MICRO-FAUNAL DIVERSITY OF CLADOCERANS (CRUSTACEA: BRANCHIOPODA : CLADOCERA) IN RICE FIELD ECOSYSTEMS OF MEGHALAYA

The rice-fields integrate salient features of aquatic and semi -aquatic environs and exhibit a rich mosaic of ecotones. These ecosystems are known to be colonized by a rich variety of aquatic organisms (Fernando et al., 1979; Fernando, 1993) during the period of paddy cultivation in general and micro-invertebrate communities in particular. The later, in turn, show interesting heterogeneity of Cladocera, an important component of micro-crustaceans. Though taxonomic studies on the Indian freshwater Cladocera were initiated by Baird (1860), previous publications from this country deal with their a-taxonomy based on collections from scattered localities from different states of India (Sharma and Michael, 1987; Michael and Sharma, 1988; Sharma, 1991). The information on ecosystem diversity of these entomostracous Crustaceans is, however, practically lacking. This generalization also holds true to the cladoceran fauna of Meghalaya (Sharma and Sharma, 1999). The present pioneering contribution on faunal diversity of cladocerans in the rice-field ecosystems of Meghalaya, therefore, assumes special biodiversity interest. Various rare and interesting species documented in this study are briefly diagnosed and illustrated. Remarks are made on nature and composition of the examined taxocoenosis and on distribution of interesting elements.


INTRODUCTION
The rice-fields integrate salient features of aquatic and semi -aquatic environs and exhibit a rich mosaic of ecotones.These ecosystems are known to be colonized by a rich variety of aquatic organisms (Fernando et al.,  1979; Fernando, 1993) during the period of paddy cultivation in general and micro-invertebrate communities in particular.The later, in turn, show interesting heterogeneity of Cladocera, an important component of micro-crustaceans.Though taxonomic studies on the Indian freshwater Cladocera were initiated by Baird (1860), previous publications from this country deal with their a-taxonomy based on collections from scattered localities from different states of India (Sharma and Michael, 1987;Michael and Sharma, 1988;Sharma, 1991).The information on ecosystem diversity of these entomostracous Crustaceans is, however, practically lacking.This generalization also holds true to the cladoceran fauna of Meghalaya (Sharma and Sharma, 1999).
The present pioneering contribution on faunal diversity of cladocerans in the rice-field ecosystems of Meghalaya, therefore, assumes special biodiversity interest.Various rare and interesting species documented in this study are briefly diagnosed and illustrated.Remarks are made on nature and composition of the examined taxocoenosis and on distribution of interesting elements.

MATERIALS AND METHODS
The present observations are based on extensive plankton samples collected, during 2004-2005 from the rice-fields located in different districts of Meghalaya (Fig. 1, a-b) and the samples collected (during 1988-1990) for the "State Fauna of Meghalaya : Zooplankton survey".The collections deposited in Freshwater Biology Laboratory, Department of Zoology, North-Eastern Hill University, Shillong as well as those in the holdings of the Eastern Regional Station, Zoological Survey of India, Shillong are examined for this systematic survey.
Qualitative plankton samples were collected from the rice-fields, during the different phases of paddycultivation (May/June-October), by towing a nylobolt plankton net (No. 25) and were preserved in 5% formalin.
Various species and their disarticulated appendages were mounted in Polyvinyl alcohol-Iectophenol mixture.

