0VERSITA
Biologia 69/4: 508—521, 2014 Section Zoology
DOI: 10.2478/s11756-014-0336-1
Benthic macroinvertebrates along the Czech part of the Labe and lower section of the Vltava rivers from 1996—2005, with a particular focus on rare and alien species
Katerina KolarIkova1, Jakub Horecky1, Marek Liska2, Martina jfchova1, Jolana Tatosova 1, Natalie Lapsanska2, Zuzana Horicka1, Pavel Chvojka3, Lubos Beran4, Vladimir Kosel5, Josef Matena6, Zuzana Ciamporova-ZatoviCova7, Ilja Krno7, Eva Bulankova5, Ferdinand Sporka7, Petr Kment3 & Evzen StuchlIk1
1 Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benatska 2, CZ-12843 Praha 2, Czech Republic; e-mail: katerina.kolarikova@natur.cuni.cz
2 Water Management Laboratory in Prague, Vltava River Authority, Na Hutmance 5a, CZ-15024 Praha 5, Czech Republic 3Department of Entomology, National Museum,, Kunratice 1, CZ-14800 Praha 4, Czech Republic
4Agency for Nature Conservation and Landscape Protection of the Czech Republic, KokoHnsko Protected Landscape Area Administration, Ceska 149, CZ-27601 Melnik, Czech Republic
5Department of Zoology/Ecology, Comenius University in Bratislava, Mlynska dolina, SK-84215 Bratislava, Slovakia 6Institute of Hydrobiology, Biology Centre AS CR, v.v.i., Na Sadkach 7, CZ-37005 Ceske Budejovice, Czech Republic 7Institute of Zoology, Slovak Academy of Sciences, Dubravska cesta 9, SK-84506 Bratislava, Slovakia
Abstract: In the Czech part of the Labe River and the lower part of the Vltava River, we examined if the benthic macroinvertebrate composition changed from 1996 to 2005 due to expected improvements in water quality resulting from socioeconomic changes in the Czech Republic since the 1990s. Special attention was given to rare and alien species. The four biological metrics used (Number of taxa, BMWP, Number of sensitive taxa, and Number of EPT taxa) demonstrated that there was indeed an improvement in water quality as well as a slight improvement of the Labe microhabitats during the investigated period. An increasing Number of taxa over time was observed at most sites. Two main concurrent ecological processes are recently in progress in the Labe: a recovery of native species and an expansion of alien species, some of which are considered invasive. The caddisfly Setodes punctatus and the beetle Pomatinus substriatus, considered as regionally extinct in the Czech Republic until 2005, were rediscovered during our investigations. Findings of the crustacean Hemimysis anomala (invasive) and the chironomids Stenochironomus sp. and Lipiniella sp. were the first records of these taxa in the Czech Republic.
Key words: benthic macroinvertebrates; water quality; recovery; alien species; invasive species; biological metrics; Elbe River, Moldau River
Abbreviations: AOX - Adsorbable Organically bound Halogens; BMWP - Biological Monitoring Working Party; BOD/COD - Biochemical/Chemical Oxygen Demand; p,p'-DDT - p,p'-dichlordiphenyltrichlorethane; EDC - Endocrine-disrupting Chemical; EPT - Ephemeroptera-Plecoptera-Trichoptera; g-HCH - gamma-hexachlorocyclohexane; ICPER -International Commission for the Protection of the Elbe River (also IKSE or MKOL); IUCN - International Union for Conservation of Nature; PAHs - Polycyclic Aromatic Hydrocarbons; PCBs - Polychlorinated Biphenyls; Red-list abbreviations: NT - nearly threatened, VU - vulnerable, EN - endangered, CR - critically endangered, RE - regionally extinct.
Introduction
Benthic macroinvertebrates are important indicators of river health (Hellawell 1986; Rosenberg & Resh 1993). Some species have bioindicative potential, so their absence or presence can give information about pollution status (Hynes 1960; Sladecek 1976; Mason 1991; Timm et al. 2001). Macroinvertebrates are suitable bioindicators of aquatic organic pollution (Rosenberg & Resh 1993). Additionally, macroinvertebrates have been shown to be sensitive to heavy metals and organochlo-
rine pesticides (Sladecek & Kosel 1984; Liess 1993; Tim-mermans 1993; Von der Ohe & Liess 2004; Malaj et al. 2012).
Since the middle of the 20th century, water quality in the Czech part of the Labe (Elbe) River has been substantially affected by numerous industrial enterprises as well as large agricultural and mining activities in its basin. Anthropogenic load steadily increased to a maximum in the 1980s and early 1990s (Dusek et al. 2005), when the Labe was considered one of the most polluted European rivers (Madler 1995; Adams
©2014 Institute of Zoology, Slovak Academy of Sciences
Springer
et al. 2001; Tockner et al. 2009). The German part has not been channelized, however, its hydro-morphological character is regulated through a system of wing dams and levees (Adams et al. 2001). The Czech part of the Labe was widely channelized and the continuity of the river is interrupted by two reservoirs (in the highest section) and 24 weirs with locks (Scholl & Fuksa 2000). Thus, nearly the whole longitudinal profile of the Labe shows potamalisation (changes resulting in slowed currents and a higher amount of fine sediments, Muhar et al. 2000). The Labe has been intensively used for boat traffic, and in Germany it is connected through a net of navigation channels to other major rivers (the Rhone, Loire, Seine, Meusel, Rhine, Main, Danube, Oder, Vis-tule, Dnieper, Bug, and Volga), and thus to the Baltic Sea, Black Sea, Sea of Azov, and the Caspian Sea. Such interconnection of large rivers is closely associated with the spread of alien species (Ketelaars et al. 1999; Josens et al. 2005; Nehring 2005; Bernauer & Jansen 2006), causing severe damage to native benthic communities in large rivers. It might therefore be expected that the reduced water quality and habitat degradation of the Labe must inevitably have had an adverse effect on the structure of the macroinvertebrate taxa. Indeed, from 1946-1990 substantial impoverishment in the occurrence of macroinvertebrates was found in the German part of the Labe due to extreme organic pollution (Madler 1995).
