Native Mussel Populations Research Articles

Ecological state of the environment and phenotypic characteristics of mussel Mytilus galloprovincialis Lamarck, 1873 in the Neum Bay (Bosnia and Herzegovina)

Mytilis galloprovincialis Lamarck, 1873 is a species widespread in the Adriatic Sea. Due to the its edibility, it is the first shellfish breed in Europe, and two farms have been registered in the Neum Bay. The paper analyzes native mussel populations of M. galloprovincialis from three populations (Neum Bay two and Mali Ston Croatia). For the purposes of the analysis, sampling was performed in the tide zone in May 2019. According to the WFD and typology, these three localities are in the type of coastal waters of polyhialine with fine-grained sediment. According to the average values ​​of physical-chemical and chlorophyll, Neum Bay is in the category of good ecological status, while Mali Ston is stated to be a reference site. Morphometric measurements of the right eyelid in 90 individuals (30 per locality) included external parameters (height, total length and width of the shell) as well as total weight, gut weight and shell weight. As the internal parameters, the characteristics of the ligament, retractor muscles and adductor muscles are analyzed. By the application of statistical analyzes (descriptive statistics, post Hoc analysis, correlation and descriptive statistics), differences in the total weight, length and parameters of the adductor and retractor muscles have been determinated. The species from Mali Ston are clearly separated from the species of the Neum Bay, which indicates more pronounced anthropogenic influences in the areas of the Neum town. Morphometric analysis is a powerful tool in monitoring the state of populations and in combination with genetic-molecular analysis can indicate changes in the environment. Determining pathogens in mussel species in Croatia, Slovenia and Italy is an impulse to control the condition of natural and breeding species, using various methods and analyzes.  

Impacts of native and invasive crayfish on three native and one invasive freshwater mussel species

Abstract Freshwater mussels and crayfish provide important ecosystem functions and services. In both groups, global declines of native species are paralleled by invasions of non‐native species. Knowledge on differences in predation susceptibility of native and invasive freshwater mussels exposed to native and invasive crayfish is essential for understanding their ecological interactions and for conservation management. In this study, we compared the predation impact of the native European noble crayfish (Astacus astacus) and the invasive signal crayfish (Pacifastacus leniusculus) on three native (Anodonta anatina, Anodonta cygnea, and Unio pictorum) and one invasive (Sinanodonta woodiana) mussel species in controlled laboratory experiments. We repeated the same experiments with the same crayfish specimens to investigate a potential learning effect of crayfish and assessed the in situ impacts in a natural stream. Mussel predation and damage caused by P. leniusculus was significantly higher than by A. astacus. Irrespective of the crayfish species, susceptibility was greater in native mussel species compared to invasive S. woodiana. Predation and damage was greatest in the thick‐shelled U. pictorum, suggesting that other factors such as shell shape are more important in explaining susceptibility than shell thickness. A predation learning effect from previous co‐exposure was evident, being most pronounced for A. astacus. Even if our experimental findings could not be confirmed in the field, the experimental results suggest that crayfish may have a negative impact on mussels and this impact will likely increase with the ongoing spread of P. leniusculus replacing A. astacus populations in Europe. The co‐occurrence of invasive P. leniusculus with the invasive S. woodiana could potentially exacerbate declines of endangered native mussel populations.

Status of Freshwater Mussels (Unionidae) in the French Creek Watershed, USA at the Onset of Invasion by Round Goby, Neogobius melanostomus

Freshwater mussels are an imperiled group of organisms that are vital to aquatic ecosystems. Services performed by freshwater mussels, coupled with their use for biomonitoring, make them an invaluable asset. Neogobius melanostomus (Round Goby), a recently introduced invasive species to the French Creek watershed, was once restricted to the watershed of Lake Erie in Pennsylvania. The Round Goby’s propensity to consume Dreissena polymorpha (Zebra Mussel) and Dreissena bugensis (Quagga Mussel) in their native habitat raises concerns about this recent introduction into Pennsylvania’s Allegheny River watershed. Since the discovery of their introduction within the watershed, we have followed the range expansion and dispersal rate of Round Gobies, which makes this study unique. The objectives of this study were to quantify baseline data on the contemporary diversity and abundance of unionid mussels in the upper French Creek watershed, and to explore potential habitat factors that influence or limit the size of the mussel populations. We gathered baseline data on freshwater mussel diversity and abundances across eight sites in the French Creek watershed and examined substrate particle size and host availability as potential limiting factors of the freshwater mussel distribution. Freshwater mussel surveys were conducted during the summer months (July–September) of 2017 using area-constrained surveys. Results showed a significant relationship between mussel diversity and substrate particle size (p < 0.05). From the data collected, we were able to calculate population estimates for the species found across the sample sites. Our results regarding the locations of native mussel populations and characteristics of their habitat provide the needed insight for establishing priority areas for the conservation of freshwater mussels, facilitating planning for protection, mitigation, and adaptation as the invasive Round Goby continues its spread.

