Aquatic molluscs of the Zemplínská Šírava dam reservoir (East Slovakia)

Abstract

The mollusc communities of the Zemplínská Šírava dam reservoir were studied in 2019. The reservoir, built in 1961–1965, is situated in the eastern part of Slovakia near the boundary with Ukraine; with its area of 33 km2 it is the second biggest dam reservoir in Slovakia. Nineteen species (13 gastropods, 6 bivalves) were recorded in the first more detailed inventory of its malacofauna. The mollusc communities in individual sites consisted of 8–14 species. The existence of littoral zone overgrown by macrophytes is important especially for populations of pulmonate snails while unionids were usually found on muddy or sandy bottom. Five non-native species were recorded. The abundant population of non-native D. polymorpha probably has a negative impact on unionids because of the shortage of suitable substrata (rocks, stones) for attachment, and as a result D. polymorpha uses shells of dead or live unionids.

Full text

FOLIA
MALACOLOGICA
The Association of Polish Malacologists
Faculty of Biology, Adam Mickiewicz University
Bogucki Wydawnictwo Naukowe
Poznań, June 2020
ISSN 1506-7629 (print)•ISSN 2300-7125 (on-line)
https://doi.org/10.12657/folmal.028.006
Folia Malacol. 28(2): 114–120
AQUATIC MOLLUSCS OF THE ZEMPLÍNSKÁ ŠÍRAVA
DAM RESERVOIR (EAST SLOVAKIA)
Luboš beran
Nature Conservation Agency of the Czech Republic, Regional Ofce Kokořínsko – Máchův kraj Protected
Landscape Area Administration, Česká 149, CZ-27601 Mělnik, Czech Republic
(e-mail: lubos.beran@nature.cz); https://orcid.org/0000-0002-5851-6048
abstract: The mollusc communities of the Zemplínská Šírava dam reservoir were studied in 2019. The
reservoir, built in 1961–1965, is situated in the eastern part of Slovakia near the boundary with Ukraine;
with its area of 33 km2 it is the second biggest dam reservoir in Slovakia. Nineteen species (13 gastropods,
6 bivalves) were recorded in the rst more detailed inventory of its malacofauna. The mollusc communities
in individual sites consisted of 8–14 species. The existence of littoral zone overgrown by macrophytes is
important especially for populations of pulmonate snails while unionids were usually found on muddy or
sandy bottom. Five non-native species were recorded. The abundant population of non-native D. polymorpha
probably has a negative impact on unionids because of the shortage of suitable substrata (rocks, stones) for
attachment, and as a result D. polymorpha uses shells of dead or live unionids.
Key words: dam reservoir, Zemplínská Šírava, aquatic molluscs
INTRODUCTION
Dams have been altering riverine ecosystems
since humans started constructing them. They have
a positive effect on civilisation through their various
designed purposes, irrigation being the most impor-
tant. At the same time, they exert an array of adverse
effects on humans and they affect ecosystems in a
negative way (HanKs 2020). On the other hand, the
dams provide appropriate habitats for aquatic mol-
luscs which prefer stagnant waters (e.g. Dvořák &
beran 2004, beran 2007, Horáčková et al. 2014).
The Zemplínská Šírava dam reservoir, 33 km2 in
area, is the second biggest dam reservoir in Slovakia.
Though aquatic molluscs of the country have been
studied for a long time, its fauna has not been inven-
toried yet. Only unpublished records of 10 species
from this reservoir, without precise location data, ex-
ist from 1978 (leg. J. šteffeK). It was the reason for
a more detailed survey done during the 22nd session
of the Czech and Slovak malacologists (“MalacoDays
2019”) in Inovce. The results are presented here.
MATERIAL AND METHODS
Samples were taken by the author in 2019. In total,
7 sites were studied (Fig. 1, Appendix 1). The main
method used was washing veg etation and sediments
using a metal sieve (diameter 20 cm, 0.8 mm mesh)
combined with hand-collecting from the surface of
stones, wood and articial materials (e.g. plastic
bags and bottles). Snorkelling in shallow parts (up
to ca. 3 m deep) was also used. The molluscs were
identied based on shell char acters or genital struc-
ture whenever purely conchological identication
was impossible. Specimens for dissection were killed
in hot water and then xed in 80% ethanol. Selected
shells and alcohol-preserved specimens are deposit-
ed in the author‘s collection. The classication used
follows Horsák et al. (2019).

