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Marine Ecology. ISSN 0173-9565

ORIGINAL ARTICLE

Environmental features and crustacean community of anchihaline hypogean waters on the Kornati islands, Croatia Sanja Gottstein1, Marija Ivkovic´1, Ivancˇica Ternjej1, Branko Jalzˇic´2 & Mladen Kerovec1 1 Department of Zoology, Faculty of Science, University of Zagreb, Zagreb, Croatia 2 Croatian Natural History Museum, Zagreb, Croatia

Keywords Anchihaline cave; co-occurrence; crustacean community; groundwater; Kornati islands; salinity; species richness; vertical distribution. Correspondence Sanja Gottstein, Department of Zoology, Faculty of Science, University of Zagreb, Rooseveltov trg 6, 10000 Zagreb, Croatia. E-mail: [email protected]

Abstract This paper reports on new distribution records of groundwater crustaceans for anchihaline habitats of the Kornati islands and presents observations on the frequency of the crustacean community. Research was conducted during September 2001 and 2003 in nine caves and two wells. Based on literature data and own research, a total of 33 crustacean taxa were determined, distributed in seven orders, 11 families and 15 genera. Our collections include four copepod species recorded for the first time for the Kornati islands, of which one species was also new for Croatia. Stygobiotic species make up 45% of the total crustacean fauna recorded at the researched localities. Most of the anchihaline crustaceans studied here are members of the order Cyclopoida. The most widespread species was Niphargus hebereri and the richest genus was Diacyclops. Vertical salinity gradients determine spatial distribution patterns of stygobiont crustaceans. The species richness of crustaceans here is strongly dependent on habitat morphology as well as on abiotic factors (e.g. salinity) and food supply. Crustacean diversity was higher in caves with steep salinity gradient. Records of crustacean species are listed with notes on their patterns of coexistence.

Problem Rupert Riedl described for the first time ‘Randho¨hlen’ or ‘marginal caves’. His contributions significantly increased our knowledge on the diversity of taxa living in marginal caves, and he also proposed a hypothesis on the function of marginal caves as the doors of migration for marine species towards the subterranean freshwaters (Riedl 1966; Riedl & Ozretic´ 1969). Anchihaline caves have traditionally been explored more by taxonomists than by ecologists, because many of the species have been rarely sampled and because of the difficulties in collecting material and measuring environmental factors during the fieldwork. Studies conducted on the groundwater crustacean community in the anchihaline caves of the Eastern Adriatic Sea coast (Schellenberg 1933; Riedl & Ozretic´ 1969; Ruffo & Krapp-Schickel 1969; 24

Ruffo & Vigna Taglianti 1969; Sket 1977, 1986a, 1988, 1996; Sket & Karaman 1990; Krsˇinic´ 2005a,b) have revealed new taxa and helped explain the distribution of cave-dwelling crustaceans. Earlier important contributions concerning groundwater crustacean fauna from the Kornati islands are those of Sket (1986a,b, 1996): crustaceans were the dominant animal group. Nevertheless, the number of surveys of groundwater crustacean distribution and ecology in anchihaline caves on these islands is still low. We therefore examine whether local environmental features explain patterns of spatial variability in diversity, abundance and community structure of the crustacean fauna in and along the vertical axis of anchihaline caves on the Kornati islands, Croatia. Another interesting question we attempt to answer is whether various environmental features of anchihaline caves (such as salinity level) can be used as predictor variables in determin-

Marine Ecology 2007, 28 (Suppl. 1), 24–30 ª 2007 The Authors. Journal compilation ª 2007 Blackwell Publishing Ltd

Gottstein, Ivkovic´, Ternjej, Jalzˇic´ & Kerovec

Crustacean community of anchihaline hypogean waters, Croatia

ing the community structure of groundwater crustaceans there. Our work therefore also examines such aspects as habitat preferences, species coexistence and biogeography. Because the crustacean community structure is postulated to be functionally related to key environmental factors, this relationship was analysed to gain a better understanding of anchihaline cave community ecology on the Kornati islands, which are part of the Dinaric karst, known as a groundwater crustacean species-rich area.

influenced by external environmental variables. The main characteristics of each cave are presented in Table 1.

