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In this study, we investigated the impact of water temperature on pearl formation and the molecular mechanisms underlying this biomineralization process in the mussel Hyriopsis cumingii. In the laboratory experiment, recipient mussels received saibo grafts from donor mussels and then were cultivated at five temperatures (16, 20, 24, 28, and 32 °C) for 1 month. We found that speed of pearl formation varied with water temperature: there was no visible pearl granules at 16 and 20 °C, tawny pearl granules were collected at 24 °C and lustrous pearl granules were collected at 28 and 32 °C. The expressions of several nacreous layer matrix protein genes (hic22, hic24, HcTyr Hc-upsalin and Hcperlucin) at 28 °C and 32 °C were peaked on day 28, and the expressions of other nacreous layer matrix protein genes (hic52 and hic74) on day 28 were significant higher than day 14. In the natural environment, pearl deposition rate also increased as water temperature rose, and the optimum range for pearl growth in H. cumingii was between 28.3 and 30.3 °C. Expression of the prismatic layer-related matrix protein genes hic31 and both prismatic and nacreous layer-related matrix protein gene silkmapin was significantly high in winter, and expressions of the nacreous layer-related matrix protein genes (hic24, hic74, HcTyr, Hc-upsalin and Hcperlucin) were always higher during higher temperature seasons compared with winter. These results indicate that high water temperature can speed up pearl formation and further regulate matrix protein secretion to accelerate pearl nacre deposition.

Understanding dreissenid mussel population dynamics and their impacts on lake ecosystems requires quantifying individual growth across a range of habitats. Most dreissenid mussel growth rates have been estimated in nutrient rich or nearshore environments, but mussels have continued to expand into deep, cold, low-nutrient habitats of the Great Lakes. We measured annual quagga mussel (Dreissena rostriformis bugensis) growth at 15 m, 45 m, and 90 m in Lake Ontario using caged mussels near Oswego, New York, USA from June 2018 to May 2019. Quagga mussel growth (starting size 12 mm) was greatest at 15 m (mean shell length increase = 10.2 mm), and was lower at 45 m (5.9 mm) and 90 m (0.7 mm). Caged mussels were obtained from near the 90-m site and those reared at 15 and 45 m developed thicker shells than those that were caged at 90 m. We observed relatively high colonization by quagga and, to a lesser degree, zebra mussels (Dreissena polymorpha) at 15 m, very few colonizers at 45 m, and none at 90 m. Higher growth potential, but low natural mussel densities observed at 15 m and 45 m suggest factors other than growth limit dreissenid abundance at these depths. The relatively slow dreissenid growth rates observed in offshore habitats are consistent with the gradual abundance increases documented in these zones across the Great Lakes and suggest new mussels that become established in these habitats may contribute to ecosystem effects for decades.

In this study, we introduced an indigenous Korean muricid gastropod Reishia bronni (Dunker, 1860), a potential natural predator of the Mediterranean mussel Mytilus galloprovincialis (Lamarck, 1819), a well-known invasive alien species successfully settled down in Korea. From the survey on the Korean ports of the east coast between 2007 and 2011, we have observed the spread of R. bronni within the Mytilus galloprovincialis community. The observed decrease of the mussel density around the gastropod assemblage led us to the idea that R. bronni is the natural predator of M. galloprovincialis. To clarify such a predator-prey interaction between both species, we performed a field observation from two Korean ports in August 2012, keeping R. bronni and M. galloprovincialis individuals together into the cages for 18 days. Then, we counted the number of latter ones consumed and estimated the average time spent feeding per individual of R. bronni. We observed the positions of the drill holes made on the consumed shells by it. Our results showed that R. bronni is the active natural predator of M. galloprovincialis with the high feeding intensity and the unique foraging behavior targeting the lateral margin of the shell.

Uroporphyrinogen III synthetase (UROS) is an important enzyme involved in the structural formation of porphyrin, which is responsible for color intensity. A UROS homolog was isolated and characterized from the pearl mussel, Hyriopsis cumingii (HcUros). The HcUros cDNA was 858 bp in length with an open reading frame that encoded a 285 amino acid protein, which contained a conserved HemD domain. HcUros exhibited widespread tissue distribution, displaying particular enrichment in the mantle and haemolymph of purple mussels, compared to white mussels. In situ hybridization of HcUros in mantle tissue demonstrated that it was specifically expressed in the dorsal epithelial cells of the mantle pallia. Additionally, HcUros expression was upregulated following implantation of the pearl sac to produce pearls. The data suggest that HcUros contributes to shell pigmentation, and nacre formation and coloring in H. cumingii.

