Stygofauna of karstic ecoystems in Ponor Mountains. Western Bulgaria: present knowledge and research challenges

Abstract

The purpose of this research is to examine the relationships between the karstic complexes and the hydrogeological characteristics of karst on one hand, and the distribution of stygobiont species, on the other. The research was conducted in the karstic region of Ponor Mountains, part of Stara Planina range, Western Bulgaria, with an area of approximately 60 km2 and average elevation of about 1000 m a.s.l. The karstic springs in the foot of the mountains are the only water source for nearly 15 000 people. Two basic rock complexes can be distinguished regarding karstifi cation: Triassic karstic complex and Upper Jurassic complex. The principal collector of the groundwater is the Triassic complex with annual discharge of 2900 dm3/s from which 80% is leaving the system through the Iskretski izvori springs. The Jurassic complex is lacking superfi cial outfl ow which determines its precipitation alimentation. The stygofauna of Ponor Mountains is very heterogeneously distributed and its composition varies greatly from one station to another. Nevertheless, the similarity calculated on the basis of presence/absence of stygobiont species is high (above 0.7) for the locations from Quaternary and Jurassic complexes. The aquifers in rocks with Triassic age do not demonstrate such similarity owing to the large percentage of local endemic species. Only in some isolated cases faunistic similarity between certain stations is higher. Some of the stations in Triassic aquifer are more similar to stations in Jurassic aquifers or to Quaternary sites, proving the hydrological connections between the Triassic and the other two complexes. Spatial distribution and relationships between Jurassic and Triassic complexes are determined by tectonic peculiarities of this part of Stara Planina Mountains.

Full text

161
ACTA ZOOLOGICA BULGARICA
Acta zool. bulg., 61 (2), 2009: 161-168
Stygofauna of Karstic Ecosystem in Ponor Mountains,
Western Bulgaria: Present Knowledge
and Research Challenges
Vesela V. Evtimova1*, Ivan S. Pandourski1, Aleksey D. Benderev2
1 Institute of Zoology, Bulgarian Academy of Sciences, 1, Tsar Osvoboditel Blvd., 1000 Sofi a, Bulgaria;
E-mails: evtimovv@tcd.ie; pandourski@gmail.com;
2 Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev str., bl. 24, 1113 Sofi a, Bulgaria;
E-mail: aleksey@router.geology.bas.bg
Abstract: The purpose of this research is to examine the relationships between the karstic complexes and the hydro-
geological characteristics of karst on one hand, and the distribution of stygobiont species, on the other.
The research was conducted in the karstic region of Ponor Mountains, part of Stara Planina range, Western
Bulgaria, with an area of approximately 60 km2 and average elevation of about 1000 m a.s.l. The karstic
springs in the foot of the mountains are the only water source for nearly 15 000 people. Two basic rock
complexes can be distinguished regarding karstifi cation: Triassic karstic complex and Upper Jurassic
complex. The principal collector of the groundwater is the Triassic complex with annual discharge of
2900 dm3/s from which 80% is leaving the system through the Iskretski izvori springs. The Jurassic
complex is lacking superfi cial outfl ow which determines its precipitation alimentation. The stygofauna of
Ponor Mountains is very heterogeneously distributed and its composition varies greatly from one station
to another. Nevertheless, the similarity calculated on the basis of presence/absence of stygobiont species
is high (above 0.7) for the locations from Quaternary and Jurassic complexes. The aquifers in rocks with
Triassic age do not demonstrate such similarity owing to the large percentage of local endemic species.
Only in some isolated cases faunistic similarity between certain stations is higher. Some of the stations in
Triassic aquifer are more similar to stations in Jurassic aquifers or to Quaternary sites, proving the hydro-
logical connections between the Triassic and the other two complexes. Spatial distribution and relation-
ships between Jurassic and Triassic complexes are determined by tectonic peculiarities of this part of Stara
Planina Mountains.
Key words: stygofauna, faunal similarity, Triassic, Jurassic karstic complexes
Introduction
The specifi c features of karstic terrains, namely al-
most complete lack of surface water fl ow and poor
xerophilous vegetation on a thin soil layer, deter-
mines the higher vulnerability of groundwater eco-
systems, their water resources and invertebrate fau-
na, inhabiting these environments. In aquifers not all
organisms are randomly distributed; they may rep-
resent in abundant populations subject to numerous
constraints. In this way, they are biological systems
controlled by ecological laws and each aquifer must
be, a priori, considered as an original biological unit
(CREUZE DES CHATELLIERS et al. 1991).
Karst covers 22.7% of the total territory of
Bulgaria. The invertebrate species, that constitute
*Corresponding author

