Evidence of long term biogeochemical interactions in carbonate weathering: The role of planktonic microorganisms and riverine bivalves in a large fluviokarst system

The infiltration of organic-rich surface waters towards groundwaters, is known to play a significant role in carbonate weathering and in contributing to the atmospheric continental carbon sink. This paper investigated biogeochemical interactions in karst critical zones, with strong surface water /groundwater interactions, and in particular the role of planktonic microorganisms and riverine bivalves through the analysis of particulate organic matter (OM) oxidation on carbonate weathering. In the large Val d'Orléans fluviokarst aquifer (France), a 20-year monthly dataset of Nitrates, Dissolved Oxygen (DO), dissolved inorganic and organic Carbon (DIC and DOC) fluxes was gathered. The surface water-groundwater comparison of geochemical trends showed that planktonic microorganisms had drastically decreased in surface waters, related to the proliferation of Corbicula bivalves spreading and a decrease in nutrients. This decrease in planktonic microorganisms was followed by a DO increase and an DIC decrease at the karst resurgence. The degradation of planktonic microorganisms consumes DO and produces NO₃, dissolved inorganic carbon (DIC) and a proton that in turn, dissolves calcite and produces DIC. Without the input from planktonic microorganisms, the fluviokarst has lost 29 % of this nitrification and 12 % of the carbonate dissolution capacities. Thus, the oxidation of particulate organic matter of planktonic microorganisms, which is part of heterotrophic respiration, appears to be a significant source of the inorganic carbon flux in riverine ecosystems. This shows how weathering can remain active under waters saturated versus calcite and suggests that the oxidation of organic matter can be a more appropriate mechanism than autotrophic respiration to explain the relationship between global warming and DIC flux change in rivers. Through the consumption of plankton, the animal life in rivers thus influences the inorganic carbon in groundwaters, creating a negative feedback in the carbon cycle.

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.

Chemical Profile of Elements in the Stingless Bee Melipona quadrifasciata anthidioides (Hymenoptera: Apidae)

Bees represent efficient bioindicators of environmental contamination, including elements that can accumulate in both biomes and bee-derived products. Therefore, the goal of this study was to evaluate the presence of metallic elements over the body surface of Melipona quadrifasciata anthidioides workers from rural and urban areas from Caatinga in Brazil. Using SEM/XEDS (scanning electron microscope/energy dispersive X-ray spectroscopy) identified magnesium (Mg), aluminum (Al), calcium (Ca), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), molybdenum (Mo), cadmium (Cd), barium (Ba), and lead (Pb) in the corbiculae of bees. The areas had similar profiles, but As was characterized as a "trace element" in the agricultural area and "minor element" in the urban area. The presence of toxic elements such as As, Cd, and Pb indicates that both areas may be contaminated, revealing the importance of metallic elements microanalysis in native bee species for environmental biomonitoring.

Dominance of harmful algae, Microcystis spp. and Micrasterias hardyi, has negative consequences for bivalves in a freshwater lake

The proliferation of cyanobacteria Microcystis spp. and the invading green alga Micrasterias hardyi in Lake Biwa has been increasing. However, the available knowledge on the dietary utilization of these cyanobacterial and algal species by bivalves, which are key species in lake ecosystems, is limited. In this study, we examined the dietary quality and utilization of these species by freshwater bivalves of the Corbicula spp., which are important fishery resources, by performing feeding experiments and field investigations based on fatty acid profiles and stomach content analysis. Although a significant increase in the dry weight and condition factor of the Corbicula spp. individuals fed on diatom was observed at the end of the experiment, for the individuals fed on Microcystis aeruginosa or M. hardyi, a dry weight increase was not observed and their condition factor decreased. Moreover, the fatty acid profile of the Corbicula spp. individuals fed on M. aeruginosa or M. hardyi indicated that they did not assimilate these diets, even though filtration was confirmed during the experiments. However, the stomach contents of wild Corbicula spp. specimens, collected from six sampling sites in Lake Biwa on four sampling occasions, showed that Microcystis spp. were the most abundant dietary items in all sites and on all occasions. Moreover, M. hardyi was detected during the analysis of stomach contents; this alga was the third most abundant algal species. As shown in the feeding experiments, they do not contribute to bivalve growth, indicating that the high occupation of Microcystis spp. and M. hardyi in the consumer's stomach may inhibit effective carbon transfer. The expansion of these unsuitable dietary organisms may affect the stability of lake ecosystems.

Acorbine, a Corbicula japonica-derived tripeptide containing non-proteinogenic amino acids, suppresses ethanol-induced liver injury

Since ancient times, Corbicula extract has been believed in Japan to have hepatoprotective effects, but it remains unclear whether these claims are true, and if so, which component is responsible for hepatoprotection. In this study, we showed that Corbicula extract exerted a protective effect against liver damage. Recent work identified acorbine (β-alanyl-ornithyl-ornithine), a novel tripeptide containing non-proteinogenic amino acids, in the extract of Corbicula japonica. Synthesized acorbine cured alcohol-induced liver damage in mice. In addition, acorbine purified from Corbicula extract exerted a protective effect against alcohol-induced hepatotoxicity in a culture liver model derived from mouse ES/iPS cells. Thus, acorbine is one of the components of Corbicula extract that protects hepatocytes against ethanol-induced death.

Phylogenomic analyses confirm a novel invasive North American Corbicula (Bivalvia: Cyrenidae) lineage

The genus Corbicula consists of estuarine or freshwater clams native to temperate/tropical regions of Asia, Africa, and Australia that collectively encompass both sexual species and clonal (androgenetic) lineages. The latter have become globally invasive in freshwater systems and they represent some of the most successful aquatic invasive lineages. Previous studies have documented four invasive clonal lineages, Forms A, B, C, and Rlc, with varying known distributions. Form A (R in Europe) occurs globally, Form B is found solely in North America, mainly the western United States, Form C (S in Europe) occurs both in European watersheds and in South America, and Rlc is known from Europe. A putative fifth invasive morph, Form D, was recently described in the New World from the Illinois River (Great Lakes watershed), where it occurs in sympatry with Forms A and B. An initial study showed Form D to be conchologically distinct: possessing rust-colored rays and white nacre with purple teeth. However, its genetic distinctiveness using standard molecular markers (mitochondrial cytochrome c oxidase subunit I and nuclear ribosomal 28S RNA) was ambiguous. To resolve this issue, we performed a phylogenomic analysis using 1,699-30,027 nuclear genomic loci collected via the next generation double digested restriction-site associated DNA sequencing method. Our results confirmed Form D to be a distinct invasive New World lineage with a population genomic profile consistent with clonality. A majority (7/9) of the phylogenomic analyses recovered the four New World invasive Corbicula lineages (Forms A, B, C, and D) as members of a clonal clade, sister to the non-clonal Lake Biwa (Japan) endemic, Corbicula sandai. The age of the clonal clade was estimated at 1.49 million years (my; ± 0.401-2.955 my) whereas the estimated ages of the four invasive lineage crown clades ranged from 0.27 to 0.44 my. We recovered very little evidence of nuclear genomic admixture among the four invasive lineages in our study populations. In contrast, 2/6 C. sandai individuals displayed partial nuclear genomic Structure assignments with multiple invasive clonal lineages. These results provide new insights into the origin and maintenance of clonality in this complex system.