Is the body condition of the invasive zebra mussel (Dreissena polymorpha) enhanced through attachment to native freshwater mussels (Bivalvia, Unionidae)?

Multiresistant bacteria: Invisible enemies of freshwater mussels

Freshwater mussels are among the most endangered groups of fauna anywhere in world. The indiscriminate use of antibiotics has led to the emergence of resistant strains. These antibiotic-resistant bacteria play a key role in increasing the risk allied with the use of surface water and in spread of resistance genes. Two endangered freshwater mussel species, Margaritifera margaritifera and Potomida littoralis, were sampled at 4 sampling sites along a 50 km stretch of River Tua. Water samples were taken at same sites. Of the total of 135 isolates, 64.44% (39.26% from water and 25.19% from mussels) were coliform bacteria. Site T1, with the lowest concentration of coliform bacteria, and site T2 were the only ones where M. margaritifera was found. No E. coli isolates were found in this species and the pattern between water and mussels was similar. P. littoralis, which was present at T3/T4 sites, is the one that faces the highest concentration of bacterial toxins, which are found in treated wastewater effluents and around population centers. Sites T3/T4 have the isolates (water and mussels) with the highest resistance pattern, mainly to β-lactams. Water and P. littoralis isolates (T3/T4) showed resistance to penicillins and their combination with clavulanic acid, and to cephalosporins, precisely to a fourth generation of cephalosporin antibiotics. The analysis provides important information on the risk to water systems, as well as the need to investigate possible management measures. It is suggested that future studies on the health status of freshwater bivalves should incorporate measures to indicate bacteriological water quality.

Invasive zebra mussel (Dreissena polymorpha) threatens an exceptionally large population of the depressed river mussel (Pseudanodonta complanata) in a postglacial lake

Freshwater mussels are in decline worldwide, with the depressed river mussel Pseudanodonta complanata being one of the rarest and most endangered species in Europe. Invasive mussels are suspected to be an important factor of decline, but there is little information on their interaction with native species.This study analyzed densities, depth distribution, and individual sizes and weights in one of the largest known populations of P. complanata in Europe in relation to the co-occurring invasive zebra mussel Dreissena polymorpha and other mussel species, using a systematic transect analysis. Pseudanodonta complanata was the dominant unionid species in Lake Siecino reaching densities of up to 26 ind/m2, with half of the specimens found at a water depth of 2.0-4.0 m. Densities were highest on sandy substrates in areas of underwater currents. In contrast, 67% of native Unio tumidus were found at depths < 1 m, indicating different habitat preference.In the study area, 91% of P. complanata, 92% of U. tumidus, and all Anodonta individuals were fouled by D. polymorpha. The dreissenid:unionid mass ratio (mean ± SD; maximum) was 0.43 ± 0.56; 4.22 and 0.86 ± 1.87; 8.76 in P. complanata and U. tumidus, respectively. Pseudanodonta complanata fouled with D. polymorpha were impaired in their anchoring capability and had shell deformations potentially affecting shell closing and filtration activity. Fouling intensity was negatively correlated with unionid density, potentially leading to accelerated population declines.The observed adverse effects of invasive zebra mussels on the depressed river mussel and the difficulties in eradicating established populations of invasive mussels suggest that D. polymorpha should be considered a serious threat to P. complanata. Therefore, the further spread of zebra mussels into habitats with native unionids needs to be avoided by all means.

Chemical oxidants affect byssus adhesion in the highly invasive fouling mussel Limnoperna fortunei

Biofouling by the invasive mussel species Limnoperna fortunei has caused severe negative consequences in various freshwater ecosystems, but there is still a lack of effective antifouling strategies for this species, particularly in drinking water treatment systems where many existing strategies cannot be used. Chemical oxidants have been proposed to potentially control fouling mussels by influencing 3,4‑dihydroxyphenylalanine oxidation involved in byssus adhesion. To test this potential control strategy, L. fortunei adults were exposed to four oxidants: sodium hypochlorite (NaClO), potassium permanganate (KMnO₄), hydrogen peroxide (H₂O₂) and chloramine T (CAT) at concentrations of 0.5, 1.0, 3.0 and 5.0 mg L^-1 for one week. The results showed that low concentrations of KMnO₄ stimulated foot protein secretion, which was beneficial to byssus production (number and length). NaClO and H₂O₂, but not KMnO₄ and CAT, significantly inhibited byssus production and reduced breaking force, causing an increased byssus shedding rate. However, only NaClO dissolved byssus and altered the failure location from the byssal thread to adhesive plaque, even when exposed at low concentrations, showing its great impacts on byssus adhesion. Further analysis of polyphenoloxidase activities and gene expression profiles of LfBP-1, LfFP-2 and LfBP-3 revealed that chemical oxidants affected byssus adhesion by altering Dopa oxidation and foot protein gene expressions. This study, therefore, suggests that a low concentration of NaClO can be used as an alternative and environmentally friendly chemical for controlling L. fortunei biofouling by weakening byssus adhesion.