Jolanta EJSMONT-KARABIN
Department of Hydrobiology, Institute of Biology, University of Białystok, Świerkowa 20 B, 15-950 Białystok, Poland, e-mail: [email protected]
DOES INVASION OF
VALLISNERIA SPIRALIS
L. PROMOTE
APPEARANCE OF RARE AND NEW ROTIFER (ROTIFERA)
SPECIES IN LITTORAL OF THE LAKES HEATED BY POWER
STATION (KONIN LAKES, W. POLAND)?
Short research contribution
ABSTRACT: Large-scale human-caused eco-system disturbances may create new habitats. A good example may be long-lasting disturbances in five lakes (area from 148 to 379 ha, max. depth from 3 to 38 m) integrated into the cooling sys-tem of the power plants near Konin (52°17.8’– 52°23.3N, 18°14.4’–18°20.7’E, West Poland). In the middle of the 1990s Vallisneria spiralis began to colonize littoral zone of three of lakes and in 2002 it appeared also in fourth one. This species formed dense patches and almost completely dis-placed other submerged macrophytes. An aim of the study was to test a hypothesis that the appear-ance of rare and new for Polish fauna rotifer spe-cies might be a result of changes in littoral habitats of these lakes particularly caused by the invasion by Vallisneria spiralis. Studies were carried out in the years 2004–2006 on 3–6 littoral stations in each lake. Five-liter samples of water with macro-phytes were collected from a center of macrophyte beds. Plankton (free-swimming) and epiphytic (connected with macrophyte surface) samples were elaborated separately.
As many as 167 monogonont species were recorded during the three-years’ studies. From among them 6 species were new in Polish fauna. These were: Asplanchnopus hyalinus Harring,
Beauchampia crucigera (Dutrochet). Lecane in-opinata Harring & Myers, Lecane shieli Segers et Sanoamuang, Lecane undulata Hauer and Le-padella apsida Harring. The species are eury-thermic or warm-stenoeury-thermic. Species new to
the rotifer fauna of Poland were not numerous as they usually constituted less than 2% of the total density of rotifers. Thus, although the hypothesis that rare and new for Polish fauna rotifer species may appear in the littoral habitats of the heated Konin lakes was confirmed, it was also clear that the colonization of the habitats by rotifer invad-ers did not lead to their domination in the rotifer communities.
KEY WORDS: Rotifera, Poland, heated lakes, Konin lakes, Vallisneria, invasive macrophyte
Human-caused changes in the natural ecosystems may create new habitats as well as patches within the habitats. Such large-scale habitat disturbances may promote the inva-sion and spread of alien (not-indigenous) species (E lton 1958, Mor a l e s and A i z e n 2002).
An example are long-lasting disturbances in five lakes (area from 148 to 379 ha, max. depth from 3 to 38 m) integrated into the cooling system of the power plants near Konin (West Poland). The lakes were included into the system in two steps, i.e. when power plant “Konin” began to function and then – pow-er plant “Pątnów” (Hi l l br i cht - I l kow s k a and Z d an ow s k i 1988). As a result the sig-nificant changes were observed in water
temperature and through-flow. Environmen-tal conditions and biota, effect of water heat-ing on the physico-chemical properties of the water, primary and secondary production, species composition and densities of plank-ton communities were a subject of long-term and diverse studies (Hi l l br i cht - I l kow s k a et al. 1988, Si m m 1988, Z d an ow s k i 1994, Z d an ow s k i et al. 2002). It was shown that temperature of the lake waters increased con-siderably, up to maximum values of 30.9°C in shallow lake – Lake Licheńskie and 27.7°C in deeper lake – Lake Ślesińskie in the summer 1995–2000 (S o ch a and Z d an ow s k i 2001).
Vallisneria spiralis appeared in Konin lakes probably in the first half of the 1990s (Hutorow i c z 2006). In the years 2002–2003 the species formed almost exclusively sin-gle-species beds in Lake Licheńskie (area of 153.6 ha, max. depth 13.3 m) and phytocoe-noses composed of Vallisneria and Potamo-geton perfoliatus L., Myriophyllum spicatum L. and other macrophyte species in Lake Ślesińskie (area 148.1 ha, max. depth 25.7 m) (Hutorow i c z 2006).
