ANNALES • Ser. Iiist. nat. ■ 12 • 2002 • 1
original scientific paper	UDC 581.5(497.5 Cres)
received: 2. 7. 2002
ECOLOGICAL CHARACTERIZATION OF A MEDITERRANEAN FRESH WATER POOL ON THE MERAG PENINSULA, CRES (CROATIA)
Pamela ZOLDA, Johanna ORTEL & Wolfgang WAITZBAUER Institute of ixology and Conservation Biology, University of Vienna, A 1090 Vienna, Althanstrafie f 4
E mail: Pamela.Zolda@univie.ac.at
ABSTRACT
In 1997, fauna, flora and water chemistry of a persisting fresh water pool was investigated on the Merag Peninsula of the Kvarner island of Cres. The pond was threatened to become totally covered by Typha angustifolia L. Different methods to remove pans of the Typha-stand have been therefore engaged. Effectiveness of the methods has been controlled qualitatively in the consecutive years 1998-2001. Water chemistry was determined before and after the removal of the phytomass. Two species were new records for the island of Cres: Orchis laxiflora Lam., which is endangered throughout the Mediterranean region, and the Water Rail Rail us aquations I.., which was found breeding successfully in the reed belt. Moreover, the water beetle Hygrobia tarda (Herbsl), a species considered to be extinct in central Europe, was collected.
Keywords: fresh water pool, fauna, flora, first records, Typha angustifolia, floating mat, Cres
CARATTERISTICHE ECOLOGICHE DI UNO STAGNO MEDITERRANEO SULLA PENISOLA
DI MERAG, SSOLA DI CHERSO (CROAZIA)
5 INTE51
Nel 1997 gli autori hanno studiato la fauna, la flora e le caratter/sí/c/ie fisico-chimiche dell'acqua di uno spec-chio d'acqua dolce permanente sulla penisola di Merag dell'isola quarnerina di Cherso. Sullo stagno combeva la minaccia di venir completamente ricoperto da Typha angustifolia L. Nel tentativo di rimuovere parte delta copertura a Typha sono stati usa ti rnetodi differenti. L'efficacia di taii metodi e stata controüata qual ilativamente negli anni consecutivi 1998-2001. Le caratteristiche fisico-chimiche dell'acqua sono state determinóte prima e dopo la rimozi-one deila fito-massa. Due specie sonó state inoltre segnalate per la prima volta sull'isola di Cherso: Orchis laxiítora Lam., minacciata neü'intera regióne mediterránea, e ¡I porciglione Ralius aquaticus L., che nidificava con successo nel canneto. E stata inoltre raccolta Hygrobia tarda (Herbstj, specle considerata ormai estinta nell'Europa cent rale,
Parole chiave: specchío d'acqua dolce, fauna, flora, prime segnalazioni, Typha angustifolia, intrico galíeggianle,
Cherso
73
ANNALES • Ser. hist. nat. • 70 • 2002 • 1
¡'anda ZOLDA et ¿1.: ECOLOGICAL CHAlWCTBllZATfON Of A VtfDtTCRRANSAN 1-RtSK WATER POOL ON 'I HE MCRAG PENINSULA, C»f5 ¡CROATIA). 73-82
INTRODUCTION
In semi-arid regions tike the Mediterranean, permanent freshwater pools constitute important "cells" that increase the biodiversity of the region. Various species of insects, amphibians, reptiles and waterfowl depend on the pools and the surrounding marsh (Raab ef al., 1996; Silveira, 1998). On Cres, more than 70 medium-sized and small pools exist and many of them never dry up (Mavrovif!, 1994). Some are of natural origin and some are man-made. In the times when the island was more densely populated than today, the Cres inhabitants increased the number of natural pools by artificial ones. Natural or man-made hollows were made impervious by ( lay. In the past, these pools have been an essential factor in the general water supply particularly for the livestock.
Since the population density has decreased due to migration, livestock has decreased as well. Hence, watering places are used infrequently, they may become heavily infested by cattail and succession to terrestriali-sation may start. Since permanent fresh water pools are especially important in semi-arid regions, it is essential to maintain the still existing ones.
