ROTIFER DIVERSITY (ROTIFERA : EUROTATORIA) OF FLOODPLAIN LAKES OF POBITORA WILD LIFE SANCTUARY, ASSAM

Floodplain wetlands, an integral component of tropical riverine systems of the world, are known to be the richest habitats for the rotifer diversity (Segers et al., 1993; Sanoamuang, 1998; Sharma and Sharma, 2001; Sharma, 2005). Various wild life sanctuaries of North-Eastern India and that of the state of Assam are characterized by myriads of floodplain lakes (locally known as "beels") providing habitat par excellence for several wild animals as well as a wide array of vertebrates and invertebrates. However, no attention has so far been focused on the micro-faunal diversity of beels of sanctuaries of N. E. region in general and that of Rotifera in particular. The members of the later Phylum invariably comprise a dominant group of micro-invertebrate communities of these interesting ecotones and contribute significantly to their productivity.


INTRODUCTION
Floodplain wetlands, an integral component of tropical riverine systems of the world, are known to be the richest habitats for the rotifer diversity (Segers et al., 1993;Sanoamuang, 1998;Sharma and Sharma, 2001;Sharma, 2005).Various wild life sanctuaries of North-Eastern India and that of the state of Assam are characterized by myriads of floodplain lakes (locally known as "beels") providing habitat par excellence for several wild animals as well as a wide array of vertebrates and invertebrates.However, no attention has so far been focused on the micro-faunal diversity of beels of sanctuaries of N. E. region in general and that of Rotifera in particular.The members of the later Phylum invariably comprise a dominant group of micro-invertebrate communities of these interesting ecotones and contribute significantly to their productivity.
The present study assumes special importance in view of the stated lacunae and deals with qualitative and quantitative diversity of summer rotifer communities of twelve perennial and seasonal floodplain lakes (beels) of the Pobitora Wild life Sanctuary, Assam.Various interesting species are briefly diagnosed and illustrated.Remarks are made on nature and composition of the examined fauna, distribution of interesting species and on richness, similarity, abundance, diversity, dominance and evenness of the rotifer communities.
Water samples, collected from the selected beels, were examined for water temperature, specific conductivity and pH with field probes while dissolved oxygen and other chemical parameters are analyzed following A.P.H.A. (1992).Plankton samples were collected with a nylobolt plankton net (No. 25, mesh size: 55 ~m) and were preserved in 5% formalin.The rotifer species present in all the samples were identified and their densities measured.Various rotifer taxa were identified following Koste (1978), Segers (1995) and Sharma & Sharma (1987Sharma ( , 1997Sharma ( , 1999Sharma ( , 2000)).The drawings were made with a Leitz-Dialux phase contrast stereoscopic microscope and measurements were indicated in micrometers (~m).Percentage similarities (Sorensen index), diversity (Shannon index), dominance (Berger-Parker index) and evenness (EI index) were calculated following Ludwig & Reynolds (1988) and Magurran (1988).Ecological correlations were examined using correlation coefficients and canonical analysis.Elsewhere: Tropics and subtropics.(Myers, 1934) (Fig. 4)

Lecane bifurca
Diagnosis : Lorica small, oval compressed and without any markings.Ventral plate slightly narrower than dorsal plate and with small posterior projections.Toe small, claws divergent.
Distribution: INDIA: Delhi and Orissa.

Lecane hastata
Characters : Lorica oval, anterior margins coincident and anterior external angles of ventral plate with two small anteriorly directed spines.Dorsal plate smaller than ventral plate.Toes parallelsided, slightly swollen at their free ends; claws distinct, with swollen bases.Elsewhere: Tropics arid subtropics.

