Streams in the Mongolian Altai Mountains are mostly fed from glaciers and are extreme conditions for mayflies because of high elevation, low temperatures and low annual precipitation. Previous information about mayflies of Western Mongolia is scarce, but with this study a total of 38 species belonging to 26 genera and subgenera and 8 families of mayflies has been recorded in the Mongolian Altai region. Study material was entirely imagos and collected from 78 sites during expeditions led by the Mongolian Aquatic Insect Survey in 2008, 2009 and 2010. Raptobaetopus tenellus, Caenis luctuosa and C. rivulorum are recorded as new to the fauna of Mongolia, and there are new distribution records for Ameletus montanus, Baetis (Acentrella) lapponica, Baetis sibiricus, Baetis (Labiobaetis) attrebatinus, Centroptilum luteolum, Procloeon pennulatum, Ephemerella aurivillii, Serratella setigera, Ephemera sachalinensis, Ecdyonurus (Afronurus) abracadabrus, Cinygmula kurenzovi, Ecdyonurus (Afghanurus) vicinus and Epeorus (Belovius) pellucidus from the Mongolian Altai region. Baetis vernus and Ephemerella aurivillii are the most frequently encountered species in this region.

Raptobaetopus tenellus , Caenis luctuosa , C. rivulorum , Biodiversity, Altai Mountain Range, Aquatic Insects

Early studies of the mayfly fauna from the Mongolian region date to 1940 by Kinji Imanishi (Landa and Soldán 1983), although the major focus of this work consisted of exploring Inner Mongolia, a province of China, and to a lesser extent, the modern state of Mongolia (Bae et al. 2000). A decade later, Tshernova (1952) was the first to thoroughly describe the Mongolian (i.e., from the current Mongolian State) mayfly fauna with a paper including describing a new species, Baetis mongolicus (later, redescribed as a synonym of Baetis (Labiobaetis) tricolor by Kluge (2012)), from Khalkh gol, Eastern Mongolia. Most recently, Soldán et al. (2009), published a review of the Mongolian mayfly fauna and listed a total of 96 species belonging to 34 genera and 14 families. Of these, 28 species were recorded from Western Mongolia (defined as Uvs, Khovd and Bayan-Olgiy provinces of Mongolia).

Most of the area of Western Mongolia is highly elevated, mostly dominated by the Mongolian Altai Mountains, which have permanent glacial snow at the highest points. The average altitude of the Mongolian Altai Mountains is about 3200–3500 m a.s.l. The air temperature of the warmest month in Mongolian Altai Mountains is 12.3 °C in the higher areas and 21.1 °C in the lower areas of the region (Altantsetseg et al. 2008). Thus, for the region sampled for this study, we consider this area of high elevation and relatively cold summers as extreme conditions for mayflies.

Mayflies occur in variety of lotic and lentic environments and these habitats, including rivers, streams, springs and lakes, occur in Western Mongolia. The entire region of Western Mongolia is included within the Central Asian Internal Watershed (CAIW) (“Internal” from, Kelderman and Batima 2006; Maasri and Gelhaus 2012) which is one of the three major basins of Mongolia (Tsegmid 1969). The CAIW is an endorheic basin but equivalent to the size of the Arctic and Pacific Ocean basins of Mongolia (Dulmaa 1979). In this watershed, streams originating from glacial melt are common, in addition to lakes that originated from tectonic and glacial processes. The largest river by its discharge is Khovd gol (“gol” refers to stream or river in Mongolian) flowing for 516 km with a drainage area of 58000 km² (Tsegmid 1969). The second largest river is Bulgan gol, which is 268 km long, and with a drainage area of about 9180 km². The Bulgan gol originates from south of the Mongol Altai Mountains and flows west into the Urungu River of China. Bodonch gol and Uyench gol are the next largest rivers after Bulgan gol (Myagmarjav and Davaa 1999). Three out of the five largest lakes in Mongolia (as measured by surface area) occur in the CAIW specifically Uvs, Khyargas and Khar-Us lakes (the first two listed are salt water lakes, the last one is a freshwater lake). Uvs nuur (“nuur” refers to lake in Mongolian) is the largest lake in Mongolia, with a drainage basin of 70712 km². In addition to these there are several smaller freshwater (Khoton nuur, Khorgon nuur, Dayan nuur and Achit nuur) and saltwater lakes (Uureg nuur) in the basin (Myagmarjav and Davaa 1999).