Since 1990, however, the Labe basin has experienced significant improvements in water quality as a consequence of the closure of several factories, the decrease or de-centralization of agricultural and industrial activities, and the introduction of modern technologies. As documented by MKOL (2010), there has been a considerable decrease of priority pollutants in industrial waste water (Table 1), as well as a general decrease of As, Cd, Pb, Hg, PAHs, PCBs, and p,p'-DDT in sediments, As, Cd, Pb, Hg and g-HCH in biofilms, Hg in water, and COD of water since the 1990s (Fuksa et al. 2006). Adams et al. (2001) reported significant declining trends for N, P, Hg, Cd, Pb, Co, Zn, Ni in the Labe between 1985 and 1999. The COD and BOD-5 parameters in the Czech Republic including the Labe basin have been reduced to 8% and 15% of their original values, respectively (Langhammer 2010). For the reasons mentioned above, a recovery of some macroinvertebrate taxa might be expected.
The Czech part of the Labe and the Vltava (Moldau) rivers in Prague have attracted the attention of biologists since the end of the 19th century (Klapálek 1891, 1894, 1897; Fric & Vávra 1903). Further studies became again more numerous toward the end of the 20th century (e.g., Landa & Soldán 1986, 1989; Novák 1989; Landa et al. 1997; Soldán et al. 1998), and especially more recently (Scholl & Fuksa 2000; Chvojka & Novák 2001; Spacek et al. 2003; Beran 2006, 2009; Adámek et al. 2010; Georg et al. 2010; Reznícková et al. 2011; Orendt et al. 2012). However, more detailed research along the longitudinal profile of the Czech part of the Labe has not yet been published.
Table 1. Comparison of waste water loads (t y 1; CODcr unit-less) in the Labe basin (Czech Republic) from important industrial sources in the period 1994-2008 (MKOL 2010).
Selected priority pollutant Year
after MKOL -
1994 2008
CODcr 35400 7780
total N 8800 3504
total P 350 53
Hg 1.85 0.095
Cd 1.18 0.005
Cu 8.21 0.479
Zn 48 9.651
Pb 3.99 0.118
Cr 8.88 0.187
Ni 0.85 0.134
AOX 302 21.92
EDC 9.03 0.134
In this study, we hypothesized that the species composition of macroinvertebrate communities at 9 sites along the longitudinal profile of the Czech part of the Labe and lower stretch of the Vltava had rapidly changed between 1996 and 2005 due to expected improvements of the water quality resulting from socioeconomic changes in the Czech Republic since the 1990s. Special attention in this publication was given to the occurrence of rare and remarkable species as potential indicators of water quality improvement. Further, attention was given to the expansion of alien species of benthic macroinvertebrates as a potential threat to aquatic ecosystems.
Study sites
The Labe River has its source on the Czech side of the Krkonose (Giant) Mountains at 1,387 m a.s.l., and after 367.6 km passes through the Czech-German border. With a total length of 1,094 km it is one of the longest rivers in Europe. The Vltava River is its largest tributary, with the confluence about 56 km downstream of Prague. Macroinver-tebrates were sampled at seven sites along the longitudinal profile of the Czech part of the Labe (abbreviation and river km from the sea for the Labe or from the confluence for the Vltava): Verdek (VER; 1 039.6), Nemcice (NEM; 978.8), Valy (VAL; 954.7), Lysa (LYS; 878.1), Obristvi (OBR; 843.5), Decin (DEC; 741.6), Hrensko (HRE; 726.6), and two sites on the lower Vltava: Podoli (POD; 56.2), Zelcin (ZEL; 4.5) (Fig. 1). Six of these sites are identical to those in the international network of monitoring stations established by the ICPER in Magdeburg (Germany) in 1990. Our investigations were done within the long-term "LABE Project", which was initiated in 1990 by the newly established Czech Ministry of the Environment to monitor selected components of the Labe ecosystem. Except for the Verdek site that is rhithral in character, all studied sites on the Labe and Vltava are potamal. The potamal sites differ in the degree of human influence unrelated to water pollution: e.g. river channelization (stone-reinforced banks and heavily modified or inaccessible natural river bottom at Valy, Lysa, Obristvi, and Hrensko on the Labe, and Podoli on the Vltava), slow-flowing waters above weirs (the artificially lentic sites Valy, Lysa, and Obristvi on the Labe, and Podoli on the Vltava),
Fig. 1. Map of sampling sites on the Labe (Czech part) and Vltava Rivers. VER — Verdek, NEM — Nëmcice, VAL — Valy, LYS — Lysa, OBR - Obristvi, DEC - Dëcin, HRE - Hrensko, POD - Podoli, ZEL - Zelcin.
Table 2. Site description.
