Mya Arenaria Research Articles

Is food supply for shellfish-eating birds in the western Wadden Sea affected by the between-species synchrony in year-to-year fluctuations of bivalve population parameters?

For a better understanding of functioning and stability of ecosystems, it is important to know to what extent constituent species show similarity in their long-term fluctuation patterns, i.e. whether their numbers and biomass frequently show simultaneous peaks and lows. Synchronic peaks and lows of important species would enhance variability in the functioning of the entire system and might affect its stability. When fluctuation patterns of individual species are largely independent, their peaks and lows would tend to extinguish each other’s effect on overall parameters (such as total zoobenthic biomass), thus promoting system stability. A long-term (46 years) monitoring study of the macrozoobenthos in a large (50 km2) tidal-flat area revealed that the 4 most important bivalve species (3 suspension feeders: Cerastoderma edule, Mytilus edulis, Mya arenaria and 1 deposit/suspension feeder: Limecola (Macoma) balthica) frequently showed peak numbers of their recruits in the same years. The annual growth rates of the three suspension feeding species showed some synchrony as well. Annual survival rates, on the other hand, did not show any synchronization, wiping out the initial synchrony of numbers within less than 2 years. As a result, annual biomass values did not show any positive between-species correlations. Annual amounts of bivalves that are accessible as bird food rarely declined to levels below 5 g AFDW m−2 and showed limited (5 to 10 fold difference between maximal and minimal values) variation. Oystercatchers left the area quicker in late winter and showed increased death rates at very low levels of food supply. Total bivalve bird food did not show any significant long-term trend. However, biomass of Mya arenaria showed an increasing trend and that of Limecola balthica a declining trend.

Non-indigenous species in soft-sediments: Are some estuaries more invaded than others?

Abstract Non-indigenous species (NIS) are increasingly widespread and abundant in coastal areas, hence being considered indicators to assess the environmental status of marine waters under the Marine Strategy Framework Directive. However, information on the effects of biological invasions on species composition and abundance is still scarce, particularly for soft-sediment benthic communities, which remain poorly understood. Therefore, the present study aimed at monitoring the benthic communities of two Portuguese estuarine systems, with a particular focus on NIS. Sampling surveys were conducted at the Tagus and Sado estuaries, in three different years. Invertebrate communities were collected at sampling stations located along the estuarine gradient, using a clam dredge, and several water and sediment parameters were measured at the same locations. NIS represented nearly one fourth (23%) of the total observed individuals across all years and estuaries, with Ruditapes philippinarum accounting for 22% of the total abundance across estuaries and years. Although both estuaries presented a similar total number of species (91 at the Tagus and 81 at the Sado), three-fold more NIS were identified at the Tagus estuary. The frequency of occurrence of the NIS Crassostrea (Magallana) gigas, Mya arenaria and Panopeus occidentalis increased significantly over the three years at the Tagus estuary and decreased significantly for Dyspanopeus sayi from 2015 to 2018. The Tagus and Sado estuaries presented distinct and diverse communities, with the abundance of R. philippinarum being eleven-fold greater at the Tagus estuary than at the Sado estuary. This study provides a baseline list of the NIS occurring in two of the main Portuguese estuarine systems, as well as an approach to estimate NIS abundance, richness, frequency of occurrence and community diversity. Although most studies on NIS impacts have focused on single species, the assessment of the environmental status of marine waters requires that overall impacts of NIS on marine ecosystems are determined. This study indicated metrics that are appropriate to evaluate changes in soft-sediment benthic communities associated to the introduction of NIS.

Influenza A Virus Detected in Native Bivalves in Waterfowl Habitat of the Delmarva Peninsula, USA.