Mytella strigata (Hanley, 1843) is an invasive mussel species that has rapidly spread in China in recent years. Here, we tested the utility of three mitochondrial gene fragments, COI, 12S, and 16S, and two nuclear gene fragments, D1 28S and 18S-ITS1, for characterizing the levels of genetic diversity among and within populations using 191 M. strigata specimens collected in China to aid ongoing efforts to identify the origin of the invasion as well as molecular genetic studies. M. strigata exhibited two sex-associated haplogroups according to the COI and 12S sequences. The ratio of female-lineage to male-lineage COI and 12S sequences was 149:22 and 72:7, and the genetic distances between haplogroups were 6.56 and 9.17, respectively. Only one haplotype was detected among the 18S-ITS1 sequences (413 bp), and three haplotypes were detected among the D1 28S sequences (296 bp). The haplotype diversity of both the female-lineage COI and 12S sequences was greater than 0.5, and the nucleotide diversity of the 12S, 16S, D1 28S, and 18S-ITS1 sequences was less than 0.005 in all six populations in China. Our findings indicated that COI is the most useful gene fragment for genetic diversity studies of M. strigata populations; D1 28S and 18S-ITS1 sequences would be useful for species identification because of their low intraspecific diversity. Our genetic analysis of the COI sequences revealed Colombia as the most likely origin of M. strigata in China and showed that the invasive populations in China have recently experienced or are currently experiencing a population bottleneck.

Reef-forming species form integral aspects of coastal ecosystems, but are rapidly degrading world-wide. To mitigate these declines, nature managers increasingly rely on the restoration of habitat-structuring, reef-forming species by, for example, introducing artificial reefs that may directly function as complex reef habitat. Since the use of biodegradable structures to restore biogenic reefs is becoming a popular technique, its effectiveness as reef habitat must be assessed. Therefore, we examine the trophic complexity on experimental large-scale biodegradable artificial reefs using food web network analysis. We placed biodegradable artificial reefs on soft-sediment intertidal flats in the Dutch Wadden Sea in a large-scale (~650 m) and 2.5-year-long experiment. We compared food web networks and biodiversity indicators between biodegradable reefs and bare controls and quantified species composition inside and near the artificial reef community to assess the expansion of the reef community. During 2.5 years, we observed that artificial reefs changed food web networks compared to bare controls: in species richness (+76%), link density (the number of interactions per species; +15%) and the fraction of basal species (species of lowest trophic level; +40%), but lowered the connectance: the realized fraction of all possible links between species (−33%). Their effects on food web networks increased over time with a higher species richness (+22%) and more complex food web (link density +13%) on the artificial reef 2.5 years after deployment compared to 1.5 years. However, the effects of the reefs did not extend beyond the reef structures; the species composition and biodiversity of macrozoobenthos near the reefs were comparable to the control. Synthesis and applications. This study shows that biodegradable artificial reefs offer an effective tool for the restoration of food web complexity and biodiversity of intertidal soft-sediment systems. However, application needs to be carefully considered as the reef-building species did not expand beyond our structures, despite the ambitious spatial extent of this experiment. Therefore, we recommend restoration practitioners to design artificial reefs in such a way that they generate ecosystem connectivity (facilitation of higher trophic levels) and biogeomorphological effects on a landscape scale (reef expansion beyond the structures).

Invasive dreissenid mussels (Dreissena polymorpha and Dreissena bugensis) have a profound effect on the total phosphorus (TP) budget in Lake Ontario, which in turn influences ecological processes such as the resurgence of the benthic alga Cladophora. A validated three-dimensional integrated hydrodynamic and ecological modeling framework is applied to quantify the impact that dreissenids have on the spatial and species distribution of TP in the lake. Model results for April to September 2013 show that dreissenids decrease TP in the water column by about 1812 metric tonnes, which is about 60% of the tributary TP loading to the lake. This reduction in TP affects other processes controlling its distribution. Physical transport of TP from nearshore to offshore waters is reduced, and the amount of TP involved in chemical reactions is reduced, while TP processed by biological transformations is increased. This study provides the first attempt to quantify the TP budget changes in Lake Ontario by dreissenids using numerical modeling, and findings of this study can be generalized to other lakes with similar conditions.

