In 2013–2014 Collembola were studied in the riparian habitats of the Prut River upper catchment area, where fluvisols (FAO soil-type classification system) predominate with a clayey and silty clay structure and organic carbon content of 3.7–5.4%. The study included two localities with a distance of about 8 km between them (Fig. 1):

Figure 1. 

Location of the riparian habitats (colour: light green - upper catchment area of the Prut River, dark green - part of the Dniester (Nistru) River catchment area; the border between Romania and Moldova is represented by the Prut River).

(1) Branişte village (47°49'1"N, 27°13'2"E; Fig. 2) - bank of the Prut River near the water; the level in July 2013 and June 2014 was high, sporadically flooding the bank covered by grassy vegetation. Further information on the water level of the river and temporal floods are provided by the State Hydrometeorological Service (http://www.meteo.md/mold).

Figure 2. 

Bank of the Prut River near Branişte.

The habitats selected on the distance gradient from the river were the following:

i) BB – 2–3 m wide, partially flooded river bank covered abundantly with herbaceous vegetation;

ii) BF – a 25–30 m wide protection forest belt plantation consisting mostly of Quercus robur mixed with Populus alba, P. nigra, Salix alba, S. triandra and S. purpurea, with moss and wooden debris; litter and humus layer ca. 3 cm thick;

iii) BM – a 45-meter wide belt of meadows along the banks with embankments for flood protection that separate the river from the meadows and nearby lake.

(2) Lake Costeşti–Stânca (47°55'1"N 27°08'3"E; Fig. 3), a water reservoir 70 km long and 59 km² in area, situated on the Prut River between Romania (Stânca village) and the Republic of Moldova (Costeşti village). The lake shore consists of a dam built in 2007 with limestone rocks poured into the water about 5 m off the bank to protect the shoreline. The habitats on the distance gradient from the lake were the following:

Figure 3. 

Shore of the Lake Costeşti-Stânca.

iv) CSB – a 1–2 m wide bank of the lake partially covered by hygrophilous grassy vegetation, in some places covered by algae and decaying residues of Phragmites australis (Cav.), partially inundated in June 2014;

v) CSP – a narrow belt of pasture about 20–25 m distance from the bank, covered with herbaceous plants (Urtica dioica L., Artemisia sp., Plantago sp., etc.) and with occasional small shrubs (Rosa canina L.), on a steep bank > 3 m above the water level.

vi) CSUB – a belt of shrub-land about 20–35 m distance from the shore formed by groups of individual shrubs, covered with small shrubs (Rosa canina L., Lycium barbarum L.) with 1.80 m high thickets of Onopordum acanthium L. behind the pasture; litter and humus layer ca. 1.5 cm thick.

Previously, the study area was part of a buffer zone of the former USSR state border, which was fenced off and strictly limited to visitors. The riverine zone of the Prut River thus remained virtually untouched by humans after 1945; in 2010 the wire fence was removed.

The overall number of soil samples taken at Branişte and Costeşti was 25 and 27, respectively. The samples consisted of soil cores of size 5 × 5 × 5 cm taken by the first author in July and November 2013, and in June and July 2014; the sampling design is specified in Table 1. Some epiedaphic collembolan specimens were collected in the Branişte meadow and Costeşti shrub-land using an exhauster to catch epigeic species that are underestimated by the soil sampling.

The collembolans were extracted from the soil using the flotation method according to Buşmachiu et al. (2015). The specimens were fixed in 96% ethyl alcohol, sorted in a binocular stereomicroscope, cleared in lactic acid and KOH and mounted on permanent slides using Marc André II solution. The specimens were identified to the species level using a LEICA 2500 phase contrast microscope and the following principally taxonomical sources: Bretfeld (1999), Potapov (2001), Thibaud et al. (2004), Fjellberg (1998, 2007), Dunger and Schlitt (2011) and Jordana (2012). Geographic distribution and ecological data of the species were excerpted from the same literature. Collembola life forms were analyzed according to Gisin (1943) and Rusek (2007); the habitat preferences of species are provided in Table 2.

For the basic comparison of Collembola community structure between sites and habitats, data from the summer (June and July) of both years were used. Box-plots for number of specimens and species richness were depicted using STATISTICA for Windows version 12.0 (StatSoft, Inc. 2013). Non-metric multidimensional scaling (NMS) ordination processed average quantitative data to examine the community structure between 29 plots differentiated by locality (12 from B - Branişte and 17 from CS - Costeşti-Stânca) and habitat. The ordination covered 16 species in total; species with dominance < 1% were excluded from the analysis due to an unclear relationship with the studied habitats. The epiedaphic collembolan specimens collected by the exhauster in meadow and shrubland were also excluded from the analysis. Autopilot, with slow and thorough mode, and Sørensen (Bray-Curtis) distance, recommended for community data, were selected. After 250 randomized runs, a two-dimensional solution was accepted as optimal. PC-ORD software (McCune and Mefford 2011) was used for the NMS analysis.