We evaluated the prevalence of influenza A virus (IAV) in different species of bivalves inhabiting natural water bodies in waterfowl habitat along the Delmarva Peninsula and Chesapeake Bay in eastern Maryland. Bivalve tissue from clam and mussel specimens (Macoma balthica, Macoma phenax, Mulinia sp., Rangia cuneata, Mya arenaria, Guekensia demissa, and an undetermined mussel species) from five collection sites was analyzed for the presence of type A influenza virus by qPCR targeting the matrix gene. Of the 300 tissue samples analyzed, 13 samples (4.3%) tested positive for presence of influenza virus A matrix gene. To our knowledge, this is the first report of detection of IAV in the tissue of any bivalve mollusk from a natural water body.

Behavioural patterns of the soft-shell clam Mya arenaria: implications for benthic oxygen and nitrogen dynamics

Behavioural patterns of the soft-shell clam Mya arenaria: implications for benthic oxygen and nitrogen dynamics

Mapping Arctic clam abundance using multiple datasets, models, and a spatially explicit accuracy assessment

Abstract Species distribution models are commonly used in the marine environment as management tools. The high cost of collecting marine data for modelling makes them finite, especially in remote locations. Underwater image datasets from multiple surveys were leveraged to model the presence–absence and abundance of Arctic soft-shell clam (Mya spp.) to support the management of a local small-scale fishery in Qikiqtarjuaq, Nunavut, Canada. These models were combined to predict Mya abundance, conditional on presence throughout the study area. Results suggested that water depth was the primary environmental factor limiting Mya habitat suitability, yet seabed topography and substrate characteristics influence their abundance within suitable habitat. Ten-fold cross-validation and spatial leave-one-out cross-validation (LOO CV) were used to assess the accuracy of combined predictions and to test whether this was inflated by the spatial autocorrelation of transect sample data. Results demonstrated that four different measures of predictive accuracy were substantially inflated due to spatial autocorrelation, and the spatial LOO CV results were therefore adopted as the best estimates of performance.

Larval metamorphosis in four bivalve species in response to NMDA receptor ligands: The NMDA receptor pathway as potential regulator of bivalve transition to spat

Over the last three decades, a variety of chemical inducers or disruptors for settlement and metamorphosis have been identified for species of clams, oysters, scallops, and mussels. Identifying inducers is important in shellfish aquaculture for increasing metamorphosis rates, and hence, spat (seed) production; however, it also has wider applications, such as in the development of marine anti-fouling agents. Previously, we have suggested the potential importance of an N-Methyl-d-aspartate (NMDA) receptor pathway in regulating bivalve metamorphosis based on preliminary work in Crassostrea gigas. In this study, we further this work by assessing the ability of several known vertebrate NMDA receptor antagonists (MK-801, ifenprodil and chlorpromazine) to induce metamorphosis in a range of bivalve species. In two oyster species (Crassostrea virginica, C. gigas) and two clam species (Mercenaria mercenaria, Mya arenaria) all three NMDA receptor antagonists induced metamorphosis, but with variability in optimal concentrations and effectiveness. Specifically, both clam species were highly responsive to the NMDA receptor antagonists, with M. mercenaria displaying up to 100% induction with both ifenprodil at 10−5 M and 10−6 M and chlorpromazine at 10−7 M to 10−5 M. There is very limited prior work on successful induction using neuroactive compounds for metamorphosis in the hard-shell clam, M. mercenaria, and no prior published work for the soft-shell clam, M. arenaria. Epinephrine and levodopa (L-DOPA), two widely used and effective inducers in Crassostrea species, also induced metamorphosis in both clam species with epinephrine at 10−4 M resulting in 44% and 75% metamorphosis and L-DOPA at 10−5 M resulting in 67% and 98% for M. arenaria and M. mercenaria, respectively. Co-exposures of L-DOPA or epinephrine in conjunction with NMDA receptor antagonists were conducted to identify putative interactions between the proposed NMDA receptor pathway and the dopaminergic or adrenergic pathways by which L-DOPA and epinephrine are believed to operate. In general, co-exposures demonstrated induction of metamorphosis similar or higher than the most effective single treatments. In experiments conducted in 2018 for both oyster species, epinephrine at 10−4 M in conjunction with ifenprodil at 10−6 M, significantly inhibited metamorphosis down to 4% from 12%. The percentage of larvae that underwent metamorphosis was similarly low in response to ifenprodil alone, 2% to 18% metamorphosis, whereas epinephrine alone had a positive inducing effect, 34% to 74% metamorphosis. Results are discussed in relation to the NMDA receptor pathway that appears to be acting independently of previously believed dopaminergic or adrenergic pathways in bivalves.