Documenting species occurrences and habitat occupancy of unionid mussels can often be challenging. Environmental DNA (eDNA) has been shown to be a reliable tool for detecting unionids with comparable or greater sensitivity than conventional sampling and has the added advantages of not disturbing individuals or occupied habitats. However, single‐species eDNA assays are limited to targeting individual species of interest and are functionally blind to the presence of other species. Community eDNA assays have the potential to characterize local species assemblages simultaneously but are currently less extensively developed and implemented than single‐species eDNA testing. We tested the effectiveness of community eDNA markers to identify unionid species assemblages, using two overlapping conserved primers that target the maternal mitochondrial 16S rDNA region. Both primer sets were optimized using three mock communities and successfully amplified 62.5%–81.6% of species with largely consistent results between the primer sets. Following optimization, eDNA from water samples from 24 reference sites with known mussel communities was amplified and sequenced to quantify species richness and diversity within and among sites. Metabarcoding results from the monitoring sites largely mirrored those from the mock communities, with >80% of species detections identified by both assays. The results were broadly consistent with species data from quadrat‐based manual field surveys, although both community eDNA and conventional sampling detected some species that the other method did not. These results demonstrate that community eDNA assays using conserved primers and next‐generation sequencing have the potential to simultaneously target eDNA from multiple unionid species and provide a powerful tool for complementing or augmenting conventional field surveys to characterize and monitor unionid species assemblages.

Heat-induced mass mortalities involving ecosystem engineers may have long-lasting detrimental effects at the community level, eliminating the ecosystem services they provide. Intertidal mussels are ecologically and economically valuable with some populations facing unprecedented heat-induced mass mortalities. Critically, mussels are also frequently infested by endolithic parasites that modify shell albedo, hence reducing overheating and mortality rates under heat stress. Using a biophysical model, we explored the topographical and meteorological conditions under which endolithically driven thermal buffering becomes critical to survival. Based on meteorological data from a global climate analysis, we modelled body temperatures of infested and non-infested mussels over the last decade (2010-2020) at nine sites spread across c. 20 degrees of latitude. We show that thermal buffering is enhanced where and when heat stress is greatest, that is, on sun-exposed surfaces under high solar radiation and high air temperature. These results suggest that new co-evolutionary pathways are likely to open for these symbiotic organisms as climate continues to change, potentially tipping the balance of the relationship from a parasitic to a more mutualistic one. However, endolithically driven reductions in body temperatures can also occur at or below optimal temperatures, thereby reducing the host's metabolic rates and making the interplay of positive and negative effects complex. In parallel, we hindcasted body temperatures using empirical data from nearby weather stations and found that predictions were very similar with those obtained from two global climate reanalyses (i.e. NCEP-DOE Reanalysis 2 and ECMWF Reanalysis v5). This result holds great promise for modelling the distribution of terrestrial ectotherms at ecologically relevant spatiotemporal scales, as it suggests we can reasonably bypass the practical issues associated with weather stations. For intertidal ectotherms, however, the challenge will be incorporating body temperatures over the full tidal cycle. info:eu-repo/semantics/publishedVersion

Recently, there is a greater interest for the development of mussel Mytilus edulis hatcheries, particularly for the production and commercialization of triploid bivalves. The aims of this study wer...

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.

Analysis of long-term data (1987–2019) was carried out on the morphology and autecology of the benthic colonial large-cell species Striatella unipunctata (Lyngbye) C. A. Agardh, 1832 in the microphytobenthos of the Black Sea and Sea of Japan, including water areas of specially protected natural areas of Russia. The species is widely found on natural and artificial substrates in the Black Sea year-round, and in the Sea of Japan, at a water temperature down to −1.5 °C. St. unipunctata quantitative data were determined by direct cell counting in the Goryaev camera under light microscopes (LMs) Biolam L-212, Axioskop 40, and Olympus BX41. Species morphology, phytogeography, and ecology are described. The cell size range of populations is presented: for the Black Sea, valves 25–148 µm long, 8–22 µm wide, frustules 36.3–50.4 µm wide, 18–24 fibulae in 10 µm, and 7–8 girdle bands in 10 µm; for the Sea of Japan, valves 85–125 µm long, 12–21 µm wide, 7–8 girdle bands in 10 µm, 20–25 fibulae in 10 µm, frustules 32.0–34.3 µm long, 10–11 µm wide, and 25 fibulae in 10 µm. For the first time, St. unipunctata valves and frustules were studied in vivo under LMs, and frustule ultrastructure, under a scanning electron microscope (SEM). For the first time, quantitative indicators of the species populations from the Black Sea and Sea of Japan were compared. The morphology of the frustule ultrastructure of St. unipunctata was studied under a Hitachi SEM, model SU3500 (Japan), in Leica EM ACE200 gold-palladium-coated samples. In the Kazachya Bay of the Black Sea near the Oceanarium, the absolute maximum abundance was recorded – 41.6·10³ cells·cm−2 with a biomass of 1.73 mg·cm−2 in January (t = +6.9 °C) in the epizoon of the cultured mussel Mytilus galloprovincialis Lamarck, 1819 at a depth of 0.5 m at excessive organic pollution of water. The minimum values were of 0.26·10³ cells·cm−2 and 0.011 mg·cm−2, respectively, in July (t = +23.5 °C) at a depth of 2.5 m. In the Paris Bay (Russky Island) of the Sea of Japan in the water area of the Marine Mammal Research Base of the Primorsky Oceanarium (Vladivostok), the abundance in the asbestos plates periphyton was of 207·10³ cells·cm−2 in the summer. For the first time, unique micrographs of the species in vivo were obtained under a LM, and of purified frustules – under a SEM.