Site Abbre- River Altitude Site Position River Shipping Stream Habitat description
viation km (m a.s.l.) charac- to weir channel- influence width
ter (Below/ ization (m)
Above/ (Left/Right
Within) bank
reinforcement)
Verdek VER 1,039.6 300 rhithral B, A
Nëmcice NEM 978.8 220 potamal
Valy VAL 954.7 200 potamal W L+R
Lysa LYS 878.1 180 potamal A L+R
Obristvi OBR 843.5 170 potamal B L+R
Dëcin DEC 741.6 150 potamal
Hrensko HRE 726.6 110 potamal L+R
Podoli POD 56.2 175 potamal W L+R
Zelcin ZEL 4.5 140 potamal
23 some littoral macrophytes above a little weir, rapids below;
stony bottom with coarse gravel, leaves and coarse organic matter R 47-72 some littoral macrophytes, local rapids;
bottom with coarse gravel and sandbanks forming a small stable island, fine sediment
+ 59 terrestrial macrophytes reaching to water;
inaccessible bottom, steep reinforced banks with sand and gravel, partly black mud
+ 98 terrestrial macrophytes reaching to water,
some littoral macrophytes; reinforced banks and bottom with some mud and sand 72 terrestrial macrophytes reaching to water, inaccessible bottom, steep banks reinforced with stones and gravel, sand and fine sediment L + 109 local rapids;
stony bottom with gravel, sand, fine sediment, detritus and mud + 103 stony bottom with fine sediment and de-
tritus, steep bank reinforced with stones + 414* terrestrial macrophytes reaching to water
reinforced banks, stony bottom covered by sandy sediment and mud L 53 terrestrial macrophytes reaching to water
bottom with stones, gravel, sand, mud
*including the island
and shipping (mainly Hrensko and DeCin on the Labe and Podoli on the Vltava, to a lesser extent Valy and Lysa on the Labe) (Table 2).
Material and methods
Field sampling
Sampling was performed at 3-year intervals during the period 1996-2005. Sites were always sampled in September, since at this time the water level is typically lower and more stable. In August 2002, an extreme flood on the Vltava and the Labe downstream of Obristvi prevented sampling in September. To describe possible changes caused by this flood, sampling was done in October 2002 and additionally in 2003. In 1996, the Decin site was not sampled due to high flow levels. Samples of benthic macroinvertebrates at each site were collected along a continuous 100 m long stretch of the river littoral zone with the kicking method (Frost et al. 1971) using a sieve of mesh size 500 цш and by manual picking of individuals from submerged objects. Care was taken to sample all microhabitats in order to collect the maximum number of taxa in each stretch (with a focus on taxonomic diversity). The sampled material was preserved in 80% ethanol except for Oligochaetes, which were fixed separately in 5% formaldehyde. In the laboratory, invertebrates were separated from the sediment and all benthic groups were identified to the species level, if possible, by specialists. Oligochaetes were not identified in 1999.
Data analysis
All identified macroinvertebrates are listed in the Appendix (supplementary materials). Metric values were calculated within the Integrated Assessment System for the Ecological Quality of Streams and Rivers throughout Europe using Benthic Macroinvertebrates (AQEM) by the software ASTERICS (version 3.3.1, Wageningen). Four metrics (ASTERICS 2012) were selected to represent biological changes in benthic macroinvertebrates over time as well as differences among investigated sites: the Number of taxa, BMWP, Number of sensitive taxa, and Number of EPT taxa. The BMWP scoring system is based on sum of the points which were assigned to each species according to their tolerance to pollution (the lower their tolerance to pollution the higher the points assigned).
The non-parametric Kruskal-Wallis test was performed at the P-level < 0.05 (STATISTICA 6.1, StatSoft) to test: 1) differences in metrics among the years when pooling the metric values from all sites; and 2) differences in metrics among the sites when pooling the metric values from all years. The similarity of sites, based on the presence/absence of particular taxa (data pooled from all years), was assessed by hierarchical clustering (STATISTICA 6.1, StatSoft). The clustering method used was Euclidean distance, which is simply the geometric distance in the multidimensional space computed from the raw data. To calculate the distances between clusters complete linkage was used, based on the greatest distance between any two objects.
Results
Diversity of macroinvertebrates
A total of 56,625 specimens of benthic macroinvertebrates from nine sites and five sampling years were identified to 371 species or higher taxa, belonging to the taxonomic groups of flatworms (Turbel-
laria), roundworms (Nematoda), leeches (Hirudinea), oligochaetes (Oligochaeta), mollusks (Mollusca), crustaceans (Crustacea), mayflies (Ephemeroptera), drag-onflies (Odonata), stoneflies (Plecoptera), water bugs (Heteroptera), alderflies (Megaloptera), caddisflies (Tri-choptera), aquatic moths (Lepidoptera), net-winged insects (Neuroptera), flies (Diptera), and beetles (Coleoptera). The list of all identified taxa is given in the Appendix (supplementary materials).
The most abundant groups were flies, with 114 taxa (70 of which were chironomids), followed by caddisflies (55 taxa), mollusks (34 taxa), beetles (32 taxa), and mayflies (31 taxa), and these groups together composed up to 72% of the total taxonomic richness.
Time-related trends
The number of taxa approximately doubled over the investigated period, both for all sites together (an average of 72 taxa in 2005 compared to 37 in 1996; see Fig. 2A) as well as for all individual sites except for Valy. The number of taxa was already significantly higher in 1999 compared to 1996 (P < 0.05), and became even more pronounced by 2005 (P < 0.01).
In 2002, the number of taxa substantially decreased at most sites due to the flood event (Fig. 2); however, this decrease was mostly due to the absence of most chironomid larvae. When excluding chironomids from the evaluation to minimize the influence of the flood in 2002 and oligochaetes because of missing data from 1999, the overall positive trend of Number of taxa at particular sites over time remained unchanged by the flood, with the exception of a decrease in Obristvi (Fig. 3).
BMWP (Fig. 2B), which is based on the number of taxa classified according to their susceptibility to organic pollution, was significantly higher in 1999 compared to 1996 for most sites (P < 0.05). In subsequent years BMWP stayed fairly level at most sites, and remained significantly higher in 2003 and 2005 compared to 1996 (P < 0.05).
The numbers of sensitive taxa (Fig. 2C) gradually increased, although with some inter-year variations. The numbers increased significantly (P < 0.05) from values < 3 in 1996 up to 9 in 2005; the most rapid increase being found at Nemcice, followed by Zelcin, Decin, and Verdek.
