Freshwater Fauna of Invertebrates of the Northern Slopes of the Central Caucasus

. Data on the degree of knowledge on different groups of aquatic invertebrates on northern slopes of the Central Caucasus are given. It is shown that the best known groups are mayflies, stoneflies, odonates and caddisflies. Other groups have been studied to a much smaller degree. The estimated number of species in the study area is several hundreds. Secondary aquatic insect groups, such as those of the order Diptera, are the most speciose. Data on the degree of study of various groups of aquatic invertebrates on the northern slopes of the Central Caucasus are presented. It is shown that the most studied groups are mayflies, stoneflies, dragonflies and caddisflies. Other groups have been studied to a much lesser extent. The estimated number of species in the study area is several hundred. Minor groups of aquatic insects, such as the order Diptera, are more diverse.


Introduction
The Caucasus region is of special interest for the study of rheophilous hydrobiont communities. Studies performed in the Terek River basin (Central Caucasus), originally of applied nature, assessing the natural food supply of fishes in small agricultural waterbodies (Selegenenko, 1976), are now oriented also towards studying and conserving the biodiversity of aquatic ecosystems of the region. Several groups of hydrobionts have been revised to date, in particular the orders Trichoptera, Ephemeroptera, Plecoptera, Odonata, Heteroptera, Coleoptera and others [1 -4] Four species of sponges and bryozoans, mostly confined to spring-fed brooks or oxbows, have been recorded in the region: Hyalinella minuta Toriumi, Spongia lacustris (L.), Eunapis flagilis (Leidy) (syn. Spongia flagilis Leidy) and Plumatella repens (L.).
Cnidarians are represented in the Caucasus by a small number of species [3]. The presence of only two cnidarian species in the region is reliably known: Hydra vulgaris Pall. and the freshwater jellyfish Craspedacusta sowerbii Lankester. The hydra is sometimes recorded in hydrobiological samples taken from macrophytes in lakes and ponds of the flatland part of the republic (Prokhladnensky and Maysky districts). We believe that it is common in standing waterbodies of the flatland part. The freshwater jellyfish was twice recorded in Mayskiye quarry lakes of Kabardino-Balkaria [4].
Only one turbellarian species has been found so far in waterbodies of the region: Dugesia gonocephala (Duges). In some places (near sources of brooks) their abundance is considerable, up to 1500 ind./m2.
The horsehair worm Gordius aquaticus Duj., a parasite of amphibiont insect larvae, is known to live in natural waterbodies of the region. It is rather often recorded in aquatic communities of rivers and brooks of the foothill zone (for instance, in Kabardino-Balkaria, environs of the Belaya Rechka and Germenchik villages). The latest records of these worms are from the Urvan River (2002), system of spring-fed brooks in foothills (2000)(2001)(2002)(2003)(2004)(2005), Nalchik River (2006) and Kauridon River (Gornaya Saniba village, 2012). The main hosts of this parasite are the larvae of Tipulidae, Limoniidae, and other large dipterans. The horsehair worm has also been found in caddisfly larvae of the genus Hydropsyche.

Research Methodology
This study is based on materials of various hydrobiont groups collected in the Central Caucasus from the 1970s-1980s to the present time. The material was collected and processed according to standard hydrobiological methods (Rukovodstvo…, 1992). Quantitative samples of benthos were collected with a Sadovsky benthometre (Sadovsky, 1948) with a bottom coverage area of 0.05 m². This benthometre is convenient for using in shallow rapid watercourses [12].

Results and Discussions
Several parasitic nematodes (including representatives of the genus Mermis) have been recorded as living in nonbiting midge larvae of the genera Chironomus (Terek River) and Orthocladius (upper reaches of glacier rivers) and in mayflies of the genus Baetis (Urvan River).
Parasites of fishes are the best studied roundworms in the region. Cystidicola farionis (Fischer) from the swimbladder of the trouts Salmo trutta fario and Salmo gairdneri, which live in foothill spring-fed brooks of Kabardino-Balkaria, and Raphidascaris acus (Bloch), collected in October 2003 in the body cavity and intestine of the Prussian carp from Lake Shakhdurey, are rather common or abundant among parasitic roundworms. Five species of acanthocephalans have also been found in fishes.
Tadpole shrimps (Apus cancriformis Schaff.) are represented by one female stored in the collection fund of the Museum of Living Nature, Kabardino-Balkar State University. This female was collected in a long standing pool within the town limits of Prokhladny. Judging by the available information, the appearance of the tadpole shrimp in this waterbody is a result of artificial release.
Of the 13 copepod species recorded, eight are parasites of fish and some other aquatic animals: amphibians (frogs and news) and reptiles (turtles).
All crawfish that live in Kabardino-Balkaria belong to the same species, Caspiastacus pachypus (Rathke). This species lives in estuaries of rivers that flow into the Black and Azov seas and the Caspian (Tsalolikhin, 1995) [20][21]. Our records are mainly confined to oxbows and ponds of the flatland part of Kabardino-Balkaria.
Taxonomic analysis of collections and processing of published data have revealed the presence of at least six species of six genera and two suborders: Arthropleona and Symphypleona. Only Podura aquatic (L.) has been recorded earlier in the Central Caucasus; Isotoma viridis Bourlet., Isotomurus palustris (Müller), and Deuterosminthurus novemlineatus (Tullberg) were recorded as possible in the North Caucasus. Proisotoma ripicola (Linnaniemi) and Sminthurides aquaticus (Bourlet) were altogether absent from the checklist of the Collembola of the North Caucasus [15][16].
The species list of adult odonates of the North Caucasus, including Kabardino-Balkaria and Stavropol krai, comprises 51 species [17][18]. The larval stages are known in Kabardino-Balkaria only in 12 such species [10].
The stoneflies and mayflies of the Northern slopes of the Central Caucasus have been well studied; the number of species reaches 48 [14].
The order Megaloptera is probably represented by several species. However, only Sialis lutaria L. is known with certainty. It has been found in quarry lakes of the Kabardino-Balkaria flatland (environs of Maysky city and Priblizhnyaya village). It is a common species. Adults fly from late May to June.
Analysis of materials on aquatic heteropterans from waterbodies of Kabardino-Balkaria and North Ossetia have revealed the presence of 32 species; one of them, Anisops sardeus sardeus Herrich-Schaeffer, is recorded for the first time in Russia. However, this group remains insufficiently studied [15][16].