Mussels are a group of bivalves that includes the dominant species of shallow-sea, freshwater, and deep-sea chemosynthetic ecosystems. Mussels cling to various solid underwater surfaces using a proteinaceous thread, called the byssus, which is central to their ecology, physiology, and evolution. Mussels cluster using their byssi to form “mussel beds,” thereby increasing their biomass per unit of habitat area, and also creating habitats for other organisms. Clustered mussels actively filter feed to obtain nutrients, but also ingest pollutants and suspended particles; thus, mussels are good subjects for pollution analyses, especially for microplastic pollution. The byssus also facilitates invasiveness, allowing mussels to hitchhike on ships, and to utilize other man-made structures, including quay walls and power plant inlets, which are less attractive to native species. Physiologically, mussels have adapted to environmental stressors associated with a sessile lifestyle. Osmotic adaptation is especially important for life in intertidal zones, and taurine is a major component of that adaptation. Taurine accumulation systems have also been modified to adapt to sulfide-rich environments near deep-sea hydrothermal vents. The byssus may have also enabled access to vent environments, allowing mussels to attach to “evolutionary stepping stones” and also to vent chimneys.

Larvae (glochidia) of Unionida mussels form obligate symbiotic associations with host fish to complete their life-cycle. To identify previously unknown host fish associations for the threatened New...

Ecosystems are degrading world-wide, with severe ecological and economic consequences. Restoration is becoming an important tool to regain ecosystem services and preserve biodiversity. However, in harsh ecosystems dominated by habitat-modifying organisms, restoration is often expensive and failure prone. Establishment of such habitat modifiers often hinges on self-facilitation feedbacks generated by traits that emerge when individuals aggregate, causing density- or patch size-dependent establishment thresholds. To overcome these thresholds, adult or juvenile habitat-forming species are often transplanted in clumped designs, or stress-mitigating structures are deployed. However, current restoration approaches focus on introducing or facilitating a single life stage, while many habitat modifiers experience multiple bottlenecks throughout their life as they transition through sequential life stages. Here, we define and experimentally test ‘life cycle informed restoration’, a restoration concept that focuses on overcoming multiple bottlenecks throughout the target species’ lifetime. To provide proof of concept, and show its general applicability, we carried out complementary experiments in intertidal soft-sediment systems in Florida and the Netherlands where oysters and mussels act as reef-building habitat modifiers. We used biodegradable structures designed to facilitate bivalve reef recovery by both stimulating settlement with hard and fibrous substrates and post-settlement survival by reducing predation. Our trans-Atlantic experiments demonstrate that these structures enabled bivalve reef formation by: (a) facilitating larval recruitment via species-specific settlement substrates, and (b) enhancing post-settlement survival by lowering predation. In the Netherlands, structures with coir rope most strongly facilitated mussels by providing fibrous settlement substrate, and predation-lowering spatially complex hard attachment substrate. In Florida, oysters were greatly facilitated by hard substrates, while coir rope proved unbeneficial. Synthesis and applications. Our findings demonstrate that artificial biodegradable reefs can enhance bivalve reef restoration across the Atlantic by mimicking emergent traits that ameliorate multiple bottlenecks over the reef-forming organism’ life cycle. This highlights the potential of our approach as a cost-effective and practical tool for nature managers to restore systems dominated by habitat modifiers whose natural recovery is hampered by multiple life stage-dependent bottlenecks. Therefore, investment in understanding how to achieve life cycle informed restoration on larger scales and whether the method it is applicable to restore other ecosystems is now required.

