The role of calcium concentration in the invasive capacity of Corbicula fluminea in crystalline basins

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.

Growth retardation and suppression of ubiquitin-dependent catabolic processes in the brackish water clam Corbicula japonica in response to salinity changes and bioaccumulation of toxic heavy metals

The brackish water clam (Corbicula japonica) is constantly exposed to stressful salinity gradients and high levels of heavy metals in the freshwater-saltwater interface of estuary environments, which are introduced from upstream regions and land. To identify the key molecular pathways involved in the response to salinity changes and heavy metal bioaccumulation, we obtained the transcriptomes of C. japonica inhabiting different salinities and heavy metal distributions in Gwangyang Bay (Korea) using RNA sequencing. Among a total of 404,486 assembled unigenes, 5534 differentially expressed genes were identified in C. japonica inhabiting different conditions, 1549 of which were significantly upregulated and 1355 were significantly downregulated. Correlation analyses revealed distinct gene expression patterns between the low and high conditions of salinity and heavy metal bioaccumulation. Functional annotation revealed significant downregulation of genes involved in "ubiquitin-dependent protein catabolic process," "tricarboxylic acid cycle," and "intracellular protein transport" in C. japonica from the high condition compared to the low condition. Transcription and translation pathways were significantly enriched in the high condition. Additionally, upon comparison of the low and high conditions by qRT-PCR and proteasome enzyme activity analyses, our findings demonstrated that environmental stress could suppress the ubiquitin-proteasome complex (UPC). Additionally, transcriptomic changes under high salinity stress conditions may be related to an increase in cellular protection by defense enzymes, which leads to more energy being required and a disruption of energy homeostasis. Ultimately, this could cause growth retardation in the clam C. japonica. In summary, this study provides the first evidence of UPC suppression induced by a combination of high salinity and heavy metal bioaccumulation stress in C. japonica, which could compromise the survival and growth of estuarine bivalves.

Drivers of ecosystem vulnerability to Corbicula invasions in southeastern North America

Invasive species introduction is one of the major ongoing ecological global crises. Identifying factors responsible for the success of invasive species is key for the implementation of effective management actions. The invasive filter-feeding bivalve, Corbicula, is of particular interest because it has become ubiquitous in many river basins across North America and elsewhere. Here we sampled bivalve assemblages, environmental indicators, and land cover parameters in the Ouachita highlands in southeastern Oklahoma and southwestern Arkansas, and in the Gulf Coastal Plain of Alabama to test three working models (using structural equation modeling, SEM) based on a priori scientific knowledge regarding Corbicula invasions. Our models tested three competing hypotheses: (1) Native mussel declines are related to land use changes at the watershed level and subsequent Corbicula colonization is a result of an empty niche; (2) Corbicula abundance is one of the factors responsible for native mussel declines and has an interactive effect with land use change at the watershed level; (3) Native mussel declines and Corbicula success are both related to land use changes at the watershed level. We found no evidence for the first two hypotheses. However, we found that environmental indicators and land cover parameters at the watershed scale were robust predictors of Corbicula abundance. In particular, agricultural land cover was positively related with Corbicula density. These results suggest that further improvement of conventional agricultural practices including the optimization of fertilizer delivery systems may represent an opportunity to manage this species by limiting nutrient inputs to stream ecosystems. Preservation of extensive floodplain habitats may help buffer these inputs by providing key ecosystem services including sediment and nutrient retention.

The combined effects of macrophytes and three road salts on aquatic communities in outdoor mesocosms

Because of environmental and societal concerns, new strategies are being developed to mitigate the effects of road salt. These include new deicers that are alternatives to or mixtures with the most common road salt, sodium chloride (NaCl), improved techniques and equipment, and biotic mitigation methods. Using outdoor mesocosms, we investigated the impacts of NaCl and two common alternatives, magnesium chloride (MgCl₂) and calcium chloride (CaCl₂) on freshwater communities. We also investigated the mitigation ability of a common macrophyte, Elodea. We hypothesized that road salt exposure reduces filamentous algae, zooplankton, and macrocrustaceans, but results in increases in phytoplankton and gastropods. We also hypothesized that MgCl₂ is the most toxic salt to communities, followed by CaCl₂, and then NaCl. Lastly, we hypothesized that macrophytes mitigate some of the effects of road salt, specifically the effects on primary producers. We found that all three salts reduced filamentous algal biomass and amphipod abundance, but only MgCl₂ reduced Elodea biomass. MgCl₂ had the largest and longest lasting effects on zooplankton, specifically cladocerans and copepods, which resulted in a significant increase in phytoplankton and rotifers. CaCl₂ increased ostracods and decreased snail abundance, but NaCl increased snail abundance. Lastly, while we did not find many interactions between road salt and macrophyte treatments, macrophytes did counteract many of the salt effects on producers, leading to decreased phytoplankton, increased filamentous algae, and altered abiotic responses. Thus, at similar chloride concentrations, NaCl alternatives, specifically MgCl₂, are not safer for aquatic ecosystems and more research is needed to find safer road management strategies to protect freshwater ecosystems.

Decay and persistence of empty bivalve shells in a temperate riverine system

Bivalve shells can persist over a geological time, acting as important physical resources to the associated fauna. However, few studies have investigated their relevance as persistent long-term ecological attributes to the ecosystem. As such, it is relevant to investigate the shell decays in riverine systems subjected to different environmental conditions. Towards this end, shells of four bivalve species (Anodonta anatina, Corbicula fluminea, Potomida littoralis and Unio delphinus) were made available individually and in clusters of different sizes. The effects of river flow and seasonality were assessed by recording the decay rates of shells in lentic and lotic habitats throughout the year. Our results evidenced that the decays varied among species and depend on shell size, water flow and season. Thin shelled species (A. anatina and U. delphinus) showed the highest mean percentage of decay per month, 3.17% (lotic) and 2.77% (lotic), respectively, and thick shelled species (C. fluminea and P. littoralis) the lowest, 2.02% (lotic) and 1.83% (lotic), respectively. Size was a relevant variable explaining decays, with the smallest shells presenting the highest values, 1.2-2.0 times higher compared to the other size classes. Also, robustness showed to be the most relevant feature explaining the decays in thick shelled species. River flow was also a relevant descriptor of the decays, with higher decays observed in the lotic compared to the lentic habitats. Furthermore, lower decays were observed mainly during summer (lentic site), and autumn (lotic site) associated to the burial effect of leaves. In summary, shells of the native species A. anatina and U. delphinus are expected to persist and contribute less as habitat engineering species, than shells of the native P. littoralis and invasive C. fluminea species. This is especially valid to lotic habitats where the decays were up to 2.13 times higher than in lentic habitats.