Material and Methods Study area

The Kornati National Park is located in the middle of the Eastern Adriatic Sea coast of Croatia, composed of Kornat Island and many small islets that contain numerous anchihaline caves that open between 10 and 50 m from the coastline. The Kornati islands are part of the Adriaticum plate (Herak 1986) in the frame of the Dinaric karst limestone (Cretaceous and Palaeocene) (Bognar & Grizelj 1996). This area has a mean annual precipitation of 900 mm and air temperature of 15 C (Climatic Atlas of SFRJ for 1931–1960). Samples were collected in nine caves and two wells on seven Kornati islands during September 2001 and 2003 (Fig. 1). The caves have a single entrance, with the water level up to 34.5 m below the earth’s surface. The maximum water depth reached by divers was 20 m. The anchihaline caves with the deepest water layer explored on Kornati islands (Vodena jama na Gustacu) typically have a freshwater layer overlying seawater and consequently have a stratified physico-chemical profile (Table 1). We report an oligohaline-limnic lens of about 2.5 m overlying a brackish-water layer, with a sharp halocline in between. The cave entrances are strongly

Sampling and analyses

The specimens from the surface and various water layers were collected using a hand net (30 cm diameter and 80 lm mesh size) and watersampler (0.5 l), while a plankton net of the same dimension and mesh size was used in the deepest part of the anchihaline pool during SCUBA diving. The watersampler was restricted to the deepest caves with salinity stratification in order to explore all variables in each stratum. Special attention was paid to microhabitats, such as places beside boulders, at various depths in anchihaline pools. Environmental variables such as air and water temperature, pH, conductivity, salinity and dissolved oxygen were recorded using a WTW Multi-Parameter Water Quality Meter. Water samples were collected approximately 5 cm below the pool surface, in the halocline and at the bottom of cave pools. Hydrogen sulphide was not measured. All samples were preserved in the field with 4% buffered formalin for subsequent identification. Specimens were sorted and counted in the laboratory using a stereomicroscope (Zeiss, Stemi 2000-C). Specimens were deposited at the Natural History Museum in Zagreb and at the Department of Zoology – GOTT collection, University of Zagreb. The organisms collected were identified to the lowest taxonomic level possible to determine the species richness of each cave. A matrix of co-occurrences was compiled, and Fager’s index of affinity (Southwood 1966) was calculated. This index is defined by: IAB ¼ 2J=nA þ nB

Fig. 1. Position of study sites on the Kornati islands (numbers according to Table 1).


25



site no.

study cave/well*

island

depth to water surface [m]

1 2 3 4 5 6

Gravrnjacˇa U vode (N part) Bunar u uvali Sˇipnate* Bunar jama na Bisagi Vodena jama na Gustacu Jama iznad uvale Velika Ropotnica Bunar jama na Kamenom Zˇaknu Bunar jama na Sˇkulju Jama iznad Vrulja Bunar u Vruljama* Jama ispod Vruljskog brda

Kurba Smokvica Kornat Bisaga Gustac Kornat

8.5 8 4.2 6 22 34.5

12 0.3 0.3 >3 >20 1

1.5–35.7 5.7 7.9 4.2–22 0.6–36 5.4

6

>1

8.9

7 22 3.5 16

0.2 6 0.5 2

7 8 9 10 11

Kameni Zˇakan Sˇkulj Kornat Kornat Kornat

water column depth [m]

where J ¼ number of joint occurrences, nA ¼ total number of occurrences of species A, and nB ¼ total number of occurrences of species B. The index provides a measure of the frequency with which species occur together (Southwood 1966). Results Physico-chemical data

Water temperature in the caves was comparatively warm and stable, between 15 and 18.8 C (Fig. 2). The upper water layer in some caves and wells is exposed to direct sunlight (study sites 2, 4, 7 and 8, and sites 3 and 10, respectively) (Fig. 1, Table 1). The largest caves (sites 1, 5, 6, 9 and 11) were characterized by a permanent absence of light and water temperatures similar to the annual external means (15 C). Surface salinity was 0.6–10.4 down to a marked halocline at a depth of about

6

22

5

18 16

4

14 12

3

10 8

2

6 4

species richness (SR)

Ta, Tw [°C]; DO [mg l–1]; S

20

1

2 0

0 1

2

3 SR

4

5 Ta

6 7 study sites Tw

8 DO

9

10

11

S

Fig. 2. Physico-chemical parameters of surface water layers, Ta – air temperature [C], Tw – water temperature [C], DO – dissolved oxygen [mgÆl)1], S – salinity, and species richness (SR) at 11 study sites on the Kornati islands.