Population‐level effects of parasitism on a freshwater ecosystem engineer, the unionid mussel Anodonta anatina

Abstract Parasites can negatively affect hosts at individual, population, and species‐level scales. However, the link between individual‐ and population‐level impacts is often poorly understood. In particular, the population‐level response to parasitism may alter wider ecosystem dynamics if animals with ecosystem engineering capabilities are infected. Here, we examine the effects of parasitism on a freshwater ecosystem engineer, the unionid mussel Anodonta anatina, at two different sites. We study three common parasites: the digenean trematode Rhipidocotyle campanula; the unionicolid mite Unionicola intermedia; and the ectoparasitic invasive zebra mussel Dreissena polymorpha. As well as demonstrating the individual‐level effects of parasitism on the native host mussel, we construct a simple model to estimate the reduction in population‐level reproductive output caused by parasites. We show that both infection prevalence and intensity were population‐specific, with one site having more than three times as many native mussels infected by trematodes and mites than the other, but more than four times fewer mussels afflicted by invasive zebra mussels. Negative reproductive consequences for individual host mussels were documented as a result of parasitism, with trematodes causing castration at both sites. Mites were also correlated with a reduction in the viability of larval offspring (glochidia) by more than 25%, but only at one site, suggesting some potential impacts of parasitism may be population specific. The population‐level model shows that parasitism alone reduces larval output of the two populations by 10% and 13%, respectively. Our study takes the important step of scaling individual‐level effects of parasitism to population‐level processes, and highlights the influence that parasites may have in the population dynamics of unionid mussels. Given the ecosystem engineering capabilities of A. anatina, such effects may have important impacts on the wider biota. Even at relatively low prevalences, the observed effects of parasites on native mussel populations suggests that parasitism must be considered in the conservation of freshwater mussels, one of the world's most globally imperilled faunal groups. Further, understanding how the effects of parasitism on individual hosts scales to the ecosystem level is a crucial and unaddressed question in freshwater biology.

The growth of juvenile native mussels (Elliptio complanata) in lakes varies with sediment characteristics and site exposure

Abstract Unionid mussels are among the largest and longest‐lived freshwater invertebrates and can play an important role in these ecosystems. They are also one of the most endangered groups of organisms. The juvenile stage is a particularly vulnerable part of mussel life history and is one of the most poorly known. I compared the growth of young Elliptio complanata at 17 nearshore sites, in shallow (polymictic) and stratified lake basins, along gradients of sediment characteristics and site exposure (effective fetch). At each site, the growth of six to 14 small (20–68 mm) mussels collected on the sediment surface was measured, using internal growth lines. The growth of very young endobenthic mussels (22–40 mm) was also measured on four to six mussels at each of two sites. Juveniles spend several years in the sediments, and I found that during this period growth is not constant but declines rapidly with age. Shifts in δ15N signatures suggest that juveniles change their habitat use towards a more planktonic baseline around the time of maturation, when they reach a length of 30–50 mm. Identical δ13C signatures in juveniles and adults suggest that both rely on food of planktonic origin, whether deposited or suspended. The growth of juvenile mussels varies in a complex but predictable manner with sediment characteristics and wind‐driven physical forces. Growth was highest in fine sediments with low organic content, in highly organic but coarse sediments, and in protected nearshore areas with low effective fetch. Interestingly, I also found high growth rates at exposed nearshore areas with fine sediments, suggesting that areas where bottom topography creates a refuge from currents and waves may provide particularly good conditions for the early growth of juvenile mussels. Some parts of the shoreline may be more important than others for native mussel populations, and if we can identify those, they may warrant additional protection.