The investigated pond of Sveti Vid on the Merag Peninsula was threatened by total coverage of the narrow leafed cattail Typha angustifolia, indicating a decreasing utilization and care for the pool by man. The aim of the study was, first of all, to characterize the pool by its flora and fauna in a half-quantitative and qualitative manner in order to document its importance for the local biodiversity. Secondly, it should serve as a basis for finding effective methods to reduce the cattail belt and to achieve the recommended 50:50 ratio of open water and vegetation (Sojda & Sojberg, 1993) and to counteract eutrophication (Blab, 1993). This paper shall give the first impression of the life community in and around the pond and studies will be continued in the following years.
MATERIAL AND METHODS Location of the pool
T he pond is situated near the deserted village of Sveti Vid on the Merag Peninsula ff'ig.l) and embedded in a formerly intensively cultivated area (vineyards, mulberry trees, laurel groves). Today, the area is only used as sheep pasture. The soil-type is a flat, the stony Terra Rossa and two thirds of the pool are surrounded by stonewalls at a distance of 3-5 m, the rest is fenced by a wire net. Shape and exposition are shown in Fig. 2. Water samples for chemical analysis were taken 30 cm below the water surface and parameters were determined Lising a Merck outdoor Test (Art. Nr. 111151). Additionally, temperature was measured in the free water-body.
Cres	. Merqg
Peninsula
lubenice v*
Mafttnšclco
srivan < «
10 km
Fig. 1: Study area - location of the Merag Peninsula on the island of Cres (Kvarner, Croatia). Si 1. Raziskovano območje - lokacija Meraškega polotoka na otoku Cresu (Kvarner, Hrvaška).
Fig. 2: Dimensions of the pond at Sv. Vid. SI. 2: Dimenzije kala pri 5v. Vidu.
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Pamela ZOU3.\ «1 a!.: tCOl.OGiCAi. CHARACItWZA'fION OF A MEPIltRRANi AN TRKH WATER TOOL OK THEMERAG PENIN5UIA, CRES (CROATIA), 73-82
---Typha stand before reduction;-------Typha stand after reduction; x Dead wood; O Salix alba
Hi
H Salix cinerea;
Ceratophyllum demersum; jgggg Orchis iaxiflora; Potamogetûn natans
Rogozov sestoj pred skrčenjem; -------Rogozov sestoj po skrčenju; x Plavajoči les
	Shady riparian jone	
t"""— — 1		1
Fig. 3: Sketch of the Typha layer before and after reduction of the herbaceous plant layer and woody plants. Fig. 3: Skica plasti ozkolistnega rogoza pred in po odstranitvi rastlinske mase in olesenelih rastlin.
Tab. 1: Water chemistry of the fresh wafer pool at Sv. Vid on the Merag Peninsula (Cres IslandCroatia), n.d.= below detection limit of the test, - not measured.
Tab. 1: Kemijske lastnosti vode v kahi pri Sv. Vidu na Meraškem polotoku (otok Crcs, Hrvaška), n.d.- pod mejo de-tekcije, - neizmerjene.
	1997		1998	MUI rj^-r.vM.vW.'n.v "■wJiriw/.iwwi ■ ■ ■ ■ ■ 1999		2000		2001
	before Typha removal	after Typha removal	June	june	September	June	September	May
temperature CO	20	21	22.8	—	25	22.5	25.5	20
pH	7.5	7.8	7.5	—	—	7.7	8.5	7.0
oxygen (m°/l>	4.9	3.65	3.0	».	2.0		1.7	5.0
phosphate fmg/l)	0.25	0.25	<0.25	—	<0.25	„	0.25	0.25
nitrate (ma/I)	n.d.	0.1	<10	—	10	10	10	0
nitrite (mg/l)	n.d.	n.d,	0.025		0.25	0.04	0.3	0
ammonium (mq/l)	0.1	0.2	n.d.	—	n.d.	• —	0.2	0.1
total hardness CdH)	17.1	15.2	18.1			18.4	18.1	14.7
carbonate hardness CdH)	17	15.5	16,4	--	-		16.8	4.6
residual hardness ('dH)	>0.5	>0.5	>0.5	-			>0.5	
75
ANNALES • Ser. hisl. nat. • 12 • 2002 • 1
Pamela ZOtDA el al.: ECOLOGICAL CHARACTERIZATION OF A MEDITERRANEAN FRESHWATER POOL ON IMC MFRAG PÍNINSULA. CRES (CROATIA),
Vegetation
Vegetation within and around the pool was recorded. The marsh fiora was investigated along two transects (Fig. 2). For the reduction of the cattail, the T. angmtifoiia stems rooting in the bottom of the pond near the shore were either pulled out by hand or cut below the water surface due to damage rhizomes infiltrated by water. A part of the floating rhizome mat in the centre of the pond was sawed into squares and, after estimating its biomass, removed from the water (Fig. 4a). The development of the Typha layer was documented photographically in spring and autumn/winter from 1997 to 2001.