The number of EPT taxa (Fig. 2D) gradually doubled on average, from 8 in 1996 to 15 in 2005.
Site differences
BMWP values differed among sites, but were only significantly different in Nemcice compared to Hrensko (P
< 0.05) (Fig. 2B).
The Number of sensitive taxa was not statistically different among the sites, except for a significantly (P
< 0.05) higher number at Nemcice compared to Podoli.
Numbers of EPT taxa were different at particular sites over the time period, but were statistically significant (P < 0.05) only in Verdek, Nemcice, and Valy compared to that in Hrensko.
Fig. 2. Time-related changes of four biological metrics at the investigated sites of the Labe and Vltava between 1996-2005: A - Total number of taxa; B - BMWP; C - Number of sensitive taxa; D - Number of EPT taxa. For site abbreviations see Fig. 1.
Fig. 3. Total number of all taxa (excluding oligochaetes and chironomids) at the studied sites between 1996-2005. For site abbreviations see Fig. 1.
In Verdek, Nemcice, and Zelcin, significantly (p < 0.05) more EPT taxa were found than in Hrensko.
The cluster dendrogram divided the sites into three groups according to the presence/absence of partic-
ular macroinvertebrate taxa (Fig. 4). The first cluster contained just Verdek, the second cluster included Nëmcice, Dëcin, Hrensko, and Zelcin, and the third one grouped Valy, Lysa, Obristvi, and Podoli.
Fig. 4. Cluster analysis of investigated sites based on the presence/absence of particular taxa (data from all years were pooled). For site abbreviations see Fig. 1.
The most euryecious taxa, which occurred along the whole longitudinal profile of the Czech stretch of the Labe, were the flatworm Dugesia polychroa, mol-lusks Bithynia tentaculata and Sphaerium corneum, oligochaetes Stylodrilus heringianus and Limnodrilus hoffmeisteri, the leech Erpobdella octoculata, the crustacean Asellus aquaticus, the mayfly Caenis macrura, damselflies Calopteryx splendens and Platycnemis pen-nipes, the caddisfly Cyrnus trimaculatus, the diving beetle Platambus maculatus, and among dipterans Bezzia sp. and several chironomid taxa: Ablabesmyia sp., Procladius sp., Cricotopus sp., Cryptochironomus defectus gr., Glyptotendipes sp., Chironomus sp., Mi-crotendipes chloris gr., Polypedilum convictum gr., P. exsectum gr., Tanytarsus sp., and Cladotanytarsus sp. However, as these chironomid larvae could not be identified to species level, the occurrence of more than one species within the genus is possible.
Lotic and lentic stretches were represented by different taxa. Concerning the crustaceans, the middle Labe was enriched with Gammarus roeselii and Or-conectes limosus, and the section near the German border with Dikerogammarus villosus and Hemimysis anomala. The lentic sites were also characterized by the presence of the mollusks Acroloxus lacustris, Lym-naea stagnalis or Anisus vortex while lotic sites had Viviparus viviparus, Ancylus fluviatilis or Sphaerium rivicola. The dragonflies prevailing in lentic sites were Coenagrion spp., Erythromma najas, Enallagma cya-thigerum, and Ischnura elegans. Most of the water bugs found occurred in lentic waters, with the exceptions of Aphelocheirus aestivalis and Aquarius najas that inhabited lotic potamal sites (Nemcice and Zelcin). The majority of the 55 taxa of caddisflies are common and
rather euryecious species occurring in a broad range of flowing-water habitats or even in standing waters. More than half of these taxa (29) were recorded in the uppermost site on the Labe in Verdek, representing the hyporhithral zone. Lotic sites were inhabited by, e.g., Cheumatopsyche lepida, Athripsodes cinereus, Psy-chomyia pusilla, and the genus Hydropsyche. Among the water beetles identified in this study, the Halipli-dae and Dytiscidae (e.g., Laccophilus hyalinus) were found in lentic sites, with the exception of the genera Oreodytes and Platambus, whereas Orectochilus villosus and the Elmidae occurred in lotic sites.
Records of ecologically remarkable/rare species Compared to the situation at the beginning of the project, many taxa newly appeared during the investigated time period whereas several other taxa were already present at the beginning and gradually occurred at an increasing number of sites. A number of species are included in the Red List of Threatened Species of the Czech Republic (Table 3) according to the IUCN (Farkac et al. 2005). Most of these threatened species were recorded near the end of the investigated period.
We recorded the sensitive oligochaete species Stylodrilus heringianus in the upper Labe and in the Vltava since 1996, and the species was also later found in the middle and lower parts of the Labe (after 2002).
The mollusk Sphaerium rivicola (NT) recovered only gradually during the investigated period. The bivalve Pisidium moitessierianum (EN) in Valy and Pi-sidium supinum (NT) were found in several sites. In the lower Vltava, there were numerous occurrences of the mollusk Viviparus viviparus (NT). Two rare species
Table 3. The occurrence of rare species included in the Red List of Threatened Species (Farkac et al. 2005), classified according to IUCN categories.