Annual winter water level drawdowns limit shallow‐water mussel densities in small lakes

Abstract Regulated water level fluctuations alter the physical, chemical, and biological environments in lakes. However, few studies have measured the effects of repeated annual winter drawdowns on freshwater mussel populations (Bivalvia: Unionida), and it is unknown whether drawdowns permanently constrain mussel populations to deeper depths or are resilient to the annual disturbance. We quantified mussel densities during normal water levels and their mortality after the initiation of drawdown in lakes with annual winter (December–March) water level drawdown regimes that have existed for several decades. We used systematic quadrat sampling and visual snorkel surveys to estimate the number of live mussels at the surface and buried, and shell length in six drawdown and three control lakes at exposed (0.5‐m) and unexposed (1‐m) depths during winter drawdown. We also estimated mortality of mussels along the exposed lakebed for nine drawdown lakes. Study lakes were dominated by Elliptio complanata and Pyganodon cataracta. During normal water levels, mussel densities were much lower in drawdown lakes than control lakes at 0.5‐m depths. When mussels were present in drawdown lakes at 0.5‐m depths, they were often burrowed in the substrate and smaller than buried mussels in control lakes. At unexposed 1‐m depths, mussel densities were primarily explained by geographic region (western versus central Massachusetts), and found higher densities in drawdown lakes compared to control lakes. Mussel mortality after a single drawdown event in nine drawdown lakes was not correlated with drawdown magnitude or rate. Concordance of shell length‐frequency distributions between dead and buried living mussels in drawdown lakes suggests annual mortality of colonising individuals, which are typically small and presumably of young cohorts. Annual winter drawdowns still limit densities of E. complanata and P. cataracta in shallow‐water habitats in the following autumn (September–October) after 4–5 months of potential recovery, and hence constrain their distribution in lakes exposed to drawdowns. The development of sustainable water level management practices will be essential to minimise impacts to native mussel populations.

Host fish status of native and invasive species for the freshwater mussel Anodonta anatina (Linnaeus, 1758)

The worldwide extinction of species especially affects freshwater ecosystems. Even widespread species like the European freshwater duck mussel Anodonta anatina face population declines in many countries and regions. Due to an obligate parasitic phase in its life cycle, knowledge on host fish use is essential for effective conservation of A. anatina. Therefore, in this study host suitability of ten different fish species (native and invasive to Europe) from four different fish families was tested by simultaneously infesting them with the glochidia of A. anatina. Nine out of ten fish species were identified as suitable hosts, but infestation rates, duration of metamorphosis phase as well as duration and rate of juvenile mussel excystment differed significantly between all host species. The bitterling (Rhodeus amarus) was the only fish species with no juvenile mussel excystment. Surprisingly, one of the tested invasive fish (Ctenopharyngodon idella) turned out to be the second best host for the larvae of A. anatina, suggesting that the general assumption that non-native fishes would be a threat to native mussel populations no longer holds true. Compared to the second native Anodonta species in Europe (Anodonta cygnea), this study revealed that A. anatina had higher infestation rates and rates of juvenile mussels excystment as well as a different host compatibility than A. cygnea. These findings illustrate that species-specific assessments of host suitability form an urgent basis for evidence-based conservation and restoration of freshwater mussel populations and the ecosystem services they provide.

Parasites and endobiotic fungi in digestive gland cryosections of the mussel Mytilus galloprovincialis in the Northern Adriatic, Croatia

Abstract Histology has been used in the past to investigate the effects of diseases and parasite infections in native mussel populations that are often used as sentinel species in coastal environmental monitoring and as stock in mariculture. This paper presents the first study of parasite diversity using cryosections of the Mytilus galloprovincialis Lamarck, 1819 digestive gland. Mussels were sampled across the annual cycle at two sampling sites: St. Andrew and ACI Marina in the Northern Adriatic (Croatia). The protozoan of the genus Nematopsis Schneider, 1892 (Apicomplexa, Gregarina) was detected in digestive tubules, while the turbellarian (Urastomidae) Urastoma cyprinae von Graff, 1913 was found in the connective tissue at the edge of the digestive gland. The filamentous fungus Alternaria sp. (Fungi, Ascomycota) was detected in epithelial cells of the digestive tubule in cryosections. Nematopsis sp. occurred with the prevalence ranging from 20 to 100%, and the intensity of infection in less than 30 oocysts in most of the cases. U. cyprinae was detected in mussels sampled at St. Andrew and had a prevalence of 20% in September. Conidia of Alternaria sp. were found in mussels sampled at St. Andrew in September and November. Cryosections provide a useful and affordable means for monitoring parasites and endobiotic fungi.

