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Ecosystem engineers alter habitat and resource availability within ecosystems, but the magnitude of these effects depends on abiotic context and spatial scale. We examined how the effects of freshwater mussels, an ecosystem engineer, changed with spatial scale. We combined a field enclosure experiment and comparative field study to evaluate associations among mussels and macroinvertebrate communities across three spatial scales: mussel individuals (~ 0.01 m2), patches of mussels (0.25 m2), and large aggregations of many mussel patches (mussel beds, ~ 1000 m2). We used canonical correspondence analysis and variation partitioning to evaluate how mussel abundance, food availability, substrate heterogeneity, and flow influenced macroinvertebrate communities. We found that mussels' influence on macroinvertebrate communities differed among spatial scales. At the smallest scale, macroinvertebrate density increased on the shells of live mussels, likely due to mussel influences on food availability to grazers. At the patch scale, we found no mussel effects, likely because they were overridden by a flood event. At the mussel bed scale, macroinvertebrate communities were primarily controlled by flow and secondarily by food availability. As such, the continued loss of freshwater mussels means the loss of habitat creation and food provisioning for other aquatic groups, and alteration of facilitation landscapes within streams. [ABSTRACT FROM AUTHOR]

Global increase in aquaculture production has created a need to reduce its environmental impacts. Nutrients could be recycled especially at land-based recirculating aquaculture systems (RAS) by cultivating green microalgae in aquaculture effluent. However, microalgae are difficult to harvest. As a multi-trophic solution, mussels could be used in harvesting microalgae. We tested three European freshwater mussels (duck mussel Anodonta anatina, swan mussel A. cygnea, and swollen river mussel Unio tumidus) for filtering two common green microalgae (Monoraphidium griffithii and Selenastrum sp.) grown in RAS effluent. Mussels decreased microalgal concentrations in the tanks 42–83% over three consecutive trials. Algal concentrations at the end of each trial were lowest for both microalgae in tanks containing Anodonta mussels. Clearance rates were higher for Anodonta mussels than for U. tumidus. Mussels biodeposited more microalgae to tank bottoms when M. griffithii was filtered. Ammonium concentration decreased or did not change in tanks with M. griffithii, but increased in tanks containing Selenastrum sp. These results suggest that of the tested species Anodonta mussels and M. griffithii show best potential for RAS effluent bioremediation application. We conclude that a co-culture of microalgae and unionid mussels could be used for recycling nutrients in aquaculture. [ABSTRACT FROM AUTHOR]

Successful aquatic biological invasions are often dependent on human vectors. The Chinese pond mussel Sinanodonta woodiana is a fast-growing, high-filtering, and highly fecund unionid bivalve that has expanded rapidly throughout Europe in the last several decades. Human-mediated vectors such as fish aquaculture and pet shop trade are believed to be primary drivers of the mussel's spread, but the specific dispersal pathways of S. woodiana remain unclear. We analyzed eleven microsatellites in 245 S. woodiana individuals from seven wild populations and three pet shops to assess genetic relatedness potential sources, and dispersal pathways of S. woodiana in Bavaria, Germany. Wild populations shared a single mitochondrial haplotype present in all European populations and shop-sourced individuals were genetically similar to wild populations. Only one wild population was structurally different than all other populations, which may be explained by its dispersal trajectory. Our results provide the first genetically informed insights into S. woodiana dispersal in the context of human activity. We underscore the value of genetic tools in invasive species management, which can uncover patterns of dispersal even on local scales. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Order Unionoida) can provide crucial ecological functions and services. However, many of them are endangered worldwide due to local extirpation and reproductive failure, which emphasizes the importance of mussel life cycle monitoring, including reproduction. Buldowskia iwakawai (Suzuki, 1939) is one such species native to the Ishikari floodplain oxbow lakes where its reproductive failure was recently reported. In this study, a species-specific environmental DNA (eDNA) assay was developed to monitor B. iwakawai abundance and winter reproduction in the laboratory and natural environment simultaneously even at times when natural lakes are covered by ice. A positive CPUE-eDNA correlation was observed across all the 14 lakes sampled prior to ice cover formation. The eDNA concentration significantly differed between gravid and non-gravid mussels in relation to their metabolic-rate differences in laboratory experiments, but the eDNA concentration increase was not detected in the intensively monitored lakes during the glochidia release period. PCR inhibition in natural water has been suggested, and reducing its effects combined with appropriate seasonal contexts has the potential to improve the applicability of this method. This research sheds new light on the applicability of the eDNA assay for monitoring mussel reproductive activities throughout their life cycle including the winter season. [ABSTRACT FROM AUTHOR]

Invasive species have far-reaching consequences for whole ecosystems. The two dreissenids zebra and quagga mussels are two of the most successful invaders in aquatic systems. Quagga mussels can colonize deeper parts of a lake while zebra mussels prefer shallow areas. Both species show large variability in shell morphology, but only quagga mussels show a shallow and deep-water morphotype. The aim of this study is to investigate the depth adaptation of quagga mussels and the potential filtration advantage of the quagga mussel compared to the zebra mussel. We conducted common garden experiments, where we measured filtration rates at different temperatures of quagga mussels collected from different water depths and compared them to zebra mussel from 1m depth. We found filtration rates to be strongly temperature dependent, and in particular, lower at 4 °C. Overall, zebra mussels fed less than quaggas. Quagga mussels collected from 1 m depth fed more at higher temperature than quaggas from 30 and 60 m. We hypothesize that deep-water quagga mussels are less sensitive to lower temperature and/or constrained to modify filtration rates at higher temperatures. [ABSTRACT FROM AUTHOR]

The establishment of invasive dreissenid mussels Dreissena polymorpha and Dreissena rostriformis bugensis in the Laurentian Great Lakes has affected multiple aspects of the ecosystem. However, the effects of their larvae (veligers) on lower trophic levels are relatively unknown. Previous research has documented that some larval fishes consume veligers, but it is unclear if they select for veligers. To assess the role of veligers in larval fish diets in Lake Huron, we examined the diets of larval burbot Lota lota, rainbow smelt Osmerus mordax, and Coregonus spp., mainly bloater Coregonus hoyi, sampled in July of 2017. Preference for available zooplankton prey was evaluated using Vanderploeg and Scavia's E*. Results indicated that veligers were on average avoided by large larval burbot, rainbow smelt, and coregonines but were sometimes preferred by small (< 7 mm) and medium-sized (7–10 mm) larval burbot. A mixed model analyzing factors contributing to veliger preference by larval burbot indicated that greater environmental zooplankton prey size is associated with more positive preference for veligers. Thus, veligers may be important for gape-limited larval fish. We also found that, on average, larval burbot and coregonines consumed larger veligers than those sampled in the environment. Overall, consideration of larval fishes' ability to exploit veligers could help managers to understand the role of dreissenid mussels in Great Lakes food webs. [ABSTRACT FROM AUTHOR]

