Chironomids (Insecta, Diptera, Chironomidae) from alpine lakes in the Eastern Carpathians with comments on newly-recorded species from Ukraine

Abstract Background The first summarising checklist of Ukrainian Chironomidae (Insecta, Diptera) consisted of 302 species. Compared to other European countries, it is obvious that the real chironomid diversity of Ukraine has not been fully documented and greater effort is needed to discover the actual richness of this family. Thus, our survey focused on the chironomid fauna of some alpine lakes situated above the treeline in the Ukrainian Carpathians (a part of the Eastern Carpathians) aiming to contribute to the knowledge of the Ukrainian chironomid fauna and create the basis for more comprehensive neo- and palaeolimnological studies of these, regionally, little-known ecosystems. New information In total, 34 species/taxa, belonging to 22 genera and 4 subfamilies were collected in June 2019. Ten species were recorded for the first time in Ukraine: Zavrelimyia melanura, Acamptocladius reissi, Cricotopusspeciosus, Cricotopuscurtus, Heterotrissocladius marcidus, Orthocladius dentifer, Psectrocladiusoligosetus, Polypedilumuncinatum, Paratanytarsus laccophilus and Tanytarsus bathophilus. The occurrence of six species previously considered as “doubtfully present” in Ukraine was finally confirmed. Generally, the surveyed lakes have a unique composition of chironomids consisting of a mixture of species typical for cold alpine lakes and acidic ponds situated at lower altitudes.


Introduction
The Chironomidae family is a group of holometabolous insects distributed with the widest range of any family of insects, with individual species occurring from Antarctica and sub-Antarctic islands to Ellesmere Island in the Canadian Arctic. In this respect, chironomids are exceeded only by a few collembolan and mite species (Cranston 1995). Chironomids are common inhabitants of most aquatic habitats and regularly dominate aquatic insect communities in both abundance and species richness, often approaching 80 or more species and occasionally exceeding 100 species per site (Ferrington 2007).
Due to their ecological diversity, ubiquity and critical position in food webs, chironomids have been important components of biomonitoring and conservation programmes (see Nicacio and Juen 2015 for review). In addition to being important for understanding contemporary, mainly anthropogenic impacts, chironomid subfossil remains represent a tool for reconstructing past environmental changes (e.g. Langdon et al. 2010).
From the estimated more than 10,000 species worldwide (Cranston 1995), nearly 1300 species have been recorded in Europe (Spies and Saether 2013). Naturally, there are considerable differences in knowledge of regional chironomid faunas, with Western Europe having the most comprehensive knowledge as a result of higher concentration of specialists and longer history of the chironomid investigation relative to other regions (e.g. Ferrington 2007.
According to the first summarising checklist, 302 Chironomidae species have been recorded from Ukraine (Baranov 2011a). However, as the author of that publication stated, most of the data are probably based on identifications of larval stages only and, thus, often not reliable. The expansion of knowledge on Ukrainian chironomids has continued in the last decade, evidenced by the discovery of new regional records and even several new species (Lietytska and Baranov 2009, Baranov 2011b, Baranov 2013, Baranov 2015, Baranov and Ferrington Jr. 2013, Baranov and Przhiboro 2014, Moubayed-Breil and Baranov 2018. Here, we provide the first inventory of the family Chironomidae from some alpine lakes of the Eastern Carpathians located in Ukraine. Out of the several thousand natural and artificial lakes in Ukraine (Polishchuk and Igumnova 1983), mountain lakes located in the Carpathians represent a tiny fraction in both number and size. Nevertheless, these alpine lakes are particularly suitable for studying ecosystem responses to environmental impacts both global (e.g. climate change, atmospheric pollution) and regional (e.g. land use change, species introductions; Catalan and Donato Rondón 2016). Our survey not only expands the knowledge on the Ukrainian chironomid fauna, but can also serve as the first step to more comprehensive neo-and palaeolimnological studies of these unique and, in Ukraine, so far largely unknown ecosystems.

Study area and sampling sites
The part of the Eastern Carpathians located in Ukraine (Ukrainian Carpathians) represents medium altitude mountains with only few peaks slightly exceeding 2000 m a.s.l. The highest massifs, Chornohora and Svydovets, show direct glacial imprints of past glaciations (Matoshko 2011). The glacial cirques and glacial valleys, usually separated by a rock step, are the most remarkable signs of glacier activity. In some cirques, lakes of glacial origin formed, although most of them are in advanced terrestrial phase or have turned to peat bogs. The present study was performed at eight lakes in Chornohora and Svydovets Massifs (Fig. 1, Fig. 2) between 23 and 26 June 2019. In case we were not aware of official lake names, we named the lakes for adjacent hills (Breskul 1, Breskul 2, Dantsyzh) or nearby named lakes (Vorozheska 2, Vorozheska 3). Due to their small size (< 2 ha, max depth < 2.2 m) and high elevation (above the upper tree line), all the study sites can be considered alpine ponds (Céréghino et al. 2007, Hamerlík et al. 2013).  Coordinates of studied lakes were identified in the field using GPS device Garmin GPSmap 64. Lake area was estimated in Google Earth Pro. Maximum lake depth was estimated in the field, except for one site, where published data were available. Basic characteristics of the studied lakes are presented in Table 1.

