No abstract

The monitoring of microplastics pollution in freshwater environments trails behind its practice in marine ecosystems. We evaluated the use of the invasive zebra mussel (Dreissena polymorpha) as a potential bioindicator of microplastic litter in freshwater lakes. Samples were collected from three sites (Lovere, Costa Volpino, Castro) at the northern end of Lake Iseo (one of the major subalpine lakes in north Italy) and compared for water physicochemical parameters, biometrical features of zebra mussels, and microplastics items/specimens (color, shape, size, and chemical composition). We hypothesized that since a wastewater treatment plant (WWTP) on the Oglio River discharges into this area of the lake, the microplastics in D.polymorpha could be measured and compared in samples from the three sites at different distances from the WWTP. There was no difference in the physicochemical water parameters and biometric features between the samples from the three sites, whereas there was a significant difference in items/specimen between the sites in decreasing order (mean ± standard deviation): Costa Volpino (0.23 ± 0.43) > Lovere (0.07 ± 0.25) > Castro (0.03 ± 0.18). The chi-square test showed a significant difference in shape, color, and chemical composition frequency in the samples from the three sites. The chemical composition of the microplastics was polyethylene terephthalate (45%), nylon (20%), polypropylene (20%), polyamide resin (10%), and polyvinyl chloride (5%). Our data show that the amount of microplastics the zebra mussel accumulated was greater the closer the sampling site to the WWTP. Our findings suggest that the zebra mussel may provide a useful tool to monitor microplastics pollution in lakes.

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We investigated the main seasonal drivers of Phragmites australis decomposition dynamics in a freshwater karst lake subject to water level fluctuations. Physical and chemical parameters were monitored every two weeks for one year and P. australis decomposition rates were measured using the leaf bag technique during two seasons (autumn and spring). Decomposition dynamics were analyzed for the contribution of macrobenthic invertebrate colonizers and the influence of intermittent water level variations. Seasonal trends for changes in physical and chemical parameters were observed in relation to the underground origin of the water supply, which also affected the macrobenthic invertebrate communities. Decomposition rates k differed significantly between seasons (k = 0.0131 in autumn and k = 0.0115 in spring) but remained within a narrow range, reflecting the trend for changes in water temperature. Our findings show that the variability in decomposition rates was largely due to water level fluctuations (46.7% relative importance), rainfall (12.4% relative importance) and macrobenthic invertebrate communities dominated by shredders (23.9% relative importance; 40.9-93.7% of the collected samples). The influence of physical and chemical changes, particularly water temperature, was less important (relative importance 1.82%).

Predictions of individual responses to climate change are often based on the assumption that temperature affects individuals’ metabolism independently of their body mass. However, empirical evidence indicates that interactive effects exist. Here, we investigated the response of individual Standard Metabolic Rate (SMR) to annual temperature range and forecasted temperature rises of 0.6-1.2°C above the current maxima, under the conservative climate change scenario IPCC-RCP2.6. As a model organism we used the amphipod Gammarus insensibilis, collected across latitudes along the western coast of the Adriatic Sea down to the southernmost limit of the species’ distributional range, with individuals varying in body mass (0.4-13.57mg). Overall, we found that the effect of temperature on SMR is mass-dependent. Within the annual temperature range, the mass-specific SMR of small/young individuals increased with temperature at a greater rate (activation energy: E=0.48 eV) than large/old ones (E=0.29 eV), with a higher metabolic level for high-latitude than low-latitude populations. However, under the forecasted climate conditions, the large individuals’ mass-specific SMR responded differently across latitudes. Unlike the higher-latitude population, whose mass-specific SMR increased in response to the forecasted climate change across all size classes, in the lower-latitude populations, this increase was not seen in large individuals. The larger/older conspecifics at lower latitudes could therefore be the first to experience the negative impacts of warming on metabolism-related processes. Although the ecological collapse of such a basic trophic level (aquatic amphipods) due to climate change would have profound consequences for population ecology, the risk is significantly mitigated by phenotypic and genotypic adaptation.

Total length (L(T)) and mass measurements of 28,596 specimens of European chub Leuciscus cephalus, collected from a variety of waterways across Italy, were used to compute standard mass (W(s)) equations by both empirical percentile (EmP) and regression line percentile (RLP) methods. The use of the EmP W(s) equation [log(10) W(s) = -4·79 + 2·68log(10) L(T) + 0·10(log(10) L(T))(2)] to compute relative mass (W(r)) of L. cephalus in Italy is suggested, as it was not influenced by length-related bias (L(T) range of application = 70-470 mm).

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The genus Eustrongylides includes nematodes that infect fish species and fish-eating birds inhabiting freshwater ecosystems. Nematodes belonging to the genus Eustrongylides are potentially pathogenic for humans; infection occurs after the consumption of raw or undercooked fish. In the two-year period 2019–2020, a total of 292 fish belonging to eight species were examined for the occurrence of Eustrongylides spp. from Lake San Michele, a small subalpine lake in northwest Italy. The prevalence of infestation was 18.3% in Lepomis gibbosus, 16.7% in Micropterus salmoides, and 10% in Perca fluviatilis. The other five fish species (Ameiurus melas, Ictalurus punctatus, Squalius cephalus, Carassius carassius, and Scardinius erythrophthalmus) were all negative for parasite presence. There were no significant differences in prevalence between the three fish species (Fisher’s exact test; p = 0.744). The mean intensity of infestation ranged from 1 (M. salmoides and P. fluviatilis) to 1.15 (L. gibbosus), and the mean abundance ranged from 0.1 (P. fluviatilis) to 0.28 (L. gibbosus). There were significant differences in the infestation site between the four muscle quadrants (anterior ventral, anterior dorsal, posterior ventral, and posterior dorsal) and the visceral cavity (Kruskal–Wallis test; p = 0.0008). The study findings advance our knowledge about the distribution and host range of this parasite in Italy.