Vltava
IUCN -
Verdek Nëmcice
Lysá Obríství Dëcin Hrensko Podolí
Zelcín
ÍOOlINWlOCiroC^COlOÍDCSC^OTlOÍOOlINCOlOCiOlINCOlOCSOJOOlOÍOOlINCOlOCiOlC^COlOÍDroOJCOlO CTCTOOOC^C^OOOC^C^OOOC^C^OOOC^C^OOOC^OOOC^C^OOOC^C^OOOC^C^OOO CTCTOOOC^C^OOOC^C^OOOC^C^OOOC^C^OOOC^OOOC^C^OOOC^C^OOOC^C^OOO HH^OIOIHHMIN^HHOJINCNHHMOIMHHOIOJMHMOIOJHH^INCNHHOIOJMHHOIOJM
OLIGOCHAETA
Uncinais uncinata EN MOLLUSCA
Radix ampla NT
Physa fontinalis NT
Viviparus viviparus NT Pisidium moitessierianum EN
Pisidium supinum NT
Sphaerium rivicola NT
Anodonta cygnea VU
Unio tumidus VU EPHEMEROPTERA
Procloeon bifidum NT
Heptagenia coerulans EN
Choroterpes picteti CR ODONATA
Gomphus vulgatissimus VU
Onychogomphus forcipatus EN
Ophiogomphus cecilia EN
PLECOPTERA
Leuctra cf. leptogaster VU
HETEROPTERA
Aphelocheirus aestivalis VU
Micronecta griseola EN
Micronecta poweri VU
Aquarius najas VU
MEGALOPTERA
Sialis morio CR
MEGALOPTERA
Sialis morio CR
Sialis nigripes CR
TRICHOPTERA
Ceraclea nigronervosa EN
Setodes punctatus RE
DIPTERA
Atherix ibis VU + -
Atrichops crassipes VU COLEOPTERA
Pomatinus substriatus* RE
Oreodytes septentrionalis CR +
Rhantus suturellus NT
Stictotarsus NT + duodecimpustulatus
+ + + ++++ ++ ++ + ++++++ + + + ++ + ++ + - + + + +
+ + + +
+ + + +
+ + + +
+ + + + +
+ ++ + + + + + +
+ + + +
Explanations: RE — regionally extinct in the Czech Republic; CR — critically endangered; EN — endangered; VU — vulnerable; NT — near threatened *The species was reclassified to CR in 2007 (Boukal 2007).
of unionids Anodonta cygnea (VU) and Unio tumidus (VU) were found in the Vltava and in Hrensko, respectively.
Among the mayflies, Alainites muticus, Procloeon bifidum (NT), Heptagenia coerulans (EN), Choroterpes picteti (CR), and Paraleptophlebia submarginata have appeared since 2002. In Decin and Zelcin, the mayfly Potamanthus luteus was found since 2002. Occasionally, but mostly in 2002, the following mayflies were found in Verdek: Baetis alpinus, Torleya major, Ecdyonurus submontanus, and E. torrentis.
Rare dragonflies from the family Gomphidae occurred in Nemcice: Gomphus vulgatissimus (VU), Onychogomphus forcipatus (EN), and Ophiogomphus cecilia (EN).
Except for the upper stretch, the Labe is not a typical biotope for stoneflies. Nevertheless, we found two interesting taxa: Siphonoperla taurica (CR) in Nemcice in 1999 and also Leuctra cf. leptogaster (VU) in Verdek, Nemcice and Zelcin during the last sampling season 2005.
The occurrence of the water bug Aphelocheirus aestivalis (VU) in Nemcice and from 2002 also in Zelcin is noteworthy. In 2005, the water bug Micronecta grise-ola (EN) was first found at three sites on the Labe, and the rare pond skater Aquarius najas (VU) was found in Verdek. Two water bug species sensitive to saprobic pollution, Micronecta poweri (VU) and Sigara distincta, were found at several sites, mainly in 2002 after the flood.
Long-term study on the Labe and lower Vltava benthic macroinvertebrates Table 4. The occurrence of alien species in the Labe and Vltava from 1996—2005.
Labe Vltava
Taxa--
Verdek Nëmcice Valy Lysa Obristvi Dëcin Hrensko Podoli Zelcin
6923569 2 3569 2 356923569235692 3 5 692 3 5 6923569235 9900099 0 0099 0 009900099000990 0 0 990 0 0 9900099000 9900099 0 0099 0 009900099000990 0 0 990 0 0 9900099000
TURBELLARIA
Dugesia tigrina MOLLUSCA
Potamopyrgus antipodarum Physella acuta Ferrissia fragilis Menetus dilatatus Corbicula fluminea Dreissena polymorpha HIRUDINEA Caspiobdella fadejewi CRUSTACEA Proasellus coxalis Orconectes limosus Dikerogammarus villosus Gammarus roeselii Hemimysis anomala
О ■ о
ООО
о о я ■ о ■
о ■ о о О о о
о O O
Total number
14554 32641166515368 232512435
12 3 1112 2
Explanations: o common, O abundant, ■ rare species.
о ■ о
о о о
In 2003 and 2005, the two critically endangered alderflies Sialis morio and S. nigripes were recorded in the upper and lower parts of the Labe, respectively, and in the Vltava sites.
We also found two interesting caddisfly species, Se-todes punctatus (RE) in Nëmcice (2005) and Ceraclea nigronervosa (EN) in Verdek (2003 and 2005).
Larvae of the dipteran Atrichops crassipes (VU) were recorded in the Labe sites from Verdek to Valy, and Atherix ibis (VU) occurred mostly in the upper Labe sites and occasionally even in Valy, Dëcin, and Zelcin. Among the chironomids, two interesting taxa were found in 2003: Stenochironomus sp., and Lipiniella sp.
The record of Pomatinus substriatus (RE) in Nëmcice in 2005 was surprising. The rheophilic beetle Oreodytes septentrionalis (CR) was last found in 1996 in Verdek. The rare beetles Stictotarsus duodecimpus-tulatus and Oulimnius tuberculatus occur only locally in the Czech Republic.
Expansion of alien species
There was a marked expansion of alien species into the Labe than into the Vltava (Table 4). The only site without the occurrence of alien species was the uppermost and relatively natural site Verdek. On the other hand, the middle section of the Czech part of the Labe was most affected by alien species (from Valy to Obristvi, with up to 8 taxa recorded - see Table 4).
