Abstract

The present publication provides a review of the soil mite (Acari; Oribatida) community’s structure and the connection between changes in environmental factors and oribatid mite diversity in the limestone quarry of Saskhori and its adjacent areas. Overall, 52 species were recorded during the study. The most abundant oribatid mite species were Steganacarus carinatus, Aleurodamaeus setosus, Xenillus tegeocranus, Ceratoppia bipilis, Oribatula tibialis, and Punctoribates punctum. Interestingly, 23 species of oribatid mites were recorded for the first time from the limestone quarry of Saskhori, and one species (Liacarus oribatelloides) was a new record for the Caucasus fauna. The following indices were analyzed: abundance (N), species diversity (S), Shannon’s diversity index (H), and Pielou’s evenness index (J’). Regarding the obtained results, the highest density of oribatid mites was recorded in the habitat with Shibliak shrubbery (332 inds/m2), while the forest habitat was characterized with the highest value for Shannon’s diversity index (2,64). In the publication, we also provide a detailed morphological description of the newly recorded species L. oribatelloides, with the respective illustration, as no figures are given in its original description.

Caucasus, Kartly Region, Liacaridae, Liacarus oribatelloides

Soil is an important reservoir of biodiversity and plays an essential role in the ecosystem (Menta 2012). Species diversity is a key component of ecosystem functioning; the variety of living organisms influences ecological processes, and different environmental factors determine the composition of soil-dwelling invertebrates (Loreau et al. 2003).

Species diversity and ecosystem stability have a special relationship with each other. Biodiversity acts as insurance for ecosystem functioning against temporal environmental changes; the functional compensations provide enhanced and more productive ecosystem properties (Loreau et al. 2003; Schmidt 2005).

Anthropogenic degradation of soil habitats leads to dramatic changes in the biotic structure of ecological communities because of either the loss of native taxa or the introduction of new species (Hooper et al. 2005). These changes could be strong enough to exceed the resilience capacity of the ecosystems, resulting in the collapse of their functions (Downing et al. 2012; Oliver et al. 2015).

The faunal diversity of soil microarthropods is an important feature of soil ecosystems and can be used to evaluate ecosystem quality and health (Moghimian et al. 2013). Thus, it can act as a warning system for ecosystem conditions (Muscolo et al. 2015). Among the soil microarthropods, oribatid mites (Acari, Oribatida) are one of the most dominant animal groups; the densities of the individuals can reach several hundred thousand per square meter (Norton and Behan Pelletier 2009). Oribatid mites are strongly responsive to external influences in their habitats, and hence it is possible to monitor changes in soil processes (Nielsen et al. 2010).

In 2018, oribatid mite communities were investigated on the territory of the limestone quarry in the surroundings of Saskhori village (Georgia) before quarry mining activities started (Murvanidze et al. 2018). The authors have investigated soil mites in different habitats of the limestone quarry of Saskhori and recorded 51 species of oribatid mites (Murvanidze et al. 2018). After four years of the above-mentioned study, we also investigated the oribatid mite community in the same area to observe the possible changes due to extensive anthropogenic disturbance. In particular, we aimed to investigate: (i) the oribatid mite species composition of the main habitat types of the limestone quarry at Saskhori village and the surrounding areas; (ii) the interaction between the oribatid mite species diversity and habitat change and thus compare new results to the published ones (Murvanidze et al. 2018); and (iii) the quantitative and qualitative parameters of oribatid communities inhabiting the study area.

In total, 983 specimens of 52 species of oribated mites belonging to 41 genera and 28 families were collected and identified; among them, 23 species were registered for the first time in the Saskhori limestone quarry (Table 2). The site Sa2 was the most diverse with mites (27 species); the second highest number of species were registered in Sa1, Sa4, and Sa7, with 22 species in each site. In terms of individual density, the most abundant species were Xenillus tegeocranus (Hermann, 1804) (120 specimens collected from six sites), followed by Aleurodamaeus setosus (106 specimens collected from six sites), Punctoribates punctum (85 specimens collected from six sites), and Ceratoppia bipilis (66 specimens collected from six sites). Thus, all four species were common in six sites out of seven, while seventeen species occurred in only one location (Table 2).

Among the studied habitats, Shibliak, or Mediterranean-type deciduous drought-resistant shrubbery (EUNIS habitat code F5.3), was the richest, represented by 37 mite species. Xenillus tegeocranus, Zetorchestes micronychus, and Oribatula tibialis were the most abundant of oribatid mites in this type of habitat (Table 2). Xero-thermophilous oak forest and mixed vegetation of the oak-hornbeam woodland (EUNIS habitat code: G 1. A) were also quite rich with 32 oribatid mite species, dominated by typical forest and ubiquitous species such as Steganacarus carinatus, Ceratoppia bipilis, Punctoribates punctum, and Scheloribates laevigatus. Rural and urban vegetation (EUNIS habitat code: I 1.3) was the poorest in mite species diversity; fauna was represented by 10 species, with the highest abundance for Lasiobelba pori Vasiliu, 1995, and Oribatula (Zygoribatula) cognata (Oudemans, 1902). Results show that agricultural land without vegetation was the worst for the development of oribatid mite communities (Table 2). According to the individual density, the highest number (191 specimens) was recorded in the Shibliak or Mediterranean-type deciduous drought-resistant shrubbery site (Sa2), which was followed by oak forests (Sa4 and Sa7) and meadows with rural and invasive plants (Sa1) (Table 3).

