Terrestrial snails of alkaline fens

Zofia Książkiewicz-Parulska The high constant humidity and basic pH of alkaline fens make them a fa-vourable environment for terrestrial snails. They are inhabited, for instance, by 3 species of protected snails of the genus Vertigo (Vertiginidae family): Desmoulin’s whorl snail Vertigo moulinsiana (Dupuy, 1849) (Fig. 33A), the narrow-mouthed whorl snail Vertigo angustior Jeffreys, 1830 (Fig. 33B), and Geyer’s whorl snail Vertigo geyeri Lindholm, 1925 (Fig. 33C). They have been included in the Habitat Directive Annex II (EEC 1992) and also in the IUCN Red List of Threatened Spe-cies (IUCN 2014). Moreover, Desmoulin’s whorl snail and the narrow-mouthed whorl snail are under strict species protection in Poland (The Act of April 16, 2004 on the Nature Conservation – Dziennik Ustaw of 2004, No 92, item 880).

According to the IUCN Red List, of the above-mentioned three snail species, only Geyer’s whorl snail shows a stable population trend in Europe (Killeen et al. 2011), while a declining number of localities was evidenced for Desmoulin’s whorl snail and the narrow-mouthed whorl snail (Killeen et al. 2012, Moorkens et al. 2012) in Ireland, Germany, France, Belgium and The Netherlands. It is be-lieved that such situation is caused, for instance, by changes in habitat’s hydrology (mostly decreasing of water level), fragmentation, transformation of habitats due to succession and improper active protection (e.g., cessation of extensive land use) or incorrect land use (e.g., intensive grazing) (Killeen et al. 2012, Moorkens

et al. 2012). On the other hand, in some countries (also in Poland) the number of known stands of these species is higher than few years ago. It is, however, a result of better recognition of the species’ distribution rather than an actual increase of the species’ localities.

The small size of the terrestrial snails (their shell does not exceed 3 mm in height) and the type of their habitats (usually wetlands which are difficult to ex-plore by humans) have contributed to insufficient knowledge of the distribution of these snails in Poland. For instance, in 2004 Geyer’s whorl snail was not found in Poland, though it was suspected to occur in the area of Białowieża (Pokryszko 1990). In addition, only 3 localities for Desmoulin’s whorl snail and ca. 30 local-ities for the narrow-mouthed whorl snail have been known (Pokryszko 2004a, b). Poland’s accession to the European Union in 2004 involved a countrywide inventory of natural resources within the Natura 2000 network. The field inven-tory in the areas of State Forests was conducted in 2007, later, the surveys were carried out also on other areas. These studies contributed to the description of new localities of vertiginid snails (e.g., Książkiewicz 2010). Currently, the litera-ture contains description of ca. 30 localities for Geyer’s whorl snail (e.g., Horsák

& Hájek 2005, Schenková et al. 2012, Zając et al. 2012, Książkiewicz et al. 2015, Pokryszko et al. 2016, Gawroński et al. 2016), over 50 localities for Desmoulin’s whorl snail (e.g., Myzyk 2005, Książkiewicz 2010, Lipińska et al. 2012, Sulikows-ka-Drozd 2014, 2015, Książkiewicz et al. 2015, Szlauer-Łukaszewska et al. 2015, Przybylska 2016), and more than 100 localities for the narrow-mouthed whorl snail (e.g., Książkiewicz 2010, Książkiewicz et al. 2012, Książkiewicz et al. 2015, Szlauer-Łukaszewska et al. 2015) in Poland. In recent years, knowledge of the biology and ecology of the whorl snails and their microhabitat requirements has increased (e.g., Kuczyńska & Moorkens 2010, Myzyk 2011, Hettenbergerová et al.

2013, Książkiewicz-Parulska et al. 2018).