26

salinity range

Table 1. The study sites on the Kornati islands in September 2001 and 2003.

5.4 3.8–12 10.4 7.7

2.5–3.5 m, below which the values increased to 22 at approximately 5 m and deeper down; salinity then increased steadily to 35 at depths below 10 m, after which it remained relatively constant, increasing to 36 below 20 m. Conductivity was related to the salinity, with a range of 1.52–17.64 mSÆcm)1. At the surface of the water columns, pH ranged from 7.26 to 7.74 and was rather uniform in all study sites. Dissolved oxygen fell from saturated at the surface water layer of most caves to a minimum of 1.76 mgÆl)1 in a well (study site 3) (Fig. 2). Crustacean distribution and habitat ecology

From all the samples and study sites, a total of 12 crustacean taxa were collected: 11 occurred in caves and one in a well (Table 2). The crustacean community in the anchihaline caves of the Kornati islands is characterised by the dominance of only one species, the amphipod Niphargus hebereri Schellenberg (Table 2). The highest density of individuals was recorded at study sites that receive high inputs of energy and matter. This species was not recorded at sites with higher salinities (>10.4) (Fig. 3). All recorded species showed a vertical distribution pattern. A total of seven species of Copepoda were recorded (Table 2). Some are considered as stygoxenes, others as stygophiles. Dyacyclops crassicaudis, D. languidoides, Megacyclops viridis and Metacyclops sp. are new copepod species recorded for Kornati islands, and Halicyclops dalmatinus was found for the first time in Croatia. The vertical salinity gradient determined the spatial distribution patterns of crustaceans. Oligohaline-limnic to mesohaline water layers were dominated by the amphipod Niphargus hebereri and cyclopoid freshwater species (Diacyclops, Megacyclops and Metacyclops), with the exception of Halicyclops species, which is a marine taxon.



Table 2. Crustacean species assemblages found in nine anchihaline caves and two wells on the Kornati islands during 2001 and 2003, with the abbreviations of taxon names used in this paper.


abbreviation with water layer affinity

taxon COPEPODA Calanoida Ridgewayiidae Badijella jalzici Krsˇinic´, 2005 Cyclopoida Cyclopidae Diacyclops bicuspidatus (Claus, 1857) D. crassicaudis (Sars, 1863) D. languidoides (Lilljeborg, 1901) Halicyclops dalmatinus Petkovski 1955 Megacyclops viridis (Jurine, 1820) Metacyclops spp. Harpacticoida OSTRACODA Podocopida Candonidae MALACOSTRACA Amphipoda Niphargidae Niphargus hebereri Schellenberg 1933 Niphargus pectencoronatae Sket & G. Karaman, 1990 Hadziidae Hadzia fragilis S. Karaman, 1932

co-occurrence

total N

%

n

%

Bjc

1

9

1

8

Dbb Dcb Dlb Hdb Mvb Ma Hc

1 2 2 2 1 1 5

9 18 18 18 9 18 45

2 4 3 4 2 1 5

17 42 17 25 8 8 33

Caa

3

27

3

8

Nha,b Npb

10 1

90 9

12 1

83 17

Hfa,b

2

18

3

42

N ¼ total number of caves/wells in which the species occurred; % ¼ percentage of caves/wells in which the species occurred; n ¼ number of samples in which the species co-occurred with another species; % ¼ percentage of samples in which the species co-occurred with another species. Bold letters indicate obligate groundwater species. a Oligohaline-limnic water layer (salinity > 0.5 < 5). b Mesohaline water layer (salinity ¼ 5–18). c Polyhaline water layer (18–36).

