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Abundance and distribution of freshwater (Spongillidae)in Danube floodplain waters near Vienna, Austria

Iris Dröscher1, Johann Waringer1

Keywords: Spongillidae, Danubian floodplain waters, Vienna

Introduction Although the phylum Porifera comprises more than 6000 species, less than 300 are known from freshwaters (Frost, 1991) with 6 species being recorded in Central Europe (Arndt, 1926; Pronzato & Manconi, 1987): lacustris, fragilis, fluviatilis, E. mülleri, horrida and stepanowii. A further species (Eunapius carteri), well known from tropical and subtropical Africa and Asia and from Lake Balaton in Hungary has been reported from cooling water outlets of a nuclear power plant in Germany (Gugel, 1995). Unfortunately, there is a paucity of data on ecological parameters influencing distribution patterns of freshwater sponges. The purpose of the present study was, therefore, to obtain quantitative information on abundance and habitat requirements of species in typical Danubian floodplain waters.

Methods Freshwater sponges were collected during a summer (28 June – 14 July, 2004) and autumn census (19 September – 10 October, 2004) at 32 sampling sites located at floodplain waters within the confines of the National Park “Donau-Auen” east of Vienna, Austria. At each site, each substrate type (macrophytes, dead wood, mineral substrate including riprap) was thoroughly checked for sponges either from the shore or by boat throughout a 30 minute period (CPUE; catch per unit effort). The colony size was measured using a transparent grid, sponges released from the substrate using a knife and preserved in 75% ethanol. In the lab, siliceous spicules of sponges and gemmulae were isolated using 10% Sodium Dichloro- Isocyanurate (Hooper, 2000), transferred to slides, embedded and investigated under a microscope. Species were identified using the keys by Bartsch (1957) and Streble & Krauter (2002). Spicules were measured using an ocular micrometer and checked for anomalies; up to 300 spicules were investigated per specimen. For SEM investigations (JOEL JSM – 35CF scanning microscope), spicules were transferred to 65% HNO3 for 6 (sponges) or 24 hours (gemmulae), washed in water and 100% ethanol and sputtered with gold (AGAR B7340). For checking the influence of abiotic parameters, frequency deviations were calculated (Økland & Økland, 1996) which are given by the following formula: N n i − i N n F i = * 100 n i n where Fi = frequency deviations for interval i, ni = number of sampling sites in interval i, n = total number of sites, Ni = number of sites where the species was present in interval i and N = total number of sites where the species was present. Deviations were checked by Chi-square tests. Stastistical analyses were performed using the package SPSS. For canonical correspondence analysis (CCA), environmental data were (log+1) transformed, rare species

1 Department of Freshwater Ecology, Vienna University, Althanstraße 14, 1090 Vienna, Austria

236 downweihgted and Monte Carlo unrestricted permutation tests (n= 499) were performed; for these calculations the package CANOCO was used.

Results and discussion In the National Park “Donauauen” five of the six Austrian species of freshwater sponges were recorded (Table 1). Ranked from abundant to rare, these species comprised (Linné 1758), (Linné 1758), Ephydatia mülleri (Lieberkühn 1855), Eunapius (=Spongilla) fragilis (Leidy 1851) and Trochospongilla horrida (Weltner 1893). Heteromeyenia stepanowii, already reported from Carinthia, was lacking in the samples. Trochospongilla horrida seems to be recorded for the first time in Austria. The high colonisation ability of Ephydatia fluviatilis is reflected by the fact that it was present at nearly each sampling site. Ephydatia mülleri, Eunapius fragilis and Spongilla lacustris were frequently associated in the water bodies of the Danube flood plain. For most sponges hard substratum was essential for growth. Suspended timber use in the surroundings of the water bodies and dead trees drifting in the water seems to positively influence the abundance of freshwater sponges. Eunapius fragilis, Ephydatia fluviatilis and Ephydatia mülleri significantly prefer wood over stone substrate, whereas Spongilla lacustris definitely preferred the latter (Fig. 1). Ephydatia fluviatilis significantly favoured water bodies with summer temperatures above 21°C, whereas Ephydatia mülleri significantly avoided water bodies with temperatures below 17.5°C. In addition Ephydatia mülleri and Trochospongilla horrida preferred backwaters with higher hydrological connectivity with the Danube, whilst Spongilla lacustris Table 1. Inventory of freshwater sponge species collected at 32 floodplain water bodies within the area of the National Park “Donau-Auen” near Vienna, Austria; showing the area colonized by each species (cm² with percentages) at the summer (June / July) and the autumn (September / October) census. Species Area colonized (cm²; %)