In this paper, we provide data on the species composition of mayflies in Western Mongolia and the Altai Mountains in order to contribute to the inventory of aquatic insect biodiversity in this relatively unexplored area of Mongolia and the larger Central Asian region. This study has the specificity to include a wide range of aquatic habitat types distributed along a wide latitudinal gradient.

A total of 38 species, belonging to 26 genera and subgenera and 8 families of mayflies, are recorded in this study area (Figure 8). Among these, Raptobaetopus tenellus Albadra, 1878, Caenis luctuosa (Burmeister, 1839) and C. rivulorum Eaton, 1884 are new to the fauna of Mongolia, and there are new distribution records in Western Mongolia for 13 species: Ameletus montanus Imanishi, 1930, Baetis (Acentrella) lapponica Bengtsson, 1912, Baetis (Acentrella) sibiricus Kazlauskas, 1963, Baetis (Labiobaetis) attrebatinus Eaton, 1870, Centroptilum luteolum (Müller, 1776), Procloeon pennulatum (Eaton, 1870), Ephemerella aurivillii Bengtsson, 1909, Serratella setigera (Bajkova, 1965), Ephemera sachalinensis Matsumura, 1911, Ecdyonurus (Afronurus) abracadabrus (Kluge, 1983), Cinygmula kurenzovi (Bajkova, 1965), Ecdyonurus (Afghanurus) vicinus Demoulin, 1964, and Epeorus (Belovius) pellucidus (Brodsky, 1930). The following species list gives the specific localities where a species was found as site number (#), and Figure 8 ranks the species by number of sites where each species occurred. In the species list, preceding the species name, (*) refers to a new record for the Western Mongolia and (**) refers to a new record for the country.

Figure 8. 

Species of mayflies recorded in Western Mongolia (ordered by the number of site occurrences). The different colors on the bar for each species represent the three main habitats and the length represents the number of occurrences for each type.

Ameletidae

- * Ameletus montanus Imanishi, 1930 - # 22, 26, 31

Baetidae

- * Baetis (Acentrella) lapponica Bengtsson, 1912 - # 31, 51, 59

- Baetis (Acentrella) sp. 1 - # 1, 2, 4, 24, 27, 31, 33, 43, 47, 53, 56, 63, 65, 72, 77

- * Baetis (Acentrella) sibiricus Kazlauskas, 1963 - # 3, 16, 34, 35, 49, 50

- * Baetis (Labiobaetis) attrebatinus Eaton, 1870 - # 47, 70

- Baetis vernus Curtis, 1834 - # 2, 3, 7, 8, 9, 10, 12, 14, 15, 16, 18, 19, 20, 21, 22, 23, 24, 25, 29, 32, 35, 37, 38, 40, 45, 51, 52, 53, 56, 59, 61, 62, 63, 71

- Baetis sp. 1 - # 1, 3, 15, 18, 24, 41, 60, 62, 65, 66, 68

- Baetopus sp. 1 - # 60, 64

- * Centroptilum luteolum (Müller, 1776) - # 31, 37, 39

- * Procloeon pennulatum (Eaton, 1870) - # 59, 60, 61, 64, 66

- Procloeon sp. 1 - # 13

- Pseudocentroptilum sp. 1 - # 3, 22, 43, 48, 57

- Pseudocloeon sp. 1 - # 8, 16, 17

- ** Raptobaetopus tenellus Albadra, 1878 - # 57, 61, 63, 67, 71

Caenidae

- ** Caenis luctuosa (Burmeister, 1839) - # 16, 53

- ** Caenis rivulorum Eaton, 1884 - # 13

- Caenis robusta Eaton, 1884 - # 53, 58

Ephemerellidae

- Drunella triacanhta (Tshernova, 1949) - # 23, 41

- * Ephemerella aurivillii Bengtsson, 1909 - # 5, 6, 16, 19, 28, 31, 33, 35, 36, 37, 38, 41, 65, 67, 68, 70, 71, 73, 75

