Ecological risk assessment of predicted marine invasions in the Canadian Arctic.

Climate change is impacting environmental conditions, especially with respect to temperature and ice cover in high latitude regions. Predictive models and risk assessment are key tools for understanding potential changes associated with such impacts on coastal regions. In this study relative ecological risk assessment was done for future potential introductions of three species in the Canadian Arctic: periwinkle Littorina littorea, soft shell clam Mya arenaria and red king crab Paralithodes camtschaticus. These species occur in locations connected to Canadian Arctic ports through shipping and have the potential to be introduced via ballast water discharge. The methodology proposed in this study is unique in the sense that it considers not only ballast water origin, but also the distribution of the species being assessed and the sensitivity of the receiving habitat. It combines detailed information (ballast water source of each tank, transit time, time of the year when the water is released, environmental suitability of receiving habitat, impact, and habitat sensitivity) in order to assess ecological risk. Through the use of this approach it is highlighted that domestic discharge events pose a higher relative overall risk on a vessel-specific and cumulative annual bases than international discharges. The main ports of Deception Bay and Churchill were classified as being at moderate to high relative risk for L. littorea and M. arenaria, especially from domestic vessels, while relative overall risk for P. camtschaticus was low for international vessels and null for domestic vessels due to few ships transiting from its range of distribution to Canadian Arctic ports. This work can serve as an approach to help build a list of potential high risk species-a "grey" watch list-for the Canadian Arctic, and provides useful information for consideration in future decision making actions such as the identification of high risk pathways, species and ports.

Sand gapers' breath: Respiration of Mya arenaria (L. 1758) and its contribution to total oxygen utilization in sediments.

To estimate the contribution of a Mya arenaria population to total oxygen utilization (TOU) at different temperatures, the respiration rate of M. arenaria was measured for a full size range at 5 and 15 °C. In this study we measured respiration rates in a closed system while the clams were burrowed in sandy sediment, resembling their natural habitat. Rates were measured over a sufficient time span (24 h) to average varying activity phases during the measurements. We calculated a size-dependent respiration rate for M. arenaria and its variation with temperature. Temperature strongly affects the total population respiration and the contribution of different size classes to respiration of the total M. arenaria population. M. arenaria was estimated to contribute up to 70% to the total oxygen utilization of benthic communities analyzed in this study very much depending on the size distribution of the bivalve population present. Given a specific size distribution, smaller individuals had a stronger influence on the total oxygen utilization at colder temperature, while the influence of larger individuals grew with warmer temperature. Even though sizes contribute differently, a significant relation between abundance and respiration could be drawn in most cases analyzed. However, this relation should not be used as a general rule, but when estimating a population's metabolism the size distribution within that population has to be regarded.

Variability in sediment-water carbonate chemistry and bivalve abundance after bivalve settlement in Long Island Sound, Milford, Connecticut.

Cues that drive bivalve settlement and abundance in sediments are not well understood, but recent reports suggest that sediment carbonate chemistry may influence bivalve abundance. In 2013, we conducted field experiments to assess the relationship between porewater sediment carbonate chemistry (pH, alkalinity (At), dissolved inorganic carbon (DIC)), grain size, and bivalve abundance throughout the July-September settlement period at two sites in Long Island Sound (LIS), CT. Two dominate bivalves species were present during the study period Mya arenaria and Nucula spp. Akaike's linear information criterion models, indicated 29% of the total community abundance was predicted by grain size, salinity, and pH. When using 2 weeks of data during the period of peak bivalve settlement, pH and phosphate concentrations accounted 44% of total bivalve community composition and 71% of Nucula spp. abundance with pH, phosphate, and silica. These results suggest that sediment carbonate chemistry may influence bivalve abundance in LIS.

Effects of mechanical disturbance and salinity stress on bioenergetics and burrowing behavior of the soft-shell clam Mya arenaria.