Wet alkaline habitats also host other representatives of the Vertigo genus, e.g., the marsh whorl snail Vertigo antivertigo (Fig. 33D) and striated whorl snail Vertigo substriata (Fig. 33E). Both these species can be found on lowland alka-line fens and montane spring fens (e.g., Książkiewicz 2010, Książkiewicz – un-published data). On the other hand, Vertigo pygmaea can be found in habitats characterized by different levels of humidity (from dry to wet) (Pokryszko 1990).

In addition, a whorl snail of the Columella genus, Columella edentula, may also occur in alkaline fens (Książkiewicz 2010).

The above-described whorl snails are sometimes accompanied by Pupil-la pratensis (Fig. 33F), a representative of the Pupilidae family. The shell of this species is barrel-shaped and its height reaches ca. 4.5 mm (von Proschwitz et al. 2009). Not much is known about the occurrence of this species in Poland; it is probably due to incorrect description/recognition of this species – wrongly described as Pupilla muscorum - a similar to P. pratensis and very common in Poland Pupilla species. Currently, six localities for P. pratensis are known in the

country. One of them, in Upper Silesia, was described in 1883 (Goldfuss 1883), but modern data on the occurrence of P. pratensis in this area are lacking. Oth-er localities have been reported in the Lubusz region, Great Poland (Książkiew-icz & Gołdyn 2013) and the Podlaskie Province (Horsák et al. 2012, Książkie- wicz-Parulska et al. 2015). In Norvay von Proschwitz (2010) discribed this spe-cies on wet alkaline habitats.

The other species that occur in alkaline fens is Vallonia enniensis (Fig. 33G).

Its shell is flattened, while the spire is slightly elevated, and the shell width reach-es 2.5 mm (Wiktor 2004). It is thought that V. enniensis is endangered with ex-tinction, although its distribution within its range is poorly recognized (Wiktor 2004). The species has been included in the IUCN Red List of Threatened Species with DD category (data deficient – status difficult to assess due to the lack of data, Mollusk Specialist Group, 1996) and in the Red List of Threatened Animals in Poland (category NT, Wiktor & Riedel 2002). In Poland, it is known from a few localities in the Lubusz region, Greater Poland, Mazovia, Podlasie, Lublin Upland and Lesser Poland (Wiktor 2004, Książkiewicz-Parulska & Pawlak 2016). Two other representatives of the grass snail family (Valloniidae) that can also be found in habitat 7230, are the ribbed grass snail Vallonia costata (O. F. Müller 1774) and smooth grass snail Vallonia pulchella; however the first mentioned species may also be foud in a drier environments (e.g., Wiktor 2004, Welter-Schultes 2012).

Two representatives of the Ellobiidae family may be found in alkaline fens in Polnd: the herald thorn Carychium minimum and dentate thorn Carychium tridentatum. Both species are very common in the country and frequently coexist in the same habitat. Carychium minimum, however, is found more often in wetter microhabitats than C. tridentatum (e.g., Książkiewicz-Parulska & Ablett 2017) Both species have a similar Carychium tridentatumwhitish, tower-shaped shell reaching 2.2 mm in height (Wiktor 2004). These species are often found with the dwarf snail Punctum pygmaeum, a member of the Endodontid family (Endodon-tidae) having a flattened shell with a slightly elevated spire; its shell width reaches 1.6 mm and height 0.8 mm which makes them the smallest terrestrial snails in Poland (Wiktor 2004). This tiny snail is often found on the acid base of beech forests, although larger populations form on alkaline habitats (Welter-Schultes 2012).

Habitat 7230 also hosts other common snail species, e.g., the crystal snail Vitrea crystallina, pellucid glass snail Vitrina pellucida, rayed glass snail Neso-vitrea hammonis, black gloss snail Zonitoides nitidus, glossy pillar snail Cochl-icopa lubrica and brown slug Deroceras laeve. You can also find there species of snails tolerating acidic substrate, e.g. pellucid glass snail Vitrina pellucida or rayed glass snail Nesovitrea hammonis (Welter-Schultes 2012). Also, some less common species may be found in Polish fens, such as the robust pillar snail Coch-licopa nitens or the shiny hive Euconulus alderi as well as the Roman snail Helix pomatia, which is (although common but commercially harvested) under partial protection in Poland.