Clam Spawning & Red Tide: Helping Students Learn the Hardy-Weinberg Equilibrium

The Hardy-Weinberg principle and associated calculations are often challenging for students to learn for three reasons. First, several assumptions need to be understood to correctly apply the principle. Second, a series of calculations are required for proper application. Third, the principle, assumptions, and calculations are often taught separately from students observing population changes over time. We describe a classroom activity in which students investigate how the allele frequencies of soft-shell clam (Mya arenaria) populations change over time as a result of environmental disturbances by simulating the effects on population data. These classroom population changes are then compared to authentic research data collected on populations of M. arenaria. This activity was implemented at three institutions in introductory- and senior-level biology courses. Students reported that the activity helped them better understand and apply both the principle and its calculations.

Vulnerability of juvenile clams to predation by shore crabs

Predation, especially by crabs, is a common source of mortality for natural and farmed populations of intertidal clams. Consumption of juvenile “seed clams” forces aquaculturists to try to exclude predators and/or raise juveniles in hatcheries until they can reach a size refuge. We ran a variety of lab experiments assessing vulnerabilities of juvenile clams to small, common shore crabs (Hemigrapsus spp.). Crabs <1 cm width can consume hardshell Manila clams larger than those normally used for “seed”, and can readily crush even larger softshell Mya clams. We suggest that using netting to prevent consumption by shore crabs is not practical given that smaller individuals can fit through mesh openings. Raising seed in hatcheries until they are 10–15 mm will provide a size refuge from shore crabs, but not larger cancrid crabs. Farming on beaches with little habitat (e.g., cobbles) for shore crabs can likely reduce juvenile clam mortality. A better understanding of predation threats to commercially important clams is critical, especially as the invasion of the green crab Carcinus to Washington shorelines further threatens survival of juvenile clams.

Experimental neutron pole figures of minerals composing the bivalve mollusc shells

Recently, several studies have focused on the crystallographic texture of bivalve mollusc shells. Unfortunately, these investigations have been limited to the local level. We demonstrate the similarities and differences between the texture measured over the whole shell and that measured over a small part of a shell. An analysis of the global crystallographic texture of bivalve mollusc shells of different genera was carried out using time-of-flight neutron diffraction. The reason for this analysis was to determine whether the crystallographic texture character was similar within the class Bivalvia. It was observed that the shells of mollusc species of the genus Mytilus consist of two phases, calcite and aragonite. Ostrea edulis shells consist of almost pure calcite, whereas Mya arenaria shells consist of almost pure aragonite. It was concluded that the character of the global textures of the different phases in the same shells is different. The advantages of characterisation of the global crystallographic texture are also discussed.

Estimating the distribution of harvested estuarine bivalves with natural-history-based habitat suitability models