162
Evtimova V., I. Pandourski, A. Benderev
the hypogean fauna of Ponor Mountains, are mostly
relict and endemic species from the large groups of
Crustacea, Mollusca and Oligochaeta. They need to
receive taxonomic description in order to identify
threats to ecosystem’s diversity loss. Copepods, be-
ing the most numerous group in such habitats, may
have a signifi cant role in the evaluation of environ-
mental peculiarities (one of the basic problems in
groundwater ecology) and can be used as bioindica-
tors of ecosystem’s health and contamination, and of
the typological characteristics of karstic system.
This study was fi rst presented at the poster ses-
sion of the International Symposium ‘Time in karst’,
Postojna, Slovenia, 14-18 March 2007.
Study area
Ponor Mountains (Western Bulgaria) are part of
the Balkan Range (Stara Planina Mountains), with
altitude from 400 m to 1473 m a.s.l. The region is
situated on the south limb of Berkovitsa Anticline
passing on the north limb and the core of Izdremets-
Gubesh Syncline. The central part of the mountain
is plateaus with rounded hills at about 900-1330 m
a.s.l. Rock garlands often surround them. More than
120 caves are known from the region. The massif is
formed mainly by Mesozoic rocks. According to the
karstifi cation there are two basic rock complexes:
the Triassic karstic complex, formed by limestones
and dolomites with a maximum depth of 600 m; and
the karstic complex of Upper Jurassic with depth of
100-150 m (Fig. 1). The basic collector of ground
waters is the Triassic complex with average annual
discharge of 2900 dm3/s from which 80% is leav-
ing the system through Iskretski izvori springs (N11)
(Table 1). These springs are the biggest in Bulgaria
with maximum discharge circa 35 000 dm3/s. The
Jurassic complex is characterised by lack of super-
fi cial outfl ow which determines its precipitation ali-
mentation. Its average annual outfl ow is about 120
dm3/s. Both aquifers are hydrologically differenti-
ated (BENDEREV 1989). The spatial situation and the
relationships between these two complexes are de-
termined by the tectonic features of this part of Stara
Planina Mountains. The carbonate complexes have
been subject to active karstifi cation by rainfall and
river waters, nourishing the groundwaters, mainly in
the Triassic complex.
Material and Methods
Due to diffi cult accessibility to karstic groundwater
ecosystems by human, faunal samples are collected
at their natural access, caves and springs, by direct
fi ltering of water at the outlet using phreatic net of
CVETKOV (1968), plankton nets of mesh size between
38 and 100 μm, and hand-held plankton net. Faunal
material was collected also with Bou-Rouch pump
and using the methods of artifi cial substrates or
Karaman-Chappuis method (MATHIEU et al. 1991). It
was collected during low-water and high-water peri-
ods from different hydrodynamic zones of karst: the
infi ltration and the saturated zones.
The hydrological connection between the moun-
tain surface rivers and Iskretski izvori springs (N11)
Table 1. Sampling stations in Ponor Mountains.
Num-
ber Station Geological
index
1 Iskretska river (hyporheic) Q
2 Tserovska river (hyporheic) Q
3 Tserovo village well Q
4 Studena reka river (phreatic
water) Q
5 Marina dupka cave J3
6 Travninata cave J3
7 Elata cave J3
8 Dinevata cave J3
9 Tsarkveto cave T2-3
10 Dushnika cave T2-3
11 Iskretski izvori springs T2-3
12 Sanatoriuma springs T2-3
13 Yamata cave T2-3
14 Vodnata cave T2-3
15 Tserovo quarry
(fi ssure water) T2-3
16 Skaklia spring T2-3
17 Mecha poliana mine
galleries T2-3
18 Katsite cave T2-3
19 Iskrets church spring T2-3
20 Chernovodtsi spring T2-3