Bioturbation of sediments by burrowing organisms plays a key role in the functioning of coastal ecosystems. Burrowing is considered an energetically expensive activity, yet the energy costs of burrowing and the potential impacts of multiple stressors (such as salinity stress and wave action) on bioenergetics and burrowing performance of marine bioturbators are not well understood. We investigated the effects of mechanical disturbance and salinity stress on the burrowing behavior, aerobic capacity and energy expense of digging in a common marine bioturbator, the soft-shell clam Mya arenaria from the Baltic Sea (control salinity 15). Mya arenaria showed large individual variability in the burrowing efficiency, with an average of ∼7% of the body energy reserves used per burial. Clams with higher mitochondrial capacity and lower energy expenditure per burial showed higher endurance. Acclimation for 3-4 weeks to low (5) or fluctuating (5-15) salinity reduced the burrowing speed and the number of times the clams can rebury but did not affect the mitochondrial capacity of the whole body or the gill. Acclimation to the fluctuating salinity shifted the predominant fuel use for burrowing from proteins to lipids. Our data indicate that the reduced burrowing performance of clams under the salinity stress is not due to the limitations of energy availability or aerobic capacity but must involve other mechanisms (such as impaired muscle performance). The reduction in the burrowing capacity of clams due to salinity stress may have important implications for survival, activity and ecological functions of the clams in shallow coastal ecosystems.

Overcoming hydrodynamic challenges in suspension feeding by juvenile Mya arenaria clams.

We present some of the few suspension-feeding measurements and to our knowledge the first velocity-field measurements for early post-settlement juvenile bivalve clams. We verify and extend our experimental results with numerical simulations. For 1.8-2.8 mm shell length Mya arenaria clams, pumping rates ranged 0.03-0.22 µl s-1, inhalant siphon Reynolds numbers (Re) ranged 0.16-0.79 and mean inhalant velocities ranged 0.8-3.2 mm s-1 Owing to the low Re at which they pump and the small diameters of their siphons, juvenile clams are subject to unique hydrodynamic challenges, including high siphon resistance and susceptibility to refiltration. At least three features of juvenile clam siphons differentiate them from those of adults-shorter inhalant siphon length, a more rapid increase in inhalant siphon diameter with shell length, and the presence of a prominent exhalant siphon extension. These features are probably adaptations to the challenges of suspension feeding at low Re.

Field and laboratory transmission studies of haemic neoplasia in the soft-shell clam, Mya arenaria, from Atlantic Canada.

A two-year laboratory and field study was initiated in 2001 in response to mass mortalities associated with haemic neoplasia (HN) in 1999 in Prince Edward Island (PEI) soft-shell clams, Mya arenaria. A laboratory proximity experiment (cohabitation) and an inoculation challenge were conducted with clams and mussels (Mytilus edulis). Three field exposure experiments were also conducted, in which naive clams were held in sediment (in trays) or out of sediment (in mesh bags) at three high HN prevalence sites on PEI. There was a conversion to HN positive in clams in the proximity experiment and in clams injected with whole blood and cell-free homogenate, but not at statistically significant levels. No mussels or control clams became HN positive. There was a significant conversion to HN positive in as little as 24 and 58 days after transfer with clams held out of sediment and in sediment, respectively. The laboratory and field experiments' results suggest that HN-infected clams are spreading the disease through water from infected clams to naïve individuals and via transplantation from affected to unaffected sites. Some environmental conditions (e.g. abnormally high water temperature and hypoxia-induced sea lettuce [Ulva lacteus] invasion) may make clams susceptible to infections or exacerbate the proliferation of HN.

Tracking larvae with molecular markers reveals high relatedness and early seasonal recruitment success in a partially spawning marine bivalve.

The partial synchronized spawning strategy adopted by some marine invertebrate broadcast-spawners can lead to the production of many distinct pools of larvae within a single reproductive cycle. Following the fate of these larval groups from birth to settlement with molecular markers might shed light on mechanisms regulating their population recruitment. Larvae and recruits of Mya arenaria, a partially spawning marine bivalve, were monitored and collected over 13 consecutive weeks during an entire reproductive cycle. Each sampled individual (n = 218) was sorted according to size (early veligers, late veligers, post-larval recruits) and genotyped at seven microsatellite loci for comparisons among samples and with adult reference samples (n = 270). While traditional differentiation statistics (e.g., pairwise Δ(ST), allelic richness) suggested the absence of sweepstakes reproductive success, the level of relatedness found within and among larvae and recruit samples suggested otherwise. Four samples out of ten were observed to have higher within-sample relatedness values than randomly expected, including the very first group of early veligers produced in the season (E1) and the last group of post-larvae who survived recruitment (P10). E1 individuals were also found to be more related than randomly expected to individuals of more than 80% of all other samples including the last surviving recruits (P8 and P10). These results suggest that the first larvae produced in the season were the most successful to survive recruitment. Results also show direct evidence for larval retention and demonstrate for the first time larval and post-larval kin aggregation in a marine bivalve.