After 2002, the flatworm Dugesia tigrina was found at all sites except Verdek. The alien leech Caspiob-della fadejewi was found in the Vltava in 2005. Several alien mollusk species were also found during this study. The Ponto-Caspian zebra mussel Dreissena polymorpha was recorded in the middle Labe since 1996
and later also in Dëcin and Hrensko. The first record of Potamopyrgus antipodarum from our study is dated to 1999 (in Hrensko and Dëcin). Similarly, Corbicula fluminea has been found in Hrensko since 1999 and in Dëcin since 2002. In the middle Elbe, three alien mol-lusks were recorded: Ferrissia fragilis since 1999, Physella acuta since 1999, and Menetus dilatatus since 2002. Besides the mollusk species, the second most numerous group of aliens were crustaceans. The killer shrimp Dikerogammarus villosus was first found in Hrensko in 2002. Since then its abundance has increased (Table 4), and it had spread further upstream to Obristvi by 2005. In Podoli (the Vltava), the species first appeared in 2005. The Balkan crustacean Gammarus roeselii was first recorded in Nëmcice and Valy in 1999 and in the following years it also spread downstream to Lysa and Obristvi. From our data, there was no evidence of a negative influence of G. roeselii on other crustaceans in the Labe. The Ponto-Caspian species Hemimysis anomala was repeatedly found at the border site Hrensko in 2003 and 2005. The crustacean Proasellus coxalis (Isopoda) was present at some of the investigated sites already in 1996. P. coxalis clearly coexists with Asellus aquati-cus, but was always present in lower abundances. The North American invasive crayfish Orconectes limosus was found in the Labe several times during the investigated time period from the border up to Valy.
Discussion
A substantial increase in diversity had already been previously reported for the upper German part of the Labe between 1988 and 1994 (from 30 to 55 taxa; Madler 1995) and for the middle part between 1990 and 1993 (from 9 to 47 taxa; Dreyer 1994). In our study on the
Czech part of the Labe and the lower Vltava, we observed a similar increase in the number of taxa, with the average number of taxa at all sites nearly doubling (from 37 in 1995 to 72 in 2005). We attribute this increase to two main ecological processes: the recovery of native species as a consequence of improvements in water quality after 1990, and the expansion of alien species.
Site differences
The cluster dendrogram divided the sites into three groups in accordance with their character (Table 2). The Verdek site is alone in the first cluster, and is the only site having a rhithral character. The neighboring cluster included Nëmcice, Dëcin, Hrensko, and Zelcin, which are lotic - not influenced by slow-flowing waters above weirs, with an accessible natural river bottom, and can be characterized as a group of lotic potamal sites. The last cluster grouped the Valy, Lysa, Obristvi, and Podoli sites, which are characterized as lentic pota-mal due to the unnatural slow-flowing waters above weirs. Thus, species occurrences were closely related to the site characteristics.
The lotic and lentic stretches were represented by different taxa, mostly in accordance with their ecology as described in the literature. The mollusks Acroloxus lacustris, Lymnaea stagnalis and Anisus vortex are typical for lentic sites (Beran 2002), while Viviparus viviparus, Ancylus fluviatilis or Sphaerium rivicola are typical for lotic sites. The dragonflies Coenagrion spp., Erythromma najas, Enallagma cyathigerum, and Is-chnura elegans inhabit lentic sites (Castella et al. 1991). Most water bugs found are typical inhabitants of lentic waters, with the exceptions of Aphelocheirus aesti-valis and Aquarius najas that inhabited lotic pota-mal sites (e.g., Wroblewski 1980). Most of the cad-disfly taxa found are common and rather euryecious species occurring in a broad range of flowing-water habitats or even in standing waters; only Hydropsy-che spp., Cheumatopsyche lepida, Athripsodes cinereus, and Psychomyia pusilla occurred much in lotic waters (Graf et al. 2008). Among the water beetles found in this study, Haliplidae and Dytiscidae (with the exception of the genera Oreodytes and Platambus) are typical for lentic biotopes, whereas Orectochilus villosus and Elmidae (with the exception of Oulimnius tubercula-tus present also at lentic habitats) are typical for lotic biotopes (Sporka et al. 2003; Boukal et al. 2007).