Stygofauna of the Karstic Ecosystem in Ponor Mountains...
163
at the lowest altitude in the area of (Fig. 1; Table 1) is
proved by colouration. The time delay of the indica-
tors to reach the spring was 1-2 days during the high-
water period and 7-8 days during the low-water peri-
ods. The position of the springs is determined by the
local structural peculiarities. Iskretski izvori springs
are a complex of separated outlets with changing
numbers and altitudes, depending on the hydrologi-
cal cycle. They are overfl ow springs situated at the
lowest part of the Triassic Water Bearing Bed, near
the tectonic contact with the non-karstifi ed rocks of
Lower Palaeozoic (BENDEREV et al. 2005).
The qualitative composition of stygofauna in
the selected stations (Table 2) was determined us-
ing both original data and data from the available lit-
erature (PANDOURSKI & BENDEREV, 1998; APOSTOLOV,
1997). The similarity between the locations was cal-
culated only for the stations with typical stygobiont
species on the basis of the presence/absence of the
species, using Hierarchical Cluster Analysis, STATA
8 software application (Fig. 2).
Results and Discussion
The distribution of Ponor Mountains’ stygofauna is
very heterogeneous (Table 2). Its composition can
vary greatly from one station to another. At present 25
stygobionts are known from Ponor Mountains: from
Mollusca (2), Hirudinea (1), Acari (2), Copepoda
(18), Syncarida (1), Isopoda (1) and Amphipoda
(3). From the aquifers in rocks with Triassic age are
found 25 species while from Jurassic aquifers are
found only 7. The common species for both aquifers
are 5 species, amongst which with higher frequency
of occurrence are Niphargus bureschi, Speocyclops
lindbergi and Stygoelaphoidella elegans.
Fig. 1. Schematic geological map and distribution of Diacyclops clandestinus and Acanthocyclops iskrecensis
Legend: a – Upper Jurassic karstic rock complex; b – Triassic karstic complex; c – Wells revealing porewaters
in alluvium and prolluvium; d – Cave waters; e – Karstic springs; f – Porewaters in mine galleries; g – Distribution of
Diacyclops clandestinus; h – Distribution of Acanthocyclops iskrecensis
Sampling stations:
1. Iskretska river (hyporheic); 2. Tserovska river (hyporheic); 3. Tserovo village, well; 4. Studena river (phreatic
water); 5. Marina dupka cave; 6. Travninata cave; 7. Elata cave; 8. Dinevata cave; 9. Tsarkveto cave; 10. Dushnika
cave; 11. Iskretski izvori springs; 12. Sanatoriuma spring; 13. Yamata cave; 14. Vodnata cave; 15. Tserovo quarry; 16.
Skaklia spring; 17. Mecha poliana mine gallery; 18. Katsite cave; 19. Iskrets church spring; 20. Chernovodtsi spring

164
Evtimova V., I. Pandourski, A. Benderev
The copepod Diacyclops clandestinus is the
most common species found in samples from 7 of
the stations (Fig. 1). It inhabits the main springs
of Triassic autochthonous complex Iskretski izvori
springs (N11) and Skaklia spring (N16). Together
with D. languidoides they are typical for the fi ssure
waters (Tserovo quarry N15 or Chernovodtsi spring
N20) and interstitial waters, but we have not found
them in the Jurassic complex.
We have found Acanthocyclops iskrecensis
at 6 of the studied stations, both in caves from the
Jurassic (Elata cave N7 and Dinevata cave N8) and
the Triassic karstic complexes (Katsite cave N18);
and in the spring and porewaters of Tserovo quarry
(N15) and Iskretski izvori springs (N11). This distri-
bution (Fig. 1) demonstrates possible direct hydro-
logical connections between large parts of the two
complexes.
Table 2. Qualitative composition and distribution of the stygofauna in Ponor karstic system.
Taxa Station number
Mollusca
Cavernisa zaschevi (Angelov 1959)
Iglica acicularis Angelov 1959
11, 13, 16
11
Hirudinea
Dina absoloni JOHANSSON 1913 (s. lat.) 8
Acari
Soldanellonyx chappuisi WALTER 1917
Halacaridae gen. sp.
8, 16
13, 16
Crustacea
Copepoda
Cyclops abyssorum divergens LINDBERG 1936
Acanthocyclops radevi PANDOURSKI 1992
A. propinquus (PLESA 1957)
A. iskrecensis PANDOURSKI 1992
A. stygius (CHAPPUIS 1924) (s. lat.)
Diacyclops clandestinus (KIEFER 1926)
D. pelagonicus saetosus PANDOURSKI 1993
D. languidoides LILLJEBORG 1901 (s. lat.)
Speocyclops lindbergi DAMIAN 1957
Graeteriella unisetigera (GRAETER 1910)
Eucyclops sp.
Maraenobiotus parainsignipes APOSTOLOV 1991
Stygoelaphoidella elegans APOSTOLOV 1989
Elaphoidella iscrecensis APOSTOLOV 1997
E. cavernicola APOSTOLOV 1992
E. elaphoides (CHAPPUIS 1924) (s. lat.)
Elaphoidella sp. CHAPPUIS 1929
Parastenocaris bulgarica APOSTOLOV 1992
Syncarida
Bathynella sp. VEJDOVSKY 1882
Isopoda
Sphaeromides bureschi bureschi STROUHAL 1963
Amphipoda
Niphargus bureschi (FAGE 1926)
Niphargus sp. I
Niphargus sp. II
18
13, 14, 19, 20
11, 19
7, 8, 11, 13, 17, 18
11, 12
1, 2, 3, 10, 11, 15, 16
10
1, 10, 11, 16, 20
5, 6, 9, 11, 15
2, 11, 16
16
11
1, 5, 9, 11
11, 17
13, 14, 18
3
10, 11
10
4, 5
10, 13, 14
6, 7, 13, 14
16
12, 18