The number of taxa per cave showed a slight positive trend associated with the presence of a vertical salinity gradient, and the total number of taxa was higher in salinity-gradient caves (Table 3). Co-occurrence

Fig. 3. Different abundances of the amphipod Niphargus hebereri in anchihaline caves on the Kornati islands during the present study, in relation to salinity and depth at each site.

Polyhaline water layers were inhabited by typical marine calanoids (Badijella jalzici Krsˇinic´, 2005) and harpacticoids (Fig. 4, Table 2).

From 11 study sites (11 caves and 2 wells) on the Kornati islands, one yielded no species, one had one species, and 9 were scored with two or more species (Fig. 2). The amphipod which normally co-occurred with other amphipods and copepods (co-occurrence > 80%) is the widely distributed Niphargus hebereri, with nine records in the caves and one record in the well (Tables 2 and 4). The pairs of species with the highest affinity index (0.40 or more) were: Diacyclops crassicaudis–Halycyclops dalmatinus, Diacyclops languidoides–Metacyclops spp., D. crassicaudis–Hadzia fragilis, H. dalmatinus–H. fragilis, H. fragilis–Harpacticoida spp., and H. fragilis–Niphargus pectencoronatae (Table 4). The most frequent crustacean


27



Fig. 4. Vertical distribution of crustacean species in highly stratified anchihaline caves on the Kornati islands.

combinations are D. crassicaudis–N. hebereri, H. dalmatinus–N. hebereri, Harpacticoida spp.–N. hebereri, with four records each (Table 4). No combination of the three most frequent species was recorded. Discussion Based on our research and literature data, the anchihaline caves on the Kornati islands contain more than 30 crustacean species, 15 of them being regarded as stygobiotic.

The earliest overview of groundwater crustaceans known from anchihaline caves here was made by Sket (1986a,b, 1996), who listed 24 crustacean taxa. Our research shows that the distribution of the largest amphipod, Niphargus pectencoronatae, is apparently restricted to the salinitygradient caves with huge amounts of oligohaline-limnic water, where it lives behind boulders in low abundance and deeper than N. hebereri. The latter filtrates small detritus particles from the water surface. The distribution pattern of N. pectencoronatae (Sket & Karaman 1990), as well as its ecology, size (2.3 cm) and morphology, allows us to hypothesize a predatory behaviour. Records of copepod fauna in anchihaline habitats of the Kornati islands are scarce. Sket (1986a,b, 1988, 1994, 1996) significantly advanced our knowledge on the zoogeography and ecology of subterranean fauna (including copepod, ostracod and amphipod species) in the karstic area of the east Adriatic coast. He noted Diacyclops species as being common in anchihaline habitats. Halicyclops dalmatinus was described by Petkovski (1955) in interstitial samples along the coast of Herceg Novi, Budva and Bar. As it was recorded to inhabit brackish underground waters, it was no surprise that we found it also in Kornati anchihaline habitats. We know little about the ecology and origin of these copepods. Fresh or brackish coastal waters are often occupied by representatives of generally marine taxa, e.g. Halicyclops and Cyclopina among the cyclopoids, and Schizopera and Delamarella among the harpacticoids (Huys & Boxshall 1991). The origin of the species in these habitats remains unknown. Certain genera, such as Halicyclops and Nitocrella, could have their direct origins in the sea, along coastal habitats following sea regressions or tectonic uplift and the freshening of coastal interstitial waters. The other genera – Speocyclops, Bryocamptus, Elaphoidella, Moraria and Diacyclops – successfully colonized the underground habitats from surface freshwater bodies

Table 3. Comparison of crustacean taxa composition and their number between non-salinity gradient caves and salinity-gradient caves on the Kornati islands during September 2001 and 2003. non-salinity gradient caves

taxa abbreviations

no. taxa/cave

salinity-gradient caves

taxa abbreviations

no. taxa/cave

U vode Bunar u uvali Sˇipnate Jama iznad uvale Velika Ropotnica Bunar jama na Sˇkulju