Records of ecologically remarkable/rare species The occurrence of the oligochaete Stylodrilus heringia-nus likely indicates good water quality as this species is sensitive to pollution (Uzunov et al. 1988). The mollusks Unio tumidus, Anodonta cygnea, Pisidium supinum and P. moitessierianum are rare species included in the Red List (Farkac et al. 2005). In addition to these rare bivalve and mollusk species found in this study, Beran (2005, 2009) also found the endangered bivalve Pseudanodonta complanata in the Labe. All ecologically remarkable or rare species of mayflies (Pro-
cloeon bifidum, Heptagenia coerulans, and Choroter-pes pictetii) appeared after 2002 and mainly in 2005, thus possibly indicating ongoing improvements in water quality. Several species occasionally found in Verdek and mostly in 2002 (Baetis alpinus, Torleya major, Ecdyonurus submontanus, E. torrentis) require good water quality (Soldán et al. 1998). Although they might have been washed down from the upper stretch or tributaries, they likely could not have survived in the Labe if the water quality was not acceptable. Three taxa of red-listed dragonflies from the family Gomphidae, found in Nëmcice, are sensitive to pollution and hydromorpho-logical changes: Gomphus vulgatissimus, Onychogom-phus forcipatus, and Ophiogomphus cecilia (Bulánková & Némethová 2007). The Labe is not a typical biotope for stoneflies except in the upper stretch. Nevertheless, two notable stonefly species were found: the rare Siphonoperla taurica and the sub-Atlantic species Leuc-tra cf. leptogaster (Bojková 2009; Bojková et al. 2013). The regular occurrence of the water bug Aphelocheirus aestivalis (in Nëmcice since 1999 and Zelcín since 2001) could indicate improved conditions, as this species requires sufficient amounts of dissolved oxygen (e.g., Thorpe 1950; Wróblewski 1980). The return of A. aes-tivalis has recently been documented throughout central Europe by an increasing number of records (Am-brus et al. 1995; Bulánková & Némethová 2007; Hoffman 2008). The recolonization of this species following phosphorus removal by a sewage treatment plant was even documented in the hyporhithral and epipota-mal of the Fulda River (Siebert 1998). The water bug Micronecta griseola that was first found at three sites of the Labe and Vltava in 2005 also requires sufficient amounts of dissolved oxygen (Wróblewski 1958, 1980; Kment & Smékal 2002). Both A. aestivalis and M. griseola were recorded in the Labe in Hradec Králové during the first half of the 20th century (unpublished data). The rare pond skater Aquarius najas is typical for rivers or canals with natural banks, so its occurrence in Verdek in 2005 can be considered to reflect the natural character of this site. Micronecta poweri, recorded only once in Podoli (1999), is not typical for large rivers (Wróblewski 1958, 1980; Kment 2001), and is likely to have been washed out from small Vltava tributaries (unpublished data). Sigara distincta is not a typical species for large rivers either, as this species requires lower temperatures and higher water quality (avoiding eutrophic waters) (Wróblewski 1980; Kment 2001). In the Czech Republic, this species is predominantly found at higher altitudes (unpublished data). Therefore, it was most probably washed down from small tributaries as well. The caddisfly Setodes punctatus, which used to be a common species in the Labe and Vltava at the turn of the 19th century (Klapálek 1891, 1894, 1897), was not found during the second half of the 20th century and was classified as regionally extinct. The species was rediscovered during this project as well as in the Dyje River (Chvojka et al. 2009). Ceraclea nigroner-vosa, found only sporadically during the second half of the 20th century (unpublished data) was also recorded
during this study. Two interesting chironomids were documented for the first time in the Czech Republic in 2003: Stenochironomus sp., which lives in submerged woods and is thus hard to find using common sampling methods (Borkent 1984), and Lipiniella sp. Larvae of the dipteran Atrichops crassipes are difficult to find in streams as they have up to 2 hibernations during development and are burrowers (Bulankova 2011). Thus, floods may be responsible for their appearance in the Labe in places where they usually live in the hyporheos. Records of the beetle Stictotarsus duodecimpustulatus in lentic habitats is also an interesting finding, considering a recently reported local occurrence in the Czech Republic at the eastern border of its distribution area (Boukal et al. 2007). The riffle beetle Oulimnius tuber-culatus is considered to be rare in the Czech Republic, although locally abundant (Boukal et al. 2007). It is the only elmid species found in this study, and is typical for slow flowing streams and small rivers (Sporka et al. 2003; Boukal et al. 2007). The finding of Pomati-nus substriatus in Nemcice in 2005 was surprising as it was formerly classified as regionally extinct (Farkac et al 2005). This rheophilic species requires a high amount of dissolved oxygen and was reclassified as critically endangered in 2007 after its finding in the Orlice tributary (Boukal et al. 2007, 2012).
The expansion of alien species
To identify factors that have allowed the middle Labe to be successfully invaded by a higher number of alien species would need more detailed research. For example, in the Meuse River Josens et al. (2005) showed linkage between a gradient of invasibility and a gradient of anthropogenic impacts, and found the upper course and tributaries had higher resistance to invasions compared to impounded sections. Indeed, the most affected sites at the Labe are the most anthropogenically modified sites (artificially lentic) whereas Verdek remained unaffected, similarly as in the Meuse River.
After 2002, the flatworm Dugesia tigrina was found at all sites except Verdek. This species was introduced into the Czech Republic unintentionally by aquarists; however, since the first findings in our country no negative effects to native fauna have been reported (Oprav-ilova 2006).
The finding of the alien leech Caspiobdella fadejewi in the Vltava in 2005 was one of the first records in the Czech part of the Labe watershed; previous records were from Vltava reaches in 1993 (unpublished data) and in 2004 (Schenkova et al. 2009). This species parasitizes on fish, though it is also often found on substrates. Identifying the timing and method of its spread into the Czech part of the Labe is problematic, as it is likely that C. fadejewi has been confused with Piscicola geometra. One possible explanation could be introduction along with fish transfers. Schenkova et al. (2009) observed rapid spreading of C. fadejewi along rivers in suitable habitats.
The Ponto-Caspian zebra mussel Dreissena poly-morpha is an important invasive species throughout Eu-
rope. This species was introduced into the Czech Republic already at the end of the 19th century (Blazka 1893). Between the 1950s and 1970s, it was considered to have probably disappeared due to water pollution in the Labe, which was supported by a lack of findings (Be-ran 2006a). Since 1990, the number of reported findings has increased, which could be partly attributed to improved water quality (Beran 2002). Surprisingly, in our samples D. polymorpha was first found in the middle Labe (Lysá and Obríství) in 1996. Later, it was documented upstream up to Nemcice and also downstream from Obríství, thus colonizing the whole longitudinal profile of the Labe except the rhithral stretch. In more detailed research by Beran (2005), D. polymorpha was found at 25 of 27 sites in the Labe between Nemcice and Hrensko. A negative effect of D. polymorpha on union-ids has been reported in several studies (e.g., Haag et al. 1993; Gillis & Mackie 1994; Nalepa 1994; Baker & Hornbach 2000; Martel et al. 2001).