Stygofauna of the Karstic Ecosystem in Ponor Mountains...
165
Speocyclops lindbergi have been found in rim-
stone pools and puddles of caves situated at high alti-
tude above the local erosion level in both the karstic
complexes and in Iskretski izvori springs.
The rest of the species are localised in from one
to four stations and probably they are connected to
specifi c habitat requirements.
There are species which are characteristic of only
the groundwater of Triassic rocks and others that can
be found in both karstifi ed complexes. The biodiver-
sity is greater in the main discharge points in the au-
tochthonous Triassic limestone, such as, Iskretski iz-
vori springs (N11) and Dushnika cave (N10); Vodnata
(N14) and Yamata (N13) caves; Skaklia spring (N16)
and Katsite cave (N18). In Iskretsi izvori springs is
registered the highest hypogean faunistic diversity:
a total of 13 species are found. It is due to the large
catchment area of the spring which includes many of
the other sampling stations.
The large diversity in hypogean environments
is determined by their complex and prolonged paleo-
geographic evolution. The origin of some of them
is connected to ancient marine transgressions during
late Cretaceous (PANDOURSKI & BRESKOVSKI, 1995).
In the alluvial-prolluvial sediments of Studena reka
river before the infl ow in the karstifi ed Triassic lime-
stones we have found only one bathynellid species.
The possible reason for that could be the shallow
groundwater level and the higher altitude resulting in
the more signifi cant annual temperature amplitude.
Based on the cluster analysis Ponor Mountains’
territory could be divided into two groups of locations,
exhibiting a corresponding degree of faunal similarity,
and several more independent units (Fig. 2).
The fi rst group includes the greatest number of
stations: ((N1+ (N2+ N3+ N15)) + (N4 + (N5+ N9)) +
(N19+ N20)). It includes mainly karstic sources situ-
ated along Brezenska and Iskretska rivers (exclud-
ing Iskretski izvori springs). A clearly defi ned sub-
group with very high similarity includes the aquifers
of Quaternary sediments of Tserovo river (N2) and
Tserovo well (N3), and Tserovo quarry (N15) devel-
oped in Triassic rocks. There are two pairs with very
high similarity belonging to the same main group. The
fi rst pair is Marina dupka (N5) and Tsarkveto caves
(N9), which are geographically close to each other but
in rocks with different age. The other pair is Iskrets
church spring (N19) and Chernovodtsi spring (N20).
In the second group there is high similarity be-
tween the caves in Jurassic rocks (N6, N7, N8) and
Mecha poliana mine gallery (N17) due to the direct
contact between the Jurassic rocks and the aloch-
thonous Triassic rocks. Similar to this group are the
other spring emerging also from the alochthonous
Fig. 2. Degree of faunal similarity between the sampling stations in the Ponor karstic system.
Legend: 1. Iskretska river (hyporheic); 2. Tserovska River (hyporheic); 3. Tserovo village, well; 4. Studena River
(phreatic water); 5. Marina dupka cave; 6. Travninata cave; 7. Elata cave; 8. Dinevata cave; 9. Tsarkveto cave; 10. Du-
shnika cave; 11. Iskretski spring; 12. Sanatoriuma spring; 13. Yamata cave; 14. Vodnata cave; 15. Tserovo quarry; 16.
Skaklia springs; 17. Mecha poliana mine gallery; 18. Katsite cave; 19. Iskrets church spring; 20. Chernovodtsi spring.

