, short-lived oxygen and nitrogen centered radicals. Previously, steady state concentrations of nitric oxide, ascorbyl radical (A·) and the labile iron pool (LIP) were determined in digestive gland of freshly collected animals from the North Sea bivalve Mya arenaria. The application of a simple kinetic analysis of these data based on elemental reactions allowed us to estimate the steady state concentrations of superoxide anion, the rate of A· disappearance and the content of unsaturated lipids. This analysis applied to a marine invertebrate opens the possibility of a mechanistic understanding of the complexity of free radical and LIP interactions in a metabolically slow, cold water organism under unstressed conditions. This data can be further used as a basis to assess the cellular response to stress in a simple system as the bivalve M. arenaria that can then be compared to cells of higher organisms.

Winter distribution of Greater Scaup Aythya marila in relation to available food resources

The European wintering population of Greater Scaup has declined significantly over the last 20years and some of the main threats appear to be at the wintering grounds. This contribution aims at describing the local distribution of Scaup in the Dutch Wadden Sea, one of the most important wintering sites for Scaup in relation to available food resources. Data on the distribution of Scaup was obtained from annual aerial counts in January during 1999–2009. This data was related to benthos data of regular shellfish surveys in the sublittoral part of the western Dutch Wadden Sea. Boosted regression tree models were applied to quantify the relative importance of different potential prey items to explain the presence of Scaup. Scaup preferred sites with high abundances of small sized Mya arenaria. A negative influence on Scaup preference for sites with high abundances M. arenaria was found when there was a high abundance of large Cerastoderma edule at the sites, which increased Scaup searching time for M. arenaria.

DNA integrity assessment in hemocytes of soft-shell clams (Mya arenaria) in the Saguenay Fjord (Québec, Canada)

The purpose of this study was to examine the effects of pollution on DNA integrity in the feral soft-shell clam (Mya arenaria) in the Saguenay Fjord. Intertidal clams were collected downstream and upstream of the fjord at sites under anthropogenic pollution. DNA integrity was assessed by following changes in single- and double-stranded breaks, variation in DNA content and micro-nuclei (MN) incidence in hemocytes. The results revealed that clams collected at polluted sites had reduced DNA strand breaks (lower DNA repair activity), increased DNA content variation and MN frequency in hemocytes. The data revealed that DNA content variation was closely related to MN frequency and negatively with DNA strand breaks formation. Water conductivity was also related to reduced MN frequency and DNA content variation, indicating that, in addition to the effects of pollution, the gradual dilution of saltwater could compromise mussel health.

The influence of sedimentation on metal accumulation and cellular oxidative stress markers in the Antarctic bivalve Laternula elliptica

Recent rapid climate warming at the western Antarctic Peninsula (WAP) results in elevated glacial melting, enhanced sedimentary run-off, increased turbidity and impact of ice-scouring in shallow coastal areas. Discharge of mineral suspension from volcanic bedrock ablation and chronic physical disturbance is expected to influence sessile filter feeders such as the Antarctic soft shell clam Laternula elliptica (King and Broderip, 1832). We investigated effects of sedimentary run-off on the accumulation of trace metals, and together with physical disturbance, the cumulative effect on oxidative stress parameters in younger and older L. elliptica from two stations in Potter Cove (King George Island, Antarctica) which are distinctly impacted by turbidity and ice-scouring. Fe, Mn, Sr, V and Zn concentrations were slightly higher in sediments of the station receiving more sediment run-off, but not enriched in bivalves of this station. The only element that increased in bivalves experimentally exposed to sediment suspension for 28 days was Mn. Concentration of the waste accumulation biomarker lipofuscin in nervous tissue was higher in L. elliptica from the “exposed” compared to the “less exposed” site, whereas protein carbonyl levels in bivalve mantle tissue were higher at the less sediment impacted site. Tissue metal content and lipofuscin in nervous tissue were generally higher in older compared to younger individuals from both field stations. We conclude that elevated sediment ablation does not per se result in higher metal accumulation in L. elliptica. Instead of direct absorbance from sediment particles, metal accumulation in gills seems to indicate uptake of compounds dissolved in the water column, whereas metals in digestive gland appear to originate from enriched planktonic or detritic food. Accumulation of cellular waste products and potentially reactive metals over lifetime presumably alters L. elliptica physiological performance with age and may contribute to higher stress susceptibility in older animals.

