Faunal diversity of Cladocera (Crustacea: Branchiopoda) of Nokrek Biosphere Reserve, Meghalaya, northeastern India

Thirty-four species of Cladocera, belonging to 24 genera and seven families, documented from the Nokrek Biosphere Reserve of Meghalaya indicate fairly speciose and diverse taxocoenosis and comprise 57.7% of species known from this state. Coronatella anodonta is the first confirmed report from India and two species are new records from Meghalaya. Disperalona caudata is an interesting Australasian element and a number of species show regional distributional importance. The Cladocera of the Nokrek Biosphere Reserve show tropical characteristics with Cosmopolitan > Cosmotropical species, and are characterized by a distinct richness of the littoralperiphytonic members of the Chydoridae as well as a paucity of limnetic elements. The species richness of Cladocera in various localities ranges between 11–24 (15±3) species.


INTRODUCTION
The systematic studies on Indian freshwater Cladocera were initiated by Baird (1860) but there is yet limited information on faunal and ecosystem diversity of these entomostracous crustaceans from different states of India in general (Sharma & Michael 1987;Michael & Sharma 1988;Sharma 1991) and in aquatic ecosystems of its conservation areas in particular.The studies on occurrence and distribution of these fishfood organisms in aquatic biotopes of conservation areas of northeastern India are limited to the reports from two Ramsar sites (Sharma & Sharma 2008, 2009) and two preliminary lists from Meghalaya by Hattar et al. (2004) and Sharma (2010a).This pioneering study on Cladoceran alpha diversity of the Nokrek Biosphere Reserve, Meghalaya is interesting in view of the paucity of biodiversity studies of this area.An inventory of the documented species is presented.Comments are made on the biogeographically interesting species as well as on the richness, nature and composition of Cladoceran fauna.

MATERIALS AND METHODS
The present study is a part of our investigations on faunal diversity of zooplankton of the Nokrek Biosphere Reserve (NBR) which is spread over parts of East, West and South Garo Hills districts of the state of Meghalaya, northeastern India (Fig. 1).It was declared a national park in 1997 and was designated a biosphere reserve in May, 2009 abounds in various wildlife including elephants, hoolock gibbons, rare varieties of birds and pheasants, rare orchids and is a 'National Citrus Gene Sanctuary' to a very rare endemic species of Citrus indica (locally called 'memang narang' or 'orange of the spirits').
One hundred and ten qualitative plankton samples were collected from 33 localities (four localities only partially sampled) of the Nokrek Biosphere Reserve (25 0 21'-25 0 34'N & 90 0 14'-90 0 29'E), during July and September 2009 and January 2010, by towing a nylobolt plankton net (# 55µm) and were preserved in 5% formalin.The sampled biotopes, in this otherwise hilly terrain, include shallow rain-fed water bodies and some perennial ponds, often with filamentous algae, semi-terrestrial vegetation and a few with Eichhornia crassipes.All the samples were screened with a wildstereoscopic binocular microscope and the cladocerans were isolated.Permanent mounts of different species made in a Polyvinyl-alcohol lactophenol mixture were examined with a Leica DM 1000image analyzer.The Cladocera were identified following Smirnov (1971Smirnov ( , 1974Smirnov ( , 1996)), Michael & Sharma (1988), Sharma & Sharma (1999, 2008) and Van Damme et al. (2010).An account of faunal diversity of Rotifera present in our collections was published recently by Sharma & Sharma (2011).

