CLADOCERA FAUNA COMPOSITION IN A RIVER-LAGOON SYSTEM OF THE UPPER PARANÁ RIVER FLOODPLAIN, WITH A NEW RECORD FOR BRAZIL

Cladocera communities were studied in lotic and lentic environments of the Upper Paraná River floodplain, State of Mato Grosso do Sul, Brazil. A total of 63 species of Cladocera were identified in 108 samples. Of these, 24 species are considered new records for that floodplain, and one is a new record for Brazil. Chydoridae was the most representative family with 19 genera and 39 species.


INTRODUCTION
River floodplains are non-equilibrium systems whose ecological integrity depends upon a certain level of disturbance (Ward et al., 1999).These environments, strongly influenced by water level fluctuations, are heterogeneous landscapes with high biological diversity.The Upper Paraná River floodplain is one of the few remaining non-dammed stretches of the Paraná River in Brazil.Multidisciplinary studies have shown that this remnant floodplain retains high biodiversity and that it is fundamental in maintaining those species already eliminated from the other areas of the Paraná River basin (Agostinho & Zalewski, 1996;Paggi, in press).
Numerical data on the Cladocera fauna of Neotropical river floodplain systems are still too few and most studies have considered primarily pelagic species.Lack of data on the littoral fauna of these environments can basically be attributed to sampling difficulties and taxonomical problems.Good estimates of the number of species occurring in neotropical regions can be found in Paggi & José de Paggi (1990) and Paggi (1995).The preliminary biogeographical synthesis of the Neotropical Cladoceran fauna given by Paggi (1993Paggi ( , 1995) ) points out the basic features of this fauna: (i) it is poor in endemics at high taxonomic levels, contrasting with Holarctic and Australasian regions; (ii) only the families Macrothricidae and Chydoridae have endemic genera; (iii) there is no endemism in neotropical regions shared with the Ethiopian region, with the exception of Moina reticulate; (iv) Sididae, Macrothricidae, and Chydoridae are more diverse in tropical and subtropical waters.

MATERIAL AND METHODS
The Ivinhema River (22º49'S, 53º34'W) is the main meandering tributary of the upper Paraná River right bank.The average declivity is 10.8 cm.km -1 and the average current speed in the river channel is 0.85 m.s -1 .Patos Lagoon (22°49'S, 53°33'W) is a small marginal lagoon (~1.2 km 2 ) with depths ranging between 2.8 and 4.8 m.It is connected year-round with the Ivinhema River by a permanent channel and is therefore directly influenced by the oscillation of the river water level (Fig. 1).
The marginal vegetation of both river and lagoon is composed of trees, shrubs, grass (Panicum sp.), and dense stands of aquatic macrophytes of the genera Eichhornia, Salvinia, and Polygonum, among others.Samples were collected at nine sites.The type of environment, whether lentic or lotic, and the predominant marginal vegetation are described in Table 1.
The sampling sites were visited at monthly intervals from March 1993 to February 1994.A total of 108 samples were collected.High temperatures, neutral pH, and low electrical conductivity are common to both environments (Thomaz et al., 1997).Low oxygen concentrations occur during the high water periods and high oxygen concentrations occur during the low water ones (Thomaz et al., 1997).
Cladocerans were collected by filtering 1 m 3 of surface water through a 68 µm mesh conical net, with the aid of a motorized pump.
A constancy index (c) for each species per site was calculated according to Dajoz (1973).According to this index, constant species are those present in more than 50% of the samples; accessory species are those present in 25% to 50% of the samples, and accidental species are those present in up to 25% of the samples.
The occurrence and frequency of each species were obtained as follows: S = n/N.100,where n is the number of samples in which the species occurred and N is the total number of samples.

