Water mites (Acari, Hydrachnidia) in three forest and landscape reserves in Roztocze

The materials of water mites collected in 1973–1974 in aquatic environments of three nature reserves in Roztocze were characterized. The collections comprised 995 Hydrachnidia belonging to 49 species. Twenty-eight species were collected in the Nad Tanwią Reserve, 30 species – in the Czartowe Pole Reserve, and 24 species – in the Szum Reserve. The analyzed reserves cover short river sections, therefore, the evaluated fauna can be regarded as relatively rich. The fauna of the examined reserves included widely distributed species as well as species typical of montane and submontane areas. In the analyzed reserves, the water mite fauna was dominated by rheobionts and rheophiles, and it was characteristic of upland rivers in the Lublin Region. One species new to Poland was identiied: Atractides albaruthenicus Cich. et Bies. A comparison of the water mite fauna from the Nad Tanwią Reserve with the materials collected in 2001–2002 points to a signiicant reduction in the number of water mite species and considerable changes in the structure of synecological


INTRODUCTION
Water mites (Hydrachnidia) in the aquatic ecosystems of Roztocze and the Sandomierz Lowland (south-eastern Poland) were studied in [1973][1974].The majority of biological specimens from those regions have been described in published studies (4,5,6,11,12,13,14,17).Rich as well as ecologically and regionally diversiied fauna of water mites was found.In springs 40 species were caught (11 new for the fauna of Poland), 85 species in streams and rivers (one news for the science -Mideopsis roztoczensis Bies.et Kow., 12 rare species for Poland), 57 species in standing waters (7 rare species).Characteristic in water mite fauna of the studies area is the signiicant contribution of mountain species, especially Carpathian ones in streams and rivers as well as postglacial relicts in springs and astatic waters.This paper analyzes the remaining collections of water mites collected in the rivers and streams of three forest and landscape reserves in Roztocze: Nad Tanwią (Tanew River), Czartowe Pole (Sopot River) and Szum (Szum River).
The objective of this study was to analyze the species composition, quantitative structure and environmental diversity of synecological groups of water mites in the rivers and streams of reserves characterized by unique scenic and natural values.

AREA OF INVESTIGATION
The three investigated reserves of Roztocze -Nad Tanwią near the village of Rebizanty (area of 41.3 ha), Czartowe Pole near Hamernia (63.7 ha), and Szum near Górecko Kościelne (17.0 ha) -are situated in deep valleys of rivers Tanew, Sopot and Szum, outside the Roztocze National Park (Fig. 1).The analyzed reserves are located in the southern boundary zone of Roztocze in water gap areas where rivers and streams resemble mountain springs.River beds feature a series of rocksteps of limestone and sandstone, and stone heaps that create small waterfalls, referred to as rapids.In the Sandomierz Basin, outside the boundary zone of Roztocze, the analyzed rivers resemble lowland watercourses with a moderate or slow current and a sandy bottom.Sopot and Szum are left tributaries of the Tanew River.In the evaluated reserves, deep river valleys are overgrown by alder carr, steep valley slopes are covered by irs, spruces, pines as well as various shrubs and herbaceous plants, including many rare and protected species (9).

MATERIALS AND METHODS
Water mites were collected with a sweep net in four habitats: lotic (fast-lowing) streams, lentic (slow-lowing) streams, river habitats and springs.Water mites colonizing springs had been described in an earlier study (5), and those indings were used in this study as a source of information about the species composition and abundance of water mites in nature reserves.Biological samples were collected three times in each season (spring, summer, fall of 1974).11 sites were selected for the studies: 4 in each of the nature reserves Nad Tanwią and Czartowe Pole as well as 3 in the Szum nature reserve.995 water individuals belonging to 49 species were collected.The number of species in the evaluated environments was evaluated in a quantitative analysis.The structure of synecological groups in reserves and habitats, and the dominance of water mites were analyzed.Three dominance classes were identiied: eudominant species (D 1 ) -dominance > 10%, dominant species (D 2 ) -4.0-10%, and recedent species (D 3 ) < 4.0%.
The identiied species were classiied into synecological groups (3).It should be noted that the ecological characteristics of selected species could be regionally determined.

