Preliminary indoor evidences of microplastic effects on freshwater benthic macroinvertebrates

Plastics are to date considered one of the main detrimental drivers for the health of aquatic ecosystems, both in marine and inland waters. Regarding the latter habitat, it seems surprising how the plastic effects on benthic invertebrates are neglected since macroinvertebrates have a long tradition in the water quality assessment activities. In this context, we propose timely indoor observations on the exposure of caddisfly Odontocerum albicorne and mayfly Ephemera danica to various microplastic polymers (ABS, PET, PP, PS, PVDF). Three different experimental designs were performed on caddisflies and mayflies by exposing their larvae to natural and microplastic substrates. Our findings highlighted how microplastics affected both caddisflies in rebuilding its own case (after having removed the natural one) and mayflies burrowing. Particularly, all caddisflies rebuilt cases using the microplastic polymers provided instead of natural items only. Moreover, we provide the first evidence that mayflies burrow mainly in microplastic substrates rather than in natural ones. Our research highlights that macroinvertebrate larvae would use naturally occurring microplastics and this could be of particular concern in freshwaters with high contamination by plastics. Indeed, larvae appear to not necessarily perceive microplastics as a direct stressor. Further studies ought to be conducted to understand the chronic perturbation on larvae fitness and for example, on drift behaviour. Also, further investigations are needed to understand the potentialities of using plastics by benthic macroinvertebrates.

Bioaccumulation of heavy metals in Ephemera danica larvae under influence of a trout farm outlet waters

Trout farms are one of the major sources of pollution of highland streams and rivers. Since river sediment burdened with organic pollution binds greater amounts of heavy metals we investigated the influence of the trout farm on the accumulation of metals in the sediment, water and Ephemera danica larvae. Research was conducted seasonally (April, July, and October of 2015 and January of 2016) at one control locality (SK1) and three localities downstream from the farm (SK2–SK4). In agreement with the hypothesis the fish farm discharge induced localized and statistically significant increase of concentrations of Fe, Cu, Cr, Ni, Pb and Cd in sediment and E. danica larvae, but not in water at locality SK2 just below the fish farm indicating that sediment is the main source of heavy metals for this organism. However, according to the values of Biota sediment accumulation factor (BSAF) only metals with low sediment concentrations (As, Cd and Cu) accumulated in the larvae. Moreover, BASF values for toxic metals (As, Cd and Cr) showed negative correlation with their concentrations in sediment indicating existence of defense mechanisms in E. danica against assimilation of these metals in high concentrations lethal for it. On the other hand, BSAF values for essential microelements (Cu and Fe) were positively correlated with their sediment concentrations. In conclusion the trout farm induced accumulation of heavy metals in river sediment and E. danica larvae proved to be a good bioindicators of the pollution of river systems by As, Cd and Cu.

Mayfly (Ephemeroptera) assemblages of a Pannonian lowland mountain, with first records of the parasite Symbiocladius rhithrogenae (Zavrel, 1924) (Diptera: Chironomidae)

Despite increasing numbers of studies on aquatic insects in South-East European streams, there are still gaps in the knowledge about their distribution and assemblage composition in many regions. As one of the most abundant and sensitive aquatic insects, mayflies are widely used as bioindicator taxa. With the main goal of improving the knowledge of South-East European mayflies, a study was conducted of 15 streams along a Pannonian lowland mountain, in spring and summer 2017. A total of 18 mayfly taxa were recorded, where Ephemera danica Müller, 1764 and Baetis rhodani (Pictet, 1843) were the most widespread. All sites were characterized with the domination of rhithral elements, with similar shares of grazers/scrapers and detritivores. Nevertheless, sites at lower altitudes generally had a higher share of potamal and littoral elements, and a higher share of detritivores than at higher altitudes. NMDS analysis separated sites mainly based on sampling period. Although Heptageniidae nymphs were recorded in all streams, the parasitic chironomid Symbiocladius rhithrogenae (Zavrel, 1924) was recorded attached to three nymphs of Rhithrogena group semicolorata, each in a different stream. These records represent the first report of this species for Croatia. The current study contributes significantly to our knowledge of mayfly assemblages and species distribution in South-East Europe. Moreover, with a newly recorded species, this study indicates that the knowledge of the Croatian chironomid fauna is still growing.

Influence of a trout farm on antioxidant defense in larvae of Ephemera danica (Insecta: Ephemeroptera)

The aim of this study was to establish the influence of a trout farm on the activity of enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), and total glutathione concentration (GSH), in larvae of Ephemera danica, and on environmental parameters in the receiving watercourse. The investigations were carried out seasonally (April, July, and October of 2016 and January of 2017) at four localities (SK1–control, and SK2, SK3, and SK4–30 m, 330 m and 630 m below the fish farm, respectively) along the Skrapež River. Discharged water had the greatest effect on the concentrations of dissolved oxygen (DO), ammonium ions, nitrates (NO3−), and total phosphorus. In the case of SOD and GSH, seasonal changes were greater than longitudinal, with maximal values attained in spring and summer and minimal in autumn and winter. SOD showed the strongest correlation with DO, and GSH with total nitrogen. Activity of GPx demonstrated greater longitudinal variability with maximum at SK2 in all seasons and the strongest correlation with NO3−. The obtained results indicate that GPx activity was the most sensitive to the trout farm effects, while SOD and GSH were more influenced by natural seasonal changes of environmental parameters.

Ephemera danica (Ephemeroptera: Ephemeridae) As a Resource for Two Commensals: Ciliated Protozoans (Sessilida) and Chironomids (Diptera)

The distribution and coexistence of two unrelated commensals, the chironomid Epoicocladius ephemerae (Kieffer 1924) and ciliate Carchesium polypinum L. 1758, on one host species, Ephemera danica Muller 1764, sampled in two small lowland rivers in 2009, 2010 and 2011, were investigated. We analyzed 288 mayfly specimens from the Bzura River and 101 from the Mroga River. The number of commensals on a single mayfly specimen varied between 0 and 18 chironomids, and from 0 to 46 colonies of ciliates. Prevalences were >48% for chironomids and ∼30% for ciliates, whereas mean intensities were low (4.01±6.04 commensals on one host). The spatial distribution of each commensal species was investigated on different parts of the host body. Neither chironomids nor ciliates infected the whole mayfly body. The co-occurrence of these two commensals was not random and showed a negative association. Chironomids were most frequent on two or three parts of the body (two parts of the abdomen, with gills and without gills, and legs), whereas ciliates were found on two parts (the whole abdomen). Coexistence of the two commensal species led to partitioning of resources that was host body size dependent: small mayflies (optimal size 11.63 mm) were primarily settled by ciliated protozoans while larger specimens (optimal size 28.77 mm) were settled by chironomids.