Habitat suitability models are useful to estimate the potential distribution of a species of interest, particularly in the case of infaunal bivalves. Sampling for these bivalves is time- and cost-intensive, which is increasingly difficult for organizations or agencies that are limited by personnel and funds. Consequently, we developed a framework to identify suitable bivalve habitat in estuaries (FISBHE) – a habitat suitability index (HSI) modeling framework for NE Pacific estuaries that was parameterized with published natural-history information and existing habitat datasets, without requiring extensive field sampling of bivalves. Spatially explicit, rule-based habitat suitability models were constructed in a GIS for five species of bay-clams (Clinocardium nuttallii, Mya arenaria, Tresus capax, Saxidomus gigantea, and Leukoma staminea) that are popular targets for recreational and commercial harvest in estuaries of the U.S. Pacific Northwest. Habitat rasters were produced for Yaquina and Tillamook estuaries (Oregon, USA) using environmental data (bathymetric depth, sediment % silt-clay, wet-season salinity, and burrowing shrimp presence/absence) from multiple studies (1953–2015). These habitat rasters then served as inputs in the final model which produced HSI classes ranging from 0 to 4 (lowest to highest suitability), dependent upon the number of habitat variables that fell within the sensitivity limits for each species of bay-clam. The models were tested with validation analyses and bay-clam occurrence data (reported in benthic community studies, 1996–2012) within each HSI class; logistic regression and Kendall's correlation coefficient both showed correspondence between predicted HSI classes and bay-clam presence/absence. Results also showed that the greatest presence probabilities occurred within habitats of highest predicted suitability, with the exception of M. arenaria in Tillamook Bay. The advantage of FISBHE is that disparate, independent sets of existing data are sufficient to parameterize the models, as well as produce and validate maps of habitat suitability. This approach can be transferred to data-poor systems with modest investment, which can be useful for prioritizing estuarine land-use decisions and could be used to estimate the vulnerability of this valued ecosystem good to changes in habitat quality and distribution.

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.

Creature from the Ria de Aveiro Lagoon. Did I just catch an alien species?

Event Abstract Back to Event Creature from the Ria de Aveiro Lagoon. Did I just catch an alien species? Francisco R. Maia1* 1 Portuguese Institute of Ocean and Atmosphere (IPMA), Portugal The present communication reports the occurrence of the alien soft-shell clam Mya arenaria (Linnaeus, 1758) in the Ria de Aveiro lagoon (NW Portugal). A total of 47 living specimens were collected in spring 2013 (April) and winter 2019 (January) in an intertidal mudflat located at the upstream end of Mira channel (400 32’ 23 N; 80 45’ 56 W). In this area, the soft-shell clam was able to maintain a well-established population in close coexistence with another endobenthic bivalve species, the native clam Scrobicularia plana. The soft-shell clam Mya arenaria is native to the Atlantic coasts of North America and its probably the first marine invasive species recorded in European waters. Presumably, it was introduced in the North Sea by the Vikings in the 13th century (Peterson et al., 1992), from which it spread throughout its current distribution. At present, it is commonly found along the coasts of the North and the Baltic Seas, northern Adriatic Sea, the Black Sea, on all British and Irish coasts, France, Spain, Portugal and in the Mediterranean Sea. The ability to survive in a wide range of habitats; the capacity to tolerate a broad set of environmental conditions at all life stages; the high fecundity levels; and the long-lived planktonic larval stage, have been proposed to explain the long-distance dispersal of this species and its success as an invader. To our knowledge, there isn’t any scientific evidence reporting negative effects of Mya arenaria on Ria de Aveiro ecosystems. Nevertheless, some authors refer that this species has the capacity to change the surrounding environment through its burrowing, feeding and excretory activities, and it is capable to outcompete native bivalve species for space and food, reducing diversity, distribution and abundance of those species. For this reason, more research is needed to better evaluate and fully understand the long-term impacts of Mya arenaria on the native bivalve assemblages of Ria de Aveiro lagoon. References Petersen K.S., Rasmussen, K.L., Heinemeier, J., and Rud, N. (1992). Clams before Columbus? Nature, 359:679 Keywords: Mya arenaria, soft-shell clam, alien species, Invasions, Ria de Aveiro lagoon, Portugal Conference: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019. Presentation Type: Poster Presentation Topic: Global Change, Invasive Species and Conservation Citation: Maia FR (2019). Creature from the Ria de Aveiro Lagoon. Did I just catch an alien species?. Front. Mar. Sci. Conference Abstract: XX Iberian Symposium on Marine Biology Studies (SIEBM XX) . doi: 10.3389/conf.fmars.2019.08.00039 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 06 Apr 2019; Published Online: 27 Sep 2019. * Correspondence: Dr. Francisco R Maia, Portuguese Institute of Ocean and Atmosphere (IPMA), Lisbon, Portugal, maia.francisco@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Francisco R Maia Google Francisco R Maia Google Scholar Francisco R Maia PubMed Francisco R Maia Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Potential impacts of logging on intertidal infaunal communities within the Kitimat River estuary

