The filter feeder Dreissena polymorpha affects nutrient, silicon, and metal(loid) mobilization from freshwater sediments

Characteristics of arsenic speciation in mainly cultured shellfish from Sanmen Bay, Zhejiang Province, China

Sanmen Bay plays a crucial role in economic shellfish aquaculture in China, yet few studies exist on the arsenic speciation of shellfish from this area. In this study, arsenic speciation of 11 cultured shellfish species from Sanmen Bay were analyzed by HPLC/ICP-MS. The results showed that organic arsenic particularly AsB, was the dominant arsenic species, constituting 21 %-71 % of the total arsenic. Conversely, the levels of inorganic arsenic were relatively low, ranging from 0.007 to 0.093 mg/kg, only accounted for 0.2 %-5.7 % of the total arsenic. There was no significant level correlation between inorganic arsenic and total arsenic in Sanmen Bay shellfish, so the concentration of inorganic arsenic did not increase with the total arsenic. Overall, the present study firstly revealed the arsenic speciation of shellfish from Sanmen Bay and also suggested that the proportion of inorganic arsenic should be considered in the revision of arsenic limit values.

What we know and don't know about the invasive zebra (Dreissena polymorpha) and quagga (Dreissena rostriformis bugensis) mussels

We summarized existing knowledge on Dreissena polymorpha (the zebra mussel) and D. r. bugensis (the quagga mussel), including data on their taxonomy, systematics, evolution, life cycle, reproduction, feeding, growth and longevity, population dynamics, interspecific competition, habitat requirements, and distribution within and among waterbodies. We analyzed the history of spread of both species and the major pathways and vectors of their spread in Europe and North America. Special consideration was given to their ecological and economic impacts and their natural enemies, like waterfowl, fishes, and parasites, as well as the prevention of their introduction, early detection, control, and containment. We also outlined the most salient ecosystem services provided by zebra and quagga mussels, including water purification, nutrient recycling, culling the effects of eutrophication, biomonitoring, and their role as a food resource for fish and waterfowl. Finally, we identified major knowledge gaps and key studies needed to better understand the biology, ecology, and impacts of these aggressive freshwater invaders. Our review indicates that much crucial information on the quagga mussel is still missing, including key life history parameters, like spawning cues, fecundity, and longevity, particularly for the profundal zone of deep lakes.

A global synthesis of ecosystem services provided and disrupted by freshwater bivalve molluscs

Identification of ecosystem services, i.e. the contributions that ecosystems make to human well-being, has proven instrumental in galvanising public and political support for safeguarding biodiversity and its benefits to people. Here we synthesise the global evidence on ecosystem services provided and disrupted by freshwater bivalves, a heterogenous group of >1200 species, including some of the most threatened (in Unionida) and invasive (e.g. Dreissena polymorpha) taxa globally. Our systematic literature review resulted in a data set of 904 records from 69 countries relating to 24 classes of provisioning (N = 189), cultural (N = 491) and regulating (N = 224) services following the Common International Classification of Ecosystem Services (CICES). Prominent ecosystem services included (i) the provisioning of food, materials and medicinal products, (ii) knowledge acquisition (e.g. on water quality, past environments and historical societies), ornamental and other cultural contributions, and (iii) the filtration, sequestration, storage and/or transformation of biological and physico-chemical water properties. About 9% of records provided evidence for the disruption rather than provision of ecosystem services. Synergies and trade-offs of ecosystem services were observed. For instance, water filtration by freshwater bivalves can be beneficial for the cultural service 'biomonitoring', while negatively or positively affecting food consumption or human recreation. Our evidence base spanned a total of 91 genera and 191 species, dominated by Unionida (55% of records, 76% of species), Veneroida (21 and 9%, respectively; mainly Corbicula spp.) and Myoida (20 and 4%, respectively; mainly Dreissena spp.). About one third of records, predominantly from Europe and the Americas, related to species that were non-native to the country of study. The majority of records originated from Asia (35%), with available evidence for 23 CICES classes, as well as Europe (29%) and North America (23%), where research was largely focused on 'biomonitoring'. Whilst the earliest record (from 1949) originated from North America, since 2000, annual output of records has increased rapidly in Asia and Europe. Future research should focus on filling gaps in knowledge in lesser-studied regions, including Africa and South America, and should look to provide a quantitative valuation of the socio-economic costs and benefits of ecosystem services shaped by freshwater bivalves.