The highest diversity (Shannon’s diversity, H) was revealed for Sa2 (H = 2.72), and the lowest value was in Sa6 (rural and urban habitat) (H = 1.9). Regarding Pielou’s evenness index, the highest value belonged to Sa5 (0.87), while the lowest belonged to Sa1 (0.77) (Table 3).

The extrapolation curve was modeled for 21 survey samples from 7 sites. The asymptotic pattern indicates that more sampling should increase the number of detected species (Fig. 2) to a maximum expected number of species equal to 67 (88 species as an upper confidence limit).

The cluster analysis, based on the Sorensen index (Sø), grouped oribatid mite communities from Sa1 and Sa2 sites as well as Sa3 and Sa4 sites together (Fig. 3). The comparison of the mite communities at each site showed the greatest similarity between Shibliak shrubbery and steppe habitats. Cluster analyses confirmed that the oribatid mite community found in arable land (Sa6) is most distinct from the communities of natural and semi-natural habitats (Fig. 3).

Figure 2. 

Rarefaction/extrapolation curves as a function of the number of survey sites from the Saskhori limestone quarry. The dotted part of the curve indicates the expected species diversity, along with an increasing sample size. The confidence intervals of the curve, after 100 butstrap replicates, are indicated by the shaded area along the curve.

Figure 3. 

Cluster analysis of community similarity based on Sorensen index (Sø) among the six study locations: 1-Sa1, 2-Sa2, 3-Sa3, 4-Sa4, 5-Sa5 and 6-Sa6.

Redescription of new recorded species

Liacarus (L.) oribatelloides Winkler, 1956

Fig. 4A

Diagnosis

Large-sized species (1084–1198 × 657–728). Rostrum truncate, with two incisions and small projections laterally, lamellar cusps well developed, distally concaved with strong inner and outer teeth. Translamella with medial tooth; rostral, lamellar and interlamellar setae strong, setiform and slightly barbed. Bothridial setae spindle-form, apex noticeably longer than head, slightly barbed. Notogastral setae are short, thin, and smooth. Epimeral and anogenital setae are setiform and thin. Leg IV trochanters and femora with teeth from the lateral view.

Measurements

Body length: 1084–1198 (four individuals); body width: 657–728 (four paratypes).

Integument

Body color brown to dark brown. Notogaster and anogenital surfaces are punctuated with small foveolae. External margin of lamellae, tutoria with striations. Lateral parts of the body granulate with small foveolae.

Prodorsum

The rostrum is truncate dorso-anteriorly, with two incisions and small lateral teeth. Lamellae longer than half of prodorsum with well-developed translamella and tooth medially. Lamellar cusps are well developed, broad, and extend nearly to the end of the rostrum; the inner cusps are longer (33–36) than the outer ones (15–18). Rostral (68–71), lamellar (94–123), and interlamellar (193–205) setae are setiform and slightly barbed. Sensilli (128–132) spindle-form slightly barbed; the apical part is longer (57–68) than the length of the head (34–41). Notogaster slightly narrows anteriorly and posteriorly, with very small humeral projections. Notogaster with eleven pairs of minutes, glabrous setae (15-18) except seta p1, which is longer (34-38), and easily separated from the other ones. Ventral side. Epimeres I–III well separated with parallel lines, laterally integument granulated; epimeral formula 3:1:3:3. Epimeral setae setiform, slightly barbed, 1a, 2a and 3a short, 1b, and 3b longer than other setae.

Anogenital region

Six pairs of genitals, one pair of aggenital, two pairs of anal and three pairs of adanal setae setiform. Genital plate wider than long (87–91 and 57–63, respectively). Anal plate nearly as long as wide (132–136 and 119–125, respectively). Length of anal setae 22–27.

Legs. Legs three-clawed. Formulae of leg setation and solenidia: I (1–5–3–4–20) [1–2–2], II (1–4–2–4–16) [1–1–2], III (2–3–1–3–15) [1–1–0], IV (1–2–2–3–12) [0–1–0]; All setae setiform, slightly barbed on the dorsal sides of the legs. Leg IV trochanter and femora have a long, slender appendage from the lateral view.