- Ephemerella mucronata (Bengtsson, 1909) - # 3, 38

- Ephemerella nuda Tshernova, 1949 - # 1, 3, 10, 11, 29, 30, 40, 53, 65, 66

- Ephemerella sp. 1 - # 30, 60

- Serratella ignita (Poda, 1761) - # 24, 43, 45, 54, 59, 61, 63, 66, 76

- * Serratella setigera (Bajkova, 1965) - # 43

- Uracanthella punctisetae Matsumura, 1931 - # 33, 37, 38, 39, 40, 41, 42, 43

Ephemeridae

- * Ephemera sachalinensis Matsumura, 1911 - # 43

Heptageniidae

- Cinygmula cava (Ulmer, 1927) - # 6, 17, 18, 19, 23, 31, 36, 65, 68, 69, 70, 73, 74, 75

- * Cinygmula kurenzovi (Bajkova, 1965) - # 4, 63

- * Ecdyonurus (Afghanurus) vicinus Demoulin, 1964 - # 18, 20, 22, 24, 45, 46, 47, 61, 65, 66, 72, 77, 78

- * Ecdyonurus (Afronurus) abracadabrus (Kluge, 1983) - # 43

- * Epeorus (Belovius) pellucidus (Brodsky, 1930) - # 3, 33, 36, 39, 40, 41, 42, 43, 47, 61

- Epeorus sp. 1 - # 19

- Heptagenia flava Rostock, 1878 - # 53, 54, 60

- Heptagenia sulphurea (Müller, 1776) - # 3, 53

- Rhithrogena lepnevae Brodsky, 1930 - # 2, 3, 24, 39, 40, 41, 42, 43, 44, 60, 78

- Rhithrogena sibirica Brodsky, 1930 - # 4, 19, 31, 32, 38, 55, 64, 67, 73

Polymitarcyidae

- Ephoron nigridorsum (Tshernova, 1934) - # 53

Siphlonuridae

- Siphlonurus lacustris Eaton, 1970 - # 12, 14, 56, 57, 71, 75, 78

Of the 38 species recorded as adults, 36 occurred along streams and rivers. Three species, Caenis robusta, Baetis (Acentrella) sibiricus and Rhithrogena lepnevae, were found along both lotic and lentic habitats. Only two species, Procloeon sp. and Caenis rivulorum, were recorded from a lake (# 13- Khoton nuur). Five species were taken around cold springs although none was found exclusively along this habitat.

The most frequently encountered species was Baetis vernus, which was recorded from 34 of the 78 sites (Figure 8). Ephemerella aurivillii, Baetis (Acentrella) sp. 1 and Cinygmula cava were found at 19, 15, and 14 different sites, respectively. In contrast, seven species were recorded as adults only at one site: Serratella setigera (site # 43), Ephoron nigridorsum (site # 53), Ephemera sachalinensis (site # 43), Epeorus sp. 1 (site # 19), Ecdyonurus (Afronurus) abracadabrus (site # 43), Procloeon sp. 1 (site # 13), and Caenis rivulorum (site # 13). The remaining species occurred at between two to 13 sites.

Taxa richness at rivers and lakes varied between one and 16 (Figure 9). The highest taxa richness was found along Bulgan gol (16 species) with 15 and 11 species along the rivers Khovd and Sagsai, respectively. The lowest species richness (one species) was observed at 18 rivers (e.g. Bodonch gol, Bortiin gol, Buural gol etc.).