The ecosystem services approach to conservation is becoming central to environmental policy decision making. While many negative biological invasion-driven impacts on ecosystem structure and functioning have been identified, much less was done to evaluate their ecosystem services. In this paper, we focus on the often-overlooked ecosystem services provided by three notable exotic ecosystem engineering bivalves, the zebra mussel, the quagga mussel, and the golden mussel. One of the most significant benefits of invasive bivalves is water filtration, which results in water purification and changes rates of nutrient cycling, thus mitigating the effects of eutrophication. Mussels are widely used as sentinel organisms for the assessment and biomonitoring of contaminants and pathogens and are consumed by many fishes and birds. Benefits of invasive bivalves are particularly relevant in human-modified ecosystems. We summarize the multiple ecosystem services provided by invasive bivalves and recommend including the economically quantifiable services in the assessments of their economic impacts. We also highlight important ecosystem disservices by exotic bivalves, identify data limitations, and future research directions. This assessment should not be interpreted as a rejection of the fact that invasive mussels have negative impacts, but as an attempt to provide additional information for scientists, managers, and policymakers. [ABSTRACT FROM AUTHOR]

An increase in extreme droughts and floods is expected with current and future climate changes. Such extreme climate events may have long-lasting impact on more sessile organisms, such as unionid freshwater mussels, which are highly imperiled. The objective of our study was to test specific predictions for the impact of an extreme drought in 2011/2012, extreme flooding in 2017, and long-term changes by comparing recent and historical mussel community data from an understudied yet biodiverse region of Texas, USA. Drought had the most detrimental impact leading to community-wide declines, indicated by a significant decline of abundances, species richness and occupied sites. Flooding led to shifts in community composition and spatial distribution. Both severe declines and a distinct community shift occurred over the long-term, where the dominance of species shifted to those more tolerable of disturbance. Saltwater intrusion likely caused a significant increase post-flood of a species known to be tolerant of brackish water (Glebula rotundata). The impact of flooding was likely buffered by connectivity with extensive backwater areas, forming large wetlands, which may act as crucial refuges for mussels during extreme climatic events. Thus, protecting wetlands is crucial to protect freshwater mussels and the ecosystem services they provide. [ABSTRACT FROM AUTHOR]

Native freshwater mussels form a critical component of benthic foodwebs, but are endangered worldwide, making their study an important conservation issue. Many unionids live in shallow environments where they are potentially vulnerable to natural disturbances, but the impact of physical forces on their growth and the role of sediments as a refuge is poorly understood. Here, we validate the use of two types of shell internal lines (nacreous, prismatic) as indicators of physical disturbance and shell coloration as an indicator of sedimentary habitat. We use these indicators to test (1) whether the sediments provide an effective refuge for juvenile and young adult mussels from natural disturbances and (2) whether disturbance events affect their growth. Elliptio complanata (Eastern Elliptio) emerge from the sediments when they are 20–50 mm in size and 2.5–7 years old. Juvenile and young adults lay down more disturbance lines at more exposed nearshore sites, but also in small lake basins with dense mussel populations. Disturbance lines are produced during both endo- and epibenthic growth periods, but in contrast to adults, they are not associated with growth anomalies. Sediments accumulating in shallow nearshore areas of lakes provide an imperfect but effective refuge for native mussels that warrant protection. [ABSTRACT FROM AUTHOR]

Native freshwater mussels (unionids) are indicators of water quality, with unique behaviors and movement patterns. Many of these species are endangered, yet basic movement and co-occurring community data are lacking for successful unionid conservation. In this study, movement, community, and habitat use among Ligumia recta, an endangered unionid in Michigan, were analyzed across four rivers in central Michigan. The effects of sex, community, substrate use, and other abiotic factors on the movement and occurrence of L. recta were quantified. 24 L. recta individuals were found with variable male:female ratios and were monitored bi-weekly. Over the recapture period, L. recta moved an average minimum convex polygon of 1.43 m2 per day but was variable among rivers. 19 unionid species were found occurring with L. recta; ~13 species in the same river reach as L. recta and ~5 species in closer proximity to L. recta. The tribe Lampsilini most often occurred in close proximity to L. recta. This study identified basic movement and occurrence patterns of L. recta and provides a better understanding of the status of L. recta in Michigan. Our study highlights useful methods in understanding imperiled unionids, expanding the knowledge of their movement, behavior, community assemblages, and habitat use. [ABSTRACT FROM AUTHOR]

The freshwater pearl mussel Margaritifera margaritifera is an endangered bivalve which is usually regarded as sedentary, although individual movement has been observed both vertically and horizontally. Little is known about the causes and rates of mussel movement. The objective of this study was to test the effect of microhabitat characteristics on the horizontal movement distance and rates of freshwater pearl mussels. A total of 120 mussels (length range 40–59 mm) were marked individually with passive integrated transponder tags, placed in stream microhabitats differing in their sediment composition and monitored biweekly over a period of 10 weeks. Mussels situated in sand-dominated habitats had a significantly higher mean movement rate (3.2 ± 4.2 cm/day, mean ± SD) than mussels situated in gravel-dominated (1.9 ± 2.7 cm/day) or stone-dominated habitats (1.8 ± 3.2 cm/day). The direction of the movements appeared random; however, an emigration from sandy habitats was observed, probably to avoid dislodgment from these hydraulically unstable habitats. This study demonstrates that freshwater pearl mussels can actively emigrate from unsuitable microhabitats. Once suitable streams with respect to physical, chemical, and biological quality were identified, it is therefore only necessary to identify suitable mesohabitats (area of 10–30 m2) when reintroducing or relocating mussels. [ABSTRACT FROM AUTHOR]

Quagga mussels (Dreissena bugensis) are considered one of the most deleterious invasive species in freshwater ecosystems because they can alter food webs by changing energy and nutrient flows. Generally, the predicted effect of quagga mussels on the trophic niche of co-occurring fish is a decrease in trophic level and a shift to use of more littoral-based energy, especially in pelagic-feeding fishes. We evaluate variation, in trophic niche of fishes in Lake Powell using stable isotopes to see if they conform to this expected pattern, and we compare current trophic niche of fishes to trophic niche measured prior to full colonization by quagga mussels. After colonization by quagga mussels in Lake Powell, trophic niche of all five fish species changed, but the direction and magnitude of change varied significantly between regions of the lake. In the southern region of the lake, some species exhibited a trend of decreasing δ15N, (i.e., decreased trophic level), and an enrichment of δ13C, indicating a littoral energy shift consistent with the expected effect of quagga mussels. However, in the northern region of the lake some species exhibited an increase in trophic position and a shift toward the pelagic energy pathway across the same time period. Regional differences in the lake, including extreme fluctuations in water level and high input of sediments from the Colorado River, may ameliorate the effect of quagga mussels. [ABSTRACT FROM AUTHOR]