Characteristics of whorl snails species occurring in Poland, included in the Habitats Directive Annex II

Desmoulin’s whorl snail Vertigo moulinsiana

Desmoulin’s whorl snail (Fig. 33A) is a calcicole species. Its native range is the Atlantic to Mediterranean Sea. (Pokryszko 1990). In Poland, its distribution is limited to the lowland part of the country, included into the continental bioge-ographic region (Lipińska et al. 2012). Desmoulin’s whorl snail occurs mostly in young-glacial landscape and habitats accompanying early stages of lake succes-sion (Książkiewicz & Gołdyn 2015).

High groundwater level seems to be one of the most important factors in-fluencing the distribution of Desmoulin’s whorl snail (Killeen 2003). Represen- tatives of this species are most abundant in the microhabitats where the water level oscillates around the ground surface (Tattersfield & McInnes 2003). For this reason, alkaline fens and sedge meadows are favourable for the occurrence of this species (e.g., Książkiewicz 2010). Localities for this species very often are scattered along river valleys, which seems to be associated with both the availa-bility of convenient habitats (Książkiewicz 2010) and also with the possiavaila-bility of passive dispersion with stream current (Myzyk 2005, Killeen 2003).

Desmoulin’s whorl snail can be relatively easily observed in natural habitats because it shows a tendency to climb plants (even to the height of 2 m; Cameron 2003). Individuals of this species can be observed most abundantly on leaves and stems of monocotyledons in summer and late autumn (Killeen 2003). Adult snails more often than juvenile ones remain on plants also over winter (Książ- kiewicz-Parulska et al. 2018). Desmoulin’s whorl snail can be active till November if the weather conditions are favourable (Myzyk 2011). In localities near Sępolno (The Pomerania Province), Myzyk (2011) recorded the beginning of the breed-ing season in April/May and its end in July/August. The dynamics of this spe-cies population reveals fluctuations. Desmoulin’s whorl snail reaches the highest population densities usually in August – October, depending on the habitat and weather conditions (Książkiewicz-Parulska & Ablett 2016). Duration of embry-onic development depends on the temperature, and can last 10 – 67 days (related with the presence of fully developed shell); these snails reach maturity after 70 – 119 days, while their lifespan is 422 – 508 days (Myzyk 2011).

Narrow-mouthed whorl snail Vertigo angustior

The narrow-mouthed whorl snail (Fig. 33B) has a European range (Pokrysz-ko 1990); it is a calcicole species with climate-dependent changing preferences for humidity (Pokryszko 2004a). In Poland, it has only not been found at higher altitudes in the mountains (Karkonosze Mts., Babia Mt., Tatra Mts., Książkie- wicz et al. 2012). The localities for this whorl snail in Poland are open ones (e.g., Książkiewicz 2010). In the lowlands, it occurs in microhabitats of a moderate humidity, and most often it can be observed in sedge meadows or ridges of al-kaline fens (e.g., Książkiewicz 2010, Książkiewicz et al. 2015). In the mountains, it prefers more humid microenvironments and abundantly colonizes spring fens with valerian-sedge vegetation (e.g., Książkiewicz et al. 2012).

The narrow-mouthed whorl snail lives within the litter layer and rarely climbs up vegetation. It can be found at the sedge leaf base in late autumn where it climbs up to a height of 10 – 15 cm (Cameron 2003). In Poland, this snail begins repro-duction in March and ends it in July/August (Myzyk 2011). It reaches the highest density (even over 1 200 individuals/m²) usually in September or October, de-pending on habitat type and weather conditions (Książkiewicz-Parulska & Ablett 2016). Depending on the temperature, its embryonic development lasts from 11 to 16 days, it reaches sexual maturity (associated with fully developed shell) after 40 – 55 days, and its lifespan is 200 days (Myzyk 2011). The narrow-mouthed whorl snail (both adult and juvenile) spends the winter in microhabitats rich in mosses and litter (Książkiewicz-Parulska et al. 2018).