Novel insights into habitat suitability for two Unionida freshwater mussels, Castalia ambigua Lamarck, 1819 (Hyriidae) and Anodontites elongatus (Swainson, 1823) (Mycetopodidae), are presented on the basis of hydraulic variables linked with the riverbed in six 500‐m reaches in an eastern Amazonian river basin. Within the reaches, there was strong habitat heterogeneity in hydrodynamics and substrate composition. In addition, we investigated stressors based on landscape modification that are associated with declines in mussel density. We measured hydraulic variables for each 500‐m reach, and landscape stressors at two spatial scales (subcatchment and riparian buffer forest). We used the Random Forest algorithm, a tree‐based model, to predict the hydraulic variables linked with habitat suitability for mussels, and to predict which landscape stressors were most associated with mussel density declines. Both mussel species were linked with low substrate heterogeneity and greater riverbed stability (low Froude and Reynolds numbers), especially at high flow (low stream power). Different sediment grain size preferences were observed between mussel species: Castalia ambigua was associated with medium sand and Anodontites elongatus with medium and fine sand. Declines in mussel density were associated with modifications linked to urbanization at small scales (riparian buffer forest), especially with percent of and distance from rural settlements, distance to the nearest street, and road density. In summary, the high variance explained in both hydraulic and landscape models indicated high predictive power, suggesting that our findings may be extrapolated and used as a baseline to test hypotheses of habitat suitability in other Amazonian rivers for Castalia ambigua and Anodontites elongatus and also for other freshwater mussel species. Our results highlight the urgent need for aquatic habitat conservation to maintain sheltered habitats during high flow as well as mitigate the effects of landscape modifications at the riparian buffer scale, both of which are important for maintaining dense mussel populations and habitat quality., Random Forest algorithms with complex hydraulic variables and landscape stressors predicted that Amazonian mussels are associated with riverbed stability at high and low flows and mussel density is higher with low substrate heterogeneity and hydrodynamic energy. Local riparian buffer modification by urbanization leads to mussel density declines, and there is an urgent need for landscape and riverscape management and conservation for maintenance of mussel populations and habitat quality.

Horse mussels Modiolus modiolus can occur in dense aggregations and form areas of ecological and biological significance. In the Bay of Fundy, Canada, aggregations of horse mussels are associated with flow parallel bedforms, and this area is under consideration for designation as a sensitive benthic area which would provide protective measures. Basic demographic information is required to inform the development of effective conservation and management strategies and although general life-history characteristics of M. modiolus are known, detailed quantitative demographic information on this population is limited. The objective of this study was to characterize the population structure of horse mussels in the Bay of Fundy and assess change in key demographic characteristics since the last study in this area in 1997/1998. There have been significant changes in the population since 1998: the 2017 population contains larger, older, mature individuals, with significantly more females; 35% of the current population is over 20 yr of age. Direct evidence that this population has been impacted by bottom-contact fishing gear was also observed. Consistent with M. modiolus populations worldwide, this population demonstrates life-history traits (e.g. slow growth rates, late age of maturity, long lifespan) that make it sensitive and susceptible to disturbance. Coupled with the knowledge that this population overlaps with significant fishing activity, this study supports the assumption that this population is vulnerable to bottom-contact fishing and that recovery from adverse impacts would be slow and uncertain.

Studies of climate change effects on individuals and populations are mostly couched in terms of lethal temperature limits, but 2 other elements make predictions difficult: the effects of sublethal stress and intraspecific variability. Sublethal stress, such as exposure to highly variable temperatures, can cause carryover effects that influence how an animal responds to subsequent events and its long-term fitness. Additionally, intra-specific genetic variability can allow more complex species responses to climate change. We used 2 genetically distinct lineages of the intertidal mussel Perna perna to investigate the effects of sublethal temperature variability and genetic identity on thermal sensitivity estimates derived from standard metabolic rate measurements. Mussels were exposed to one of 3 acclimation treatments: measurements done immediately after collection (i.e. field fresh), or exposure to 2 wk of either constant temperature or fluctuating temperatures. The mussels were then exposed to rising temperatures within the range normally experienced in the field while oxygen consumption was recorded. We found no effect of lineage or treatment on the aerobic standard metabolic rate of mussels, but Q10, a proxy for thermal sensitivity, was influenced by treatment. While Q10 values under constant temperature did not differ significantly from those for field-fresh mussels, both were significantly lower than for fluctuating temperatures. Thus, temperature variability increased thermal sensitivity, but our results indicate that this was independent of genetic identity. Chronic increased temperature variability and repeated exposure to high (but sublethal) temperatures under climate change are likely to increase mussel temperature sensitivity and decrease performance. Such alterations to fitness are expected to occur before animals are exposed to lethal temperatures.