The original article can be found online at https://doi.org/10.1007/s10750-020-04346-3.Publisher Correction: Hydrobiologia (2020) 847:3409–3425https://doi.org/10.1007/s10750-020-04346-3In the above-mentioned publication, the authors names were scrambled during the production process and should have read Daniel F. R. Cleary and Ana R. M. Polónia.The original article has been corrected.Publisher's NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.By Daniel F. R. Cleary and Ana R. M. PolóniaReported by Author; Author [Extracted from the article]

Recruitment of mussels is a complex process with the successful arrival of individuals hinging on the availability of suitable habitats. We examined the effects of adult mussels as settlement habitat and the degree to which the suitability of habitat they offer is species-specific by comparing the recruitment success of intertidal mussels. We hypothesised that mussel recruitment and early growth are dictated by the quality of habitat offered by conspecifics adults. We used a unique experimental arena on the south coast of South Africa, where Mytilus galloprovincialis and two lineages of Perna perna co-exist. Treatments were based on the translocation of individuals of M. galloprovincialis, western- and eastern lineage of P. perna to a single site, where artificial beds were created and sampled monthly over one year. Recruit's number, their sizes and growth were greater within beds of the western lineage of Perna than eastern lineage or Mytilus beds. The results clearly demonstrate that the quality of settlement habitat offered by adult beds differs among adult lineages/species and affects rates of settlement and the early growth of recruits. This effect extends to the intraspecific level; we found greater differences in density and growth of recruits between lineages of Perna than between either lineage and M. galloprovincialis. [ABSTRACT FROM AUTHOR]

Freshwater mussels are important functional components of aquatic ecosystems. Westralunio carteri is a threatened freshwater mussel species, endemic to south-western Australia, which has suffered a recent, dramatic decline in range. The density, size structure and distribution of adult mussels of this species within river reaches were investigated using quadrat searches and modelled against a range of microhabitat factors. Mussels were found from 26 sites in 14 different rivers at a mean density of 28.4 ± 2.3 individuals m−2. The distribution of W. carteri was highly aggregated within river reaches. The most important factors explaining mussel distribution were substrate grain size, substrate debris and distance from the riverbank, with finer substrate, the presence of woody debris and proximity to the riverbank associated with greater abundance of mussels. In all rivers where mussels were found, most populations appeared to be actively recruiting. However, no mussels were found in six sites, despite them having been recorded as present within the last 20 years, which suggests that the range of the species is still in decline. The identification of microhabitat requirements for W. carteri will assist in identifying suitable release sites for translocation and/or captive propagation, which may be required to prevent extinction of the species. [ABSTRACT FROM AUTHOR]

Although the invasion dynamics and establishment of quagga mussels (Dreissena rostriformis bugensis) into the nearshore areas of north-temperate lakes are well studied, their continued expansion into deep profundal zones is poorly understood, having implications for offshore benthic and pelagic communities. To assess the expansion of quagga mussels into the Lake Michigan profundal, we used U.S. EPA's Great Lakes National Program Office long-term benthic monitoring data (2007–2022) to document changes in density, biomass, average length, and size-frequency distributions within and across three distinct depth zones (> 30–50 m; > 50–90 m; and > 90 m). We found significant differences in mussel density, biomass, and average length across depth zones. While the average dreissenid density at the > 50–90 m and > 90 m depth zones declined throughout the study period, biomass remained unchanged, and the average length of mussels at > 50–90 m depth zone increased, conflicting trends were found at the station level. We found the greatest variation of station size-frequency in the shallowest zone, while deeper zones followed similar demographic patterns. Our results indicate that the management of quagga mussels requires a combined approach that includes demographic data and considers within station variation. [ABSTRACT FROM AUTHOR]

Fish hosts are critical for freshwater mussels. However, correlation between mussel and fish species richness (SR) is variable. Here, we examine how the environment affects this variability. We calculated mussel–fish SR ratios for 459 stream sites to capture the different responses of mussel and fish SR to environmental variables. We used Random-Forests (RF) to model how the SR ratio varied with environmental gradients. We also modeled the percent SR of mussel guilds with different hosting and life-history strategies. The SR ratio was generally low, but highly variable across sites. The ratio variability strongly affected mussel-fish SR correlations and can be explained by environmental factors. Given that environmental gradients also differ among datasets or regions, mussel-fish SR correlation can be expected to vary. The responses of the SR of mussel guilds agree with the expectations. However, land-use and climate co-vary with other environmental variables, and their effects are difficult to assess. We conclude that mussel and fish respond differently to many environmental variables; the importance of fish SR to mussel SR may vary with the environmental settings of streams but often appears to be low. Thus, environmental data may be generally sufficient for mussel-SR modelling and mussel diversity conservation planning. [ABSTRACT FROM AUTHOR]

Non-indigenous freshwater bivalves negatively affect invaded ecosystems through different mechanisms, including inter-specific competition for trophic resources. Here, we investigated in Lake Trasimeno (Central Italy) the diet of the invasive Dreissena polymorpha and the native Anodonta anatina. δ15N and δ13C stable isotopes were measured in winter and summer in bivalves, phytoplankton, and sedimentary organic matter (SOM); the relative dietary contributions of the two resources were determined using Bayesian mixing models. To elucidate the different carbon and nitrogen pools characterizing the study site, isotopic analyses were extended to zooplankton and to representatives of the benthic flora and macroinvertebrate fauna. Independently from the season, the two bivalves showed a limited trophic overlap, as mixing models indicated for D. polymorpha a diet based primarily on phytoplankton, while A. anatina relied mainly on SOM. Dietary differences were less marked in summer, when comparable isotopic values characterized phytoplankton and SOM. In winter, conversely, the trophic differentiation between the two species was more evident, and corresponded with a significant enrichment in SOM δ13C values, likely due to a substantial contribution of carbon deriving from decaying macrophytes. Whether differences in ecological and behavioral traits alone can explain the observed trophic segregation between the two species, or if they have actively shifted their diet to reduce competition for food is discussed. We conclude emphasizing the need of an advanced resolution of the influence of non-indigenous species on the flux of energy and matter in invaded lentic systems, including Lake Trasimeno. [ABSTRACT FROM AUTHOR]