RESULTS
A total of 63 species of Cladocera were identified.Of these, twenty-four are new records for the Upper Paraná River floodplain, and one is a new record for Brazil.Chydoridae was the most representative family with 19 genera and 39 species.Sididae followed with 3 genera and 7 species and Macrothricidae with 4 genera and 5 species (Fig. 2).
The  The greatest number of constant species was found in the littoral sampling sites of the lagoon (sites 2 and 5) and the river (site 7).The lowest number of constant species was found in the pelagic region of the canal and the lagoon (sites 1 and 3), and in the littoral region of the lagoon where Panicum was the dominant macrophyte (site 4).The Ivinhema River had a greater number of constant species than the lagoon did (Table 2) (Figure 3).
Bosminopsis deitersi, Ilyocryptus spinifer, and Disparalona daday were the only species constant at all sampling sites.B. hagmanni, A. cf.fasciculata, C. pubescens, C. eurynotus, and M. spinosa were constant at most sampling sites.However, B. hagmanni was classified as an accessory species in the littoral region of the lagoon, with large stands of E. azurea (site 2), and M. spinosa was classified as an accessory species in the pelagic region of both the canal and the lagoon (sites 1 e 3).Among the Chydoridae, A. cf.fasciculata was classified as an accessory species in the pelagic region of the lagoon (site 3); C. pubescens was classified as an accessory species in the pelagic region of the lagoon (site 3) and in the littoral region of the lagoon in the presence of Panicum sp.(site 4); and C. eurynotus was classified as an accessory species in the pelagic region of the lagoon (site 3) and in the littoral region of the lagoon near Poligonum sp. and E. azurea stands (site 6) (Table 2).
Alona monacantha was an accessory species at most sampling sites, but at site 2 near extensive stands of E. azurea it was constant.Thirty species were accidental in the entire study area.Of these, only M. reticulata was recorded at all sites.Diaphanosoma birgei, Simocephalus serrulatus, and Leydigiopsis curvirostris were registered at eight of the nine sampling sites.Daphnia gessneri, D. polyspina, D. spinulosum, Dadaya macrops, Eurycercus lamellatus, Ephemeroporus barroisi, and Pseudochydorus globulosus were not observed in the Ivinhema River sites (Table 2).The greatest number of accidental species, 37, was observed in the pelagic region of the channel (site 1) and the least, 21, on the right bank of the river which did not have marginal vegetation (site 9).

DISCUSSION
According to Korovchinsky (1996), the estimate of the number of fresh water cladoceran species in the world is in the range of 600.Of these, only 129 species can be considered as valid species or as sufficiently well described, while about 146 species are relatively well described, and the status of all other species is vague.The number of Cladocera species recorded in this study (63) is higher than the total recorded previously (40) from different environments of the Upper Paraná River floodplain (Lima et al., 1996;Lansac-Tôha et al., 1997).With respect to other neotropical floodplain systems, Cladocera inventories have registered 68 species in rivers and lakes in the Central Amazon (Robertson, pers. com.), 62 species in the Orinoco River basin (Zoppi de Roa & Vásquez, 1991), and 90 species in the floodplain of the middle Paraná River in Argentina (Paggi & José de Paggi, 1990).Villar (1988) registered in different puruvian water bodies 76 species of which 31 were new records for Peru.
The addition of 24 new records raises the total number of Cladocera species known in the upper Paraná floodplain to 64.Leydigiopsis brevirostris, Onchobunops tuberculatus, and Scapholeberis sp., previously recorded as accidentals by Lansac-Tôha et al. (1997) in the Upper Paraná floodplain, were not found in this study.Chydorus strictomarginatus is the first record for Brazil.It was originally described as a subespecies of Chydorus eurynotus in Argentina (Paggi, 1972).
The typical littoral families contributed most to species richness.Chydoridae was represented by 39 species, 16 being new occurrences for the study area.This is probably due to the intensive sampling near macrophyte stands that harbour the littoral species.According to Frey (1986), the number of chydorid species depends on the structural diversity of the habitat, and any environmental factor that increases the distribution and diversity of macrophyte stands should consequently increase the number of chydorid species.Lima et al. (1996), suggest that the cladoceran community associated with macrophytes changes in composition depending on macrophyte stand size, because of the dominance of pelagic and horizontally migrating species in small macrophyte beds, and dominance of littoral, non-migrating species in larger beds.It is estimated that the neotropical Chydoridae are represented by 25 genera distributed among three subfamilies (Paggi, 1995).The most representative genera in this study were Alona, Chydorus, Disparalona, and Ephemeroporus.The most constant species were Disparalona dadayi and Chydorus eurynotus, which are amply distributed on the Upper Paraná River floodplain (Lansac-Tôha et al., 1997).Another littoral species common on the floodplain is Ilyocryptus spinifer.The pelagic species B. deitersi, B. hagmanni, C. cornuta, and M. minuta are also frequent and often dominant on other floodplains (Brandorff et al., 1982;Robertson & Hardy, 1984;Saunders III & Lewis-Jr., 1989;Paggi & José de Paggi, 1990;Bozelli et al., 1992;Sendacz, 1997).
Inventories of cladoceran species richness in neotropical floodplains are still few, basically because of the scarcity of studies dealing with the littoral fauna.The great number of species of Cladocera registered in the floodplain of the Amazon and the middle Paraná River is probably due to the fact that these areas have been studied for a longer time, and it is also probable that further studies in the upper Paraná floodplain will reveal more species.
Study area and sampling sites in the Upper Paraná River floodplain, Brazil.Number of cladoceran species per family found in the Upper Paraná River floodplain.