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.

Modiolus kurilensis F. R. Bernard, 1983 (Mollusca, Bivalvia) can be found in Peter the Great Bay (the Sea of Japan) both on soft and hard substrates, often together with the mussel Crenomytilus grayanus (Dunker, 1853); it is a promising commercial species. This mollusc is a by-catch when catching C. grayanus. The aim of the work was to assess M. kurilensis resources and settlement structure in Peter the Great Bay. The research was carried out in 2007–2018 by scuba-diving methods of hydrobiological research at the depths of down to 20 m. In total, the data were analyzed for 2,409 stations; M. kurilensis was found at 308 stations. Sampled molluscs were measured and weighed. The material was processed statistically and cartographically; the mean biomass and distribution density of M. kurilensis settlements were calculated. In total, 870 horsemussels were analyzed for studying the settlement structure. The following indicators were estimated: index of settling (ratio of the abundance of juvenile molluscs with a shell length of 1–30 mm (spat, yearlings) to the abundance of adults with a shell length of > 50 mm); index of maturation (ratio of the abundance of pre-reproductive molluscs with a shell length of 35–50 mm to the abundance of adults with a shell length of > 50 mm); index of replenishment of the commercial stock (ratio of the abundance of molluscs with a shell length of 95–100 mm (recruits) to the abundance of molluscs of commercial length of > 100 mm). The state of M. kurilensis population in Peter the Great Bay is stable: the ratio of molluscs of non-commercial length varies 52 to 86 % in most settlements, which indicates active natural reproduction and regular replenishment of the benthic part over many years. Replenishment of settlements with settling of both spat and yearlings depends on the presence of pelagic larvae in the plankton, while replenishment of the mature molluscs depends on favorable conditions for juvenile survival. In 2007–2018, the mean values of the indices of settling and maturation in M. kurilensis settlements in Peter the Great Bay were of (0.18 ± 0.07) and (0.05 ± 0.01), respectively. M. kurilensis resources are estimated at 27.1 thousand tons, and the commercial stock – at 16.4 thousand tons. The annual replenishment of the commercial stock of M. kurilensis in Peter the Great Bay is possible in a volume of more than 3 thousand tons. The mean value of the index of replenishment of the commercial stock is of (0.21 ± 0.03).

Environmental DNA (eDNA) sampling is a powerful tool for monitoring aquatic organisms and has the potential to make significant contributions to the conservation of freshwater mussels. Conv...

Freshwater drum (Aplodinotus grunniens) may be a predator of the invasive zebra mussel (Dreissena polymorpha), which established in Lake Winnipeg in 2013. In this study, the diets, trophic position, and growth of 51 freshwater drum collected in 2019 (six years post-zebra mussel invasion) were compared to 64 freshwater drum sampled in 2000. Benthic insect larvae were the dominant food items in both years. Although mollusks occur in high densities in Lake Winnipeg, they were only consumed by a few freshwater drum in either sample year. Zebra mussels were not a frequent prey item in 2019 as they were only consumed by four of the sampled freshwater drum. Stable isotope analysis of white muscle tissue yielded similar δ13C and δ15N values in both years and were consistent with a benthic, insectivorous diet. Length-at-age data derived from otoliths revealed that the 2019 population had at least an equal growth rate to the 2000 population. Weight-at-length data suggested that fish condition was greater in 2019 than in 2000, which coincided with increased benthic macroinvertebrate density in Lake Winnipeg. Based on these findings, Lake Winnipeg freshwater drum continue to feed predominantly on insect larvae and not zebra mussels.

Assessing effects of species identity and richness on ecosystem function for globally imperiled fauna is imperative to understand how species loss affects freshwater ecosystems. Here, we ex...

The implicit assumption that properties of natural systems deduced from the average statistics from random samples suffice for understanding them focuses the attention of ecologists on the average effects of processes and responses, and often, to view their variability as noise. Yet, both kinds of effects can drive dynamics of ecological systems and their covariation may confound interpretation. Predation by crabs and snails on competitively dominant mussels has long been recognized as an important process structuring communities on rocky shores of the Northwest Atlantic Ocean. We experimentally manipulated the average intensity of predation in plots across a gradient of mussel recruitment to separately estimate the average and variability of responses of mussel recruitment and community composition. Predation did not affect the average number of mussels recruited to plots, nor the average multivariate composition of the community. Plots from which predators were excluded showed a ~ 30% increase in spatial variability of mussel recruitment. After 1 year, the spatial variability in community composition was greater than that observed among plots that predators could access. An important, but less recognized, aspect of predation is its dampening effect on variability of community structure. As accelerating rates of environmental change disrupt species interactions, variability effects of ecological processes and corresponding responses are likely to be increasingly important determinants of community dynamics.