Conservation of ecosystem engineers, which modulates the surrounding habitat by causing physical state changes in biotic or abiotic materials, is important for maintaining the functional integrity of ecosystems. This study examined the effects of endangered freshwater pearl mussels (Margaritifera laevis and M. togakushiensis) on channel morphology and flow in a low-gradient sandy river. For this, we performed a field removal experiment of mussels using three treatments in twelve 10-m reaches. Mussel abundance and biomass, and three physical variables were measured before, immediately after, and two months to one year after the treatments. Mussel removal resulted in channel degradation with a 60% increase in flow depth, a 30% decrease in current velocity, and a 50% reduction in the width-to-depth ratio two months after the treatments, whereas minimal changes were measured in reaches with mussels. The results indicated that pearl mussels act as an ecosystem engineer affecting the channel morphology and flow of sandy rivers. The conservation of the pearl mussel populations is key to preserving their far-reaching benefits in ecosystem integrity including habitats for other various organisms. [ABSTRACT FROM AUTHOR]

Mussels provide important ecological functions in freshwater ecosystems but the associations between Amazonian mussels, macroinvertebrate assemblage and habitat quality remain poorly understood. We investigated whether changes in macroinvertebrate assemblage structure and ecological functioning were associated with mussel presence. We compared sites with and without mussels, with similar habitat conditions, in an eastern Amazonian river, using field measurements of macroinvertebrate structure, hydrological variables and sediment organic matter, and laboratory experiments of mussel clearance rate and biodeposition. Sites with mussels were associated with higher macroinvertebrate abundance and number of taxa, especially for trichopterans Marilia (shredder), Oecetis (predator) and Antarctoecia (collector). Decreased chlorophyll-a in the water column and increased sediment organic matter were positively associated with mussel presence. Laboratory experiments corroborated these patterns, which were stronger with higher mussel density. Mussel filtration and biodeposition may be associated with habitat quality for other invertebrates by lowering phytoplankton density in the water column and increasing inputs of sediment organic matter. This suggests a potential role of freshwater mussels in ecosystem function associated with high taxonomic and functional diversity in the macroinvertebrate assemblages of an eastern Amazon river, enhancing the already high mussel conservation priority. [ABSTRACT FROM AUTHOR]

The metabolic activity of unionid mussels influences the oxygen fluxes and other physical and chemical characteristics in aquatic systems. Unionid oxygen consumption rate during digestion and its dependency on food availability is understudied. In laboratory conditions, we quantified the oxygen consumption rate of Anodonta anatina and Unio pictorum in response to algal concentration—0.05, 6.0 and 12.0 mg of Ash Free Dry Mass of Chlorella vulgaris L−1—and mussel dry soft-tissue mass at 19 ± 1°C. Following a 5-h feeding-period, the oxygen consumption rate (mg O2 h−1) increased with algal concentration and mussel dry mass in both species during a 2-h digestion-period. The mean oxygen consumption per gram of dry mass (mg O2 gDM−1 h−1) increased with the algal concentration in both species. The oxygen consumption rate of A. anatina was significantly greater than that of U. pictorum at a given algal concentration. The A. anatina oxygen consumption per gram of dry mass decreased with increasing dry mass. Oxygen consumption rate during digestion shows inter-specific differences and is dependent on food availability. The findings inform the species-specific quantification of oxygen consumption, and validation is required in in situ conditions. [ABSTRACT FROM AUTHOR]

The frequency and intensity of droughts are predicted to increase over the next few decades and understanding the impacts of drought on mussels is imperative for species conservation. Our objective was to examine the impacts of an exceptional drought in 2011 on mussel communities in four tributaries of the Colorado River basin in central Texas by testing hypotheses that post-drought community composition depends on (1) relative abundances pre-drought, (2) life history strategy of the mussels, (3) ability of sites to retain water, (4) changes in temperature and discharge. Surveys were conducted pre- (2005–2011) and post-drought (2017) and environmental conditions during the drought were examined using discharge data, satellite imagery, and water temperature estimations. No mussels were found at 9 out of 30 sites where mussel populations were present pre-drought. The most abundant species pre-drought tended to be the most abundant species post-drought and no significant difference between life history strategies was found. No clear effect of the ability of a site to retain water was detected, but the largest declines in species richness occurred in the tributaries with the lowest mean discharge and highest water temperatures, suggesting that mussels may be especially at risk in rivers with lower discharge. [ABSTRACT FROM AUTHOR]

Females of freshwater mussels spawn eggs which, after fertilization, are brooded until the developing larvae reach a stadium ready to infest a fish host in order to complete the obligate parasitic phase of their life. We investigated the duration of the brooding period in the endangered thick-shelled river mussel Unio crassus in two rivers in southern Poland and identified the stadia of glochidia development which could be used to assess current larval developmental stages. The eggs were fertilized in marsupia. The duration of the brooding period shortened significantly during the season, from 35 days in early spring to 9 days in summer. The break between consecutive broods was usually short but very variable: from almost no break to 17 days. 20% of brooding events inspected every other day were miscarried at different stadia of larval development. The recorded differences in brooding time may significantly influence the reproductive output of individuals and populations, depending on the thermal conditions, which may be affected by both anthropogenic impact and global climate change. The study offers a practical scheme for assessing female gravidity advancement in Unio crassus, which may be very informative for the future application of conservation measures in this endangered European species. [ABSTRACT FROM AUTHOR]

Droughts can change the distribution and alter the behaviour, phenology and physiology of many species, leading in extreme cases to high mortalities or even extirpation. In this study, a before/after comparison was performed in two Portuguese river basins (Rabaçal and Tuela) to assess the possible effects of an extreme drought on the abundance and size structure of two pearl mussel Margaritifera margaritifera populations, a Critically Endangered species in Europe. The hydrological year of 2017 was extremely dry in Portugal and this situation was responsible for a major reduction of the river flow and rapid decrease in the water levels during summer. One year after the drought, a significant reduction in abundance was observed (i.e. 27.6% for the Rabaçal and 38.7% for the Tuela basin populations). However, no differences were detected in the size structure of the two pearl mussel populations. Droughts are predicted to increase in number and intensity and it is crucial to monitor M. margaritifera populations, given the low resistance (and possibly low resilience) of this species to these extreme conditions. Management measures that could help the conservation of pearl mussels are discussed. [ABSTRACT FROM AUTHOR]

In freshwater temperate environments, waterbodies warmed by power plants can serve as a stepping stone in the spread of tropical and subtropical species. This offers a unique opportunity to acquire an insight into the life history of organisms undergoing range expansions beyond their native habitat. Here, we studied the patterns of offspring production and growth in the Asian mussel Sinanodonta woodiana inhabiting the thermal plume of the Odra River in Central Europe. Compared to the S. woodiana males, females had more convex shells and had a greater tendency to continue post-maturation growth and thus follow an indeterminate growth pattern. Gravid females were observed all-year round, and individuals with either large or more convex shells brooded more offspring. The proportion of incubating females, brood size and glochidia size were linked to gonadal activity and changed seasonally. Females with a higher amount of nutritive substances in the ovaries produced more and larger offspring. The smallest and the largest offspring occurred in the summer and in the winter, respectively. Sinanodonta woodiana incubated different offspring generations simultaneously, constantly releasing them into the environment. Using a life history evolution perspective, we discuss our results in view of allocation trade-offs between growth and offspring production. [ABSTRACT FROM AUTHOR]