RESULTS AND DISCUSSION
Water bodies are classiied into lowland, upland and mountain categories based on numerous factors, including geographical location, climate, geological structure, slope, type of substrate, water low rate, water chemistry, fertility levels and purity.Those factors signiicantly inluence the occurrence and diversity of aquatic environments and their fauna, including water mites.
The waters (springs, rivers) of the three evaluated nature reserves were inhabited by 49 water mite species.Twenty-eight species were identiied in the Nad Tanwią Reserve, 30 -in the Czartowe Pole Reserve, and 24 -in the Szum Reserve (Table 1).The number of species found in relatively short river sections were similar to those noted in other upland rivers of the Lublin Region: 37 species in Szum, 30 species in Krupiec ( 14), and 28 species in Bystrzyca Lubelska (10).A long-term study of rivers in the Lublin Region (tributaries of rivers Wieprz and Tanew) revealed 97 water mite species (11).The 49 species identiied in the evaluated reserves account for approximately 50% of the total species richness of Hydrachnidia fauna in the Lublin Region, which testiies to their high ecological value.
The following number of water mite species were identiied in the analyzed aquatic habitats in nature reserves: 10-18 in lotic habitatas, 8-10 in lentic habitats, 9 and 17 in river habitats (Table 1).Crenophiles were reported in springs and, very rarely, in stream environments: 4 species in the Nad Tanwią Reserve, 11 species in the Czartowe Pole Reserve, and 11 species in the Szum Reserve.
A total of 17 species of crenophiles, 15 species of rheophiles, 13 species of rheobionts and only 4 species of stagnophiles were identiied in the waters of the analyzed nature reserves.Low diversity and low abundance of stagnophilic species testify to the high speciicity of the evaluated water mite fauna.The following families were most abundant: Hygrobatidae -723 individuals (72.8% of total abundance, 7 species), Sperchontidae -149 individuals (15.0%, 9 species) and Lebertidae -78 individuals (7.8%, 13 species).This structure of water mite families is characteristic of lowing water bodies (1,3,11,14).
A comparison of water mite fauna harvested in the Nad Tanwią Reserve in 1974 and in 2001-2002 (16) reveals several similarities as well as differences.Faunal richness was signiicantly reduced from 28 to 17 species.Considerable changes were also noted in the ecological structure of the water mite fauna.In 1974, the abundance of rheophiles was very high (64.5%),and Hygrobates setosus was the dominant species (49.6%) in lentic habitats and in the river environment.The proportion of rheobionts was much smaller (32.9%, 12 species), excluding in lotic streams (66.0%, 8 species) (Fig. 2a).In 2001-2002, there was a clear dominance of rheobionts (74.4%, 10 species), in particular in lotic streams and on rapids (16).Rheophiles (32 individuals, 4 species) and crenophiles (45 individuals, 3 species) were least abundant.
In both collections, the same 3 species emerged as dominants: Hygrobates calliger, Atractides nodipalpis and Sperchon setiger.The species that had been represented by single individuals in 1974 (Lebertia pusilla, L. glabra and Atractides tener) were highly abundant in 2001-2002.Aturus scaber was not collected in the reserve in 1974, but it was highly common in lotic streams in 2001-2002.
The changes observed in the water mite fauna of the Nad Tanwią Reserve in the course of nearly 30 years are not easy to interpret.A decrease in faunal diversity was noted, mostly with regard to rheophilic species and crenophiles that show a preference for lentic habitats and springs.The above observations could point to changes in habitat conditions.However, the presence of relatively abundant water mite fauna, dominated by rheobionts, in lentic habitats in 2001-2002 seems to disprove this theory.The high stability of rheobiontic fauna in all analyzed habitats testiies to favorable conditions in the Tanew River in the reserve.The observed changes in the abundance of rheobiontic species could result from periodic luctuations whose causes remain unknown.
Lotic streams were inhabited by Atractides albaruthenicus, a species that has not been reported from Poland to date.The species, recently described from Belarus, from the Svisloč River (left tributary of the Nemen River) (8), colonizes fast-lowing streams.In Roztocze, Atractides albaruthenicus is relatively abundant in the Tanew River in the area of Księżpol and Osuchy (unpublished data).

SzuM RESERVE
The smallest of the analyzed reserves (17 ha) is characterized by a muddy and water-logged river valley, more than ten springs, an absence of a river environment and very poorly developed lentic habitats.The above factors could have contributed to a decline in rheobiont populations and a clear increase in the abundance of crenophiles and rheophilic species (Fig. 2c).
In the analyzed nature reserves, the water mite fauna of river sections was rich, diverse and characteristic of upland and submontane rivers.Regional speciicity was manifested by unique species composition, dominance of rheophiles and rheobionts, and the abundance of crenophiles in the Czartowe Pole and Szum Reserves.
In lotic streams, rapids overgrown with moss were colonized by many rheobiontic species, but fewer rheophiles and crenophiles, which points to a low degree The species composition and quantitative structure of water mite communities in the analyzed reserve environments are similar to those noted in upland rivers of Roztocze, the Lublin Upland (10,11,14,17) and the Pasłęka River in the Masurian Lakeland (7).
The species diversity of water mite communities determined with the use of the Shannon-Wiener index (H') was highest in the Czartowe Pole Reserve (2.64), somewhat lower in the Szum Reserve (2.52) and lowest in the Nad Tanwią Reserve (1.98).The low value of H in the latter location could be attributed to the superdominance of the rheophilic species of Hygrobates setosus (49.6%) which was highly abundant in lentic habitats and in the river environment.
Water mites are highly sensitive to stressors affecting aquatic environments, in particular water pollution (3,10,11,12).In lowing waters, rheobionts are indicator species for habitat quality.In 1973-1974, studies aiming to determine the degree of naturalness and the physicochemical parameters of water in selected springs and rivers of Roztocze revealed environmental diversity and high water quality (15).The water mite fauna in the evaluated nature reserves was characterized by signiicant richness and different ecological requirements.

3 .
river habitats -river section in the upper part of the reserve with moderate low rates, depth of 0.4-0,7 m. sandy bottom, local clusters of submerged macrophytes (luvial environments were not identiied in the Szum Reserve); 4. valley springs, slope-food springs and slope-side springs: rheocrenes (sandy or gravel bottom) and helocrenes (muddy and sandy bottom).