Introduction. Key words: rotifer, diversity, abundance, floodplain, Parana River, Brazil

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1 Hydrobiologia (2005) 546: Ó Springer 2005 A. Herzig, R.D. Gulati, C.D. Jersabek & L. May (eds.) Rotifera X: Rotifer Research: Trends, New Tools and Recent Advances DOI /s Diversity and abundance of the planktonic rotifers in different environments of the Upper Paraná River floodplain (Paraná State Mato Grosso do Sul State, Brazil) Cla udia Costa Bonecker*, Christiane Luciana Da Costa, Luiz Felipe Machado Velho & Fábio Amodeˆ o Lansac-Tôha Nupe lia, Postgraduate course in Ecology of Continental Aquatic Environments, State University of Maringa, Av. Colombo, 5790, Maringa -PR, Brazil (*Author for correspondence: bonecker@nupelia.uem.br) Key words: rotifer, diversity, abundance, floodplain, Parana River, Brazil Abstract This study proposes that diversity and abundance of rotifers show spatial and temporal variations in the Upper Parana River floodplain due to heterogeneity of the environment and hydrological level fluctuations of the main river. The structure and dynamics of rotifer assemblages were investigated by samplings carried out during the rainy (February) and dry period (August) of the year 2000, in 36 environments (rivers, channels, backwaters, open and isolated floodplain lakes). The influence of phytoplankton biomass on rotifer diversity and abundance was also investigated. 104 taxa of rotifers were identified. The highest species richness was found in rivers and open floodplain lakes, the highest abundances in the isolated floodplain lakes, and the highest values of species diversity in the channels, especially during the rainy period. b 2 -diversity values were higher in the channels, especially during the dry period. Flow differences and food availability were predominant factors influencing the structure and dynamics of the rotifer communities. Introduction Floodplains present a great environmental heterogeneity influenced by the variable flow regime of the main river. This fluctuation is responsible for the spatial and temporal distribution patterns of aquatic communities due to alterations of limnological characteristics of the environments during high and low water (Neiff, 1990). Dodson (2000) added that environmental heterogeneity is the result of patches of different kinds of habitat in the landscape and of processes occurring at different times. Rotifers have ecological relevance in aquatic environments, filtering suspended material of different sizes (from bacteria to filamentous algae) and using different strategies to obtain food, which classifies them as generalists or specialists. Their high population renewal rates distinguish them as an important link in energy flow and nutrient cycling (Esteves, 1998). Another important characteristic is their high tolerance to changes in environmental conditions (Allan, 1976). All of these aspects probably explain the success of these organisms in aquatic environments. Studies on the Upper Parana River floodplain have shown that rotifers constitute a very diverse group, with about 230 taxa recorded (Bonecker et al., 1994; Lansac-Toˆ ha et al., 1997; Serafim, 1997; Garcia et al., 1998), in addition to representing a large part of the zooplanktonic abundance in different environments of this floodplain (Lansac-Toˆ ha et al., 1997). The objective of this study is to analyze the rotifer richness and b 2 -diversity, abundance and