A potential mechanism of global decline in freshwater mussel (Unionida: Bivalvia) abundance and diversity is disruption of their obligate parasitic life-cycle by non-native fish species, which may introduce novel interaction pathways that threaten unionid recruitment. We assessed three non-native fish (brown bullhead catfish, Ameiurus nebulosus; rudd, Scardinius erythrophthalmus; and goldfish, Carassius auratus) as glochidial hosts for the New Zealand freshwater mussel Echyridella menziesii to test the hypotheses that (i) non-native fish will have lower glochidial attachment rates than a native fish (the common bully Gobiomorphus cotidianus), and (ii) encystment rate will be lower on non-native species. We found that the non-native fish had significantly lower total glochidial attachment than the native control fish after infestation and did not produce ecologically significant quantities of juvenile mussels. This research supports the general assumption that non-native species are less suitable hosts of native freshwater mussels. However, confirming our findings in the field will indicate if removing non-native fish or enhancing native fish populations is recommended for conservation of E. menziesii populations in New Zealand. [ABSTRACT FROM AUTHOR]

Designing effective surveys for freshwater mussels (Unionidae) is a challenge, because they are spatially clustered and often found in low densities. The objective of this study was to examine how the performance (in respect to species richness, the total number of mussels per search effort, species composition and size distribution) of three different survey methods (timed searches, transect method, and adaptive cluster method) varied between different habitats at six sites in rivers of Central Texas. Habitat conditions affected the performance of search methods by either facilitating or hindering the detection of mussels, e.g., sandy substrate facilitating the detection of mussels seemed to enhance the performance of the adaptive cluster method in respect to the number of mussels found per unit search effort. Differences in detectability of mussels was also associated with the size of mussels, their behavior and morphology. Timed searches detected a larger proportion of larger mussels that tended to be less burrowed and that had shells with more sculpturing compared to quantitative methods. Our results suggest that to design effective surveys variation in detectability of mussels must be considered which depends on local habitat conditions, experience of surveyor, behavior, size and morphology of mussels. [ABSTRACT FROM AUTHOR]

Freshwater mussels face threats from climate change and changing land use that are dramatically altering their habitat. The health of mussel populations and the state of current and past environmental conditions can be monitored by measuring mussel growth and glycogen levels. In this study, we measured growth and glycogen levels in mussels from two small river basins impacted by different land uses. The Snake River in the St. Croix Basin, Minnesota, had low levels of suspended sediments and was surrounded mostly by forest and some developed land. The Chippewa, Cottonwood, and Le Sueur rivers in the Minnesota River Basin had significantly higher annual suspended sediment loads and highly agricultural basins. Mussel growth was highest in the Le Sueur and Cottonwood rivers followed by the Chippewa and the Snake rivers. Mussels in the Minnesota Basin rivers all had higher mussel foot glycogen concentrations than the Snake River. These patterns were similar for two mussel species, suggesting that environmental conditions are likely determining levels of growth. Although agriculture had a negative effect on mussel population abundance and diversity, it had a positive effect on growth and glycogen levels. [ABSTRACT FROM AUTHOR]

Ecological impacts caused by invasive alien species can be severe but may vary depending upon environmental conditions. Many European populations of the native mussel, Mytilus edulis, have been invaded by the Pacific oyster, Crassostrea (Magallana) gigas. Although widespread invasions have occurred, interactions between M. edulis and C. gigas have largely been investigated with regards to competition for space and food as well as effects on species assemblages. Experimental investigation of competitive interactions on physiological responses of the two species requires further exploration. To this end, we used a 12-month field manipulation experiment to examine growth rates, mortality and condition indices of the two species occurring in monospecific and heterospecific groups. Growth rates and mortality of both species were similar in monospecific and heterospecific groups, whereas condition indices were significantly reduced for both species in heterospecific groups. Growth rates and condition indices also differed amongst experimental sites, potentially due to differing water motion. Shell weight-length relationships did not explain the observed differences in condition for either species. We show that coexistence between the two species may occur but could be detrimental for both species. We also provide a preliminary viewpoint that water motion can mediate competitive interactions between these species. [ABSTRACT FROM AUTHOR]

Mass mortality of blue mussels occurs every summer due to hypoxia in eutrophic estuaries and the oxygen consumption of decaying mussels is suspected to accelerate the hypoxia. In the present study, the solution of transplanting 3600 and 6000 t-WW of mussels from donor areas with frequent hypoxia to more suitable growth areas was tested as a tool to mitigate hypoxia in the Limfjorden. The environmental effects in the donor area were estimated by a 3D ecological model in FlexSem. Model results showed that hypoxia mitigation was most efficient at water depths of 3–5 m with highest changes in mussel biomass and oxygen levels close the ecosystem hypoxia threshold of 3.4 mg l−1. Mussel biomass soon recovered from the fishing pressure during summer due to the better oxygen conditions. These effects led to reduced Chl a concentrations and increased Secchi depths in the model. Negative effects of dredging on Secchi depth and oxygen levels were short-lived, locally and exceeded by the positive effects during the following summer period. In conclusion, mussel transplantation can prevent mass mortalities and limit the extent of the hypoxic events and the associated negative environmental effects, which is important knowledge for the management of eutrophic systems. [ABSTRACT FROM AUTHOR]

Marine lakes represent a unique aquatic environment. Here, we tested if prokaryotic communities of water, sediment, jellyfish, mussel and sponge biotopes differed in composition, higher taxon abundance and diversity. All of these proved to differ significantly among biotopes. In addition to this, we also observed significant differences in composition and diversity in mussel populations from different marine lakes. Diversity was particularly low in jellyfish populations, which were dominated by a single OTU, assigned to the genus Endozoicomonas, although individual samples also contained relatively abundant OTUs assigned to other phyla (e.g., Tenericutes). In contrast to jellyfish, Brachidontes mussels from different lakes housed highly distinct prokaryotic communities in terms of diversity and composition. An OTU assigned to the genus Endozoicomonas dominated mussels from a lake with limited connection to the open sea. Prokaryotic communities in mussels from a more connected marine lake were, in contrast, much more diverse. Sponges housed prokaryotic communities that were similar, but still distinct, to those found in water. Our results show that benthic and pelagic communities of marine lake organisms house distinct prokaryotic communities. Future research should focus on the functional implications of these differences and how they contribute to maintaining a healthy lake environment. [ABSTRACT FROM AUTHOR]