Figure 9. 

Number of species occurring at each site in Western Mongolia.

Our study shows that the Ephemeroptera fauna of Western Mongolia comprise more than one-third of the total species recorded for the country. In addition, three new species were recorded for Mongolia for the first time, Raptobaetopus tenellus, Caenis luctuosa and C. rivulorum. Raptobaetopus tenellus is a Transpalaearctic (also referred as Entire Palaearctica, Beketov (2009)) species (Bauernfeind and Soldán 2012). Distribution of this species is known from west Palaearctic (Iberian Peninsula through Europe to the northern Ural Mountains) to Eastern Palaearctic (lower Ob' River and basin in Siberia to Primoriye region) (Bauernfeind and Soldán 2012). Caenis luctuosa and C. rivulorum are both Palaearctic species. C. luctuosa was known previously from Fennoscandia east to Russia and Middle Asia, south to the Balearic Islands, Iberian Peninsula and Asia minor, and some Mediterranean Islands and North Africa (Bauernfeind and Soldán 2012). C. rivulorum is a widespread species and is considered part of the Siberian fauna (Bauernfeind and Soldán 2012). Ameletus montanus, Baetis (Acentrella) lapponica, Baetis (Acentrella) sibiricus, Baetis (Labiobaetis) attrebatinus, Centroptilum luteolum, Procloeon pennulatum, Ephemerella aurivillii, Serratella setigera, Ephemera sachalinensis, Ecdyonurus (Afronurus) abracadabrus, Cinygmula kurenzovi, Ecdyonurus (Afghanurus) vicinus and Epeorus (Belovius) pellucidus are new to Western Mongolia. Of these, Baetis (Labiobaetis) attrebatinus, Procloeon pennulatum, Ephemera sachalinensis, Ecdyonurus (Afronurus) abracadabrus and Ecdyonurus (Afghanurus) vicinus were recently recorded in Mongolia for the first time by Enkhtaivan and Soldán (2004) and Soldán et al. (2009). The remaining species were previously known in Mongolia, from the Pacific Ocean basin and Arctic Ocean basin (Bajkova and Varykhanova 1978; Braasch 1986; Kluge 2009; Landa and Soldán 1983). Baetis (Acentrella) lapponica has been recorded previously in Mongolia (Kluge 2009) in the Selenge River Basin, based on imaginal, reared from larvae, records. However, this species was not included in the checklist of the mayflies of Mongolia (Soldán et al. 2009) due to incomplete locality records. Our finding of Baetis (Acentrella) lapponica in Western Mongolia, based on adult specimens confirms the species occurrence in Mongolia and brings the Mongolian mayfly fauna to 100 species.

Mayflies are generally diverse in lotic ecosystems as the majority of species prefer well-oxygenated habitat (Merritt et al. 2008). Consequently, the highest species diversities in this study were recorded along rivers, streams and springs. Fewer species including Caenis robusta, Baetis (Acentrella) sibiricus and Rhithrogena lepnevae were sampled around both lotic and lentic habitats. Caenis robusta was collected near a river (Khovd Gol) and also a brackish lake (Shaazgai nuur). Baetis (Acentrella) sibiricus and Rhithrogena lepnevae were found at more lotic habitats rather than lentic habitats. Procloeon sp. and Caenis rivulorum were recorded only in Lake Khoton. Larvae of Caenis rivulorum were previously recorded in lakes with stony substrate as well as rivers at variable elevations between 200–500 m a.s.l. in Europe (Bauernfeind and Soldán 2012). However, the elevation of Lake Khoton is 2086 m a.s.l. making this site the highest elevation record for the species.

Baetis vernus was the most commonly encountered taxon in Western Mongolia and occurred in 45% of the sampled sites. This species was found at a variety of lotic habitats including streams and springs. The elevation range of this species in Western Mongolia extended from 1172 to 2798 m a.s.l. The wide occurrence of this species among our sampled sites is most likely due to its very broad ecological range (Bauernfeind and Soldán 2012).