2 406 species diversity of the rotifer community in different environments of the Upper Parana River floodplain, in addition to determining spatial and temporal changes in these variables and the influence of available food (phytoplankton biomass). Materials and methods This study was carried out in 36 environments including rivers, channels, open and isolated floodplain lakes, and backwaters. Backwaters are lentic environments connected to the river and formed by sedimentation of the island shore. These environments were located in the stretch of the Parana River characterized by a braided channel, with low declivity and an extensive floodplain (Souza-Filho, 1993). The Environmental Protection Area of the Islands and Va rzeas of the Parana River (22 o o 50 S and 53 o o 40 W) is on this floodplain (Table 1 and Fig. 1). Collections were made in February (rainy period) and in August (dry period) of the year 2000 (Fig. 2). These periods were differentiated according to daily data of the flow level of the Parana River (Agência Nacional de Energia Ele trica ANEEL), which demonstrated the absence of a prolonged period of flooding. Thomaz et al. (1997) suggested that the flood begins in this floodplain when the hydrological level is above 350 cm. Rotifers were sampled below the surface of the pelagic region of each environment using a motorized pump and a plankton net of 70 lm mesh size by filtering 1000 l of water per sample. The concentrate was fixed in a final solution of 4% formaldehyde, buffered with calcium bicarbonate. Concurrently, water samples were collected using a Van Dorn bottle to analyze chlorophyll-a (lg l )1 ) (Goltermann et al., 1978). Rotifer richness was estimated according to the stabilization of the species increment curve per sample, using the basic literature (Koste, 1978; Koste & Robertson, 1983; José de Paggi, 1989; Segers, 1995) for identification. Changes in the species composition of each environment and system (formed by different rivers Parana, Baı a and Ivinheima), and in both hydrological periods, were evaluated using the b-diversity index (b 2 ) (Whittaker, 1960) from the equation [(R/a max ))1]/[n)1], where a max is the maximum species richness value of all n samples analyzed and R is the sum of the number of species in n samples (Harrison et al., 1992). The species diversity (H ) of the community was estimated using the Shannon Wiener index (Pielou, 1975). Abundance was determined using a Sedgwick Rafter slide in an optical microscope at 100 Table 1. List of the environments (sampling stations) studied on the Upper Paraná River floodplain in February and August Numbers of sampling stations as indicated in Figure 1 Rivers Open floodplain lakes System Isolated floodplain lakes System Paraná 25 Garças 27 Paraná Clara 23 Paraná Ivinheima 8 Pombas 14 Paraná Pousada 26 Paraná Baía 28 dos Patos 6 Ivinheima Genipapo 22 Paraná Channels System Finado Raimundo 9 Ivinheima Osmar 17 Paraná Ipoitã 4 Ivinheima Peroba 1 Ivinheima Capivara 7 Ivinheima Cortado 13 Paraná Sumida 11 Ivinheima Jacaré 10 Ivinheima Curutuba 15 Baía Boca do Ipoitã 5 Ivinheima Zé do Paco 3 Ivinheima Baía 33 Baía Porcos 31 Baı a Cervo 12 Ivinheima Backwater Maria Luiza 34 Baı a Ventura )2 Ivinheima Bilé 20 Paraná Onça 36 Baı a Pousada das Garças 30 Baía Leopoldo 21 Paraná Guaraná 19 Baı a Fechada 29 Baía Manezinho 16 Paraná Gavião 35 Baı a Aurélio 32 Baía Pau-Véio 24 Paraná Traíra 18 Baía

3 407 Figure 1. Location of the sampling area and collecting stations. magnification, counting at least 50 individuals in three subsamples (1.7 ml), obtained with a Stempel pipette (Bottrell et al., 1976). In samples with low densities all individuals were counted. The final density was estimated in individuals m )3 and expressed as log-transformed data (log x + 1). Analysis of variance (ANOVA) was used to determine if the spatial variation in richness, abundance, and species diversity was related to the collection periods (Sokal & Rohlf, 1991), using these ecological attributes as the dependent variables and the two periods as the influencing factor. The abundance data were log-transformed. Figure 2. Monthly levels of the Paraná River recorded from January to November The collecting months are marked.