RESULTS AND DISCUSSION
All the sampled floodplain lakes (Table 1) are characterized by low ionic concentrations (mean conductivity: 138.9 ± 3S.7 /lS/cm).Water temperature (29.S-31.S0C) affirms a tropical range concurrent with geographical location of these ecosystems.Dissolved oxygen (4.8-7.9 mg/l) indicates oxygenated nature of all the beels which also record occurrence of free CO 2 (4.0-12.0mg/l).pH indicates slightly acidic character (6.7S-6.82) of two beels, three show nearly neutral nature (7.02-7.07)while seven exhibit alkaline waters (7.10-7.S6).Nine beels exhibit soft or nearly soft-waters and the rest indicate marginally hard-waters.The recorded salient features confirm with earlier observations of Sharma (2000aSharma ( , 2000b, 200S) , 200S) and Sharma & Sharma, 2001) in several floodplain lakes of upper and lower Assam.In addition, the studied beels are "Calcium-poor" water bodies with lower concentrations of micronutrients, sulphate, chloride and dissolved organic matter.
Sixty-four species recorded presently indicate fairly rich a-diversity of summer rotifer communities of the floodplain lakes of the Pobitora Wild-life sanctuary.The documented species form a notable fraction of North-Eastern Indian Rotifera (33.9%) and that of the fauna of Assam (37.5%).Total richness compares with the report of an identical number of species from five beels of upper Assam (Sharma, 2000a) while it is certainly higher than the reports of 29 species from four beels {Goswami, 1997), 48 species from 33 beels (Sarma, 2000), and 9 species from one beel (Goswami & Goswami, 2001) of Assam state, respectively.The observed richness is also higher than the report of 37 species from two Ox-bow lakes (Khan, 2002) and 38 species from 9 floodplain lakes (Khan, 2003) of South-eastern West Bengal.
Trichocerca kostei.Epiphanes brachionus and Lecane bifurca are new records from N .R. India.Among these rare elements, the palaeotropical T. kostei is so far known from India only from Kerala, E. brachionus is recorded from Kashmir and Delhi while the last lecanid is reported from Delhi and Orissa.Besides, Macrochaetus longipes, Lecane monostyla and Filinia camasecla deserve special mention because their occurrence is so far restricted to N. E. India.In addition, the examined material indicates several species of regional distributionalilocal importance namely Brachionus donneri, B. mirabilis, Keratella lenzi, Lecane hastata, L. sola, Trichocerca bicristata and Testudinella parva.
In general, the similarity range noted presently is higher than 42.9-80.4%(Sharma & Sharma, 2001) and 37.3-68.8%(Sharma, 2000b) reported earlier from the beels of the upper Assam.Further, the rotifer taxocoenosis of the perennial beels shows 74.2 % similarity with species recorded from the seasonal beels.
The rotifer richness (31-Sl, 37 ± S species) in different beels (Table 3) is a little lower than 42-68 species noticed in summer communities of certain other floodplain lakes of Assam (Sharma,200S) while it is certainly higher than 11-20 species observed during the corresponding season in five floodplain lakes of upper Assam (Sharma, 2000b).Peak richness in Sitalmari (Sl species) is followed by occurrence of 44 species in Solmari while 31-39 species are recorded in rest of the beels.The rotifer richness registers significant direct correlations with density (r = 0.62S, P = O.OS), specific conductivity (r = 0.626, P = O.OS), alkalinity (r = 0.801, P = 0.01) and hardness (r = 0.642, P = O.OS) while it shows an inverse relationship with water temperature (r = -0.S74, P = O.OS).
The present study, though limited to collections during summer season, provides valuable information on qualitative and quantitative diversity of the rotifer communities of beels of the Brahmaputra river basin, lower Assam.Besides, it presents a pioneering account of the rotifer diversity of Rotifera of wetlands of any wild-life sanctuary of N.E.India The richness (31-51, 37 ± 5 species) in different beels registers significant direct correlations with density, specific conductivity, alkalinity and hardness and shows an inverse relationship with water temperature.The rotifer abundance (101-257, 166 ± 57 nil) records variations in different beels; it shows significant direct relationships with alkalinity, hardness and chloride and an inverse correlation with water temperature.Seven abiotic factors namely water temperature, pH, conductivity, dissolved oxygen, free CO 2 , alkalinity and hardness indicate a cumulative influence of nearly 63% (R2 = 0.6289) while nine abiotic factors (water temperature, pH, conductivity, dissolved oxygen, free CO 2 , alkalinity, hardness, chloride, dissolved organic matter) result in still higher cumulative influence (R 2 = 0.7889).Brachionidae > Lecanidae > Lepadellidae contribute mainly to rotifer abundance.Of the individual species only K. tropica shows quantitative importance.

SUMMARY
The rotifer diversity (2.666-3.393, 3.193 ± 0.207) records insignificant relationships with richness, density and abiotic factors.The rotifer communities are characterized by low dominance and higher evenness.The dominance shows significant direct correlations with alkalinity, hardness and chloride and an inverse relationship with water temperature.The evenness records significant inverse correlations with dominance, alkalinity, hardness and chloride while it shows a direct correlation with water temperature.

Table 1 .
: Abiotic parameters of floodplain lakes of Pobitora Wildlife Sanctuary.