ABSTRACTEfficiently evaluating industrial activities plays an essential role in determining the extent to which human–ecosystem interactions may lead to species loss, disrupted community dynamics, and degraded ecosystems. Intertidal habitats offer a unique opportunity in this regard, as they are species rich ecosystems that exhibit rapid community turnover and pronounced responses to ecological disturbances. In an attempt to use these dynamic communities to identify the impact storage of harvested logs is having on the Kitimat River estuary, surveys evaluating the biotic and abiotic conditions within surrounding mudflats were conducted. The intertidal mudflats of the Kitimat River Estuary varied spatially and temporally, and with differences in the infaunal community, as well as the abiotic sediment conditions between reference mudflats, and mudflats potentially impacted by logging activities. While these differences were pronounced, we cannot at this time link these differences to the logging activities at impacted sites. We also observed evidence that suggests that the infaunal community of these intertidal mudflats have changed substantially since the 1970s, with the establishment of a community of polychaetes, as well as the appearance of the invasive clam Mya arenaria, and the invasive Cumacea Nippoleucon hinumensis. Beyond contrasting impacted and reference mudflats, the current health of these mudflats, as indicated by the infaunal community assemblage, is currently unclear. More research is required to determine if organic enrichment has occurred at these habitats, as well as to further elucidate the current health of these intertidal mudflats.

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.

Interactive effects of osmotic stress and burrowing activity on protein metabolism and muscle capacity in the soft shell clam Mya arenaria

Bioturbators such as sediment-dwelling marine bivalves are ecosystem engineers that enhance sediment-water exchange and benthic-pelagic coupling. In shallow coastal areas, bivalves are exposed to frequent disturbance and salinity stress that might negatively affect their activity and physiological performance; however, the mechanisms underlying these effects are not fully understood. We investigated the effects of osmotic stress (low and fluctuating salinity) and repeated burrowing on aerobic and contractile capacity of the foot muscle (assessed by the activity of succinate dehydrogenase and myosin ATPase) as well as the levels of organic osmolytes (free amino acids) and biochemical markers of protein synthesis and proteolysis in key osmoregulatory and energy storing tissues (gills and hepatopancreas, respectively) in a common bioturbator, the soft shell clam Mya arenaria. Osmotic stress and exhaustive exercise altered the foot muscle capacity of soft shell clams and had a strong impact on protein and amino acid homeostasis in tissues not directly involved in locomotion. Acclimation to constant low salinity (5 practical salinity units) depleted the whole-body free amino acid pool and affected protein synthesis but not protein breakdown in the gill. In contrast, fluctuating (5–15) salinity increased protein breakdown rate, suppressed protein synthesis, caused oxidative damage to proteins in the gill and selectively depleted whole-body glycine pool. Clams acclimated to normal salinity (15) increased the aerobic capacity of the foot muscle upon repeated burrowing, whereas acclimation to low and fluctuating salinity reduced this adaptive muscle plasticity. Under the normal and low salinity conditions, exhaustive exercise induced protein conservation pathways (indicated by suppression of protein synthesis and catabolism), but this effect was disrupted by fluctuating salinity. These findings indicate that exhaustive exercise and osmotic stress interactively affect whole-body protein homeostasis and functional capacity of the foot muscle in soft shell clams which might contribute to reduced burrowing activity of bivalve bioturbators in osmotically challenging environments such as estuaries and shallow coastal zones.