RESULTS
The details of the sampled localities of the NBR are given in Table 1 along with the number of species collected from each locality.In addition, Table 2 includes a systematic list of the Cladocera examined in this study.
The Australasian Disperalona caudata (Image 3) is a biogeographically interesting species observed from the Nokrek Biosphere Reserve.Described from Australia, this species is known outside of Australia to this date only from Thailand and northeastern India; the latter report refers to its occurrence in Assam (Sharma & Sharma 2007, 2008) while the present study extends its distributional range to the adjoining state of Meghalaya.Alonella clathratula (Image 4), A. pulchella, A. guttata tuberculata, Simocephalus serrulatus, Camptocercus uncinatus (Image 5), Chydorus ventricosus and Graptoleberis testudinaria (Image 6) are examples of regional distributional interest in India.
Amongst the stated species, Alonella clathratula was formerly treated as a subspecies of A. excisa by Smirnov (1971) while Smirnov (1996) subsequently resurrected its specific status based on an elongated body and postabdomen as well as a different distributional range.The former occurs in Australia, the Ethiopian and neotropical regions, and Java while A. excisa shows a cosmopolitan distribution.A. clathratula is apparently overlooked in the Indian works, until its reports from Bihar (Sharma & Sharma 2001), Assam (Sharma & Sharma 2008, 2010) and Meghalaya (Sharma 2010a).Alona guttata tuberculata, treated as a subspecies of A. guttata by Smirnov (1971), is distinctly characterized by rounded pits or tubercles on its head shield and valves.The former is known only from Europe, Columbia, and former USSR as against the nominate Alona guttata which apparently is a cosmopolitan species.A. guttata tuberculata is, however, recently documented from India from Meghalaya (Sharma 2008) and Assam (Sharma & Sharma 2010).Simocephalus acutirostratus appears to occur in central India and southwards (Sharma 1991) while S. serrulatus is so far only known from southern India, Assam and Meghalaya.The cosmopolitan Graptoleberis testudinaria shows a disjunct occurrence in India, with records from Kashmir, Uttaranchal, Meghalaya, Assam and Andhra Pradesh.Smirnov (1971) described Camptocercus uncinatus from Lake Nikolaevskoe (Russia) while Smirnov (1998) again provided a detailed description of this species to resolve taxonomic anomalies, anticipating its wider occurrence, and remarked on the need for re-examination of the reports supposed to be that of C. australis, in particular.The first confirmed record of C. uncinatus from the Indian subcontinent is provided by Sharma (2008) who proposed C. latikae, described by Rane (1985) from Madhya Pradesh, as its synonym.This species is so far known from this country from the states of Assam and Meghalaya.Chydorus ventricosus, an anomalous chydorid, was re-described by Rajapaksa & Fernando (1986).This species is known from Sri Lanka, Java, Africa and South America while it is so far observed in this country from southern, central and western India.C. ventricosus is recently reported (Sharma & Sharma 2010) from northeastern India from Assam and this study extends its distribution to the state of Meghalaya.Interestingly, the stated aspects indicate that the occurrence of Alona guttata tuberculata, Camptocercus uncinatus and Chydorus ventricosus is restricted to northeastern India.Alona davidi is assigned to the genus Leberis following Sinev et al. (2005).
The Chydoridae, the largest family of Cladocera, forms a main component (20 species, 58.8%) of the reported species.This generalization concurs with the composition of the Indian Cladocera (Sharma 1991) and also with the faunas of various regions or states of this country.The chydorids essentially include the littoral-periphytonic species.On the contrary, the paucity of planktonic Cladocera, a distinctive feature of our study, is apparently attributed to a shallow ephemeral nature of the majority of water bodies in the study area and even the lack of distinct limnetic conditions in others.However, a few members of this category include Bosmina longirostris, Bosminopsis deitersi, Ceriodaphnia cornuta, and Moinodaphnia macleayi and these exhibit limited occurrences.Alona costata, Chydorus sphaericus, Diaphanosoma sarsi, Karualona karua, Macrothrix triserialis and Simocephalus mixtus show common occurrence and the rest of the listed species are observed in fewer samples.
Our collections show qualitative dominance of cosmopolitan species while cosmotropical and pantropical elements are well represented.In general, the cladoceran fauna of the NBR exhibits a 'tropical character'.The stated generalization is in broader conformity with the general composition of several tropical cladoceran communities (Fernando 1980;Fernando & Kanduru 1984;Dussart et al. 1984;Sharma & Michael 1987;Sharma 1991;Sharma & Sharma 2008, 2009).The present study raises the cladoceran richness (58 species) known earlier from this state (vide Sharma & Sharma 1999;Sharma 2008Sharma , 2010a) ) to 61 species, the highest recorded from any state of India, and is followed by the reports from Jammu & Kashmir (59 species) > West Bengal (52 species).
The limited collections examined by us from different localities (excluding four partially sampled localities of South Garo Hills) indicate total species richness ranging from 11-24 (15±3) species and this is fairly speciose.Peak richness observed in Chiring Chirapat is followed by the reports of 22 and 21 species from Mandal Chiring and Sasategre Chiring, respectively.In addition, various localities of East, West and South Garo Hills districts indicate broadly concurrent mean richness; i.e., between 16±3, 14±3 and 14±1 species, respectively.
To sum up, the cladoceran fauna of the NBR is fairly rich and diverse, reflects a tropical character with cosmopolitan > cosmotropical species, reveals certain biogeographically interesting species and is characterized by distinct richness of the littoralperiphytonic members of the Chydoridae as well a paucity of planktonic Cladocera.The fauna, however, still requires extensive future collections from the study area.Nevertheless, this study is an important contribution to our understanding of the aquatic biodiversity of the biosphere reserves and conservation areas of India.

Figure 1
Figure 1. District map of Meghalaya showing location of Nokrek Biosphere Reserve (indicated in dark green) and its core area shown in light green; (after Sharma & Sharma 2011).