Short Chain Chlorinated Paraffins in Mollusks from Coastal Waters in the Chinese Bohai Sea

As an extremely complex group of persistent organic pollutants (POPs) candidates in the Stockholm Convention, short chain chlorinated paraffins (SCCPs) have been of extensive concern in recent years. In this study, nine bivalve and two gastropod species were collected in 2009 to evaluate the spatial distributions and potential factors influencing the bioaccumulation of SCCPs in mollusks in the Chinese Bohai Sea. The concentrations of ∑ SCCPs in the mollusks were in the range 64.9-5510 ng/g (dry weight) with an average chlorine content of 61.1%. C(10) and C(11) were the predominant homologue groups of SCCPs, which accounted for about 29.7% and 34.9% of ∑ SCCPs, respectively. Six and seven chlorinated substituents were the main congener groups. Mya arenaria (Mya), Mactra veneriformis (Mac), and Crassostrea talienwhanensis (Oyster, Ost) had higher average concentrations of SCCPs than other species, implying that these bivalves could be used as sentinels to indicate SCCPs contamination in this coastal region. A significant positive linear relationship was found between SCCP concentrations and lipid content of the mollusks, whereas the lipid-normalized SCCP concentrations were negatively linear-related to the trophic levels (TL), which implied that SCCPs did not show biomagnification in mollusks in this region.

Benthic Spat Collection of Softshell Clams (Mya arenariaLinnaeus, 1758) using Mats

Supply of softshell clam (Mya arenaria) seed for culture and restoration usually comes from hatcheries or through transfers from one site to another. Natural spat collection using Astro-Turf mats installed directly onto the sediments could be a viable alternative. Here, we describe a series of experiments to examine the performance of mats for benthic collection, and how to use them efficiently. Interannual variability was studied for an 8-y period (2002 to 2009) at a commercial clam culture site located in the Havre-aux-Maisons lagoon (Îles-de-la-Madeleine, southern Gulf of St. Lawrence). Spat collection (clams, 2.5–15 mm) ranged from 883–2,422 clams/m2 (overall mean, 1,599 clams/m2). Throughout the years, clams on the mats were 7 times more abundant than in the nearby sediments. Their mean shell length varied from 7.3–9.9 mm relative to the year. Mats were deployed during an extended 5-wk period (early June to early July), and also retrieved during an extended 5-wk period (early September to early October) with no negative effect on collection success. Indeed, spat abundance was higher when mats were retrieved later in the season (late September to early October). Spat collection was greater at the mid to upper intertidal level (1,551–2,622 clams > 2.5 mm/ m2) compared with the lower intertidal (near-subtidal) level (586 clams > 2.5 mm/m2). Indeed, the lowest abundances and the smallest sizes were observed on mats deployed at the lower intertidal level. Mats were installed side-by-side in groups of 35 (7 × 5), with no negative impact on collection success compared with individual mats. Last, spat collection was examined at two different sites within the lagoon for 4 y. Although the overall mean number of clams was similar at both sites (1,538 clams > 2.5 mm/m2 vs. 1,503 clams > 2.5 mm/m2), collection success varied among sites (951–1,916 clams > 2.5 mm/m2 vs. 552–2,938 clams > 2.5 mm/m2) from year to year. Therefore, collection success with mats should be investigated for any new site and for several years.

