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

Abstract

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.

Mayfly response to different stress types in small and mid-sized lowland rivers

“…Nevertheless, at a large part of the study sites (i.e., 72 %) taxa richness was low, i.e., between zero and four taxa, corroborating previous studies (Vilenica et al 2016;2019). Mayflies inhabit both lotic and lentic habitats, although upper and middle reaches of fast-flowing streams, and ecologically intact large rivers harbour the highest mayfly diversity (Bauernfeind and Soldán 2012;Vilenica et al 2016;2018). Therefore, such low species richness, not typical for a lotic habitat (Bauernfeind and Moog 2000;Zedková et al 2014;Vilenica et al 2018), could be a consequence of various disturbances present at those sites, such as channelling, eutrophication, pollution, and microhabitat homogeneity (Axelsson et al 2011;Carvalho et al 2013;Ligeiro et al 2013).…”

“…The composition of mayfly assemblages in terms of the trophic structure and longitudinal zonal associations of species at each study site was analysed using the classification given by Buffagni et al (2009;, while the methodology was described in Vilenica et al (2018). Study sites without mayfly records, and sites with one taxon where we could not identify the specimens to the species level (i.e., sites 17 and 18) were excluded from the analysis.…”

“…Mayflies inhabit both lotic and lentic habitats, although upper and middle reaches of fast-flowing streams, and ecologically intact large rivers harbour the highest mayfly diversity (Bauernfeind and Soldán 2012;Vilenica et al 2016;2018). Therefore, such low species richness, not typical for a lotic habitat (Bauernfeind and Moog 2000;Zedková et al 2014;Vilenica et al 2018), could be a consequence of various disturbances present at those sites, such as channelling, eutrophication, pollution, and microhabitat homogeneity (Axelsson et al 2011;Carvalho et al 2013;Ligeiro et al 2013). In many cases, we observed shoreline erosion, as the emergent vegetation along the habitat edges, together with surrounding vegetation was mowed.…”

“…The Zelina stream in Božjakovina (site 22) and Toplica River upstream from Daruvar town (site 36) showed somewhat higher species richness, yet their assemblages mainly consisted of species inhabiting a wide range of habitats, such as Baetis rhodani, Centroptilum luteolum, Serratella ignita and Caenis luctuosa (Buffagni et al 2009;Bauernfeind and Soldán 2012). The most interesting finding was a record of Oligoneuriella rhenana at Toplica River, which is considered rare in Croatia (Vilenica et al 2015;2018). Although the species can tolerate some variations of environmental factors, its presence indicates that the ecological condition of Toplica River upstream from Daruvar town is not as poor as at the majority of other sites (Găldean, 1999;Petrovici and Tudorancea 2000).…”

What is new in Croatian mayfly fauna?

“…On the other hand, more detailed faunistic and especially ecological studies of mayflies in the Balkan Peninsula started only approximately two decades ago, and our knowledge is far from complete (e.g. Petrović et al, 2015;VidinoVa, 2003;Vilenica et al, 2015;2016;2017, 2018a2019;2020). Many regions are still rather poorly and unevenly investigated.…”