Ecosystem services provided by the exotic bivalves Dreissena polymorpha, D. rostriformis bugensis, and Limnoperna fortunei

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.

Organic matter degradation and redistribution of sediment associated contaminants by benthic invertebrate activities

The fate of sediment associated compounds is the combined result of chemical properties and biological activities. Yet, studies simultaneously addressing the effects of biota on the redistribution and bioaccumulation of contaminants are scarce. Our aim was therefore to assess the effect of benthic invertebrate activities on organic matter degradation and the redistribution of metals and Polycyclic Aromatic Hydrocarbons (PAHs) in contaminated sediment. To this end, we introduced egg ropes of the non-biting midge Chironomus riparius into wastewater treatment plant sludge and allowed these to either develop until fourth instar larvae or to fully complete their life cycle into terrestrial flying adults. Chironomid larvae enhanced sludge degradation, resulting in increased metal concentrations in the sludge and in a flux of metals into the overlying water. Moreover, they hampered PAH degradation in the sludge. Contaminant transport from aquatic to terrestrial ecosystems with emerging invertebrates as a vector is widely acknowledged, but here we showed that biomanipulation prevailed over bioaccumulation, since due to chironomid activity, the flux of metals from the sludge into the overlying water was larger than into chironomid biomass. It is therefore concluded that contaminant-macroinvertebrate interactions are bilateral relationships driven by the interplay between macroinvertebrate traits and contaminant properties.

Ionomic profile and arsenic speciation in Semisulcospira cancellata, a freshwater shellfish from a mine-impacted river in China

Freshwater aquatic environment close to cities and industrial areas is more sensitive than marine environment. The freshwater shellfish Semisulcospira cancellate was introduced as a bioindicator to monitor the heavy metal contamination in the river through ionomic profiles and arsenic speciation. The shellfish samples were collected near four cities along the Xiang River in China. The concentrations of elements including Mg, Al, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Sr, Cd, Sn, Sb, Ba, and Pb were determined using ICP-MS. Multivariate statistical analyses such as Pearson's correlation analysis and principle component analysis (PCA) were employed to identify the possible sources of the elements in the shellfish samples. Three principle components were extracted from the ionomic matrix and were associated with natural existence, biological pathways, and mining and smelting activities, respectively. The ionomic profiles of the shellfish samples were evaluated through hierarchical cluster analysis (HCA) which was exhibited in the form of heatmap. The shellfish samples were categorized according to the sampling sites with different contamination levels. Six As species including arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC) were separated and quantified using HPLC-ICP-MS. The concentrations of As(III) and As(V) were linearly increased with total As concentration increasing. However, the proportion of AsB was decreased with total As while the AsB concentration was irrelevant to total As.

Patterns of toxic metals bioaccumulation in a cross-border freshwater reservoir

In freshwater ecosystems toxic metals can follow different routes of bioaccumulation in the organisms' body mass, routes that are similar to electronic circuits, but far more complex due to their hierarchy levels. Reservoirs located on river courses have positive impacts on economic and social development because they concentrate large water volumes used for electrical energy production, water supply, irrigation, industry, aquaculture, providing ecosystems for migratory birds and aquatic species. The aim of the study was to assess the contamination with copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr) and nickel (Ni) of a cross-border reservoir located on River Prut (border between Romania and Republic of Moldova) in a temperate climate zone. Several aspects were considered: seasonal variation of water parameters and toxic metals, bioconcentration in eight fish species and transfer from prey to predator through the food chain, bioaccumulation by two freshwater molluscs separated in size groups and their role as bioindicators of toxic metals pollution. Metals concentrations were measured with an atomic absorption spectrometer (HR-CS GF-AAS). Cadmium, lead, nickel and chromium concentrations limits in water samples were below the detection limits (0.005 μg L^-1Cd, 0.013 μg L^-1Pb and 0.011 μg L^-1Cr) during the monitoring period, suggesting that anthropogenic contamination was insignificant in the studied ecosystem. Fish liver and kidney had specific selectivity for copper (0.9-55.56 μg g^-1) and cadmium (0.097-1.031 μg g^-1) in case of pike-perch and bighead carp. The separation of molluscs in size groups did not prove that toxic metals increase in concentration with the organism age.