Serratella setigera, Procloeon sp. 1, Ephoron nigridorsum, Ephemera sachalinensis, Epeorus sp. 1, Ecdyonurus (Afronurus) abracadabrus, and Caenis rivulorum were found only at a single sampling site. Ephoron nigridorsum and Ephemera sachalinensis are both burrowing mayflies preferring larger and lowland rivers (Bauernfeind and Soldán 2012) and were recorded at Bulgan or Khovd River, the only suitable river habitat within the sampling area. For Serratella setigera and Ecdyonurus (Afronurus) abracadabrus, both found only at Bulgan Gol (Appendix 1, site # 43), this study adds significant habitat information to what little is known on the distribution of these two species (Bauernfeind and Soldán 2012).

In this study a total of 38 species was recorded in Western Mongolia (Uvs, Khovd and Bayan-Olgiy provinces). Soldán et al. (2009) listed 28 species that have been recorded from the Khovd, Uvs and Bayan-Olgiy provinces, with more than half of these not collected in our sampling expeditions. Therefore, despite the valuable information taxonomic and geographical distribution of mayflies of Western Mongolia, this study does not constitute an inclusive checklist of the total mayfly fauna of Western Mongolia. This discrepancy could be related to a number of reasons due to sampling and current taxonomy. First, our sampling effort was restricted to July, a favorable period for emergence of aquatic insects in Mongolia, but nevertheless did not cover the complete ice-free period in Western Mongolia. Second, the sampling duration and number of samples at the different aquatic habitats was variable. Some rivers and streams were sampled thoroughly at different sites (e.g. Bulgan and Khovd River), others were only sampled overnight and in few sites was sampling occurring at the right timing during the day to encompass adult swarming. Therefore, our sampling might have been affected by different emergence patterns. Third, there were difficulties to identify some adult mayflies at the species level because of the lack of reliable identification keys for the Mongolia fauna and also having subimagos in the samples. Maasri and Gelhaus (2012) previously listed mayfly species based on larval identification and recorded 21 genera for the CAIW. However, Maasri and Gelhaus (2012) included sites throughout the whole CAIW, covering a wider geographical range. Erdenee (2011) in her previous study recorded 17 genera all included in this study. In addition to Soldán et al. (2009), Beketov (2005) in a survey of the Northeastern Altai Mountains recorded 25 species with 20 of these included in Western Mongolia. Therefore, our results and the available literature on Western Mongolia support the statement of an estimated number of mayfly species for this geographical area to be above 65 species.

We want to thank co-principal investigators of the MAIS project, Drs. J. Morse, R. Nelson and B. Hayford for providing the opportunity for B.E. to work in this project, and for their scientific guidance. A special thanks is given to the Mongolian Benthological Society for its encouragement, and to the Permanent Committee of the International Conference on Ephemeroptera for granting B.E. a scholarship to participate to the XIII International Conference on Ephemeroptera and XVII International Symposium on Plecoptera at which this research was presented. Authors are also thankful to Dr. W. Bouchard, Dr. Ya. Oyunchuluun., Ch. Suvdtsetseg, D. Enkhnasan, B. Uugantsetseg, and other members of the MAIS project. Funding of the MAIS project was provided by an award from US-NSF grant Biodiversity Inventories #0743732 "Survey and Inventory of the Aquatic Insects of the Altai and Hangai Mountain Drainages, Mongolia" to J. Gelhaus (PI), R. Nelson and J. Morse (co-PIs). The manuscript production benefited from the NSF grant Macrosystem Biology #1442595 “Collaborative Research: Hierarchical Functioning of River Macrosystems in Temperate Steppes - From Continental to Hydrogeomorphic Patch Scales” awarded to J. Thorp (PI), A. Maasri and J. Gelhaus (co-PIs, among others).