Aquatic molluscs of the Zemplínská Šírava dam reservoir 115
STUDY AREA
The Zemplínská Šírava dam reservoir is situat-
ed in the eastern part of Slovakia near the bound-
ary with Ukraine, at an altitude of 113.7 m a. s. l.
The dam was built in 1961–1965, and the reservoir
is 33 km2 in area. Its average depth is 9.5 m, with
the maximum depth 14 m. The reservoir is fed by a
canal (Šíravský kanál) of the Laborec River (tributary
of the Bodrog River, Danube river basin). The area is
primarily used for recreation (it is also called “Slovak
sea“).
RESULTS
In total, 19 aquatic molluscs (13 gastropods, 6
bivalves) were found at 7 sites of the Zemplínská
Šírava reservoir (Fig. 1). The mollusc communities
in individual sites consisted of 8–14 species (for
the list of species and estimated population density
see Table 1). Physella acuta, Unio pictorum, U. tumidus
and Dreissena polymorpha were found in all the sites,
Bithynia tentaculata, Valvata piscinalis, Radix auricularia,
Anisus spirorbis, Gyraulus cf. parvus and Anodonta ana-
tina were recorded in 4–6 sites while the remaining
species were found at only 1–3 sites. R. auricularia, P.
acuta, G. cf. parvus and D. polymorpha usually formed
abundant populations.
Rich gastropod communities with abundant pop-
ulations were found within the littoral zone over-
grown by macrophytes (sites No. 3, 4, Fig. 2) while
sites with sparse macrophyte vegetation were inhab-
ited by fewer species (e.g. sites No. 2, 5, 6, Fig. 3).
Live unionids were usually found on muddy or sandy
bottom at the depth of 1–3 m and probably occurred
also in the deeper parts which were not investigated.
Viviparus acerosus and Pseudanodonta complanata are
listed as Vulnerable in the Red List of molluscs of
Slovakia (Šteffek & vavrová 2006) while the oth-
er species are common and widespread. P. complanata
was recorded in three sites while V. acerosus only in
one site (No. 5, only few specimens).
P. acuta, G. parvus, Ferrissia californica, Sinanodonta
woodiana and D. polymorpha are non-native invasive
species. In the case of G. parvus the identication
is only preliminary due to its similarity to G. laevis
(Alder, 1838) so this taxon is mentioned only as G. cf.
parvus in this study (see Discussion).
Fig. 1. Map of the Zemplínská Šírava reservoir with the distribution of the sampling sites

116 Luboš Beran
Table 1. List of aquatic molluscs recorded from the Zemplínská Šírava reservoir
Species/Site No. 1 2 34567Σ
Viviparus acerosus (Bourguignat, 1862) × 1
Bithynia tentaculata (Linnaeus, 1758) × ×× × × 4
Valvata piscinalis (O. F. Müller, 1774) × × × × 4
Galba truncatula (O. F. Müller, 1774) × 1
Radix auricularia (Linnaeus, 1758) ××× ×× ××× ×× ×× ×× 6
Lymnaea stagnalis (Linnaeus, 1758) × ×× 2
Physella acuta (Draparnaud, 1805) ××× ××× ××× ×× ××× ×× ××× 7
Anisus spirorbis (Linnaeus, 1758) ×× ×× ×× ×× 4
Gyraulus albus (O. F. Müller, 1774) × × 2
Gyraulus crista (Linnaeus, 1758) × 1
Gyraulus cf. parvus (Say, 1817) ××× ××× ××× × ××× 5
Hippeutis complanatus (Linnaeus, 1758) ×× 1
Ferrissia californica (Rowell, 1863) × 1
Unio pictorum (Linnaeus, 1758) × ×× × × × × ×× 7
Unio tumidus Philipsson, 1788 ×××××××7
Anodonta anatina (Linnaeus, 1758) × × × × × 5
Pseudanodonta complanata (Rossmässler, 1835) ××× 3
Sinanodonta woodiana (Lea, 1834) ×× × × 3
Dreissena polymorpha (Pallas, 1771) ××× ××× ××× ××× ××× ××× ××× 7
Number of species 11 8 12 14 9 89
× – few specimens, ×× – scattered occurrence, ××× – abundant occurrence.
Fig. 2. Bank with overgrown bight (site No. 4); littoral zone overgrown by macrophytes. Photo: Luboš beran