Differential diagnosis

According to the morphological diagnostic features of the available specimens of Liacarus oribatelloides collected from the limestone quarry of Saskhori and L. coracinus collected from Machakhela National Park (Gratiashvili et al. 2022), the various characteristics are different between these closely related species.

Compared to L. coracinus, which has a more oval-shaped body and a yellow-brown color, L. oribatelloides has an elongated body with a dark-brown or black color.

The species is distinguished most readily by the lamellar cuspids. L. oribatelloides has strongly elongated tips of the lamellar cuspids on both the inner and outer sides (Fig. 4A), whereas L. coracinus has strong inner and indistinct outer teeth of the lamellar cusps. The distance between the outer teeth of the lamellar cusps is also noticeably different between the species; they are wider for L. oribatelloides than for L. coracinus, and represent 36–38 and 25, respectively.

Liacarus oribatelloides and L. coracinus also differ from each other by the length of leg IV, which is 225 and 165, respectively. In addition, the femur of leg IV of L. oribatelloides has clearly distinguishable inner teeth (Fig. 5). In having the combination of a shape of lamellae with well-developed lamellar cusps, a shape of sensilli, and the presence of an inner tooth in the femur of leg IV, L. oribatelloides differs from L. coracinus.

Remarks

The taxonomic status of Liacarus oribatelloides is unclear. Weigmann (2006) registered L. oribatelloides in southern Germany and gave the differential diagnosis with the drawings for L. coracinus and L. oribatelloides.

During a long period of time, Liacarus oribatelloides was registered as a valid species, but in the latest world catalog of oribatid mites (Subías 2023) and some other publications (Schatz 2018), the species is synonymized with L. coracinus. According to the literature data, L. oribatelloides is distributed in the Czech Republic, Southern Germany, Austria, Italy, Slovakia, Poland, the Central Alps, and the Tatra Mountains (Fischer & Schatz 2013; Schatz 2016; Miko 2016; Wierzbicka et al. 2020; Miko 2021; Jászayová et al. 2023). Before our finding, the species distribution was known only from Central Europe, and the species had never been found in the Caucasus region.

The taxonomy of Liacarus oribatelloides and similar taxa needs to be studied further. In particular, using the molecular genetic framework is necessary in order to better understand species status and delineate interspecific boundaries.

Figure 4. 

A: Lamellae with inner and outer cusps of Liacarus oribatelloides Winkler, 1956; B: Lamellae with inner and outer cusps of Liacarus (L) brevilamellatus Mihelčič, 1955.

Figure 5. 

Liacarus oribatelloides Winkler, 1956. Femur of leg IV with inner tooth

Oribatid mite community structure in the limestone quarry of Saskhori was studied from the habitats that will be subject to the mining processes and the neighboring semi-natural and natural areas. The oribatid mite fauna studied shows high proportions of rare species. According to the results of the previous study by Murvanidze et al. (2018), 51 species were recorded, with 22 singleton and 18 doubleton taxa. In the current study, we recorded 52 species, of which 19 were singletons and 11 were doubletons.

Perhaps more interesting is that only 39% of taxa (29 species) were common between Murvanidze et al. (2018) and the current study. Such a great difference in oribatid mite composition is most probably a result of incomplete sampling in the past and current research rather than due to faunal turnover in a short time period. Indeed, the rarefaction curve shows that the maximum expected species number is around 75, which nicely matches the total number of taxa found in both studies. However, changes in species composition, especially species relative density, are also apparent. For instance, Steganacarus carinatus, Camisia horrida, C. lapponica, Hermanniella punctulata, Arthrodamaeus femoratus, Eupelops acromios, and Punctoribates punctum were collected in only one location by Murvanidze et al. (2018), while in the current study, each of these species was found in more than one sampling site. Further, Murvanidze et al. (2018) noted that two oribatid species, Xenillus tegeocranus and Scheloribates laevigatus, were most common and recorded in all four types of habitats. In the current study, two additional species, Aleurodamaeus setosus and P. punctum, were the most common with wide distribution in the limestone quarry of Saskhori. According to Murvanidze et al. (2018), P. punctum, Tectocepheus velatus, and S. laevigatus were the most abundant in degraded habitats; however, our data showed unexpected findings of high numbers of Lasiobelba pori in rural habitats, which is hard to explain with the current level of knowledge.

Overall, oribatid mite density and diversity were much lower in the heavily grazed sites where the soil structure was destroyed, while in sites with more or less natural vegetation, the mite diversity was higher. Based on the comparison of the results of the current study with literature data, it is evident that community change has taken place, which most probably is because of the ongoing limestone mining process. However, the extent and design of our study do not allow for further prediction of possible faunal changes; rather, they provide baseline information for future monitoring purposes.

We thank the reviewers for their valuable comments. We would also like to thank editor Levan Mumladze for his suggestions and polishing of the text. The authors would like to thank Heidelberg Cement Caucasus for financing the investigation.