The introduction of alien aquatic plants into littoral zone may alter the complex web of biotic and abiotic interactions. The reduction Table 1. Frequency (in 97 samples) and maximum numbers of most frequent and new to Polish fauna rotifier species met amongst Vallisneria (plankton-free swimming species) and on macrophytes (epi-phyton) in the years 2004–2006.
Species Plankton Epiphyton Frequency % Maximum numbers (ind. l–1) Frequency % Maximum numbers (ind. g–1 DW) Free-living
Lecane hamata (Stokes) 94 2691 75 3600
Euchlanis dilatata Ehrenberg 91 96 48 628
Lecane closterocerca (Schmarda) 91 248 94 2709
Lepadella patella (Muller) 91 3407 79 1710
Brachionus quadridentatus Hermann 88 171 56 748
Keratella cochlearis (Gosse) 82 469 14 129
Trichocerca elongata (Gosse) 82 116 46 68
Lecane bulla (Gosse) 79 988 65 2169
Lecane luna (Muller) 79 296 60 1258
Testudinella patina (Hermann) 71 911 63 1465
Lecane aculeata (Jakubski) 65 1297 41 1205
Colurella uncinata (Muller) 62 62 32 241
Lepadella acuminata (Ehrenberg) 62 34 49 910
Polyarthra remata Skorikov 56 742 8 144
Polyarthra vulgaris Carlin 56 116
Pompholyx sulcata Hudson 53 123 5 24
Trichocerca porcellus (Gosse) 50 148 48 2106
Sessile
Limnias ceratophylli Schrank 56 1210 46 4877
Ptygura furcillata (Krllicott) 26 14 52 140
Rare and new in Polish fauna
Cupelopagis vorax (Lidy) 59 420 62 3700
Lecane shieli Segers & Sanoamuang 35 25 27 568
Asplanchnopus hyalinus Harring 9 20 2 7
Lepadella apsida Harring 3 1 5 40
Trichocerca mus Hauer 3 1
Lecane inopinata Harring & Myers 2 68
Lecane undulata Hauer 2 52
of the habitat complexity may lead to reduc-tion of macroinvertebrate diversity (Kr u l l 1970, Ke a st 1984). Thus, also microinverte-brates (e.g. rotifers) may probably response in similar way to colonization of L. Licheńskie and L. Ślesińskie lakes by Vallisneria spiralis.
Introduction of new species of macro-phytes usually has significant influence on animal comunities (Po s e y 1988, Ta l l e y and L e v i n 2001) and may result in co-invasion of new species of invertebrates. Although it has been found that native biotic interactions exclude many potential invaders (Shu r i n 2000), Vallisneria occupying large areas (i.e. creating single-species phytocoenoses oc-cupying the bottom to a depth of 2.5 m) of a near-shore zone creates new littoral habitat, which can help invading species to compete successfully with native communities. As two studied lakes are artificially heated and warm water is supplied to the Lake Licheńskie all year round, littoral communities of Rotifera may be enriched with exotic warm-steno-thermic species. Mor a l e s and A i z e n (2002) have shown that alien plant (exotic flowers) species could facilitate the invasions of some exotic flower visitors to disturbed habitats.
An aim of the study was to test a hypoth-esis that the appearance of rare and new for Polish fauna rotifer species may be a result of changes in the littoral habitats of Konin lakes through heating lake waters and invasion of Vallisneria spiralis.
Samples were collected:
– in July 2004 on 8 littoral stations of Lake Licheńskie; 4 stations with single-species Vallis-neria beds and 4 stations with mix-species beds (Ejsmont-Karabin and Hutorowicz, in press);
– in 2005, monthly from April till Octo-ber in Lake Licheńskie and from August till October in Lake Ślesińskie. Six stations with single-species Vallisneria beds were studied in the former and three stations in the latter lake.
– in August 2006 on 14 stations (7 sta-tions in 2 locasta-tions covered with exclusively Vallisneria beds) in Lake Licheńskie.
Five-litre samples of water were taken from the middle of macrophyte beds, filtered through a plankton net of 30-m mesh size and fixed with 2% formalin.