4 408 Differences between periods were considered significant at p < A Pearson Correlation Analysis was carried out (data log-transformed) in order to test if rotifer abundance was related to phytoplankton biomass, derived from concentrations of chlorophyll-a, for each environment and sampling period. Correlation was considered significant at p < Data were analyzed using the statistical package STATISTICA version 5.0 (Statsoft Inc., 1996). Results Rotifer richness One hundred and four rotifer taxa (19 families) were recorded, with the majority belonging to Brachionidae, Lecanidae and Trichocercidae (Table 2). Some of these taxa represent new floodplain occurrences: Brachionus forficula, Kellicottia bostoniensis, Trichocerca dixonnuttalli and T. macera. The highest species numbers were found in the rivers and open floodplain lakes, especially during the rainy period (Fig. 3). b 2 -diversity The b 2 -diversity results were not high, varying from 2.90% to 10.38%. The highest value was observed in the channels, followed by the one obtained in rivers (8.48%). The lowest values were recorded in the isolated (2.98%) and open (3.65%) floodplain lakes. Concerning the periods and systems studied, during the dry period, higher b 2 - diversity values were observed in the Baı a system (17.78%), although the systems did not differ markedly (Parana : 17.48%, Ivinheima: 16.36%). In the rainy period, the spatial variation was similar to that of the dry period, i.e. higher values recorded in the Baı a (17.53%) and Parana (17.48%) systems and lower values in the Ivinheima (16.36%) system (Fig. 4). Species diversity (Shannon Wiener index) The rotifer community had higher species diversity during the rainy period, especially in the channels, due to a higher evenness. In contrast, a lower diversity was found in the isolated floodplain lakes, probably due to lower evenness and lower richness values. During the dry period, the species diversity was similar in all environments, and so were evenness and species richness (Figs. 3 and 5). Abundance The rotifer community showed higher densities in the floodplain lakes during both sampling periods, particularly in the isolated floodplain lakes during the rainy period, when greater densities were also recorded in the rivers (Fig. 6). Lecane proiecta was abundant in the floodplain lakes, backwaters and rivers, showing wide distribution among the environments. Brachionus falcatus was abundant in the isolated floodplain lakes and Filinia opoliensis in the open floodplain lakes and backwaters. Polyarthra sp. was the most abundant species in the channels, and Euchlanis dilatata in the channels and rivers. On the other hand, lowest abundances were found in the channels and rivers during the dry period (Fig. 6). In this period Polyarthra sp. was widely distributed among the environments with higher densities in the channels, rivers, open floodplain lakes and backwaters. E. dilatata was also dominant in the channels, while Ploesoma truncatum showed great abundance in the rivers. Keratella cochlearis was the most abundant species in the open floodplain lakes and backwaters, and Synchaeta pectinata in the open and isolated floodplain lakes and backwaters. Keratella americana and Hexarthra intermedia were dominant in the isolated floodplain lakes. Integration of results The ANOVA showed that only the abundance data varied between the environments in the two periods ( p = ) (Fig. 6). The correlation between rotifer abundance and chlorophyll-a concentration in the two periods showed a positive relationship, mainly in the floodplain lakes (Fig. 7), where we found high phytoplankton densities. These results confirmed that phytoplankton, as measured by chlorophyll-a concentration, was an important food resource during the development of the rotifer communities during the rainy period.