Fauna
The fauna associated with the pond was recorder! qualitatively considering the different habitats: free water body, benthos, Typha-stand (standing crop and floating mat). Population densities of two vertebrate species were estimated for an area of about 250 m2: Gambusia affinis was caught in a constrained area for 30 mtrt by hand nets. Projection of the number of individuals caught yielded an estimation for the total population size. Population density of Rana ridibunda was estimated by observing the sunny shore of the pond for several times during june 21x1 - 14,h 1997.
RESULTS AND DISCUSSION Biotope parameters of the pond
The surface area of the pond is approximately 1,200 m2 arid its maximum depth is 2.16 m. Further dimensions are shown in Figure 2. Water chemistry parameters are summarised in Table 1. The pH value of 7.5 and the low values for nitrate and nitrite indicate rather good water quality. Removing of Typha did not influence water chemistry neither immediately nor in longer term. Slight differences between the years may be due to differences in water level and temperature: during the season, the water level of the pool changed between high water after winter rainfall and extensive desiccation during the summer. Seasonal fluctuations between 130 cm and 170 cm are apparently normal. During the study period, the highest water level in the pool of Merag rose up to approximately 215 cm (November 1998, see also Fig. 4f) and the lowest level fell down to 40 cm (August 2000, see also Fig. 4j). Under the extreme summer conditions, the water line could recede along the East-West-line down to 9.5 m from the shore with a reduction of the water volume of about 85%. At that time, it is particularly the fish population that gets very crowded in the highly restricted zone of life.
Tab. 2: List of the most abundant plant species growing on the Typha-rhizome mat in the fresh water pool at Sv. Vid on the Merag Peninsula (Cres Island, Croatia). Tab. 2: Seznam najštevilnejših rastlinskih vrst, rastočih na plavajoče m rogozu v kalu pri Sv, Vidu na Meraškem polotoku (otok Cres, HrvaŠka).
Bryophyta	Calliergonelia cuspidata Au/acomnium palustre Plagiomnium undulatum Orepanociadus aduncus
Ranunculaceae	Ranunculus lingua
Cyperaceae	Cat ex sylvatica Carex cf. acutiformis Carex vulpina
Typhaceae	Typha angustifolia
! Rubiaceae	Galium album
Rosaceae	Potentilla reptans
Polygonaceae	Rumex conglomerate ;
Salicaceae	Salix cinerea Salix alba
Orchidaceae	Orchis laxiflora
Asteraceae	Eupatorium cannabinum Pulicaria dysenterica
Onagraceae	Epilobium hirsuium
Very low water does not only cause general problems for the aqtiatic fauna, it also influences the ecological balance by changes of the hydrochemical and -physical life conditions, especially by a low rate of oxygen combined with high wafer temperatures (Tab. 1). The water surface in the summer is also covered with a dense algae mat (see also Fig. 4i), which flinders the exchange of oxygen. Values for ammonium (0.1-0-2 mg/1) and oxygen indicate a water quality of 2-3 and this corresponds to the occurrence of Potamogeton natans and Ceratophyllum demersum (Bellmann, 1988) The presence of Potamogetum natans indicates p-rnesosa probe water quality (Streble & Krauter, 1988) and Ceratophyl-!um demersum is typical for eutrophic shallow waters and a resistant species of eutrophic lakes (Toivonen & Back, 1989).
Phosphor rates of 0.05 mg/l are considered critical. The measured phosphate and nitrite values of 0.25 rng/l in autumn 1999 and 2000 are relatively high and may result from a sheep cadaver, which was found lying in the water in the autumn.