Samples of epiphyton (= rotifers living on the surface of macrophytes) were taken
con-currently to plankton samples. Epiphytic ro-tifers were removed from macrophytes using a soft bristle brush, condensed on a plankton net of 30-m mesh size, transferred into bot-tles and fixed. The plant material devoid of epiphyton was dried overnight at 60°C and weighed.
In total 97 samples were elaborated. The concurrently taken qualitative sam-ple was analysed alive. Some of species con-sidered as rare or new for fauna of Poland were described and photographed using a NIKON E600 microscope and the system of computer image analysis (LUCIA).
An analysis of taxonomic structure of rotifer communities inhabiting Vallisneria assemblages showed that the communities were relatively rich in species if compared to littoral communities of some lakes in the Masurian Lakeland ( like Lake Kuc, Lake Łuknajno and Lake Mikołajskie) (Mu i r-h e a d et al. 2006). As many as 169 mono-gonont species were recorded during the three-years’ studies. Although littoral plank-ton may be enriched in pelagic species, the community was consistedwith markedly less rotifer species (115) than epiphyton (144). The most common genera were Lecane (with 24 species), Trichocerca (with 20 spe-cies) and Cephalodella (with 16 species). 44 species (26%) were encountered only once. As many as 42 species occurred in more than 20% of both plankton and epiphyton samples and from among them 19 species were found in more than 50% of plankton samples (Table 1). The most frequent and abundant species were: Lecane closterocerca (Schmarda), Lepadella patella (Müller), Lec-ane hamata (Stokes), Lecane bulla (Gosse), Brachionus quadridentatus Hermann, Lec-ane luna (Müller) and Testudinella patina (Hermann), Euchlanis dilatata Ehrenberg, Cupelopagis vorax (Leidy). Most of them are very common in Polish fauna, with an exception of Cupelopagis vorax, which was found only twice, by C z api k (1958) in the vicinity of Cracow and by Ejsmont-Karabin in the littoral of the River Biebrza ( East Po-land ) (unpubl. data). This large (1 mm max. length) (Photo 1) and predatory species cre-ated very dense populations in Vallisneria beds reaching up to 3700 ind. g d. wt–1 of the macrophyte (Table 1).
Photo 1. Cupelopagis vorax, an alive female
Photo 2. Beauchampia crucigera, a contracted female out of its tube
Photo 3. Lecane shieli, contracted
Photo 4. Lecane undulata, contracted
Photo 5. Lepadella apsida, contracted
Photo 6. Trichocerca mus, contracted
Among rotifers found on and close to Vallisneria as many as 6 species seem to be new in Polish fauna. These are:
1. Asplanchnopus hyalinus Harring – large i.e. ca 400 μm long animal with long and telescopically jointed foot; oviparous, predatory, cosmopolitan (Jo s e D e Pag g i 2002); during the present study females of the species were found in August both in epi-phyton (7 ind. g d.wt–1) and in littoral plankton (5 to 20 ind. l–1) (Table 1); 2. Beauchampia crucigera (Dutrochet)
– large (up to 500 μm long), ses-sile rotifer with a characteristic very long dorsal antenna (Pe n n a k 1978) (Photo 2); cosmopolitan (S e ge rs 2007). It was found only once, in June 2005 on Vallisneria in a warm-water canal between lakes (Table 1).
3. Lecane inopinata Harring & Myers – small, loricate rotifers with head ap-erture margins straight with angulate corners; characteristic feature are toes fused over proximal 1/3 and short, separated claws; warm-stenothermic and cosmopolitan species (S e ge rs 1995). Its individuals were found in September 2005 on Vallisneria in a warm-water canal connecting two lakes (Table 1).