Altogether, 2963 individuals of Collembola belonging to 77 species were found in the habitats along the Prut River (Table 2): 1916 individuals were collected in the riverine habitats of Costești and 1047 individuals in that of Branişte. In spite of the difference between the numbers of individuals, the number of species was similar, i.e. 52 in Costeşti and 54 in Branişte. Although the sites are rather close to one another, being located on the same bank of the river, only 28 collembolan species were common to both.

According to the life forms, 26 collembolan species were epiedaphic, 22 hemiedaphic and 25 euedaphic. The largest portions were woodland (26) and grassland (25) species, followed by eurytopic species (10) and species preferring interstitial habitats (4). Moreover, the riparian communities of the Prut River area included seven hygrophilous and one hydrophilous (Podura aquatica) species, representing 10.3% of the total species number.

The majority of species have a wide geographic occurrence, namely European (29.5%), cosmopolitan (25.9%) and Palaearctic or Holarctic species (16.9%); two species have a Mediterranean distribution range and two species have a range limited to Moldova (Neanura moldavica, Arrhopalites prutensis).

Nine species, namely Ceratophysella stercoraria, Mesaphorura rudolfi, M. simoni, Isotomurus antennalis, Orchesella villosa, Lepidocyrtus arrabonicus, Oncopodura crassicornis, Stenacidia violacea and Sminthurus nigromaculatus were new for the fauna of the Republic of Moldova. Two species, Folsomides sp. and Pseudachorutes sp., are potentially new for science.

Collembola in Branişte were more abundant in the forest belt, and in Costeşti higher numbers of them were recorded in pasture and under shrubs. Protaphorura sakatoi, Isotomiella minor and Mesaphorura critica were abundant and frequent in all habitats of both localities, representing hemiedaphic and/or euedaphic life forms. Similarly, Schoettella ununguiculata, Mesaphorura yosii, M. florae, Parisotoma notabilis, Neelus murinus and Sphaeridia pumilis were present in all or most habitats, but in lower number of specimens. Anurida ellipsoides was dominant in Branişte, and together with A. tullbergi, Micranurida pygmaea, Neanura moldavica, N. muscorum, Tomocerus minor, Pogonognathellus flavescens and Podura aquatica occurred exclusively in this locality (Table 2). In contrast, Oncopodura crassicornis, Cyphoderus albinus and C. bidenticulatus were found only in pasture soil in Costeşti. Friesea truncata, Pseudosinella imparipunctata and Isotomodes productus were abundant and frequent in the riparian habitats near the lake.

The low bank of the Prut River covered by forest belt in Braniște was associated with a higher number of hygrophilous species (7) than the pasture and shoreline of the lake (2 species; Table 2); hygrophilous Anurida ellipsoides was abundant on the flooded river bank.

High dominance of a few species was observed in the pasture, specifically Protaphorura sakatoi, Parisotoma notabilis and Pseudosinella imparipunctata, which shared 54.1% of the total community dominance.

A high proportion of epiedaphic collembolans was observed in the meadow near the river, but this was affected by additional collection with an exhauster. These forms were relatively numerous on both banks of the river and lake, consisting mainly of isotomid and entomobryid collembolans. The pasture near the lake showed a very high proportion of hemiedaphic forms, dominated by P. sakatoi, P. notabilis and P. imparipunctata. A lower dominance of euedaphic forms was evident in open habitats, such as meadow and pasture, compared to other habitats.

A box-plot diagram of Collembola number of specimens (Fig. 4a) showed higher median values in the forest belt in Branişte and in all three habitats near the lake, and lower values on the river bank and in the meadow near the river. The pasture and shrub-land near the lake had apparently higher non-outlier ranges of number of specimens compared with the others. A box-plot of species richness (Fig. 4b) documented the high median values in the shrub-land and meadow, while the lowest median was observed on the river bank. The pasture had a high non-outlier range of this community parameter.

Figure 4. 

Box-plot diagram of Collembola specimens’ number (a) and species richness (b) in riparian habitats of the Prut River. For abbreviations see Materials and methods.

An NMS ordination diagram (Fig. 5) outlines the Collembola community composition at localities/habitats during the summer (June and July) of both years. For the analysis, a two-dimensional solution was recommended by Autopilot and confirmed by the Monte Carlo permutation test, with a significant P < 0.005, a mean stress of 23.3 for real data and 250 runs for both real and randomized data. This best two-dimensional solution had a final stress of 17.8, P < 0.00001 after 110 iterations. The diagram shows that habitats along the river (Branişte) were rather dissimilar, with river bank and meadow communities showing a specific composition, where Anurida ellipsoides and Mesaphorura macrochaeta were abundant on the bank and Hemisotoma thermophila in the meadow. In contrast, forest plantation of the same locality was similar to the habitats of Costeşti, especially to the shrub-land with Mesaphorura critica, M. yosii, Deutonura albella and Isotomiella minor as the common species. In general, habitats near Lake Costeşti-Stânca had similar species composition.

Figure 5. 

NMS ordination of Collembola species in riparian habitats of the Prut River from June–July 2013 and 2014, species with dominance ≥ 1% included. Colour circles and triangles represent localities and habitats, for abbreviations see Materials and methods, black dots represent species, for species abbreviations see Table 2. Variance explained by the first two axes was 38% and 34%, respectively.