Vegetation
The northern shore of the pool is shaded by trees of Acer campestre and A. monspessulanum, whereas the southern shore is treeless and heavily grazed by sheep. Typical herbs of this sun-exposed area are: Stachys erecta, Marrubium peregrinum, Gaiactiles tomentosa,
ANIMALES • Ser. hist, nat. -12- 2002 • 1
Pamela ZOl. DA eiel.: CCOIOCICAI. CHARACTERIZATION Of A.MEDITERRANEAN FRESH WATER POOL ON THE MERAG PENINSULA, CREStCKOAFIA), 73-82
Tab. 3: Animalcommunity associated with the permanent fresh water pool at Sv. Vid. Tab. 3: Živalska združba, povezana s sladkovodnim kalom pri Sv. Vidu.
Gastropoda	_ Acroloxidae	Acro/oxus /acustris
Araneae	Lycosidae Tetragnathidae	Pirata sp. Tefra^oafha sp.
Odonata	Coenagrionidae Aeshnidae Libeflulidae	Ojenagrion pue/la Coenagrion scitu/um Ceriagrion tenellum ¡schnura elegans Enallagma cyatñigerum Anax imperator Orthetrum caí ¡celia tum Crocothemis erythraea Ubellula depressa
Ensifera	Gryllotalpidae Gryllidae Tettigonidae	Gryllotalpa gryüotalpa Pteronemobius heydeni Phohdoptera ¡ittoralis
Caelifera	Acrididae	Aiolopus strepens
Heteroptera	Notonectidae Nepidae	Noionecla sp. Nepa sp.
Coleóptera	Carabidae Dytiscidae Hygrobiidae Rvdrophilidae	Oodes helopioides Cybister latenmarginalis \ Noterus sp. Scirtes sp. Cyphon sp. Hygrobia tarda Enochrus testáceos
Díptera	Stratiomyidae Syrphidae	Slraliomys longicornis Stratiomys. potamida Las ¡opa vilhsa Odontomyia ornata Eristalis s¡milis Eurirnyia linéala
Pisces	Poecilitdae	Gambusia affínis
Amphibia	Hylidae Ranidae	tlyla arbórea Rana ridibunda
Reptilia	Lacertidae Colubridae	Podareis melisellensis Nat.rix natrix Elaphe situía Elaphe quatuorlineata
Aves	Ratlidae	Ratlus aqi/aí/cus
Plantago media, Trifolium repens, Dactylis glomer-ata. Willows {Salix alba, S. cinerea) of 0.3 m (min.) to 2.75 tn (max.) circumference grow in the northern part of the pooi (Fig, 3).
About three quarters of the water surface were covered by T. angustifolia, the rest of the surface partly by Potamogetum natans and Ceratophyllum demersum (Fig. 3). In the centre of the pond, T. angustifolia forms a floating rhizome mat on which marsh flora is growing (Tab. 2). Tl le mat of the cattail has its maximum thickness in the central part, which suggests that it originated in the centre of the pool, and expands towards the shore. Since the mat works as a physical and chemical filter (Ennabili et a!., 1998), other plant species were found in a characteristic distribution pattern. However, factors like light condition, interspecific competition and nutrient supply may also be responsible.
All four recorded moss-species are widely distributed and typical for marshy habitats. Aulacomnium palustre is typical for weakly to strongly acidic bogs (Frahm & Frey, 1983; Jahns, 1987). Epihbium hirsutum is typical of terrestrialisation communities and eutrophic species like Rumex conglomerate, Pulicaria dysenterica and Eupatorium cannabium indicate nitrification.
Noteworthy is the first record of Orchis laxiflora on the island of Cres. This endangered orchid is distributed throughout the northern Mediterranean, but rare due to loss in habitats (Baumann & Künkele, 1982). In 1997, the population of 150-200 individuals bloomed in the centre of the rhizome mat. From 1998 to 2000, no orchids were found blooming. This may be. due to sheep grazing in the central part of the Typha- stand during the low water leve!, in May 2001, around 150 orchids were found blooming again.