Aquatic molluscs of the Zemplínská Šírava dam reservoir 117
DISCUSSION
This survey is the rst more detailed inventory
of aquatic molluscs of this extensive reservoir built
more than 50 years ago, therefore it is impossible
to compare its results with any previous research.
Only records of 10 species from the reservoir exist,
albeit with no precise location data. J. šteffeK (un-
published) made the records in 1978. He mentioned
the occurrence of Borysthenia naticina (Menke, 1845),
V. piscinalis, G. truncatula, R. auricularia, R. labiata
(Rossmässler, 1835), G. albus, G. crista, G. laevis, U.
pictorum and A. anatina. All species except B. naticina,
R. labiata and G. laevis were found during the present
survey. Previously, B. naticina was known in Slovakia
only from the Danube River and its oodplain (Ložek
1956, LisicKý 1991, Horsák et al. 2019) and its oc-
currence in the dam reservoir is doubtful; the record
probably resulted from misidentication of V. piscina-
lis. R. labiata is common and widespread, it inhabits
especially nutrient-poor habitats and its occurrence
in the reservoir 10–15 years after its lling is possible.
The abundant occurrence of G. cf. parvus was docu-
mented during this survey instead of G. laevis men-
tioned by J. šteffeK in 1978. Both species (G. laevis,
G. parvus) are very similar and the difference between
them is hardly perceptible, so it is not certain which
species occurred in the reservoir on the previous oc-
casion. The status of the two forms is still uncertain,
hence material was collected for genetic analysis.
The malacofauna of the Zemplínská Šírava res-
ervoir includes only 13 species of freshwater snails
out of the 52 aquatic snail species known in Slovakia
(Horsák et al. 2019). Similarly, few gastropod spe-
cies were found in other dam reservoirs in Slovakia, e.
g. in the Oravská Priehrada reservoir (13–14 species;
Šteffek & NageL 2004), in the Vĕstonice reservoir
(14 species; beran 2013) and in small dam reser-
voirs in the Slovak Carpathians – a maximum of 12
species (čejka 2011). Similar numbers of freshwater
snail species were found in most of dam reservoirs in
Poland in Upper Silesia (strzeLec 2005, strzeLec et
al. 2005) while 21 gastropods were recorded in the
Slapy reservoir built on the Vltava River in the Czech
Republic (beran 2007).
There was a positive dependence between the
presence of macrophytes on the one hand, and the
abundance and species richness of pulmonate snails
Fig. 3. Bank with a beach and boat mooring site nearly devoid of vegetation (site No. 2). Photo: Luboš beran