5 409 Table 2. Checklist of the rotifers recorded in different environments of the Upper Paraná River floodplain in February and August 2000 Monogononta Asplanchnidae Gastropodidae Testudinellidae Asplanchna sieboldi (Leydig, 1854) Ascomorpha ecaudis Perty, 1850 Pompholyx sp. Asplanchna sp. A. saltans (Bartsch, 1870) Testudinella mucronata (Gosse, 1886) Brachionidae Gastropus hyptopus (Ehrenberg, 1838) T. ohlei Koste, 1972 Anuraeopsis fissa (Gosse, 1851) Hexarthridae T. patina (Hermann, 1783) Brachionus angularis Gosse, 1851 Hexarthra intermedia (Wieszniewski, 1929) Trichocercidae B. budapestinensis Daday, 1885 H. mira (Hudson, 1871) Elosa sp. B. calyciflorus Pallas, 1766 Flosculariidae Trichocerca bicristata (Gosse, 1887) B. caudatus Barrois & Daday, 1894 Floscularia sp. T. bidens (Lucks, 1912) B. dolabratus Harring, 1914 Ptygura sp. T. capucina (Wierzejski & Zacharias, 1893) B. forficula Wierzejski, 1891 Lecanidae T. cylindrica (Imhof, 1891) B. mirus Daday, 1905 Lecane aculeata (Jakubski, 1912) T. chattoni (Beauchamp, 1907) B. falcatus Zacharias, 1898 L. amazonica (Murray, 1913) T. dixonnuttalli (Jennings, 1903) B. quadridentatus Hermann, 1783 L. bulla (Gosse, 1851) T. elongata (Gosse, 1886) B. q. mirabilis (Daday, 1897) L. closterocerca (Schmarda, 1859) T. iernis (Gosse, 1887) B. urceolaris (O. F. Mu ller, 1773) L. cornuta (O. F. Mu ller, 1786) T. inermis (Linder, 1904) Kellicottia bostoniensis (Rousselet, 1908) L. curvicornis (Murray, 1913) T. insignis (Herrick, 1885) Keratella americana Carlin, 1943 L. elsa Hauer, 1931 T. macera (Gosse, 1886) K. cochlearis (Gosse, 1851) L. hamata (Stokes, 1896) T. pusilla (Lauterborn, 1898) K. lenzi Hauer, 1953 L. leontina (Turner, 1892) T. scipio (Gosse, 1886) K. tropica (Apstein, 1907) L. ludwigii (Eckstein, 1893) T. similis (Wierzejski, 1893) Plationus macracanthus (Daday, 1905) L. luna (O. F. Mu ller, 1776) T. stylata (Gosse, 1851) P. patulus (O.F. Mu ller, 1786) L. lunaris Ehrenberg, 1832 Trichocerca sp. Platyias q. quadricornis (Ehrenberg, 1832) L. monostyla (Daday, 1897) Trichotriidae P. q. brevispinus (Daday, 1905) L. papuana (Murray, 1913) Macrochaetus sericus (Thorpe, 1893) P. leloupi (Gillard, 1957) L. proiecta Hauer, 1956 M. collinsi (Gosse, 1867) Conochilidae L. quadridentata (Ehrenberg, 1832) Trichotria tetractis (Ehrenberg, 1830) Conochilus coenobasis (Skorikov, 1914) L. scutata (H. & M., 1926) Trochosphaeridae C. dossuarius (Hudson, 1875) L. signifera (Jennings, 1896) Filinia longiseta (Ehrenberg, 1834) C. natans (Seligo, 1900) L. stichaea Harring, 1913 F. opoliensis (Zacharias, 1898) C. unicornis rousselet, 1892 L. ungulata (Gosse, 1887) F. pejleri Hutchinson, 1964 Dicranophoridae Lepadellidae Filinia sp. Dicranophorus claviger (Hauer, 1965) Lepadella benjamini Harring, 1916 Horaella thomassoni Koste, 1973 Epiphanidae L. ovalis (O. F. Mu ller, 1786) Synchaetidae Epiphanes macrourus (Barrois & Daday, 1894) Mytilinidae Ploesoma truncatum (Levander, 1894) E. clavulata (Ehrenberg, 1832) Mytilina macrocera (Jennings, 1894) Polyarthra vulgaris Carlin, 1943 Euchlanidae M. ventralis (Ehrenberg, 1832) Polyarthra sp. Beauchampiella eudactylota (Gosse, 1886) Notommatidae Synchaeta pectinata Ehrenberg, 1832 Euchlanis dilatata Ehrenberg, 1832 Cephalodella mucronata Myers, 1924 S. stylata Wierzejski, 1893 E. incisa Carlin, 1939 Cephalodella sp. Bdelloidea Dipleuchlanis propatula (Gosse, 1886) Notommata sp. Philodinidae Dissotrocha aculeata (Ehrenberg, 1832)

6 410 Figure 3. Rotifer richness recorded in the different environments (open lakes = floodplain lakes and backwater) during the rainy and dry periods (symbol = average, bar = standard deviation). Figure 4. b-diversity of the rotifer community recorded in the different environments (open lakes = floodplain lakes and backwater) and systems formed by the main rivers (rainy and dry periods). Discussion Rotifer families with greater species richness (Brachionidae, Lecanidae and Trichocercidae) matched the typical species associations known from tropical floodplain environments. These families are commonly recorded in freshwater aquatic environments of Brazil (Bozelli, 1992; Bonecker et al., 1998; Lansac-Toˆ ha et al., 1997; 1999). The highest rotifer richness values, especially in rivers and open floodplain lakes during the