DISCUSSION
Zooplankton communities of the rice-fields of Meghalaya state reveal thirty-five of Cladocera, exhibit fairly rich faunal diversity of these micro-crustaceans and, hence, reflect greater environmental heterogeneity of the sampled environs.The last aspect is attributed to complex rice-field limnology (Fernando, 1995) caused due to various aspects namely water level fluctuations, tilling of soil, application of fertilizers, plantation and growth of paddy and growth of aquatic weeds.The stated conclusion on ecosystem diversity re-affirms the authors earlier observations based on the rotifer communities of the rice-fields of Meghalaya (Sharma, 2006).
The cladoceran richness recorded in the present study reflects the highest qualitative diversity of these branchiopod crustacens known till date from the ricefields of the Indian subcontinent (Fernando, 1980(Fernando, , 1995)).
The richness, however, assumes special importance in light of a conservative estimate (Fernando and Kanduru, 1984;Sharma and Michael, 1987) of occurrence of upto 60-65 species of cladocerans from tropical and subtropical parts of India.Interestingly, the cladoceran communities reflect greater higher diversity (26 genera) as compared with 36 genera so far known from India (Sharma, 1991).The generic richness in the sampled rice fields is well comparable to the reports of 29 genera each in the cladoceran faunas of the states of Meghalaya (Sharma and Sharma, 1999) and Tripura (Venkataraman and Das, 2000).Besides, all the seven families of freshwater Cladocera known to occur in the Indian inland aquatic biotopes are represented in the examined collections.These, in turn, represent two phylogenetic stems of Cladocera (Smirnov and Timms, 1983)   Guernella raphaelis exhibits disjunct distribution in this country (Sharma and Sharma, 2001), with reports from West Bengal, Bihar and Rajasthan.Diaphanosoma senegal is recorded from Gujarat and Maharashtra; Ceriodaphnia reticulata is examined from Rajasthan, Bihar and Gujarat; Chydorus pavus is reported from Kerala, Tamil N adu and Andhra Pradesh; Moinodaphnia macleayi is examined from West Bengal, Bihar, Kerala while Alona verrucosa pseudoverrucosa is recorded only from West Bengal (Sharma and Sharma, 1985).The distribution ranges of the stated taxa are presently extended to Northeast India.
Among other species, Macrothrix spinosa is observed from Tripura, Manipur, Rajasthan, Tamil Nadu and Andaman & Nicobar islands; C. pubescens is known from Bihar, West Bengal, Assam and Tripura; Alona pulchella is recorded from Tripura, West Bengal, Gujarat, Rajasthan and Tamil Nadu and Dunhevedia serrata is observed from Tripura, West Bengal, Gujarat, Rajasthan, Tamil Nadu and Andhra Pradesh.In addition,

Simocephalus acutirostratus appears to occur in
Central India and southwards (Sharma, 1991) while S.
serrulatus is so far known from S. India and Meghalaya.
The cladoceran communities of the rice-fields of Meghalaya are characterized by qualitative predominance of Cosmopolitan species and occurrence of several Cosmotropical species; these features impart a general "tropical character" to the examined fauna.
namely the Ctenopoda and the Anomopoda; the former includes only the family Sididae while members of six families of the latter (Macrothricidae-Ilyocryptidae-Chydoridae-Bosminidae-Moinidae-Daphniidae) are reported in this account.Six species namely Diaphanosoma senegal, Ceriodaphnia reticulata, Moinodaphnia macleayi, Guernella raphaelis, Chydorus pavus and Alona verrucosa pseudoverrucosa are new records from Northeast India.In addition, four species i.e., Macrothrix spinosa, Chydorus pubescens, Alona pulchella and Dunhevedia sermta are new records fromMeghalaya.The present study, therefore, raises the cladoceran richness (41 species) known earlier from this state(Sharma and Sharma, 1999) to 51 species.Overall diversity from Meghalaya now ranks the third highest from India and figures next to that of Jammu & Kashmir (59 species) > West Bengal (52 species).The Chydoridae (18 species) > Daphniidae (6 species) form a dominant fraction of the documented species.Such a feature confirms with the general composition of the Indian Cladocera(Sharma, 1991) and also with the faunas of various regions/states of this country.The present study indicates several examples of local and regional distributional interest from India.
Meghalaya and  Tripura.India : Madhya Pradesh, Maharashtra, Tamil  Nadu, Karnataka.Elsewhere: Australia, S.E.Asia and Sri Lanka.Assam and Tripura, India: Madhya Pradesh, Bihar and Tamil Nadu.Elsewhere: Europe, Asia, Africa, North America, South America and Australia.West Bengal, Bihar, Kerala.Elsewhere : tropical and subtropical regions of America, Africa and Southeast Asia.