Haemocytic leukemia in Prince Edward Island (PEI) soft shell clam (Mya arenaria): Spatial distribution in agriculturally impacted estuaries

Intensive farming of potatoes in Prince Edward Island (PEI) relies on the repeated and widespread application of fertilizers and pesticides. In PEI the main potato farming areas are in close proximity and drain directly to estuaries. Runoff from high agricultural activity watersheds could impact benthic organism health in the depositional zone of downstream estuaries. The estuarine filter feeder Mya arenaria (soft-shell clam) could be particularly vulnerable to both particle-adsorbed and water soluble contaminants. M. arenaria is susceptible to haemocytic leukemia. In May 2009, we established that heavily proliferated leukemia (HPL) prevalence was generally higher in PEI estuaries located downstream of high intensity potato farming (Dunk and Wilmot estuaries) watersheds than in estuaries downstream of lower intensity areas. Using Mab-1E10 based immunocytochemistry we observed that leukemic haemocytes from the Dunk and Wilmot estuaries were 1E10 negative whereas those from the Ox/Sheep estuary (low potato farming intensity) were 1E10 positive. The expression of genes in the p53 tumour suppressor pathway enabled us to differentiate groups of leukemic and normal M. arenaria, validating our diagnoses. In October 2009, we confirmed that HPL prevalence was elevated in the Dunk and Wilmot estuaries compared to reference (Souris River). Moreover, leukemia prevalence declined with distance from the river mouths along transects through the Dunk and Wilmot estuaries. The pesticides ß-endosulfan and α-endosulfan were detected in surface sediments from the Dunk and Wilmot estuaries, but not in sediments from either the Souris River or several other lower intensity potato farming watersheds. Our study provides evidence of an association between intensity of potato farming and prevalence of clam leukemia at downstream estuaries in PEI.

Invasion risk posed by macroinvertebrates transported in ships’ ballast tanks

Invasions by non-indigenous macroinvertebrates often cause ecological and economic problems, and commercial ships have been implicated as a principal mechanism for their dispersal. We explored the presence and species diversity of adult macroinvertebrates transported by transoceanic and coastal vessels arriving to ports on the Atlantic coast of Canada. We sampled 67 ballast tanks from 62 ships operating along discrete geographic pathways and tested whether mid-ocean exchange or voyage length affects the probability for translocation of macroinvertebrates. Additionally, we assessed the relationship between macroinvertebrate presence and the amount of sediment in ballast tanks. We document the presence of highly invasive European green crab (Carcinus maenas), mud crab (Rhithropanopeus harrisii), common periwinkle (Littorina littorea), soft shell clam (Mya arenaria) and blue mussel (Mytilus galloprovincialis) in ballast tanks of surveyed ships. Mid-ocean exchange did not affect macroinvertebrate occurrence, suggesting that current ballast water management regulations are ineffective for this taxonomic group. Viable individuals were recorded in vessels undertaking shorter voyages (average and maximum of 4.5 and 15 days, respectively) and presence was not related to the amount of sediment in tanks. While presence and densities of macroinvertebrates were low, invasion risk may nonetheless be significant during reproductive seasons owing to high fecundity of some taxa. The highest risk may be posed by decapods since gravid females may carry thousands to several million eggs per clutch, and after several weeks of brooding, two or more subsequent clutches may be fertilized by retained sperm from an earlier mating.

Isolation and Characterization of New Microsatellite Markers for the Invasive Softshell Clam, Mya arenaria (L.) (Bivalvia: Myidae)

The invasive softshell clam (Mya arenaria Linnaeus, 1758) is native to the northwestern region of the Atlantic Ocean. This species has been introduced in the northeast Pacific and along the European coasts, due to intense naval transports and aquaculture, and it is now present in all the European seas. In this paper we describe seven new microsatellite loci for Mya arenaria. The isolated loci are polymorphic with a number of alleles per locus between 6 and 14. The observed and expected heterozygosities ranged from 0.417 to 0.951, and from 0.643 to 0.895, with an average of 0.716 and 0.775, respectively. These microsatellite markers should be useful in analyzing this species’ genetic diversity, which could explain various processes of its invasion history.