Habitat complexity and benthic predator-prey interactions in Chesapeake Bay

In Chesapeake Bay, the soft-shell clam Mya arenaria (thin-shelled, deep-burrowing) exhibits population declines when predators are active, and it persists at low densities. In contrast, the hard clam Mercenaria mercenaria (thick-shelled, shallow-burrowing) has a stable population and age distribution. We examined the potential for habitat and predators to control densities and distributions of bivalves in a field caging experiment (Mya only) and laboratory mesocosm experiments (both species). In the field, clams exposed to predators experienced 76.3% greater mortality as compared to caged individuals, and blue crabs were likely responsible for most of the mortality of juvenile Mya. In mesocosm experiments, Mya had lower survival in sand and seagrass than in shell hash or oyster shell habitats. However, crabs often missed one or more prey items in seagrass, shell, and oyster shell habitats. Predator search times and encounter rates declined when prey were at low densities, likely due to the added cost of inefficient foraging; however, this effect was more pronounced for Mya than for Mercenaria. Mercenaria had higher survival than Mya in mesocosm experiments, likely because predators feeding on Mercenaria spent less time foraging than those feeding on Mya. Mya may retain a low-density refuge from predation even with the loss of structurally complex habitats, though a loss of habitat refuge may result in clam densities that are not sustainable. A better understanding of density-dependent predator-prey interactions is necessary to prevent loss of food-web integrity and to conserve marine resources.

Impacts of habitat, predators, recruitment, and disease on soft-shell clams Mya arenaria and stout razor clams Tagelus plebeius in Chesapeake Bay

Soft-shelled clams, Mya arenaria, and razor clams, Tagelus plebeius, in Chesapeake Bay have been in decline since the 1970s, with severe declines since the early 1990s. These declines are likely caused by multiple factors including warming, predation, habitat loss, recruitment limitation, disease, and harvesting. A bivalve survey was conducted in Chesapeake Bay to examine influential factors on bivalve populations, focusing on predation (crab, fish, and cownose rays), habitat type (mud, sand, gravel, shell, or seagrass), environment (temperature, salinity, and dissolved oxygen), recruitment, and disease. M. arenaria and T. plebeius were found more often in more-complex habitats such as seagrass or shell than any other habitat. Pulses in bivalve density associated with recruitment were attenuated through the summer and fall when predators are most active, indicating that predators likely influence temporal dynamics in these species. Mya arenaria, which is near the southern extent of its range in Chesapeake Bay, was negatively associated with high water temperatures. Recruitment of M. arenaria in Rhode River, MD, declined steadily between 1980 and 2016. Infection by the parasitic protist Perkinsus sp. was associated with stressful environmental conditions, bivalve size, and environmental preferences of Perkinsus sp, but was not associated with bivalve densities. It is likely that habitat loss, low recruitment, and predators are major factors keeping T. plebeius and M. arenaria at low densities in Chesapeake Bay. Persistence at low densities may be facilitated by complex habitats, whereas further reductions in habitats such as seagrass could result in local extinction of these important bivalve species.

Stable C and N Isotope Composition of Primary Producers and Consumers Along an Estuarine Salinity Gradient: Tracing Mixing Patterns and Trophic Discrimination