The first record of the alien mollusk Potamopyr-gus antipodarum in the Czech Republic was in 1981 from the Drínov Lake in the north-western part of the country (Kuchar 1983). It's first findings in our study are dated to 1999 (in Hrensko and Decín). A large expansion of P. antipodarum in the 1990s was reported by Beran (2006b), mainly for artificial biotopes in that same area and for the Labe and its floodplain. Similarly, the mollusk Corbicula fluminea, found in Hren-sko since 1999 and later in Decín, is an extension of the German populations (Beran 2006c). Beran (2000) reported its later spread upstream to within 83 km of the Czech-German border (Beran 2006). None of the three other mollusks found, Ferrissia fragilis, Physella acuta, or Menetus dilatatus, were found in the upper or lower sections or even in the Vltava. F. fragilis is now common in the middle Labe and in its river arms and pools; however, there have not yet been any negative effects to native fauna reported (Beran 2006d; Beran & Horsák 2007). Both F. fragilis and P. acuta were already known in the Czech Republic in the first half of the 20th century (Beran 2006d, e), while M. dilatatus was found in the Czech Republic for the first time in 1994 in a sandpit connected with the Labe in Kolín (Beran 1994).
The most successful recent invasive crustacean in the Labe is considered to be Dikerogammarus villosus. This Ponto-Caspian species spread through the so-called "southern corridor" from the Danube River through man-made canals (Berezina & Duris 2008). In the German part of the Labe, this species was first found already in 1998 (Pfeiffer 2005), probably near Magdeburg (Tittizer et al. 2000), whereas in the Czech part of the Labe, we first found D. villosus in Hren-sko in 2002 and since then it has spread further upstream. The ability of D. villosus to successfully invade large rivers has been documented in many other rivers across Europe (Bij de Vaate et al. 2002; Josens et al. 2005; Bernauer & Jansen 2006; Grabowski et al. 2007; Bacela et al. 2008). Due to its predatory behavior, fast growth rate, large body size, high fecundity, and toler-
ance to fluctuations in abiotic parameters, D. villosus poses a threat to native macroinvertebrate taxa (mainly to other amphipods) in freshwater ecosystems throughout Europe. Severe damage resulting in depressed populations of native crustaceans or in their local extinction has already been documented (Josens et al. 2005; van Riel et al. 2007). Nevertheless, our data does not yet indicate effects on other crustacean species. Its spread further upstream and to tributaries might be expected; however, similarly as found by Josens et al. (2005), it seems that D. villosus usually remains in the main river and does not propagate to non-navigable streams or tributaries, which thus could serve as refugium for native species.
The Balkan crustacean Gammarus roeselii is native to the Czech Republic only in the Morava catchment (Straskraba 1958), and spread into the Labe from the Orlice tributary, where it was possibly introduced with fish fry (J. Spacek, pers. comm.). Grabowski et al. (2007) defined G. roeselii as an old well-established colonizer in Polish waters rather than an invasive species. Similarly, from our data no negative influence of G. roeselii on other crustaceans in the Labe was observed. Nevertheless, if Dikerogammarus villosus spreads further upstream it will be interesting to see if it outcompetes G. roeselii, similarly as was found for the alien Gammarus tigrinus in the Rhine (Bij de Vaate et al. 2002).
The repeated findings of Hemimysis anomala in Hrensko were the first records of this species in the Czech Republic (Horecky et al. 2005). H. anomala originates from the Caspian Sea and after several subsequent introductions as a fish food (reviewed by Bij de Vaate et al. 2002) was found for the first time in the Baltic Sea in 1992 (Salemaa & Hietalahti 1993). From there it invaded in-flowing rivers and spread into continental Europe. It poses a threat rather to plankton (Ketelaars et al. 1999; Borcherding et al. 2006) than to macro-zoobenthos, as the species acts like nekton during the night. However, H. anomala so far occurs in Central Europe only in river ecosystems, and no influence has yet been demonstrated (Petrusek 2006).
The Mediterranean species Proasellus coxalis is considered to be alien in most of Western Europe. Nevertheless, the first documentation of P. coxalis in the Czech Republic comes already from the 1940s (Flasarova 1975), and an even earlier presence cannot be excluded (Horecky et al. 2006). It was later identified in pools, reservoirs and other streams in the Labe catchment and also at 3 sites in the Morava catchment (reviewed in Horecky et al. 2006). P. coxalis clearly coexists with Asellus aquaticus, but was always present in our samples in lower abundances. From our data, we did not find any negative influence of P. coxalis on indigenous macroinvertebrates.
The North American invasive crayfish Orconectes limosus is generally widespread in the Labe catchment due to upstream migration from Germany (Filipova et al. 2006), and was first documented near 0sti nad Labem in 1988 (Hajer 1989). O. limosus causes severe
damage to populations of native crayfish species due to its ability to carry the crayfish plague (Aphanomyces astaci) while not being influenced itself (Filipova et al. 2006).
Conclusions
Our data has confirmed the hypothesis that the macroinvertebrate taxa composition significantly changed during the investigated period, and this is most probably connected with improvements in water quality in the Labe and Vltava since the 1990s. The increase in number of taxa is likely a consequence of two main ecological processes: a recovery of native species as a consequence of improvements in water quality after 1990, and an expansion of alien species.
Acknowledgements
The data were collected within long-term research of the Labe (1991-2005), which was funded by a series of consecutive projects: MR Labe (1991-1994), MR/5/95 (19951998), and Labe IV SA/650/5/03 (2003-2005). We thank the Ministry of the Environment of the Czech Republic for financial support (VaV/650/5/03) and the Grant Agency of Czech Republic for the grants GACR 206/04/P163 and GACR 526/09/0567. This work was even partly supported by the Ministry of Culture of the Czech Republic (DKRVO 2013/11, National Museum, 00023272). We would also like to thank to Jirí Hájek from the National Museum, Tomás Soldán from the Institute of Entomology, AS CR, and Daniela Illésová from the Slovak Academy of Sciences for their participation in species identification. We sincerely thank Anna Lamacová for creating the map.
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Received April 30, 2013 Accepted December 16, 2013