166
Evtimova V., I. Pandourski, A. Benderev
Triassic complex, Sanatoriuma spring (N12), and
the percolation waters in Katsite cave (N18) devel-
oped in autochthonous Triassic rocks in the higher
parts of Ponor Mountains.
Yamata (N13) and Vodnata (N14) caves dem-
onstrate high similarity owing to the relatively ho-
mogenous composition of the fauna. They form a
separate group because of the presence of common
endemic crustacean species.
In Dushnika cave (N10) the hydrodynamic
conditions change dramatically throughout the year:
during high-water periods the cave discharges the
overfl ow waters of Iskretski izvori springs (N11),
the main discharge point of Ponor massif, while dur-
ing low-water periods further inside the cave there
is a siphon lake. This sampling site is somewhat
independent unit but demonstrates similarity with
Quaternary group, as well as, with stations from
Jurassic complex, the alochthonous Triassic and
Katsite cave (N18).
The main springs collecting the groundwater of
Ponor Mountains: Iskretsi izvori springs (N11) and
Skaklia spring (N16) are differentiated and do not
demonstrate clear similarity with any of the other
stations.
The studied hypogean faunistic community
may be used as a natural indicator of the hydrogeo-
logical division of karst, potential subsurface water
connections, hydrological regime, transformation
and bioaccumulation of contaminants. The main
challenges to be faced in the future are to understand
and clarify regional and fundamental issues concern-
ing structure and functioning of subterranean aquatic
ecosystems; to specify the zones with high diversity
and measures for their protection and management
to be proposed; to evaluate the role of groundwater
– surface ecotone as a zone of exchange of energy,
matter and contaminants between subsurface and
surface environments.
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Received: 16.01.2009
Accepted: 20.05.2009

Stygofauna of the Karstic Ecosystem in Ponor Mountains...
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Стигофауната на карстовата екосистема в Понор
планина, Западна България: съвременни познания
и изследователски предизвикателства
В. Евтимова, Ив. Пандурски, Ал. Бендерев
(Резюме)
Целта на това изследване е да се потвърдят връзките между карстовите комплекси и хидрогеоложки-
те характеристики на карста от една страна, и разпределението на стигобионтните видове от друга.
Изследването е проведено в карстовия район на Понор планина, част от веригата на Стара планина,
Западна България, с площ от около 60 km2 и средна надморска височина от около 1000 m. Карстовите
извори в подножието на планината са единственият източник на питейна вода за почти 15 000 души.
Два основни скални комплекса могат да бъдат разграничени по отношение на карстификацията: три-
аски и горно-юрски карстови. Основен колектор на подземните води е триаският комплекс с годишен
отток от 2900 dm3/s, като 80% от него напускат системата през Искрецките карстови извори. В юр-
ския комплекс липсва повърхностен отток, което определя неговото подхранване пряко от валежите.
Стигофауната на Понор планина е изключително хетерогенно разпределена и нейният състав вари-
ра значително от една станция към друга. Въпреки това, сходството, изчислено въз основа на при-
съствие/отсъствие на стигобионтни видове е високо (над 0,7) за станции от кватернерния и юрския
комплекси. Водоносните хоризонти в скали с триаска възраст не показват такова сходство поради
високия процент на локални ендемични видове. Само в изолирани случаи, отделни станции показ-
ват по-високо фаунистично сходство помежду си. Някои станции в триаския водоносен хоризонт са
сходни със станции в юрския водоносен хоризонт или с такива от кватернерния комплекс, доказ-
вайки хидроложките връзки между триаския и останалите два комплекса. Този факт се определя от
тектонските особености в изследваната част от Стара планина.