Dc, Hd, Hf, Nh, Db, H, Nh H, Nh

4 3 2

Gravrnjacˇa Bunar jama na Bisagi Vodena jama na Gustacu

Bj, Ca, Dc, H, Nh Ca, Dl, M, Nh Ca, M, Nh

5 4 3

Dl, Hd, Nh

3

Mv, Nh

2

Bunar u Vruljama Jama ispod Vruljskog brda

– Nh

0 1

Bunar jama na Kamenom Zˇaknu Jama iznad Vrulja

H, Hf, Nh, Np

4

total taxa composition total range of no. taxa per cave/total no. taxa

Dc, Db, Dl, H, Hd, Hf, Nh 0–4/7

total taxa composition total range of no. taxa per cave/total no. taxa

Bj, Ca, Dc, Dl, H, Hf, M, Mv, Nh, Np 2–5/10

28




Table 4. Matrix of co-occurrences from 10 caves and 1 well on the Kornati islands. Lower part shows the number of records in which the species co-occurred. Upper part shows the Fager’s affinity index (·100). For abbreviations of species (taxon) names, see Table 2.

ella jalzici (Calanoida), live in oxygen-depleted waters below the halocline (Fig. 4). The high surface salinity in some caves (study sites 7 and 11) may be associated with the minimal surface input of water. Most of the anchihaline groundwater systems examined along the Adriatic Sea coast (Riedl 1966; Riedl & Ozretic´ 1969; Sket 1981, 1986a,b, 1996) as well as on the Yucatan Peninsula, Bermuda, and in flooded sinkholes of north-western Australia (Iliffe 1992, 2000; Humphreys 1999) have a freshwater lens overlying sea water. The main difference between the anchihaline caves on the Kornati islands and those of the Yucatan peninsula is a standing freshwater lens versus groundwater with current, respectively. The species assemblages here were based on species with similar environmental requirements such as water conditions (temperature, salinity, dissolved oxygen, ion concentration), food availability and habitat morphology. Environmental factors such as water salinity play an important role in the biodiversity and ecological function of anchihaline caves and they could be frequently used as predictor variables in determining the community structure of groundwater crustaceans.

Bj Bj Db Dc Dl Hd Mv M H Ca Nh Np Hf

0 0 0 0 0 0 1 0 0 0 0

Db

Dc

Dl

Hd

Mv

M

H

Ca

Nh

Np

Hf

–

– –

– – –

– – 44 –

– – – – –

– – – 50 – –

25 22 33 – 36 – –

– – 25 – – – – –

– 20 35 29 18 20 11 32 19

– – – – – – – – – 11

– – 50 – 57 – – 40 – 29 50

0 0 0 0 0 1 0 2 0 0

0 2 0 0 2 1 4 0 2

0 0 1 0 0 3 0 0

0 0 2 0 4 0 2

0 0 0 2 0 0

0 0 1 0 0

0 4 0 2

2 0 0

1 3

1

during different geologic ages, as a result of drastic climatic changes (Huys & Boxshall 1991). We found several species of the genus Diacyclops in the Kornati islands, and not all of them are stygobiotic. The genus Diacyclops is very diversified and widespread: Diacyclops species often contain several different cryptic species. These species are mainly stygobiotic, inhabiting springs, caves and interstitial water of Dinaric karst as well as interstitial habitats outside the karstic area (D. languidoides-group) (Pospisil & Stoch 1999). On the other hand, certain species of this genus can be considered to be stygophilic or stygoxenes because they regularly live, besides in groundwaters, in a wide range of epigean freshwater bodies such as lakes, rivers, marshes or brackish coastal lagoons (e.g. D. crasssicaudis, D. bicuspidatus). We also recorded a facultative groundwater species, Megacyclops viridis, which regularly inhabits surface waters but can frequently be found in groundwater (Galassi 2001). Earlier sets of data (crustacean community structure and key environmental conditions) were spatially patterned, and they indicated a common spatial vertical distribution of some cyclopoid, amphipod and thermosbaenacean species (Sket 1986b, 1996), but our data on the vertical distribution pattern of the hypogean calanoid Badijella jalzici is new. Some other members of Ridgewayiidae were observed in great diversity in marine caves of the Bahamas (Fosshagen & Iliffe 1998). As shown above, salinity was the primary environmental factor controlling both crustacean abundance and crustacean community structure. Salinity also controls other environmental features in the Kornati caves, such as oxygen concentration, which is commonly used to explain crustacean presence in various layers of mixohaline cave waters (Sket 1986b, 1996). Some crustaceans, e.g. Tetysbaena halophila (Thermosbaenacea) (Sket 1996) and Badij-