The composition and diversity of animal microbiomes is shaped by a variety of factors, many of them interacting, such as host traits, the environment, and biogeography. Hybrid zones, in which the ranges of two host species meet and hybrids are found, provide natural experiments for determining the drivers of microbiome communities, but have not been well studied in marine environments. Here, we analysed the composition of the symbiont community in two deep-sea,Bathymodiolusmussel species along their known distribution range at hydrothermal vents on the Mid-Atlantic Ridge, with a focus on the hybrid zone where they interbreed. In-depth metagenomic analyses of the sulphur-oxidising symbionts of 30 mussels from the hybrid zone, at a resolution of single nucleotide polymorphism analyses of ~2500 orthologous genes, revealed that parental and hybrid mussels (F2–F4 generation) have genetically indistinguishable symbionts. While host genetics does not appear to affect symbiont composition in these mussels, redundancy analyses showed that geographic location of the mussels on the Mid-Atlantic Ridge explained most of the symbiont genetic variability compared to the other factors. We hypothesise that geographic structuring of the free-living symbiont population plays a major role in driving the composition of the microbiome in these deep-sea mussels.

Recent freshwater mussel research has resulted in rediscovery of several species presumed extinct. We report the rediscovery of Amblema plicata (Say, 1817) in 2019 from the Choctawhatchee River, Florida, USA. Amblema plicata has not been reported in the Choctawhatchee river basin since 1958, more than 61 years ago. This species was collected during the long-term monitoring of freshwater mussels in Florida streams. We provide genetic confirmation of our voucher identification using a DNA barcoding approach and discuss potential risks to A. plicata populations in the Choctawhatchee river basin.

Self-organized, regular spatial patterns emerging from local interactions among individuals enhance the ability of ecosystems to respond to environmental disturbances. Mussels self-organize to form large, regularly patterned biogenic structures that modify the biotic and abiotic environment and provide numerous ecosystem functions and services. We used two mussel species that form monospecific and mixed beds to investigate how species-specific behavior affects self-organization and resistance to wave stress. Perna perna has strong attachment but low motility, while Mytilus galloprovincialis shows the reverse. At low density, the less motile P. perna has limited spatial self-organization compared with M. galloprovincialis, while when coexisting, the two species formed random spatial patterns. At high density, the two species self-organized in similar ways, while when coexisting, patterns were less strong. Spatial pattern formations significantly shaped resistance to hydrodynamic stress. At low density, P. perna beds with strong attachment and M. galloprovincialis beds with strong spatial organization showed higher retention rates than mixed beds. At high density, the presence of strongly attached P. perna significantly increased retention in mixed and P. perna beds compared with M. galloprovincialis beds. Our study emphasizes the importance of the interplay of species-specific behaviors to spatial self-organization and stress tolerance in natural communities. National Research Foundation of South AfricaNational Research Foundation - South Africa [64801]; Fundacao para a Ciencia e Tecnologia (FCT-MEC, Portugal); French Ministere de l'Enseignement Superieur et de la Recherche; Hauts de France RegionRegion Hauts-de-France; European Funds for Regional Economical Development

The Mekong and Chao Phraya rivers harbor a species-rich freshwater mussel assemblage containing a large radiation of the Pseudodontini species. Members of the genera Bineurus Simpson 1900 and Thaiconcha Bolotov et al., 2020 primarily inhabit small and medium-sized tributaries of these rivers. Here, we present an integrative taxonomic review of these genus-level clades. We show that Bineurus contains four species: B. mouhotii (Lea, 1863), B. exilis (Morelet, 1866) stat. rev., B. anodontinum (Rochebrune, 1882) stat. rev., and B. loeiensis sp. nov. In its turn, Thaiconcha comprises three species: T. callifera (Martens, 1860), T. munelliptica sp. nov., and T. thaiensis sp. nov. Two species, Pseudodon ovalis Morlet, 1889 and P. thomsoni Morlet, 1884, are considered here as questionable taxa. These findings further highlight that Southeast Asia represents a significant evolutionary hotspot of freshwater mussels, which requires further international collaborative research and conservation efforts.