Low hydrogen peroxide production in mitochondria of the long-lived Arctica islandica: underlying mechanisms for slow aging.

The observation of an inverse relationship between lifespan and mitochondrial H2O2 production rate would represent strong evidence for the disputed oxidative stress theory of aging. Studies on this subject using invertebrates are surprisingly lacking, despite their significance in both taxonomic richness and biomass. Bivalve mollusks represent an interesting taxonomic group to challenge this relationship. They are exposed to environmental constraints such as microbial H2S, anoxia/reoxygenation, and temperature variations known to elicit oxidative stress. Their mitochondrial electron transport system is also connected to an alternative oxidase that might improve their ability to modulate reactive oxygen species (ROS) yield. Here, we compared H2O2 production rates in isolated mantle mitochondria between the longest-living metazoan--the bivalve Arctica islandica--and two taxonomically related species of comparable size. In an attempt to test mechanisms previously proposed to account for a reduction of ROS production in long-lived species, we compared oxygen consumption of isolated mitochondria and enzymatic activity of different complexes of the electron transport system in the two species with the greatest difference in longevity. We found that A. islandica mitochondria produced significantly less H2O2 than those of the two short-lived species in nearly all conditions of mitochondrial respiration tested, including forward, reverse, and convergent electron flow. Alternative oxidase activity does not seem to explain these differences. However, our data suggest that reduced complex I and III activity can contribute to the lower ROS production of A. islandica mitochondria, in accordance with previous studies. We further propose that a lower complex II activity could also be involved.

Physiological effects of temperature and a herbicide mixture on the soft-shell clam Mya arenaria (Mollusca, Bivalvia).

The aim of the current study was to investigate effects of temperature and a mixture of herbicides on the physiological status of the bivalve Mya arenaria. Bivalves acclimated to two temperatures (7 and 18°C) were exposed for 28 d to 0.01 mg/L of a pesticide formulation containing dichlorophenoxyacetic acid (2,4-D), 2-(2-methyl-4-chlorophenoxy) propionic acid (mecoprop), and 3,6-dichloro-2-methoxybenzoic acid (dicamba). At days 7, 14, and 28, mortality, immune parameters (hemocyte number, phagocytic activity, and efficiency), biomarkers of oxidative stress (catalase [CAT] and superoxide dismutase [SOD] activities and malondialdehyde [MDA] content), the metabolic enzyme cytochrome C oxidase (CCO), a biomarker of pesticide exposure (acetylcholinesterase [AChE]), and the activity of an enzyme related to gametogenesis (aspartate transcarbamylase [ATCase]) were monitored in clam tissues. Gonadosomatic index (GSI), condition factor (CF), and sex were also assessed. In clams acclimated to 7°C, exposure to pesticide enhanced CCO activity and CF and decreased MDA content, hemocyte number, CAT, and SOD activities. In clams kept at 18°C, pesticide effects appeared minor compared with samples kept at 7°C. In bivalves acclimated to 18°C, CCO, SOD, and ATCase activity and MDA content were enhanced, and hemocyte number, CAT, and AchE activities and phagocytosis were suppressed. In samples exposed to pesticides, increased temperature enhanced MDA content and CCO and SOD activity and suppressed hemocyte number and CAT and AchE activity. A gradual sexual maturation was observed in both sexes through experimental time, but females had a higher sensitivity to temperature and pesticides compared to males. Increased temperature altered the ability of the sentinel species Mya arenaria to respond to pesticide exposures. Further work is needed to understand the impacts of increasing temperature on the whole St. Lawrence estuary ecosystem.

Relationships between intertidal clam population and health status of the soft-shell clam Mya arenaria in the St. Lawrence Estuary and Saguenay Fjord (Québec, Canada).