7 411 Figure 5. Species diversity of the rotifer communities recorded in the different environments (open lakes = floodplain lakes and backwater) during the rainy and dry periods (symbol = average, bar = standard deviation). Figure 6. Rotifer abundance recorded in the different environments (open lakes = floodplain lakes and backwater) during the rainy and dry periods (symbol = average, bar = standard deviation). rainy period, are probably contributed by species originating from lentic environments, not previously connected to the rivers. Koste & Robertson (1983) suggested that rotifer richness in lentic environments of flooded areas tends to increase during the period of higher flow levels, due to the incorporation of benthic and periphytic taxa associated with decomposing aquatic vegetation. An increase in the lake area generally occurs during this hydrological period (rainy) due to marginal flooding. The exchange of water masses between the littoral and pelagic regions in these environments contributes to the increase in species

8 412 Figure 7. Relationship between rotifer abundance (ind. m )3 ) and chlorophyll-a concentration (lg l )1 ) recorded in the environments (open lakes = floodplain lakes and backwater) in the rainy and dry periods. richness of the entire environment. This, along with the permanent connection to the river, favors the occurrence of a large number of taxa in the open floodplain lakes. This characteristic has been described in various studies on floodplains (Brandorff & Andrade, 1978; Bonecker et al., 1994; Lansac-Toˆ ha et al., 1997). On the other hand, the lowest richness values observed during the dry period in all environments reinforces the importance of flows for the increase in diversity of floodplain environments. Highest b-diversity values in channels, rather than in floodplain lakes, demonstrates that the change of rotifer community composition is more intense in lotic environments and less pronounced in the lentic ones. Just as for other biotic parameters analyzed, flow appears to be a predominant factor in this diversity estimate. The lowest b-diversity values observed in the Ivinheima system may be related to the low Secchi disk values in previous studies (Thomaz et al., 1997), and so may be low diversity values found in some floodplain lakes in February. The reduced transparency appears to be due to a large quantity of suspended biogenic and/or abiogenic material. For the Ivinheima system, Thomaz et al. (1997) highlighted the large quantity of suspended inorganic material in the water column. The higher species diversities during the rainy period is apparently influenced by the increase of species numbers in all environments and the absence of high species dominances, especially in the channels. According to Marzolf (1990), in environments with high current flow transport loss of organisms is higher than their reproductive rate, which prevents large populations from developing. On the other hand, Corrales (1979) and Jose de Paggi (1981) recorded higher zooplankton diversity in the Parana River and secondary channels during the dry period. The highest densities of rotifers in the isolated floodplain lakes during the rainy period reflect the large development of planktonic populations in lentic environments, probably due to the absence

9 413 of pronounced flood and consequent overflow. In contrast, we recorded lowest abundance values in the channels and rivers during the dry period. This fact could be the result of the lower connectivity and faunal exchange between lotic and lentic environments during this period. The variation of abundance between the environments in both the periods was especially due to differences in the number of individuals found in the isolated floodplain lakes and channels, as the other environments presented the same variation patterns. In an open floodplain lake and a river (Baı a river and Guarana lagoon) Bonecker et al. (2002) showed that densities were much more variable in the dry period than during the period of higher flow, which is also confirmed by us. Phytoplankton seems to be an important food resource that influences the