Potential impacts of the invasive species Corbicula fluminea on the survival of glochidia

A systematic review of invasive non-native freshwater bivalves

The introduction of invasive species has become an increasing environmental problem in freshwater ecosystems due to the high economic and ecological impacts it has generated. This systematic review covers publications from 2010 to 2020, focusing on non-native invasive freshwater bivalves, a particularly relevant and widespread introduced taxonomic group in fresh waters. We collected information on the most studied species, the main objectives of the studies, their geographical location, study duration, and type of research. Furthermore, we focused on assessing the levels of ecological evidence presented, the type of interactions of non-native bivalves with other organisms and the classification of their impacts. A total of 397 publications were retrieved. The studies addressed a total of 17 species of non-native freshwater bivalves; however, most publications focused on the species Corbicula fluminea and Dreissena polymorpha, which are recognised for their widespread distribution and extensive negative impacts. Many other non-native invasive bivalve species have been poorly studied. A high geographical bias was also present, with a considerable lack of studies in developing countries. The most frequent studies had shorter temporal periods, smaller spatial extents, and more observational data, were field-based, and usually evaluated possible ecological impacts at the individual and population levels. There were 94 publications documenting discernible impacts according to the Environmental Impact Classification for Alien Taxa (EICAT). However, 41 of these publications did not provide sufficient data to determine an impact. The most common effects of invasive bivalves on ecosystems were structural alterations, and chemical and physical changes, which are anticipated due to their role as ecosystem engineers. Despite a considerable number of studies in the field and advances in our understanding of some species over the past decade, long-term data and large-scale studies are still needed to understand better the impacts, particularly at the community and ecosystem levels and in less-studied geographic regions. The widespread distribution of several non-native freshwater bivalves, their ongoing introductions, and high ecological and economic impacts demand continued research. Systematic reviews such as this are essential for identifying knowledge gaps and guiding future research to enable a more complete understanding of the ecological implications of invasive bivalves, and the development of effective management strategies.

Impact of habitat engineering by invasive Corbicula clams on native European unionid mussels

Biological invasions cause biodiversity erosion on a global scale. Invasive species spreading beyond their natural range compete with native fauna for food and space, push native species to suboptimal habitats, impairing their behaviour and thus limiting their occurrence. Freshwater ecosystems are especially vulnerable to biological invasions and their ecological and economic impacts. The invasive Asian clams (Corbicula spp.), due to their opportunistic life style, can occur at densities of thousands ind. m-2. They act as ecosystem engineers transforming bottom substrata through accumulation of shells. Our goal was to determine the effect of substratum modification by living Corbicula and their shells on substratum choice and behaviour of Unio tumidus and Anodonta anatina, two European freshwater mussel species of the highly imperilled Unionidae family. We assessed their substratum selection in pairwise choice tests (pure sand vs. sand modified by living Corbicula or their shells, sand modified by shells vs. living Corbicula). Next, we tested locomotion and burrowing of unionids on pure substratum and substrata modified by Corbicula. Unionids avoided sand modified by living Corbicula and their empty shells, not distinguishing between these two types of substratum modification. In the presence of Corbicula, their burrowing was shallower or it took them longer to obtain the same depth as in the pure sand. Additionally, on sand modified by Corbicula shells, we observed a locomotion increase (U. tumidus) or slowing down (A. anatina). Our research showed a novel mechanism of negative impact of Corbicula on unionids, consisting in pushing them away from their optimal habitats. This may contribute to their habitat loss and future declines in invaded ecosystems.

Chemical Treatments on Invasive Bivalve, Corbicula fluminea

The Asian clam Corbicula fluminea is a native aquatic species in Eastern Asia and Africa but has become one of the ecologically and economically harmful invasive species in aquatic ecosystems in Europe, North America, and South America. Due to their natural characteristics as a hermaphroditic species with a high fecundity and dispersal capacity, Asian clams are extremely difficult to eradicate once they have infiltrated a waterbody. This is an emerging issue for states in the Northeastern United States, as Asian clams expand their range farther North due to climate change. There has been extensive research conducted to develop chemical treatments for reactively controlling invasive mollusc populations and proactively preventing their further spread. However, treatments are mostly targeted toward biofouling bivalves in industrial settings. A comprehensive review of Asian clam chemical treatments used in natural open-water systems was performed to evaluate molluscicides and identify the toxicity ranges of emerging treatments that maximize Asian clam mortality and minimize the negative impact on water quality and non-target species. The potential chemical applications in Asian clam control and management are summarized in this report to assist resource managers and practitioners in invasive Asian clam management.