4. Lecane shieli Segers & Sanoamuang – the species described in 1994 from one locality in Thailand (S e ge rs and S an o amu ang 1994); females found in the Konin lakes were al-most identical with those described from Thailand, i.e. their lorica was soft and irregularly folded (Photo 3), head aperture margins coincident and straight with sharp and straight spines in antero-lateral corners, toes long, parallel-sided and with weakly curved claws. The species occurred in relatively high numbers (up to 568 ind. g d. wt–1 of Vallisneria) at all stud-ied stations, exclusively in August. 5. Lecane undulata Hauer – small
lo-ricate rotifer, which resembles L. in-opinata, but differs from the latter by toes fused only basally (S e ge rs 1995) (Photo 4). Females of the spe-cies were found in August 2005 on
Vallisneria in a warm-water canal. 6. Lepadella apsida Harring – rare but
cosmopolitan species, found pre-viously in Senegal and Burundi (B ar i bwe g u re and S e ge rs 2001). The species (Photo 5) occurred in summer on Vallisneria in Lake Licheńskie and the warm-water ca-nal. Its highest density reached 40 ind. g d.wt–1 of the macrophyte. Besides Cupelopagis vorax, there was an-other species considered to be rare in Polish fauna of Rotifera, i.e. Trichocerca mus Hauer (Photo 6). Although the distribution of the species is poorly known (S e ge rs 2003), some records (e.g. D e R i d d e r 1985) indicate that the species is thermophilic. In Poland T. mus was recorded previously only once, by R a d -w an (1971), in pelagic -waters of Lake Sumin (Łęczyńsko-Włodawskie Lake District, East Poland). A few individuals were found among Vallisnera in the littoral zone of Lake Ślesińskie. Species new to the rotifer fauna of Poland did not play an important role in the studied habitats. They occurred in 34% of the sam-pling points in epiphyton and 39% in the plankton occurring between the plants. Their contribution to the total monogonont rotifer density did not exceed 53% in epiphyton and 2% in plankton. However, even in epiphyton they usually constituted less than 2% of the total density. The species were present exclu-sively at stations covered with single-species Vallisneria beds and no one specimen be-longing to this group of Rotifera was found in mix-species macrophyte assemblages (Ejsmont-Karabin and Hutorowicz, in press).
Results of the studies conducted in the heated Konin lakes suggest that co-invasion of new sites by exotic species of Rotifera has taken place. Disturbed habitats are recognized as especially vulnerable to invasion (E lton 1958, He y wo o d 1989). There are many fac-tors promoting such invasion in the studied habitats, all of them producing disturbances in rotifer habitats at different scales:
• an increase in temperature of the lake waters up to 25.2°C in the Lake Ślesińskie and 28.0°C in the Lake Licheńskie due to warm waters sup-plies to the Lake Licheńskie all year round and to the Lake Ślesińskie in summer.
• very fast colonization of the littoral zone by single-species beds of the ex-otic Vallisneria spiralis.
• high susceptibility of Vallisneria to damages due to grazing by macro-invertebrates and fish (Li et al. 2010) and wave action. The latter is evidenced by a presence of high densities of sessile rotifers in plankton samples (Table 1). The effect of high temperature is evi-denced by the above mentioned appearance of new for Polish fauna and warm-stenothermic species, like Lecane inopinata, L. shieli and Lepadella apsida. However, without distur-bance effects colonization of sites created by Vallisneria by new species of Rotifera could have been unsuccessful. According to Shu r i n (2000) zooplankton communities are nearly saturated with species, thus biotic interac-tions may exclude many potential invaders. All the mentioned disturbances may thus weaken defense of native populations against invaders. They may also explain the success-ful expansion of more than 20 alien species in the system of Konin lakes. There are among them three species of bryozoans, crustaceans (Corophium robustrum (Sars), C. curvispinum (Sars), Echinogammarus ischnus (Strebbing), as many as seven species of mollusks ( Sinan-odontawoodiana (Lea), Potamopurgus antipo-darum (Gray) and Physella acuta (Draparn-aud), among others, and at least 6 species of fish (Kr a s z e w sk i and Z d anow sk i 2007).
Results of the studies confirm the hy-pothesis that rare and new for Polish fauna rotifer species may appear in the littoral hab-itats of the heated Konin lakes and that the process is promoted by heating their waters and invasion of Vallisneria spiralis. However, the colonization of the habitats by rotifer in-vaders did not lead to their domination in the rotifer communities.
ACKNOWLEDGEMENTS: The study was financially supported by the Polish Ministry of Science and Higher Education grant no. 2 PO4G 088 26.
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