Sampling methods
Floating chironomid pupal exuviae and drowned adults were collected along the shores of lakes at stretches by skimming the water surface with a hand net (mesh size 250 μm, frame diameter 25 cm) with a telescopic handle. The collected material was placed into labelled plastic bottles and preserved with 75% ethanol. Sorted exuviae and adult males were mounted on microscopic slides and identified using Schlee (1968), Langton and Visser (2003), Ekrem (2008)

Taxa
Lake name

Nes Bre1 Bre2 Dan Ger Vor1 Vor2 Vor3
Prodiamesa olivacea (Meigen, 1818) -  The number of species/taxa in a single lake varied from 4 to 13 with the mean diversity being 8.5 taxa per lake. Notes: Larvae of the subgenus Isocladius are widespread in mountain lakes in the Alps (Boggero 2018) and the Tatra Mountains (Bitušík et al. 2006), but species composition is insufficiently known due to identification difficulties. C. (I.) speciosus belongs to the sylvestris group, members of which are mostly eurythermic and euryoecious. There is a considerable gap in the knowledge of the species' ecologies. Langton and Visser (2003)  Notes: Belongs to the most widespread and often most abundant species in lakes of the Alps ) and the Tatra Mountains (Bitušík et al. 2006 Notes: Apparently a cold-stenothermic species occurring in lakes in mountain regions (e.g. Rieradevall et al. 2007, Bitušík and Svitok 2006, Bitušík et al. 2007, Boggero 2018 Distribution: Holarctic species recorded from a small number of European countries; however, its distribution from Scandinavia to Greece indicates its potential occurrence all over Europe.

Notes:
The species belongs to typical chironomid generalists for temporary wetlands, with adaptation to survive dry periods in moist soil (Dettinger-Klemm 2003). Distribution: Holarctic species, primarily distributed in northern and Western Europe, records are lacking from the southern and eastern part of the continent.

Materials
Notes: Euryoecious species occurring in ponds and lakes (Langton and Visser 2003). It belongs to typical colonisers of both natural ) and artificial water bodies (Bukvová and Hamerlík 2015). However, the species is not characteristic for high mountain lakes. While Boggero (2018)  Distribution: Palaearctic species widespread in Europe, but with a major gap in occurrence extending from the Baltic Republics to Southern Europe (apart from Romania) and the Balkans.
Notes: Larvae live mainly in lakes but also in flowing waters (e.g. Rossaro et al. 2006). It is the most commonly encountered species of the genus in alpine lakes in the Tatra Mountains (Bitušík et al. 2006), but apparently missing in alpine lakes of the South Carpathians (Tatole 2004, Cogălniceanu et al. 2009).

Discussion
Our study contributes to the knowledge of the chironomid fauna of alpine lakes in the Ukrainian part of the Eastern Carpathians. We report a total of 34 species/taxa, while almost one third (10 species) of them were recorded for the first time in Ukraine. We are aware that this inventory is far from complete, as evidenced by the comparison with data from the Tatra Mountains (Western Carpathians) and the South Carpathians (Tatole 2004, Bitušík et al. 2006, Cogălniceanu et al. 2009).
The most common species of the Tatra Mts. lakes (Western Carpathians, Bitušík et al. 2006) and the Retezat Mts. (South Carpathians, Cogălniceanu et al. 2009), Heterotrissocladius marcidus and Paratanytarsus austriacus were found only in a few of the Ukrainian lakes. On the other hand, the most characteristic species of the surveyed lakes were either not present in the Tatra Mts. lakes (e.g. Cladotanytarsus atridorsum and Paratanytarsus laccophilus) or were very rare (e.g. Chironomus spp., Synendotendipes sp.) (Bitušík et al. 2006). Nevertheless, the last two taxa can be common in acidic Tatra Mts. ponds situated in lower altitudes (Novikmec et al. 2015, Hamerlík et al. 2016. Absence of the members of the Diamesinae subfamily, typical for cold, nutrient-poor alpine lakes, from the Ukrainian samples is also interesting; however, it does not necessarily mean that they are not present in the lakes; their absence was most likely caused by spring emergence of the adults (e.g. Raunio et al. 2010). In general, chironomid communities of Ukrainian alpine lakes represent a mixture of species typical for cold alpine lakes and acidic ponds situated in lower altitudes.
The results of this "snap-shot" survey are important for at least two reasons: 1) it is the first insight into species composition of chironomid assemblages of Ukrainian alpine lakes in the context of the whole Carpathians and 2) the data can be useful in determining the ecological conditions in the alpine lakes and can create a basis for future (paleo)limnological studies extended to the whole "alpine lake district" in the Ukrainian Carpathians.