Overwinter survival of Corbicula fluminea in a central Minnesota lake

Although Corbicula fluminea has been one of the more prolific freshwater invasive species in the world, previous studies have suggested a low probability for overwinter survival in northern latitudes without an artificially created thermal refuge. The discovery of live C. fluminea in a central Minnesota lake absent any known thermal refuge in 2020 presented an opportunity to further evaluate the overwinter survival and population structure of C. fluminea at the presumed edge of their potential range. The population was monitored from December 2020 through September 2021 alongside water temperature to better understand at which temperatures C. fluminea survived and if the population structure suggested reproduction occurring in the lake. We documented live C. fluminea in temperatures as low as 0.3°C. Shell size of recovered individuals suggested multiple cohorts, and the appearance of a new cohort at the end of the study, indicating active reproduction in the lake and suggesting the population had likely been present in the lake for at least two winters by the conclusion of the study period. Our findings provide evidence of the survival below historically documented lower lethal temperature limits and suggests adaptations to modeling predicting suitable habitat, both present and in a changing climate, are necessary to better assess risk of invasion by this species.

Assessment of endangered freshwater pearl mussel populations in the Northern Iberian Plateau in relation to non–native species: xenodiversity as a threat

In the last two decades, small populations of freshwater pearl mussels, Margaritifera margaritifera, have been recorded in Mediterranean rivers of the Iberian Northern Plateau. A survey was carried out in Castilla and León in 2018 to assess the development of populations of this species in all the rivers of known distribution and to update the threat classification. Thirty sections in the rivers Negro, Tera, Alberche and Águeda were positive for its presence, and another 50 stretches of seven rivers were negative. The species is currently distributed over about 22.5 km. Águeda and Tera populations have decreased dramatically in the last 14 years and are on the threshold of extinction. The Negro river supports the largest population, although the species has now disappeared in at least 61 % of the stretches that were inhabited in 2004. All populations showed very low densities and an ageing population structure, with no recruitment for decades. The presence of non-native invasive alien species (NIS) was higher than in a previous regional survey, with the signal crayfish representing the greatest threat. We observed changes in benthic microhabitats and direct predation of adults and glochidia conglutinates. In the Alberche River, in strict syntopy with M. margaritifera and two other mussel species, 10 NIS were detected. The current hydrological and ecological conditions in the Duero watershed support the settlement of exotic species to the disadvantage of native mollusks, which are more demanding in terms of microhabitats.

Identifying potential drivers of distribution patterns of invasive Corbicula fluminea relative to native freshwater mussels (Unionidae) across spatial scales

This study aimed to identify the importance of ecological factors to distribution patterns of the invasive Clam (Corbicula fluminea) relative to native mussels (family: Unionidae) across seven rivers within the Mobile and Tennessee basins, Southeast United States. We quantitatively surveyed dense, diverse native mussel aggregations across 20 river reaches and estimated mussel density, biomass, and species richness along with density of invasive C. fluminea (hereafter Corbicula). We measured substrate particle size, velocity, and depth in quadrats where animals were collected. Additionally, we characterized reach scale environmental parameters including seston quantity and quality (% Carbon, % Nitrogen, % Phosphorous), water chemistry (ammonium [ NH 4 + ], soluble reactive phosphorous [SRP]), and watershed area and land cover. Using model selection, logistic regression, and multivariate analysis, we characterized habitat features and their association to invasive Corbicula within mussel beds. We found that Corbicula were more likely to occur and more abundant in quadrats with greater mussel biomass, larger substrate size, faster water velocity, and shallower water depth. At the reach scale, Corbicula densities increased where particle sizes were larger. Mussel richness, density, and biomass increased with watershed area. Water column NH 4 + increased at reaches with more urban land cover. No land cover variables influenced Corbicula populations or mussel communities. The strong overlapping distribution of Corbicula and mussels support the hypothesis that Corbicula are not necessarily limited by habitat factors and may be passengers of change in rivers where mussels have declined due to habitat degradation. Whether Corbicula is facilitated by mussels or negatively interacts with mussels in these systems remains to be seen. Focused experiments that manipulate patch scale variables would improve our understanding of the role of species interactions (e.g., competition, predation, facilitation) or physical habitat factors in influencing spatial overlap between Corbicula and native mussels.