The purpose of this study was to examine the impacts of anthropogenic activity on the health status of intertidal clam populations of the Saguenay Fjord and the St. Lawrence Estuary (Québec, Canada). Clams were collected during low tide at sites subject to direct contamination and at sites far from human activity. Clams were analyzed for tributyltin and dibutyltin total levels and toxic stress (glutathione S-transferase, gonadal lipid peroxidation and DNA strand breaks), immunocompetence (phagocytic activity, hemocyte count and viability), reproduction (gonado-somatic index, gamete maturation, and vitellogenin-like proteins), energy status (temperature-dependent mitochondrial electron transport, and gonad lipids), and individual status (age, condition factor, and growth index). These responses were compared against population characteristics such as live clam density, number of empty shells, and sex ratio. The results show that clam density decreased with distance from the estuary (high salinity level) to upstream of the fjord (low salinity). There was no clear relationship between the number of empty shells and distance or site quality. Clam density values corrected against distance were significantly correlated with hemocyte viability, phagocytic activity, mitochondrial electron transport (MET), DNA damage in gonad, and temperature-dependent mitochondrial electron transport activity. A canonical analysis of the various groups of biomarkers revealed that population metrics were more strongly related with immunocompetence, followed by energy status and temperature-dependent mitochondrial electron transport activity. However, toxic stress biomarkers were strongly associated with energy status and reproduction. This was further confirmed by non-linear modeling using adaptive artificial neural networks (genetic selection and back propagation learning paradigms), where the following parameters were able to predict population parameters with <20% error: gonad maturation and somatic index, MET (at 4 degrees C), gonad LPO, DNA damage, and phagocytic capacity. Intertidal clam populations were influenced by a distance gradient effect (salinity), where immunocompetence, in addition to energy status, was the strongest physiological parameter related to clam population metrics.

Physiological effects of polycyclic aromatic hydrocarbons on soft-shell clam Mya arenaria.

The aim of this study was to investigate the effects of polycyclic aromatic hydrocarbons (PAHs) on the physiological status of the bivalve Mya arenaria. Specimens were exposed to four different sources of PAHs: aluminium smelter soot, sediment from an industrial discharge pound, charcoal fine particles and dietary PAHs assessed by feeding clams with phytoplankton freshly impregnated with dissolved PAHs. The exposure period lasted 30 days and bivalves were let to recover for an additional 20 days. At days 8, 15, 30 and 50, immune parameters (phagocytic activity and efficiency) were monitored in haemocytes. Oxidative stress measures such as catalase and lipid peroxidation were quantified in digestive gland as well as concentrations of bioaccumulated PAHs. In a second experiment, clams were exposed to [(14)C]-pyrene via the phytoplankton, and the tissue distribution of radiolabelled compound was studied. Glycogen levels in gonad and digestive gland were also measured and gametogenesis stages were investigated. Results showed a high bioaccumulation in clams exposed to dietary PAHs and contaminated sediments. Tissue distribution of [(14)C]-pyrene revealed that the radiolabelled compound persisted mainly in the gonad during 14 days. A decrease of phagocytosis was observed in contaminated male clams. The lipid peroxidation (malondialdehyde) was found to increase in the digestive gland tissues of clams exposed to dietary PAHs, smelter soot and discharge, but no differences were observed in the catalase activity. A delay in gametogenesis occurred in all exposed males and in females contaminated with coke dust and dietary PAHs. Males were more sensitive than females to PAH exposure. A dysfunction in steroid synthesis is suspected to occur due to the exposure to all sources of PAHs.

Adaptive evolution of tetrodotoxin resistance in animals.

Tetrodotoxin (TTX), first isolated from pufferfish (tetraodontids), is a highly potent neurotoxin that selectively binds to voltage-gated sodium channels (Na(v)) in muscle and nerve tissues causing paralysis and death. Saxitoxin (STX) is a TTX-related neurotoxin produced by dinoflagellates. Recent investigations have implicated diverse substitutions in the P-loop regions of skeletal muscle and neuronal Na(v) channels in the convergent evolution of neurotoxin resistance in pufferfish, garter snakes and softshell clams, which has enabled them to feed on TTX- and STX-bearing organisms.