Geyer’s whorl snail Vertigo geyeri

Geyer’s whorl snail (Fig. 33C) is a Boreal-Alpine species probably endem-ic to Europe (Kerney 1999). This species has been recorded in humid and wet-land habitats, including alkaline fens, calcareous fens with Cladium mariscus, and transition mires (e.g., Cameron et al. 2003; Horsák & Hájek 2005, Książ- kiewicz-Parulska et al. 2015). It is linked with microhabitats with high relative humidity (over 80%) and a high level of groundwater (ca. 0.1 m below ground surface) (Kuczyńska & Moorkens 2010). This snail lives among mosses and at the base of sedges (Cameron et al. 2003). The biology of Geyer’s whorl snail is not known. Until recently, in Poland, it was only known from subfossil posi-tions, later it was thought to occur only in eastern Poland, but recently it was also found in Bukowskie Bagno in the Drawa Forest (Pokryszko et al. 2016) and in the Mechowisko Krąg reserve in Pomerania (Gawroński et al. 2016).

Protection of whorl snails on alkaline fens: practical aspects

The implementation of proper conservation measures is based on an assess-ment of species distribution, monitoring of population condition and habitat sta-tus, among other things. At present, knowledge of the distribution of Desmou-lin’s, narrow-mouthed and Geyer’s whorl snails in Poland is decidedly better than even 15 years ago, though still incomplete. However, countrywide monitoring is limited to some specific areas occupied by these species. Of course, increasing the number of sites surveyed within the monitoring program remains difficult due to financial and personnel constraints. However, since a decline in the number of localities for Desmoulin’s and narrow-mouthed whorl snails has been noted throughout its whole distribution range (due to, for example, improper land use) (Killeen et al. 2012, Moorkens et al. 2012), it is recommended to increase the number of sites where the populations and habitats of these species are surveyed.

Moreover, the currently used monitoring methods comprise (especially in the case of the narrow-mouthed whorl snail) a time-consuming analysis of sam-ples collected during field study. Moreover, the sample collection is connected with the killing of snails (not only those under examination) and interference with the environment, often protected (e.g., Książkiewicz et al. 2012, Lipińska et al. 2012). Recent studies have demonstrated that it is possible to apply decidedly less invasive methodology that is more beneficial for the whorl snails (and other co-occurring species). These new methods are based on counting snails in the field, by which reliable results can be obtained (Książkiewicz-Parulska & Gołdyn 2017). Such a method was tested for Desmoulin’s and narrow-mouthed whorl snails. Therefore, the implementation of such a live and more efficient monitor-ing procedure would be worth considermonitor-ing in the future.

The implementation of measures aiming to actively protect whorl snails is still rare in our country. Usually they involve the realization of well-considered schedules of extensive mowing programs (taking into account, for example, snail species and habitat size). Such actions improve both the condition of the snail population and their habitat (Książkiewicz 2014). At present, such programs are in progress, with a satisfactory outcome at several localities for Desmoulin’s and narrow-mouthed whorl snails in the valleys of the Ilanka River and Pliszka River (Lubuskie voievodship). However, the significance of appropriate mowing plan, its intensity (delineation of correct habitat parts), frequency (i.e. mowing of cho-sen fragment of the habitat once every 2-3 years), and schedule determined by type of habitat as well as snail species, should be stressed. Such procedures car-ried out in an incorrect way (i.e. intensive mowing with heavy equipment) can worsen the status of the protected molluskan population.

Fig. 33. Presentation of terrestrial species: Desmoulin’s whorl snail Vertigo moulinsiana – A; narrow-mouthed whorl snail Vertigo angustior – B; Geyer’s whorl snail Vertigo

geyeri – C; marsh whorl snail Vertigo antivertigo – D; striated whorl snail Vertigo substriata – E; Pupilla pratensis – F; Vallonia enniensis – G

(source: Z. Książkiewicz - Parulska).