Enhancing robustness of activated sludge with Aspergillus tubingensis as a protective backbone structure under high-salinity stress

High salt seriously destroys the stable interactions among key functional species of activated sludge, which in turn limits the performance of high-salinity wastewater biological treatment. In this study, pelletized Aspergillus tubingensis (AT) was used as a protective backbone structure for activated sludge under high-salinity stress, and a superior salt-tolerant AT-based aerobic granular sludge (AT-AGS) was developed. Results showed that the COD and NH₄⁺-N removal efficiencies of salt-domesticated AT-AGS were 11.83% and 7.18% higher than those of salt-domesticated flocculent activated sludge (FAS) at 50 gNaCl/L salinity. Compared to the salt-domesticated FAS, salt-domesticated AT-AGS showed stronger biomass retention capacity (with a MLVSS concentration of 7.92 g/L) and higher metabolic activity (with a dehydrogenase activity of 48.06 mgTF/gVSS·h). AT modified the extracellular polymeric substances pattern of microbes, and the total extracellular polysaccharide content of AT-AGS (80.7 mg/gVSS) was nearly twice than that of FAS (46.3 mg/gVSS) after salt-domestication, which demonstrated that extracellular polysaccharide played a key role in keeping the system stable. The high-throughput sequencing analysis illustrated that AT contributed to maintain the microbial richness and diversity of AT-AGS in high-salt environment, and Marinobacterium (with a relative abundance of 32.04%) became the most predominant genus in salt-tolerant AT-AGS. This study provided a novel insight into enhancing the robustness of activated sludge under high-salinity stress.

Benthic macrofauna associated to the invasive bivalve Mytilopsis leucophaeata (Dreissenidae) in a coastal lagoon in Rio de Janeiro, Brazil

The invasion record for the estuarine bivalve Mytilopsis leucophaeata in Brazil is in Rio de Janeiro city, including the Rodrigo de Freitas Lagoon, where high densities of this invader were registered. This work aimed to (1) assess the composition and structure of the benthic macrofauna associated with this invader in Rodrigo de Freitas Lagoon, (2) analyze the spatiotemporal variation of richness, density and diversity of the associated benthic community, and (3) correlate changes on the density of the associated benthic species with some water quality variables and the density of M. leucophaeata. Clusters of M. leucophaeata were collected monthly (two years) in four sites. Nine taxa associated with M. leucophaeata were found; Heleobia sp. (Gastropoda) and Melita mangrovi (Amphipoda) showed the highest densities. The structure of the benthic macrofauna slightly differed among sampling sites, but not between dry and wet seasons. The water quality parameters, specific patterns of each taxon and high densities of M. leucophaeata contribute to variations in density of the associated species. Oscillations in the densities of M. leucophaeata and the native bivalve Brachidontes darwinianus suggest some agonistic relationship between them, such as a competition for space.

The role of anthropogenic habitats in freshwater mussel conservation

Anthropogenic freshwater habitats may provide undervalued prospects for long-term conservation as part of species conservation planning. This fundamental, but overlooked, issue requires attention considering the pace that humans have been altering natural freshwater ecosystems and the accelerated levels of biodiversity decline in recent decades. We compiled 709 records of freshwater mussels (Bivalvia, Unionida) inhabiting a broad variety of anthropogenic habitat types (from small ponds to large reservoirs and canals) and reviewed their importance as refuges for this faunal group. Most records came from Europe and North America, with a clear dominance of canals and reservoirs. The dataset covered 228 species, including 34 threatened species on the IUCN Red List. We discuss the conservation importance and provide guidance on how these anthropogenic habitats could be managed to provide optimal conservation value to freshwater mussels. This review also shows that some of these habitats may function as ecological traps owing to conflicting management practices or because they act as a sink for some populations. Therefore, anthropogenic habitats should not be seen as a panacea to resolve conservation problems. More information is necessary to better understand the trade-offs between human use and the conservation of freshwater mussels (and other biota) within anthropogenic habitats, given the low number of quantitative studies and the strong biogeographic knowledge bias that persists.