ANNALtS • Ser. hist. nat. ■ 12 • 2002 • 1
ANN ALES • Ser. hist nat. • 12 ■ 2002 • 1
Fig. 4: Documentation of the removal of the cattail belt and its recovery in 4 consecutive years at the pond at Sv. Vid, Merag:
a. removal of the rhizome; b. Typha stand before reduction in spring 1997; c. Typha stand after reduction in spring 1997; d. atrium/? 1997; e. spring 1998; f. winter 1998; g. spring 1999; h. autumn 1999; i. spring 2000; }. autumn 2000; k. spring 2001.
SI. 4: Dokumentacija o odstranitvi pasu ozkolistnega rogoza in njegovi ponovni rasti v 4 zaporednih letih v kalu pri Sv. Vidu na Meraškem polotoku:
a. odstranitev rizoma; b. sestoj ozkolistnega rogoza pred krčenjem spomladi 1997; c. sestoj ozkolistnega rogoza po krčenju spomladi 1997; d. jesen 1997; e. pomlad 1998; f. zima 1998; g. pomlad 1999; h. jesen 1999; i. pomlad 2000; j. jesen 2000; k. pomlad 2001.
Typha
During the fast years, the open surface of the pond decreased dramatically due to the expansion of T. an-gustifolia. Total coverage would threaten the existence of the pond. Therefore it was decided to remove some parts of the cattail belt. Just by doing that, it was discovered that the centre of the 7yp/ia-stand consisted of a floating rhizome mat. The original margins of the Typhastand and the margins after removing the cattail are given in Figure 3. Cattail rooting near the shore was pulled out by hand or cut beneath the water surface and about 25 m2 of the floating mat with an average thickness of 40 cm, which corresponds to a biomass of 5.1 t fresh weight (3.1 t dry weight), were removed. Controls
in the following years (1998-2001) showed that the rhizome layer did not expand where it had been cut (see also fig. 4). In September 1997, only cattails removed by hand sprouted again, whereas nearly none recovered amongst those that had been cut below the water line. Hence, the rhizomes may have been damaged by penetrating water. In June 1998, the cattail was cut again and by September 1998 nearly none of the cut cattail had recovered (see Fig. 4f).
Fauna
Gambusia affinis holbrooki (Poec.iliidae) was introduced to Europe at the beginning of the 20lh century especially for mosquito control (Kinzelbach & Krupp,
79
ANNALES • Ser. Iiist. nat. ■ 12 • 2002 • 1
Pamela ZOLDA rt st: fCOLOGIOK. CHARACTERIZATION Of A MEDITERRANEAN' fSESH WATER POO I ON THE mkag PENINSULA. CR£5 ÍCROA1IA}, 73-82
1982) and is established throughout S-Europe since 1930. As G. affinis prefers shallow sun-exposed water regions, the population density was estimated on the sunny pari of the pond. The projection yielded about 5000 individuals/250 m2 surface of the pooi. The population size indicates that even a small body of water exists during the whole year. G. affinis is capable to tolerate water temperatures up to 40°C (Al Habbib & Yacoob, 1993), which is far more than the pool temperature measured on several occasions in late spring and in September.
Seven amphibian and twenty-one reptilian species are known for Gres ÍSehnal & Schuster, 1999). In total, five species were found at the pond at Sv. Vid (Tab. 3). The abundance of Rana ridibunda was estimated, and yielded 20 adults and 3 sub-adults. Several times, individuals of Natrix natrix and Elaphe quatuorlineata were recorded swimming, whereas 4 juvenile individuals of E. situla were observed in the surrounding stone wait. Many specimens (if Podareis melisellensis were recorded resting on stones near the shore.
A peculiarity of the pond is the first evidence of a brood of the Water Rail Rallas aquaticus for Cres in 1997. Ten eggs hatched successfully in May 1997 and in September of the same year the pond was still used by these birds.
The pool ot Sv. Vid is also a life zone of an interesting invertebrate biocoenosis, which includes common species along with endangered and rare ones (Tab. 3). The fauna of soldier flies (Stratiornyidae) with aquatic larvae feeding on algae is relative rich in species and individuals. Slratiomys longicornis, S. potamida, Lasiopa villosa and Odontomyia órnala were recorded. High numbers of larvae of Stratomyidae were found in the benthos. The maggots of two species of hover flies, Eristalis simiiis (- E. pratorum) and En rimy ¡a lineata, were found developing in the pond.