Summary Faunistic and ecological studies on four facultative and one obligate groundwater crustacean were conducted for the first time in anchihaline hypogean waters on the Kornati islands. Eight caves and two wells were examined for the first time. The mean surface salinity and bottom salinity of pools was 5.6 and 18.9, respectively. Temperatures of cave pools and wells ranged from 15 to 18.8 C. In total, 33 crustacean taxa were determined, distributed in 7 orders, 11 families and 15 genera. The present research shows that stygobiotic species make 45% of the total crustacean fauna recorded here. The remaining collected species are epigean macro- and microcrustaceans and are considered to be stygoxenes and stygophiles. Most of the anchihaline crustaceans were members of the order Cyclopoida. The most widespread species was Niphargus hebereri and the richest genus was Diacyclops. The highest species richness was found in those caves with a gradual vertical distribution of salinity and abundant food. We recorded five new copepod species for the Kornati islands: Diacyclops crassicaudis, D. languidoides, Megacyclops viridis, Metacyclops sp. and Halicyclops dalmatinus, the latter being also a new species for Croatia. Vertical salinity gradients generally determine the spatial distribution patterns of stygobiont crustaceans. Oligohaline-limnic to mesohaline water layers were dominated by amphipods and some copepod species, while calanoids and harpacticoids were dominant in polyhaline water layers.


29


Acknowledgements This work would not have been possible without the support of numerous people. In particular we thank Z. Ruzˇanovic´, D. Lackovic´ and Z. Godec for much help in the field sampling. We are grateful to Dr F. Krsˇinic´ (Laboratory for Plankton Ecology, Dubrovnik) for the identification of Badijella jalzici. We would like to thank the anonymous reviewers for their suggestions on the improvement of this paper. This work was supported by the Kornati National Park and Scientific Research Council of the Republic of Croatia. References Bognar A., Grizelj M. (1996) Geomorfolosˇke znacˇajke arhipelaga Kornata. In: Mesˇtrov M. (Ed.), Kornati: priopc´enja sa simpozija prirodna podloga, zasˇtita, drusˇtveno i gospodarsko valoriziranje. Ekolosˇke monografije 7. Hrvatsko ekolosˇko drusˇtvo, Zagreb: 23–35. Fosshagen A., Iliffe T.M. (1998) A new genus of the Ridgewayiidae (Copepoda, Calanoida) from an anchihaline cave in the Bahamas. Journal of Marine Systems, 15, 373–380. Galassi D.M.P. (2001) Groundwater copepods: diversity patterns over ecological and evolutionary scales. Hydrobiologia, 453/454, 227–253. Herak M. (1986) A new concept of geotectonics of the Dinarides. Acta Geologica, JAZU, 16(1), 1–42. Humphreys W.F. (1999) Physico-chemical profile and energy fixation in Bundera Sinkhole, an anchialine remiped habitat in north-western Australia. Journal of the Royal Society of Western Australia, 82, 89–98. Huys R., Boxshall G.A. (1991) Copepod Evolution. The Ray Society, Natural History Museum, London: 468 pp. Iliffe T. (1992) Anchialine cave biology. In: Camacho A.I. (Ed.), The Natural History of Biospeleology. Museo nacional de ciencias naturales, Madrid: 614–636. Iliffe T. (2000) Anchialine cave ecology. In: Wilkens H., Culver D.C., Humphreys W.F. (Eds), Subterranean Ecosystems. Ecosystems of the World 30. Elsevier, Amsterdam: 59–76. Krsˇinic´ F. (2005a) Badijella jalzici – a new genus and species of calanoid copepod (Calanoida, Ridgewayiidae) from an anchialine cave on the Croatian Adriatic coast. Marine Biology Research, 1, 281–289. Krsˇinic´ F. (2005b) Speleohvarella gamulini gen. et sp. nov., a new copepod (Calanoida, Stephidae) from an anchialine

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