Variability of the reproductive cycle in estuarine and coastal populations of the mussel Mytilus galloprovincialis Lmk. from the SE Bay of Biscay (Basque Country)

Mussel commercial production depends on wild populations to obtain the seed. Therefore, any new farming initiative needs deep knowledge on reproductive cycle of native mussel populations. The reproductive cycle of Mytilus galloprovincialis Lmk. from five sites, three estuarine and two coastal, along the coast of the Basque Country were assessed using gonad index and stereology over 2 consecutive years (2010 and 2011). Sex ratios, developmental stages of gonads, as well as reserve tissue cycle were analyzed. The onset of gametogenesis was observed from winter to spring, with spawning occurring from spring till summer. A resting phase followed with an increase in reserve tissues (adipogranular cells) was observed in fall. Mussels stayed ripe during winter until favorable environmental conditions were met in spring. Differences in reproductive cycles were found among populations, and also, year-to-year variability was observed within each population. In two of the studied sites asynchrony in the timing of spawning was observed between genders. These timing differences, however, did not prevent mussels at those sites from reproducing successfully. The Bidasoa estuary points to the potential of such studied sites for becoming the main source of wild mussel spats for future expected commercial mussel farming in the Basque Country. To ensure year-to-year maximum reproductive output, however, wild mussels harvest should be avoided from spring to the end of summer in this region.

The change of nature and the nature of change in agricultural landscapes: Hydrologic regime shifts modulate ecological transitions

AbstractHydrology in many agricultural landscapes around the world is changing in unprecedented ways due to the development of extensive surface and subsurface drainage systems that optimize productivity. This plumbing of the landscape alters water pathways, timings, and storage, creating new regimes of hydrologic response and driving a chain of environmental changes in sediment dynamics, nutrient cycling, and river ecology. In this work, we nonparametrically quantify the nature of hydrologic change in the Minnesota River Basin, an intensively managed agricultural landscape, and study how this change might modulate ecological transitions. During the growing season when climate effects are shown to be minimal, daily streamflow hydrographs exhibit sharper rising limbs and stronger dependence on the previous‐day precipitation. We also find a changed storage‐discharge relationship and show that the artificial landscape connectivity has most drastically affected the rainfall‐runoff relationship at intermediate quantiles. Considering the whole year, we show that the combined climate and land use change effects reduce the inherent nonlinearity in the dynamics of daily streamflow, perhaps reflecting a more linearized engineered hydrologic system. Using a simplified dynamic interaction model that couples hydrology to river ecology, we demonstrate how the observed hydrologic change and/or the discharge‐driven sediment generation dynamics may have modulated a regime shift in river ecology, namely extirpation of native mussel populations. We posit that such nonparametric analyses and reduced complexity modeling can provide more insight than highly parameterized models and can guide development of vulnerability assessments and integrated watershed management frameworks.

Exotic species replacement: shifting dominance of dreissenid mussels in the Soulanges Canal, upper St. Lawrence River, Canada

During the early 1990s, 2 Eurasian macrofouling mollusks, the zebra mussel Dreissena polymorpha and the quagga mussel D. bugensis, colonized the freshwater section of the St. Lawrence River and decimated native mussel populations through competitive interference. For several years, zebra mussels dominated molluscan biomass in the river; however, quagga mussels have increased in abundance and are apparently displacing zebra mussels from the Soulanges Canal, west of the Island of Montreal. The ratio of quagga mussel biomass to zebra mussel biomass on the canal wall is correlated with depth, and quagga mussels constitute >99% of dreissenid biomass on bottom sediments. This dominance shift did not substantially affect the total dreissenid biomass, which has remained at 3 to 5 kg fresh mass /m2 on the canal walls for nearly a decade. The mechanism for this shift is unknown, but may be related to a greater bioenergetic efficiency for quaggas, which attained larger shell sizes than zebra mussels at all depths. Similar events have occurred in the lower Great Lakes where zebra mussels once dominated littoral macroinvertebrate biomass, demonstrating that a well-established and prolific invader can be replaced by another introduced species without prior extinction.

Cellular biomarkers in native and transplanted populations of the mussel Perumytilus purpuratus in the intertidal zones of San Jorge Bay, Antofagasta, Chile.