structure and dynamics of rotifer communities during the rainy period, mainly in the floodplain lakes where we recorded high phytoplankton densities. Bonecker & Lansac- Toˆ ha (1996) and Train et al. (2001) described highest phytoplankton and rotifer abundances in floodplain lakes during the dry period and showed the importance of the algae community for the development of rotifer populations. Finally, we suggest that flow differences and food availability were predominant factors for the structure and dynamics of the rotifer communities. Acknowledgements We thank Dr. Luis Carlos Gomes for suggestions. The constructive criticism of the editor and one anonymous referee also is appreciated. Supported by PELD/CNPq and Nupélia/UEM. References Allan, J. D., Life history patterns in zooplankton. American Naturalist 110: Bonecker, C. C. & F. A. Lansac-Toˆ ha, Community structure of rotifers in two environments of the high river Paraná floodplain (MS), Brazil. Hydrobiologia, 325: Bonecker, C. C., F. A. Lansac-Toha & A. Staub, Qualitative study of rotifers in different environments of the high Paraná river floodplain (MS), Brasil. Revista Unimar 6: Bonecker, C. C., F. A. Lansac-Tôha & D. C. Rossa, Planktonic and non planktonic rotifers in two environments of the upper Paraná river floodplain-ms, Brazil. Brazilian Archives of Biology and Technology 41: Bonecker, C. C., F. A. Lansac-Tôha, L. M. Bini & L. F. M. Velho, Daily fluctuation in rotifer population abundance in two environments of the upper Paraná River floodplain, Brazil. Amazoniana 17: Bottrell, H. H., A. Duncan, Z. Gliwicz, E. Grygierek, A. Herzig, A. Hillbricht-Illkowska, P. Larsson & T. Weglenska, A review of some problems in zooplankton production studies. Norwegian Journal of Zoology 24: Bozelli, R. L., Composition of the zooplankton of Batata and Mussurá lakes of the Trombeta River, State of Pará, Brazil. Amazoniana 2: Brandorff, G. O. & E. R. Andrade, The relationship between the water level of the Amazon river and the fate of the zooplankton population in Lago Jacaretinga, a varzea lake in the central Amazon. Studies on Neotropical Fauna and Environment 13: Corrales, M. A., Contribuicio n al conocimiento del zooplâncton de alto Paraná. Ecosur 6: Dodson, S. I., Effects of environmental heterogeneity in aquatic ecology. Internationale Vereinigung fu r Theoretische und Angewandte Limnologie, Verhandlungen 27: Esteves, F. A., Fundamentos de Limnologia (2nd edn.) Interciência/FINEP. Rio de Janeiro, 602 pp. Garcia, A. P. P., F. A. Lansac-Toˆ ha & C. C. Bonecker, Species composition and abundance of rotifers in different environments of the floodplain of the upper Paraná river, Brazil. Revista Brasileira de Zoologia 15: Golterman, H. L., R. S. Clymo & M. A. M. Ohmstad, Methods for Physical and Chemical Analysis of Fresh Waters. Blackwell Scientific Publications, Oxford, 214 pp. Harrison, S., S. J. Ross & J. H. Lawton, Beta diversity on geographic gradients in Britain. Journal of Animal Ecology 61: José de Paggi, S., Variaciones temporales y distribuición horizontal del zooplancton en algunos cauces secundarios del rio Paraná Medio. Studies on Neotropical Fauna and Environment 6: José de Paggi, S., Rotíferos de algunas provincias del noroeste argentino. Revue d Hydrobiologie Tropicale 23: Koste, W., Rotatoria. Die Rädertiere Mitteleuropas, begru ndet von Max Voigt. Monogononta I. Gebru der Borntraeger, Berlin, 673 pp. Koste, W. & B. Robertson, Taxonomic studies of the Rotifera (Phylum Aschelminthes) from a Central Amazonian varzea lake, Lago Camaleão (Ilha de Marchantaria, rio Solimoes, Amazonas, Brazil). Amazoniana 8: Lansac-Toˆ ha, F. A., C. C. Bonecker, L. F. M. Velho & A. F. Lima, Composição, distribuic ão e abundância da comunidade zooplanctônica. In Vazzoler, A. E. A. M., A. A. Agostinho, & N. S. Hahn (eds), Planície de Inundação do Alto Rio Paraná: Aspectos Físicos, Biolo gicos e Socioeconoˆ micos. Maringá-PR, Eduem, Lansac-Toˆ ha, F. A., L. F. M. Velho & C. C. Bonecker, Estrutura da comunidade zooplanctônica antes e apo s a

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