118 Luboš Beran
on the other. A similar dependence was observed by
JurKiewicz-KarnKowsKa (2002) who studied mol-
lusc communities of the Sulejów dam reservoir in
Poland.
Dam reservoirs provide favourable habitats for
abundant populations of unionids preferring stand-
ing waters (e.g. Dvořák & beran 2004, šteffeK
& NageL 2004, beran 2007, gołąb et al. 2010,
Horáčková et al. 2014). On the other hand, hu-
man-induced transformation of running into stand-
ing waters favours common unionids, and dramat-
ically reduces habitat for species which inhabit
mostly streams and rivers (burLaKova et al. 2011).
Five unionid species (U. pictorum, U. tumidus, A.
anatina, P. complanata, S. woodiana) out of the seven
species known from Slovakia were recorded from
the Zemplínská Šírava reservoir. Only U. crassus
Philipsson, 1788, a typical inhabitant of running wa-
ters (e.g. beran 2019) was missing, as was A. cygnea
(Linnaeus, 1758), which on the other hand prefers
standing waters including dam reservoirs. P. com-
planata, declining in most European countries and
listed in the IUCN Red List of Threatened Species
as Vulnerable (van damme 2011) was found in
the Zemplínská Šírava. The species is a typical in-
habitant of rivers (e.g. beran 2002, KiLLeen et
al. 2004, beran 2019) but it is also known to oc-
cur in lakes (e.g. van damme 2011, PiecHocKi &
wawrzyniaK-wydrowsKa 2016) and dam reser-
voirs (Horáčková et al. 2014). This unionid usually
occurs in low densities and belongs to the rarest na-
tive unionids (e.g. zettLer 1998, 1999, KiLLeen et
al. 2004, beran 2019); also in the Zemplínská Šírava
it is rare and only 1–3 specimens per site were found.
The species is rare in Slovakia and is known mostly
from lowland rivers along the Danube (Podunajská
nížina) and in the south-eastern part of Slovakia
(Východoslovenská nížina) (LisicKý 1991, čejka et
al. 2015, Horsák et al. 2019).
Dam reservoirs, especially those used for recre-
ation, are often a place of mass occurrence of alien
invasive molluscs which often dominate in such hab-
itats (strzeLec 2005, strzeLec et al. 2005), for ex-
ample P. acuta in the Vĕstonice dam reservoir (beran
2013). This also applies to Zemplínská Šírava, where
the dominants are P. acuta, G. cf. parvus and D. pol-
ymorpha. The abundant population of D. polymorpha
probably has a negative impact on the unionid pop-
ulations including the vulnerable P. complanata, be-
cause of the decit of suitable attachment substra-
ta (rocks, stones) and as a result D. polymorpha uses
valves of dead or live unionids (Fig. 4). The popu-
lations of native unionids can also be negatively af-
fected by the invasive Chinese giant mussel S. woodi-
ana. This bivalve can compete with native unionids
for food, increase resistance to glochidia in potential
host shes and serve as a vector for introduction of
new parasites and diseases (LoPes-Lima et al. 2017,
Fig. 4. Live Unio tumidus (left) and Pseudanodonta complanata (right) with sessile specimens of Dreissena polymorpha. Photo:
Luboš beran

Aquatic molluscs of the Zemplínská Šírava dam reservoir 119
donrovicH et al. 2017, DouDa & čaDková 2018).
An abundant occurrence of G. cf. parvus was observed
in most of the sites but without any obvious effect on
the native species; the same was true of P. acuta and
F. californica.
ACKNOWLEDGEMENTS
I would like to thank tomአčejka for providing
historical data of J. šteffeK and the anonymous re-
viewers for their valuable comments.
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APPENDIX 1
List of sampling sites, data as follows: site number, geographical co-ordinates, name of the nearest settle-
ment, site description, date of sampling.
1. 48°47'19.6"N, 21°56'47.5"E, Vinné, Zemplínská Šírava dam reservoir at the inow of the Šíranský kanál
canal, 25.06.2019;
2. 48°47'55.6"N, 22°00'02.8"E, Kaluža, north-western edge of Zemplínská Šírava reservoir, 27.06.2019;
3. 48°48'29.6"N, 22°01'45.5"E, Klokočov, northern edge of Zemplínská Šírava reservoir by the church,
25.06.2019;
4. 48°48'31"N, 22°02'19.7"E, Klokočov, overgrown bight of Zemplínská Šírava reservoir (Fig. 2), 24.06.2019;
5. 48°46'37.8"N, 22°02'24.7"E, Lúčky, south-eastern edge of Zemplínská Šírava reservoir, 26.06.2019;
6. 48°46'00.1"N, 21°59'35.8"E, Malé Zalužice, southern edge of Zemplínská Šírava reservoir, 26.06.2019;
7. 48°46'40.1"N, 21°57'14.3"E, Michalovce, western edge of Zemplínská Šírava reservoir, 25.06.2019.