The mixing pattern along a summer salinity gradient in the estuary Odense Fjord was evaluated using nutrient concentrations as well as 13C and 15N isotope signatures of suspended and sediment organic matter, immobile macrophytes (Fucus vesiculosus and Ruppia maritima), and benthic fauna (Mya arenaria, Hediste (Nereis) diversicolor, and Arenicola marina). Trophic discrimination (Δ13C and Δ15N) of the infaunal consumers (suspension feeders and detritivores) was assessed from the obtained mixing patterns along the estuarine gradient. Correspondence between salinity, DIC, and DIN in Odense Fjord implies conservative mixing as also evident from linear relationships between salinity and δ13C and δ15N signatures of most living organic pools. Isotope signatures of suspended organic matter (i.e., diatoms) indicate that the river to marine DIC and DIN end-members have daily/weekly δ13C and δ15N averages during summer from − 10 to 0‰ and 10–12 to 0–5‰, respectively. Stable isotope signatures of long-lived macrophytes stationary at specific locations in Odense Fjord showed δ13C levels that were about 7‰ higher than for suspended particles and 3–4‰ higher than for sediment organic matter, while no such difference was evident for δ15N. The food of invertebrate consumers (M. arenaria, H. diversicolor, and A. marina) determined from the estuarine δ13C and δ15N patterns provided the first ever reported trophic discrimination of these animals. Thus, Δ13C was 1.9, 1.6, and 1.3‰ and Δ15N was 4.4, 5.0, and 3.5‰ for the three species, respectively. Accordingly, benthic suspension and deposit feeders in Odense Fjord are largely supported by a diet consisting of benthic and pelagic microalgae, however, with a possible slight shift in diet proportions or to other food sources in the lower reaches of the estuarine gradient.

Multimarker response to salinity stress in two estuarine bivalves of different genetic diversity: Mya arenaria and Limecola balthica from the Gulf of Gdańsk (southern Baltic Sea)

AbstractThe estuarine bivalves Limecola balthica and Mya arenaria are common inhabitants of marine soft bottom habitats in the Northern Hemisphere. Both species are able to live under a wide range of environmental conditions including variable salinity. However, in L. balthica there is high genetic variability, and populations are often genetically adapted to local conditions. By contrast, genetic diversity in M. arenaria is low across the species’ geographic range, which attests to acclimatization to different conditions. We hypothesized that individuals of M. arenaria should perform better under osmotic stress. We tested this hypothesis by performing a 5‐week experiment that exposed individuals of both clam species to hypo‐ and hyperosmotic conditions. A multiple biomarker approach that included physiological, biochemical, and histological markers was used to assess bivalve performance. Exposure to the different salinities induced biological responses that particularly affected respiratory activity in both species tested, but these responses were much more pronounced in individuals of L. balthica. The results confirmed the hypothesis that the phenotypic plasticity of M. arenaria was more pronounced and reflected a different strategy of adapting to heterogeneous habitats.

Effects of cockle abundance and cockle fishery on bivalve recruitment

Understanding possible effects of cockle dredging on bivalve dynamics should include studies of the influence of cockle abundance on bivalve recruitment and of effects of fishery on survival of recruits present at the time of fishing and on future recruitments. Numerical densities of adult cockles and of recruits of Cerastoderma edule, Limecola balthica and Mya arenaria were monitored by twice annual sampling for 21 years (1973–1993) along 7 transects in the fished part of Balgzand, a 50-km2 tidal flat area in the westernmost part of the Wadden Sea. Between-year variability in recruitment success in all 3 species was negatively correlated with adult-cockle abundance. Recruit densities as estimated in August were relatively low in years of cockle fishing in all of these species. This was so already well before fishing started in September. So these low densities were not an effect of fishery, but of the high cockle abundance that made cockle dredging profitable. The proportions of recruit numbers estimated in August (just before cockle dredging) that were still present half a year after fishing (in March) were not different between fishing and non-fishing years nor between fished and unfished areas in fishing years. Densities of new recruits in years following cockle-dredging somewhere in the area were not different from densities in years not preceded by any fishery nor were they lower at the fished sites in the year after fishing than in other years. The lack of significant influences of fishery in the studied area and period was observed in all 3 bivalve species. The above results were obtained in areas with relatively muddy sediments. Earlier reported negative effects of cockle-dredging on bivalve recruitment may be limited to the minority of tidal flats characterized by relatively coarse sediments with <1% of silt.