Floodplain lakes are good metacommunity systems to study the environmental and spatial processes structuring local assemblages. They are more connected during high-water periods and are more isolated during low-water periods. We evaluated the effects of lake spatial patterning and water and sediment conditions on Unionida species assemblages. Moran Eigenvector Maps were used to generate spatial variables representing spatial patterns at different scales. We sampled 35 lakes from the Pantanal floodplain, Brazil. To understand the effects of environmental and spatial variables, we performed Redundancy Analyses and variation partitioning to separate environmental and spatial pattern effects. Environmental variables explained almost twice the variation in the Pantanal mussel assemblages than did spatial variables. Unionida species presence was driven mainly by variations in sediment coarse sand and silt contents. The weak spatial patterns observed may be related to increased connectivity between lakes during floods, which facilitates mussel host fish dispersal. Mussel abundances were driven mainly by organic matter availability, but varied between species. Changes in lake connectivity can affect the regional sediment dynamics and affect mussel assemblages. [ABSTRACT FROM AUTHOR]

Limnoperna fortunei, the golden mussel, is a bivalve mollusc native to Southeast Asia, which was introduced to South America via ballast water from commercial cargo ships from China and South Korea. In Brazil, the golden mussel is considered an invasive species, which has caused enormous economic and environmental damage. This is mainly due to the obstruction of pipes carrying water for the cooling systems within hydroelectric power plants. The presence of this invasive species also negatively impacts native fauna and flora. Early detection and rapid response during the early stages of infestation for this invasive species is essential to effectively control populations and prevent new infestations from forming. Techniques within molecular biology allow for more efficient detection of the golden mussel in all stages of development. In addition, the analysis of the genome, transcriptome and proteome of this species makes it possible to identify targets of biotechnological interest, which may be useful for the control of the golden mussel or for the generation of products of technological innovation. This review presents an overview of molecular studies involving this species and the perspectives on the prevention, control and combat of the golden mussel using these approaches. [ABSTRACT FROM AUTHOR]

Mussels are at particular risk from thermal stress and hypoxia due to limited range and mobility. Of interest to managers is whether sensitivity is uniform or varies among species and subpopulations. We used respirometry to investigate effects of temperature on energy demand and hypoxia tolerance of two narrowly distributed species (Cyclonaias petrina, Colorado River; C. necki, Guadalupe River), and two subpopulations of a widely distributed species (C. pustulosa: Colorado and Navasota rivers) in central Texas. We observed zero mortality during acclimation and respirometry runs even when mussels were exposed to hypoxic conditions for several hours at 36 °C. However, type and magnitude of sublethal effects varied across species and subpopulations as temperatures increased. C. pustulosa (Colorado River) exhibited the greatest increase in energy demand, C. petrina exhibited a decreasing ability to regulate oxygen consumption and an increase in critical dissolved oxygen concentration, C. pustulosa (Navasota River) exhibited metabolic depression, and both C. petrina and C. necki exhibited increasing frequency of valve closure. Results suggest that effects of increasing temperature on energetic requirements are more important than effects on hypoxia tolerance. Management strategies considering physiological differences among species and/or subpopulations are likely to be more effective than a simple "one-size-fits-all" approach. [ABSTRACT FROM AUTHOR]

Handling freshwater mussels may have negative impacts on their survival, growth, or reproduction, and this may affect our interpretation of how mussels respond to research and conservation actions. The goal of this study was to investigate how repeated dislodgement and emersion during handling affects survival and growth of plain pocketbook Lampsilis cardium. Sixty mussels were exposed to one of the four handling rates: (1) control (no handling), (2) handled every other week, (3) handled once per week, or (4) handled twice per week, during an 85-day laboratory experiment in 2017. Absolute daily growth rates were compared among control and treatment group mussels. Growth rates were positive for > 98% of mussels and no mortality occurred. A likelihood ratio test indicated that growth rates did not differ among treatment groups (χ2 (3) = 1.32, P = 0.72). The best growth rate model was an intercept-only model which predicted that an average mussel grew 0.0088 mm/day (95% confidence interval 0.0070–0.0106). Our results suggest that L. cardium survival and growth is not compromised by short-term, repeated handling as often as twice per week, but consideration of handling procedures and mussel characteristics is necessary to fully understand how handling may affect other mussels. [ABSTRACT FROM AUTHOR]

Freshwater biodiversity of the United States has long been recognized for its high level of species richness. The US crayfish fauna is richer than that found in any other country or continent in the world. Crayfishes are critically important members of freshwater ecosystems and have long been utilized for human consumption. Combined, these factors argue for effective conservation. When compared to other diverse aquatic groups such as fishes or unionid mussels, conservation efforts for US crayfishes are lacking. We review here, knowledge gaps that prevent effective conservation and past and ongoing crayfish conservation and management activities. We conclude by proposing a strategy of actions to improve the conservation standing of this important group of organisms. These action items include improved outreach efforts, funding and research to fill numerous knowledge gaps, and the inclusion of crayfishes in broader scale aquatic conservation activities. [ABSTRACT FROM AUTHOR]

Responsiveness to biotic factors is crucial for the survival of sessile aquatic animals. They cannot escape from danger, but developed a number of defences against predation, usually delayed in time. We checked the initial defence of the freshwater byssate zebra mussel, Dreissena polymorpha, associated with valve gaping. We tested the effect of chemical signals: fish predator scent (the roach Rutilus rutilus), conspecific alarm cue and a mixture of both, as well as a mechanical stimulus: the presence of an amphipod (Dikerogammarus villosus) mechanically irritating mussels. The alarm cues and amphipod presence made mussels spend more time with closed/narrowly open valves, which can be related to decreasing detection probability by reduced infochemical excretion and/or protecting soft tissues in the presence of an imminent threat. In contrast, reactions to the predator scent alone were much weaker. Moreover, the fish scent mixed with alarm substance induced weaker responses than the alarm substance alone. Thus, the fish infochemical might mask the presence of the alarm cue components, potentially benefiting the predator. A variety of defences exhibited by mussels demonstrates the importance of the predation cue type (direct/indirect, chemical/mechanical, originating from conspecifics/predators/mixed) for the behaviour of sessile animals. [ABSTRACT FROM AUTHOR]