The largest dytiscid beetle is Cybister laterimargina-lis. This species occurs in lakes with deep water and is not common in Europe with tendency to recede (Schmidt, 1995). Remarkable is the presence of Hygro-bia tarda (Hygrobiidae), the only species of this water beetle family in Europe, which is considered to be extinct in Central Europe (Sondermann, 1990). Both species were also found near Osor (Franciscolo, 1978).
High numbers of Cryllotalpa gryllotalpa in different developmental stages escaped from the Typ/ia-rhizome mats, which were removed from the pond. Several
specimens of the hygrophilic and warm loving (ingrisch & Kohler, 1998) grasshoppers Pteronemobius heydeni and Phoiidoptera littoral is were also found near the water.
Twenty-one dragonfly species are known from the island of Cres (Susk: & Perincic, 2000), 9 of which were identified at (he pond of Sv.Vid (Tab. 3). Typical Mediterranean species like Coenagrion scitulum, Ceriagrion tenellum and Crocothemis erytbraea, which also was abundant as larvae in the benthos, occur with species distributed throughout Middle Europe like Enallagma cyathigerum and Iscbnura elegans. Ceriagrion tenellum is abundant in the Mediterranean region and mostly found along flowing waters, whereas C. scitulum is considered to be rare throughout its distribution area (Bellmann, 1993). The same author often reported C. scitulum from very small, densely vegetated pools, which were rather isolated in a dry landscape of Istria. The fauna of freshwater snails is very poor and only Acroloxus lacustris was found in a small population tinder stones along the shore and within the cattail belt. Especially the appearance of the Emperor Dragonfly An ax irnperator, a species that is missing at desiccating ponds (Bellmann, 1993), is an evidence that the pooi does not dry up during the year.
CONCLUSIONS
The pond at Sv. Vid was heavily threatened to dry up completely due to the extensive growth of the Typha rhizome. During our investigations, this pool showed to be an important cell of biodiversity within the old cultivated area. This was underlined by the first records of two species for the island of Cres, Furthermore, a remarkable number of endangered and rare plant and animal species live around or in the pond. The removal of the Typha rhizome was apparently the right way to save the water level and to guarantee the existence of the water body for many years. A continuation of the described management would be desirable.
ACKNOWLEDGEMENTS
We wish to thank ail the students from the University of Vienna, who attended the ecological courses on Cres and helped with the acquisition of some data, and Dr. Goran SuSic from the Ekocentar, Beli for providing facilities for our research.
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Pameti ZOIDA e> a).: ECOLOGICAL CHARACTERIZATION OF A MfOll ERRANEAN FRESH WATER POOL ON THE M'RAC PENINSULA, CRLS tCROAHA), 73-S2
EKOLOŠKE ZNAČILNOSTI SREDOZEMSKEGA KALA NA MERAŠKEM POLOTOKU
NA OTOKU CRESU (HRVAŠKA)
Pamela ZOLOA. Johanna ORTEL & Wolfgang WAITZBAUER
institute of Ecology and Conservation Biology, University of Vienna, A-1090 Vienna, Althanstralk ! 4
E-inaii: Pamela.ZoJda@univie.ac.at
POVZETEK
Leta J 997 so avtorji članka na Meraškem polotoku na otoku Cresu raziskovali favno, floro in fizikalne ter kemijske lastnosti vode v kalu, ki ga je čedalje bolj prerašča! ozkolistni rogoz Typha angustifolia L. To je bil razlog za odločitev, da se z različnimi metodami poskusi odstraniti rogozov sestoj. Učinkovitost metod je bila kvalitativno nadzorovana med letoma 1998 in 2001. Fizikalne in kemijske lastnosti vode so bile ugotovljene pred in po odstranitvi rastlinske mase. Sicer pa sta bili na otoku Cresu odkriti dve novi vrsti: Orchis laxiflora Lam., ki je ogrožena v celotni sredozemski regiji, in mokož Rallus aquaticus L., ki je uspešno gnezdil v trstičevju. Poleg tega je bil odkrit tudi potapnik Hygrobia tarda (Herbst), za katerega domnevajo, da je v Srednji Evropi že izumrl.
Ključne besede: kal, favna, flora, prvi podatki, Typha angustirblia, plavajoče rastlinje, Cres
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