Cellular biomarkers were measured in the mussel Perumytilus purpuratus from intertidal zones of San Jorge Bay, Antofagasta, Chile. They were also used to measure sublethal effects on individuals exposed to Cu under laboratory conditions. Lysosomal stability in hemocytes, and the degree of vacuolization and the content of lipofuscin granules in digestive cells were the cellular responses measured. Three study sites were established in San Jorge Bay: Coloso, E.R., and Reference. Both E.R. and Coloso receive effluent discharges. Reference does not receive any sewage discharges. Before sampling, mussels from Reference were transplanted into the intertidal zone of each site. Samplings were obtained at the beginning, after 45 days, and after 90 days after transplantation. Seawater samples for total dissolved Cu analysis and adult mussels ( P. purpuratus) from native and transplanted populations were collected each time. Cellular biomarkers and Cu concentrations in gonads, gills, and remaining tissues (gut and muscle) were measured. Mussels from Reference were exposed to sublethal Cu concentrations (5, 10, 20, 30, 40, and 80 microg x L(-1)) during 45 days under laboratory conditions. Lysosomal stability was measured in mussel hemocytes by means of the neutral red retention assay. The degree of vacuolization and the extent of lipofuscin granules were determined in the digestive cells by image analysis of histological sections stained with the Schmorl's method. Seawater Cu concentrations and tissue Cu concentrations in P. purpuratus were higher in E.R. than in Reference and Coloso (p < 0.02). Native mussel populations from E.R. showed lower lysosomal stability (p < 0.05), higher vacuolization degree (p < 0.001), and lower amounts of lipofuscin granules (p < 0.001) than those from Coloso and Reference. Transplanted mussel to E.R. showed significant reduction in lysosomal stability (p < 0.05) and in extent of lipofuscin granules (p < 0.05) and significant increase in vacuolization degree (p < 0.05), whereas Reference and Coloso are not significantly dissimilar between them. Seawater Cu concentration was positively correlated with Cu content in gonads ( r2 = 0.61; p < 0.02), gills ( r2 = 0.66; p < 0.01), remaining tissues ( r2 = 0.56; p < 0.05), and the degree of vacuolization ( r2 = 0.65; p < 0.01) and negatively with lysosomal stability ( r2 = 0.79; p < 0.001) and lipofuscin granules extent ( r2 = 0.53; p < 0.05). Mussels exposed to Cu under laboratory conditions showed decreased lysosomal stability (over 30 microg Cu x L(-1)) (p < 0.02) and increased degree of vacuolization (at 80 microg Cu x L(-1)) (p < 0.05) and an increased lipofuscin granules extent (although differences among treatments were not statistically significant).

Impending extinctions of North American freshwater mussels (Unionoida) following the zebra mussel (Dreissena polymorpha) invasion

1. Freshwater mussels (Order Unionoida) are the most imperiled faunal group in North America; 60% of described species are considered endangered or threatened, and 12% are presumed extinct. Widespread habitat degradation (including pollution, siltation, river channelization and impoundment) has been the primary cause of extinction during this century, but a new stress was added in the last decade by the introduction of the Eurasian zebra mussel, Dreissena polymorpha, a biofouling organism that smothers the shells of other molluscs and competes with other suspension feeders for food. Since the early 1990s, it has been spreading throughout the Mississippi River basin, which contains the largest number of endemic freshwater mussels in the world. In this report, we use an exponential decay model based on data from other invaded habitats to predict the long‐term impact of D. polymorpha on mussel species richness in the basin. 2. In North American lakes and rivers that support high densities (&gt;3000 m−2) of D. polymorpha, native mussel populations are extirpated within 4–8 years following invasion. Significant local declines in native mussel populations in the Illinois and Ohio rivers, concomitant with the establishment of dense populations of D. polymorpha, suggest that induced mortality is occurring in the Mississippi River basin. 3. A comparison of species loss at various sites before and after invasion indicates that D. polymorpha has accelerated regional extinction rates of North American freshwater mussels by 10‐fold. If this trend persists, the regional extinction rate for Mississippi basin species will be 12% per decade. Over 60 endemic mussels in the Mississippi River basin are threatened with global extinction by the combined impacts of the D. polymorpha invasion and environmental degradation.

Cercaria tenuans, larval trematode parasite of Mytilus and its significance in mussel culture

Observattions on a larval trematode, Cercaria tenuans Cole, found in Mytilus edulis imported into Italia from the Ria de Arosa (northwest coast of Espana), are reported. Prevalence was about 4%. This parasite was not found in a survey of native mussel populations in the Laguna Veneta (Italia, Upper Adriatic). Infected mussels have a characteristic orange coloration and the sporocysts are strikingly motile thus facilitating recognition of this parasite even at the macroscopic level. Some morphological characteristics of the sporocysts and cercariae are described and a comparison is made with similar larval trematodes reported from mussels. Histological examination indicated minimum pathology at the tissue level, no overt response to healthy sporocysts being noted. Tissue damage appears to result primarily from displacement or compression of adjacent structures and occlusion of vessels, sinuses and gonoductes. It is concluded that, at he low prevalence levels heretofore reported, this parasite would be responsible for minimal losses in natural and cultured mussel populations. The potential hazard of problems that might occur in the culture of mussels as a result of epizootics of this and other parasites is discussed.