Aim. Study of a group of biochemical parameters of the hepatopancreas and gills of the Black Sea mussel Mytilus galloprovincialis Lam. and the functional indicator of cardiac system adaptivity of mussels from Sevastopol bays with different levels of recreational and anthropogenic impact.Methods. Mussels were collected from four Sevastopol water areas (Kruglaya Bay, Kazachya Bay, Matyushenko Bay and Cape Khrustalnii) in autumn 2018. The bioindication methods used were based on application of functional (cardiac system adaptability) and biochemical indicators (antioxidant enzymes activity [AEA], aminotransferases, the alkaline phosphatase [AP], and products of the lipid peroxidation [LPO] and protein oxidation [PO]) of mussel tissues. The hydrochemical parameters of the investigated areas were determined.Results. The anthropogenic impact on a complex of biochemical indicators of mussels at the sampling sites was shown. At the same time, low values of mussel heart rate (HR) recovery time (Trec) (less than 60 min.) in all sampling sites demonstrated the efficiency of biochemical changes in mussels and the possible use of all tested bays as recreational areas.Conclusion. Results of the present research allow the characterization of the ecological status of these Sevastopol sea water areas and to make recommendations about their rational use. Matyushenko and Kazachya Bays are most suitable for beach recreation and recreational fishery. Kazachya Bay also has favourable conditions for the development of water sports. Kruglaya Bay and Cape Khrustalnii are less ecologically safe and require a series of actions to improve water quality.

The biomechanics of specialized mechanical structures produced by organisms provides crucial fitness advantages. The energetic cost associated with producing these structural materials and the resulting energetic trade‐off with growth, however, is rarely quantified. We integrate resource allocation to structural material production with an energetic framework by combining an experimental manipulation with an energetic model. Mytilid bivalves produce byssus, a network of collagen‐like threads that tethers individuals to hard substrate. We hypothesized that a manipulation that induces the production of more byssal threads would result in increased energetic cost and decreased growth of the species Mytilus trossulus. In month‐long field experiments in spring and autumn, we severed byssal threads across a range of frequencies (never, weekly, daily), and measured shell and tissue growth. We then quantified the costs associated with the production of byssal threads using a Scope for Growth model. We found that byssal thread removal increased byssal thread production and decreased growth. The cost calculated per byssal thread was similar in the spring and autumn (~1 J/thread), but energy budget calculations differed by season, and depended on thread quantity and seasonal differences in assumptions of metabolic costs. This work demonstrates that the cost of producing a structural material has a substantial effect on mussel energetic state. The energetic cost of producing byssal threads was 2%–8% percent of the energy budget in control groups that had low byssal thread production, and increased six to 11‐fold (up to 47%) in mussels induced to produce threads daily. We propose that characterizing the trade‐off between the cost of biomaterial production and growth has implications for understanding the role of trade‐offs in adaptive evolution, and improved natural resource management and conservation practices. A free Plain Language Summary can be found within the Supporting Information of this article.

In mosaic marine habitats, such as intertidal zones, ocean acidification (OA) is exacerbated by high variability of pH, temperature, and biological CO2 production. The nonlinear interactions among these drivers can be context‐specific and their effect on organisms in these habitats remains largely unknown, warranting further investigation.We were particularly interested in Mytilus edulis (the blue mussel) from intertidal zones of the Gulf of Maine (GOM), USA, for this study. GOM is a hot spot of global climate change (average sea surface temperature (SST) increasing by >0.2°C/year) with >60% decline in mussel population over the past 40 years.Here, we utilize bioenergetic underpinnings to identify limits of stress tolerance in M. edulis from GOM exposed to warming and OA. We have measured whole‐organism oxygen consumption rates and metabolic biomarkers in mussels exposed to control and elevated temperatures (10 vs. 15°C, respectively) and current and moderately elevated P CO2 levels (~400 vs. 800 µatm, respectively).Our study demonstrates that adult M. edulis from GOM are metabolically resilient to the moderate OA scenario but responsive to warming as seen in changes in metabolic rate, energy reserves (total lipids), metabolite profiles (glucose and osmolyte dimethyl amine), and enzyme activities (carbonic anhydrase and calcium ATPase).Our results are in agreement with recent literature that OA scenarios for the next 100–300 years do not affect this species, possibly as a consequence of maintaining its in vivo acid‐base balance., Our study demonstrates that adult Mytilus edulis from Gulf of Maine, one of the hot spots for global climate change, are metabolically resilient to the moderate acidification scenarios for the next 100–300 years but responsive to warming as seen in changes in metabolic rate, energy reserves, metabolite profiles, and enzyme activities.