June / July September / October Total Ephydatia fluviatilis 1055 (68.0) 1140 (55.7) 2195 (61.0) (Linné 1758) Ephydatia mülleri 144 (9.3) 402 (19.6) 546 (15.2) (Lieberkühn 1855) Spongilla lacustris 189 (12.2) 443 (21.6) 632 (17.6) (Linné 1758) Eunapis fragilis 137 (8.8) 19 (0.9) 156 (4.3) (Leidy 1851) Trochospongilla 26 (1.7) 43 (2.1) 69 (1.9) horrida (Weltner 1893)

237 100%

80%

60% *

40% * * * * * 20% * * * Area colonized (cm²) colonized Area 0% fragilis mülleri lacustris Spongilla Spongilla fluviatilis Ephydatia Ephydatia horrida Trochospongilla

Fig. 1. Substrate preferences (given as percentages) of the five sponge species. Light grey: wood, medium grey: stones, dark grey: macrophytes (* = P< 0.05, ** = P < 0.001, *** = P<0.001). and Ephydatia fluviatilis were favoured by lower connectivity (Fig. 2). Sites 29 to 32, where sponges were completely lacking, are located in the backwater system of Regelsbrunn, whose flow and connectivity with the Danube has been increased within the last years. The abundances of Ephydatia mülleri and Trochospongilla horrida were significantly (P<0.05) and positively influenced by increased silica content, whereas Ephydatia fluviatilis preferred habitats with low silica content (Fig. 3). With respect to aberrant macroscleres, Ephydatia fluviatilis followed by Ephydatia mülleri and Eunapius fragilis were the most ecosensitive species, whereas aberrant macroscleres were only seldom recorded in Trochospongilla horrida and Spongilla lacustris. Anomalous hooks occurred most often, whereas centrotylots were scarcest.

238 20 0 -20 * -40 -60

Frequency deviation Frequency -80 -100 stagnant medium flow lotic Current 40

20

0 * -20

Frequency deviation -40 weak medium strong Canopy 40 20 0 -20 * -40 -60 -80 Abweichung der Häufigkeit der Abweichung -100 0.0 - 1.7 1.8 - 3.3 3.4 - 5.0 Silica

Fig. 2. Current velocity, canopy shading and silica concentration preferences of Ephydatia fluviatilis, the most common sponge species of the study area, based on frequency deviations (* = P<0.05; hatched columns: Chi-square test not possible).

1 SiO2

T. horrida Connecitivity KonnektivitätDurchströmung

E. fluviatilis

E. mülleri 0

E. fragilis

S. lacustris

-1 -1 0 1

239 Fig. 3. Canonical correspondence analysis of hydrological connectivity and silica concentration versus area colonized by the five sponge species at 32 sampling sites.

References ARNDT, W. (1926): Die Spongillidenfauna Europas. – Arch. Hydrobiol. 17: 337-365 BARTSCH, A. (1957): Das Bestimmen einheimische Süßwasserschwamme. - Mikrokosmos 47: 195-202. FROST, T. M. (1991): Porifera. – In: THORP, J.H. & COVICH, A.P. (eds): Ecology and Classification of North American Freshwater Invertebrates: 95 – 124. Academic Press, San Diego, California. GUGEL, J. (1995): Erstnachweis von Eunapius carteri (Bowerbank 1863) (Porifera, Spongillidae) für Mitteleuropa.- Lauterbornia 20: 103-110. HOOPER, J.N.A. (2000): Sponguide. Guide to sponge collection and identification. (http://www.qmuseum.qld.gov.au/organisation/sections/SessileMarineInvertebrates/index.asp ).: 1 – 129. - Queensland Museum, Australia. ØKLAND, K.A. & ØKLAND, J. (1996): Freshwater sponges (Porifera: Spongillidae) of Norway: Distribution and ecology. - Hydrobiologia 330: 1-30. PRONZATO, R. & MANCONI, R. (1987): Chiave dicotomica per il riconoscimento delle spugne d’aqua dolce Italiane. - Boll. Mus. Ist. Biol. Genova 53: 81-99. STREBLE, H. & KRAUTER, D. (2002): Das Leben im Wassertropfen: 1-428. Kosmos, Stuttgart.

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