The invasion of dreissenid mussels into inland waters of the Northern Hemisphere has received considerable attention and, both zebra mussels and quagga mussels continue to spread westward. Despite studies aimed at understanding the biology of dreissenid mussels, relatively few studies have focused on water velocity and other hydrodynamic characteristics of water flow. The objective of this review was to identify, through a search of online databases, the papers that have been made available that directly have assessed the influence of hydrodynamic characteristics of water flow on dreissenid mussel biology. Using Thompson Reuters Web of Science, Google Scholar, and other resources, 46 papers were identified. These papers detailed that metrics associated with hydrodynamics of water flow, including current, wave action, velocity, flow rate, and discharge, can influence the biology of dreissenid mussels (primarily zebra mussel, which were studied far more than quagga mussel). Hydrodynamic characteristics influenced external fertilization, larval development and settlement, juvenile recruitment and attachment, and suspension feeding, growth and abundance of adults. In most cases, the impact of higher flow rates were locally negative and may present an opportunity for applications of water flow to control the spread or establishment of dreissenid mussels. Several knowledge gaps have been identified. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Unionida) can strongly affect nutrient cycling in temperate ecosystems but data from the tropics is lacking. We quantified the effects of mussel filtration, excretion and biodeposition on nutrient and photosynthetic pigment concentrations in a tropical eutrophic lake and mesotrophic river, featuring one non-native and two native species, respectively. Changes in nutrient and pigment concentrations were measured over a 3 h period to assess effects on (1) the water column in field enclosures, and (2) water column and benthos combined in controlled laboratory experiments. In field enclosures in both systems, mussel density and biomass were significantly correlated with the magnitude of reduction in sestonic pigment concentrations. In laboratory experiments, presence of mussels led to reduced PO4 and increased TAN concentrations in both systems, lower combined sestonic and deposited pigment concentrations in the river but increases in the same in the lake. We conclude that excretion by mussels probably accelerated bioseston growth in both systems due to N-fertilisation, an effect that may be particularly common in tropical freshwaters, which are frequently N-limited. However, whilst river mussels reduced bioseston concentrations through rapid filtration, higher rates of N-excretion and/or deposition of undigested bioseston by lake mussels apparently resulted in a net increase of pigment concentrations. [ABSTRACT FROM AUTHOR]

The reproductive activity of females of the Chinese pond mussel (Sinanodonta woodiana) was investigated in a European population inhabiting cooling water. The study used histological and stereological methods to determine gonad structure, changes in reproductive follicles during gametogenesis, oocyte development, glochidia structure, and brooding periods. Water in the channel of the “Dolna Odra” power plant did not freeze during the winter, and its mean annual temperature was 18.4°C. The population sex ratio was female biased (χ2 = 25.70, df = 1, P < 0.0001). Ovaries in mussels were formed by reproductive follicles. Previtellogenic and vitellogenic oocytes were attached to the follicle wall via the cytoplasmic stalk, and mature ovulated oocytes were present in the follicle lumen. Individuals with mature oocytes in gonads were present over the whole two-year study period, which indicates the continuous activity of gonads. Hooked glochidia had a larval thread. Females incubated the offspring in gill marsupia of outer demibranchs and were characterized by multiple tachytictic brooding periods. All gravid individuals presented mature and spent stages of gonadal development. The study provides the first direct information about the reproductive dynamics of this invasive species outside its original Asiatic range. [ABSTRACT FROM AUTHOR]

Drought often causes emersion, which can seriously damage aquatic organisms in inland aquatic ecosystems. To identify mussel characteristics associated with emersion tolerance, I investigated relationships between survival duration and mussel characteristics under an experimental emersion treatment. The survival durations of six lotic unionid mussel species (Nodularia douglasiae biwae, Pronodularia japanensis, Obovalis omiensis, Lanceolaria grayii, Inversidens brandtii, and Sinanodonta japonica) during emersion in an incubator at 25°C were determined. Shell length, body mass, moisture loss per day, shell thickness, and overall shell shape (shell length/shell height) were measured, and the relationships between these characteristics and survival duration were estimated using Cox’s regression analyses both by species (single-species analysis) and overall, excluding I. brandtii (multispecies analysis). The mussels survived 0.5–8.5 days, and survival duration differed among species. Single-species analyses indicated that in P. japanensis and L. grayii, longer shells and greater mass increased survival. O. omiensis survived longer as moisture loss from their soft bodies occurred more slowly. Multispecies analyses indicated shorter survival by mussels that had relatively heavy body mass, rapid moisture loss, and thin shells. Species with such characteristics are expected to be the most sensitive to emersion and may require conservation. [ABSTRACT FROM AUTHOR]

Properties of the shells and byssus filaments secreted by marine mussels are affected by environmental and biotic factors. In this study, we investigated the effects of pH and temperature on shell and byssus in artificially created monospecific and mixed aggregations of the indigenous mussel Mytilus galloprovincialis and the invasive mussel Xenostrobus securis. The variability in the response of the mussels was mainly explained by species-specific interactions derived from the type of aggregation. In the mixed groups, acidic conditions caused a decrease in byssus strength in M. galloprovincialis, but an increase in byssus strength in X. securis. Increased temperature positively affected shell strength in X. securis, but only in mixed aggregations. Interactive effects of acidification and warming were only detected in the organic matter of shells, the strength of which decreased in M. galloprovincialis in mixed aggregations. Although the invasive mussel may be able to take advantage of changed conditions by enhancing byssal attachment, the effects that acidification has on shells may make this species more vulnerable to some predators. The study findings provide some insight into the responses of protective and attachment structures of mussels to biotic and abiotic stressors, highlighting how species interactions may shape the future of mytilid populations. [ABSTRACT FROM AUTHOR]

The presence of non-native species can affect coevolved relationships. However, rapid reciprocal changes in coevolutionary associations provide the potential to quickly respond to a new situation. We studied a system where bitterling fish ( Rhodeus amarus) parasitize unionid mussels by laying their eggs onto their gills. This association is affected by the infestation of unionid shells by the non-native zebra mussel ( Dreissena polymorpha). In a series of experiments under experimental, semi-natural and natural conditions, we compared the behavioural response to zebra mussel infestation of unionid shells, its effect on oviposition decisions and their population consequences between bitterling populations naïve to zebra mussels and those recently sympatric with zebra mussels. We found no effect of recent sympatry on bitterling preoviposition behaviour and oviposition decisions and only a weak effect on their reproductive success. Bitterling from both populations inspected infested and non-infested mussels at the same rate but preferred to oviposit into non-infested unionid hosts. However, neither bitterling population completely avoided oviposition into infested unionids and three ovipositions into zebra mussels were observed. Overall, there was a clear negative relationship between the number of zebra mussels on unionid host shells and the number of juvenile bitterling emerging from the mussels. Our study demonstrated a lack of rapid evolutionary response to adaptively modulate oviposition choice after recent zebra mussel invasion. [ABSTRACT FROM AUTHOR]

Species invasions can have profound ecological impacts, including changes in patterns of distribution, abundance and diversity of native species, altering food-web dynamics and ecosystem functioning. In the marine benthic environment temperature, predation, competition for space and wave action exposure are some of the main factors that determine invasion success; however, the importance of food availability for invasive species has been underestimated. The present study investigates the diets of two mussel species, Mytilus galloprovincialis and Perna perna, that occur in mixed-species mussel beds, using fatty acid (FA) and stable isotope (SI) approaches over two periods of time in 2012 and 2014. With the exception of one site, we found no significant differences in the SI signatures between species, while strong dissimilarities were present in their FA signatures. Both species showed signatures of exposure to good food quality, however, neither showed links to specific dietary trophic markers. The FA differences observed between species could be related to food selectivity by one or both species or more likely by different metabolic pathways. Further investigations are needed to clarify the pattern observed; however, the results suggested that the food environment was not an important factor in determining the success of the invasive species. [ABSTRACT FROM AUTHOR]

Dense blue mussel assemblages are unstable, their structure changing from year to year. Three types of models can be used to describe this instability: (1) 'exogenous' model based on regional temperature fluctuations, (2) 'endogenous' deterministic model associated with negative impact of adult mussels on juveniles and (3) 'density-linked stochasticity' model based on positive feedbacks resulting in overcrowding and destabilizing the settlement. We compared predictions deduced from these models with a time series based on the results of long-term (18 years) monitoring of abundance and demographic structure of three mussel beds at the White Sea. Most of our findings agreed well with the predictions deduced from the endogenous model. In particular, (1) long-term changes in mussel abundance and demographic structure were strictly cyclic, with non-matching periods (5-9 years) at different sites; (2) stages with the dominance of old mussels alternated with those where juveniles dominated and (3) some signals of delayed density dependence were revealed. However, the time series also contained elements of long-term trends, which may testify to the involvement of some exogenous factors (probably long-term climate changes). [ABSTRACT FROM AUTHOR]

Lakes can be sources or sinks of carbon, depending on local conditions. Recent studies have shown that the CO efflux increases when lakes recover from eutrophication, mainly as a result of a reduction in phytoplankton biomass, leading to less uptake of CO by producers. We hypothesised that lake restoration by removal of coarse fish (biomanipulation) or invasion of mussels would have a similar effect. We studied 14-22 year time series of five temperate Danish lakes and found profound effects on the calculated CO efflux of major shifts in ecosystem structure. In two lakes, where limited colonisation of submerged macrophytes occurred after biomanipulation or invasion of zebra mussels ( Dreissena polymorpha), the efflux increased significantly with decreasing phytoplankton chlorophyll a. In three lakes with major interannual variation in macrophyte abundance, the efflux declined with increasing macrophyte abundance in two of the lakes, while no relation to macrophytes or chlorophyll a was found in the third lake, likely due to high groundwater input to this lake. We conclude that clearing water through invasive mussels or lake restoration by biomanipulation may increase the CO efflux from lakes. However, if submerged macrophytes establish and form dense beds, the CO efflux may decline again. [ABSTRACT FROM AUTHOR]

The increasing spread of invasive species in the Mediterranean Sea determines several alterations in local food webs, changing the feeding habits of native organisms. The whelk Stramonita haemastoma is a widespread Mediterranean gastropod that consumes bivalves, barnacles and limpets. Previous studies showed a shift in its diet from the bivalve Mytilaster minimus to the invasive mussel Brachidontes pharaonis, presumably due to a higher energy gain. Here we tested whelks' preference among natives and a novel prey, calculating the profitability ratio, and integrating those results with biochemical analysis on prey tissues and the routine metabolism of the whelks. Further, we used the scaled functional response as a theoretical tool to describe whelk ability to obtain energy from their environment by using four different prey species: B. pharaonis, Mytilus galloprovincialis, M. minimus and Patella caerulea. Whelks evidenced a Type II functional response for all prey, while Brachidontes displayed a lower attack rate and a higher handling time. Stramonita showed a greater preference for Brachidontes, that resulted as the prey with the higher energetic content, and the second most profitable after Patella. This suggests that the higher energy gain is behind the change in the predator's diet, with possible effects on its energy budget. [ABSTRACT FROM AUTHOR]

Long-distance dispersal of freshwater mussels (order Unionoida) has been assumed to occur mainly during a parasitic larval stage (glochidia) via movements of host fishes, but its empirical evidence is largely lacking. Here, we applied a 'parasite-tag' approach to the riverine mussel Margaritifera laevis and its obligate host fish Oncorhynchus masou masou. This method examines the relationship between the prevalence of glochidia and distance from the nearest mussel population (i.e., the putative source of glochidia), a proxy that should quantify distance moved by host fish. We hypothesized that infected fish would be found in wider habitats at the end of the parasitic period (August) than at the beginning (July) if they were functioning as effective dispersal agents. In July, the prevalence of glochidia was highest in the vicinity of mussel beds but decreased rapidly with distance from the nearest mussel bed. In August, however, infected fish were distributed diffusively across the riverine network and dispersed over 4.8 km, demonstrating substantial dispersal of glochidia by the host fish. The results of our study build upon current knowledge of mussel's dispersal ecology by providing highly needed evidence: host fish can be effective in mediating long-distance dispersal of a riverine mussel species. [ABSTRACT FROM AUTHOR]

We summarize current knowledge on the effects of the invasive Asian bivalve Limnoperna fortunei (introduced in South America around 1990) on local biota. Limnoperna modifies nutrient concentrations and decreases concentrations of particulate organic matter in the water column (including phytoplankton and zooplankton), thus enhancing light penetration and stimulating growth of periphyton and macrophytes. Selective grazing and modification of the N:P ratio are responsible for strong enhancements of toxic cyanobacterial blooms. Limnoperna beds significantly enhance the numbers, biomass, and diversity of practically all accompanying invertebrates. The mussel's planktonic larvae represent an important food item for the larvae of 18 fish species, while juveniles and adults are consumed by at least 50 fish species. Limnoperna is the first and only abundant benthic filter-feeding animal in South American continental waters. The fact that it intercepts and retains in the freshwater lotic domain particulate organic matter that would otherwise be swept into the sea must represent an important energetic subsidy, but the ecosystem-wide consequences of this trophic shift have not yet been addressed. Comparison with the impacts of the zebra mussel in Europe and North America suggests important differences. [ABSTRACT FROM AUTHOR]

Today, land use impacts a major proportion of all streams. Here, landscape features in corridors along streams and water chemical factors were analyzed in relation to recruitment of the threatened freshwater pearl mussel ( Margaritifera margaritifera) and its host fish the brown trout ( Salmo trutta). Mussel recruitment and trout density were negatively related to forest clear-cuts. Mussel recruitment was negatively related to water color and turbidity. Therefore, the threats to the mussel may be severe, as low mussel recruitment may be caused by direct effects on the juvenile mussels and indirect effects on the host fish. High proportions of lakes and ponds were found to be positive for recruitment and for trout, and deciduous forest was positively related to trout. The combination of investigations at different scales at the landscape level and at in-stream levels may be applicable to find threats to other threatened species. The results indicate that forestry activities may negatively affect recruitment of freshwater pearl mussels and its host fish. Reductions of forestry activities and the retaining of intact quantity and quality of the riparian zones next to streams, both for the mussel and its host fish may be important conservation measures to restore freshwater pearl mussel populations. [ABSTRACT FROM AUTHOR]