Faunal diversity of rotifers ( Rotifera : Eurotatoria ) of Nokrek Biosphere Reserve , Meghalaya , India

Plankton samples collected from the Nokrek Biosphere Reserve of Meghalaya (Northeast India) revealed 70 species of Rotifera belonging to 24 genera and 15 families. Eight species are new records from the state of Meghalaya. The Oriental Lecane blachei and the palaeotropical L. unguitata are biogeographically interesting elements. The Rotifera taxocoenosis of Nokrek Biosphere Reserve is characterized by a distinct richness of the ‘tropic-centered’ genus Lecane, paucity of Brachionus species, greater diversity of littoral-periphytonic elements and a general ‘tropical’ character with cosmopolitan (71.4%) > tropicopolitan (17.1 %) species.

analyzed the progress in studies in the northeastern India region.The Indian literature shows a paucity of works on the faunal diversity of phylum Rotifera from aquatic biotopes of conservation areas of India in particular.The relevant works from northeastern India are limited to studies from the Pobitra Wildlife Sanctuary of Assam (Sharma 2006) and two Ramsar sites, namely Deepor Beel (Sharma & Sharma 2005b) and Loktak Lake (Sharma 2009).On the other hand, Rotifera inhabiting water bodies of various biosphere reserves of this region are yet to be examined.The present study on the faunal diversity of rotifers of the Nokrek Biosphere Reserve Meghalaya, hence, assumes special importance in view of the stated lacunae.Various species examined from this biodiversity hotspot are listed.Comments are made on the nature and composition of the rotifer fauna and on the distribution of interesting species.

Materials and Methods
Study site: The Nokrek Biosphere Reserve (25 0 20'-25 0 29'N & 90 0 13'-90 0 35'E) spreads (Fig. 1) over parts of West, East and South Garo Hills districts of the state of Meghalaya.It was declared as a national park in 1997 (47.48km 2 ) and was designated as biosphere reserve (82.0km 2 ) in May 2009.It abounds in various wildlife including elephants, Western Hoolock Gibbon, rare varieties of birds and pheasants, beside rare orchids.It is also a national citrus gene sanctuary to a very rare endemic species of Citrus indica which the locals call memang narang ('orange of the spirits').
Methods of study: One-hundred-and-ten plankton samples were collected from different water bodies of the Nokrek Biosphere Reserve in July and September 2009, and January 2010, with a nylobolt plankton net (mesh 25µm) and were preserved in 5% formalin.All the samples were screened with a Wild stereoscopic binocular microscope and the rotifer taxa were isolated.Permanent slides of different species mounted in Polyvinyl-alcohol lactophenol mixture and deposited in the holdings of the senior author (BKS) were examined with Leica DM 1000 image analyzer.In addition, specimens in the holdings of NERC, ZSI, Shillong were examined by one of the authors (SS).Rotifera species were identified following the works of Koste (1978), Sharma (1998b), Segers (1995), and Sharma & Sharma (1999, 2000, 2008).The system of classification of the Rotifera followed in this account is after Segers (2002).

Discussion
This pioneering study on aquatic biodiversity of the Nokrek Biosphere Reserve records 70 species of Rotifera.Eight species namely Brachionus mirabilis, Tripleuchlanis plicata, Lecane arcula, L. blachei, Sinantherina socialis, S. spinosa, Philodina citrina and Rotaria macroceros are new records from the state of Meghalaya.The present report raises the number of rotifer species known from Meghalaya (vide Sharma & Sharma 1999) to 138 species.In addition, a couple of new species await description.The richness, in turn, comprises 31.7% of the species known from northeastern India and 50.7% of the rotifer fauna of the state of Meghalaya.Amongst 22 families and 43 genera of phylum Rotifera recorded from northeastern India (B.K. Sharma unpublished), 15 families and 24 genera are represented in our collections.Although the examined samples reflect a low rotifer diversity of Nokrek Biosphere Reserve, the fauna appears to be fairly speciose when compared with overall rotifer richness known from northeastern India in general and the state of Meghalaya in particular.The documented species, however, present a significant contrast to only 27 species belonging to nine families and 12 genera identified by one of the authors (S.Sharma unpublished) from this biosphere reserve based on limited samples deposited in the holdings of NERC, ZSI, Shillong.
Incomplete Rotifera inventories from the conservation areas of India may not permit meaningful comparisons with our report; this generalization is affirmed by only 14 species reported from the Nilgiri Biosphere Reserve (Patil 2001).The diversity in   (2007).Lecanidae, one of the largest families of monogonont rotifers (Segers 1995), shows a distinct quantitative importance (34.3%);Brachionidae > Lepadellidae > Notommatidae form notable components (15.7, 10 and 7.1% respectively) of the rotifer fauna of the Nokrek Biosphere Reserve.Amongst different genera, the 'tropic-centered' Lecane shows high richness (24 species) while our collections are characterized by a relative paucity of species of another 'tropic-centered' genus, Brachionus; the latter is attributed to the lack of typical limnetic habitats in the sampled area.Cosmopolitan species (71.2%) distinctly dominate the rotifer fauna, tropicopolitan species (16.5 %) are well represented while pantropical (5.6%) elements are relatively fewer.In general, the rotifer taxocoenosis of the Nokrek Biosphere Reserve reflects a 'tropical character'.This generalization is in conformity with identical reports from other tropical faunas (Green 1972;Fernando 1980;Dussart et al. 1984;Segers 1996Segers , 2001Segers , 2008;;Sharma 1998a;Sharma & Sharma 2008).On the other hand, our results differ by lacking the quantitative dominance of Brachionidae, depending on ecological conditions, reported in quite a few of the listed works.
Our collections exhibit interesting variations in Rotifera richness in individual samples (2-23, 11 ± 5 species).Further, the rotifer communities are characterized by more littoral-periphytonic species and a paucity of planktonic elements.The present study shows the common occurrence of Plationus patulus, Euchlanis dilatata, Lecane bulla, L. leontina, L. luna, L. quadridentata and Testudinella patina while Brachionus bidentatus, B. calyciflorus, B. falcatus, Cephalodella forficula, C. gibba, C. mucronata, Sinantherina socialis, S. spinosa and Testudinella parva are rare species.Monogonont rotifers comprise the bulk of the recorded diversity (67 species) and in turn, show a higher richness of the members of order Ploima while the Bdelloidea include only three species.
To sum up, the Rotifera fauna of the Nokrek Biosphere Reserve reveals 70 species belonging to 24 genera and 15 families including eight new records from the state of Meghalaya, It is characterized by the occurrence of certain biographically interesting species, quantitative importance of tropic-centered' Lecane, paucity of Brachionus spp., richness of cosmopolitan species, general 'tropical' character and dominance of littoral-periphytonic species.The present species inventory, however, still requires updating based on more extensive collections as well as specific sampling of benthic and bdelloid rotifers.Nevertheless, this study is an important contribution to aquatic biodiversity of the biosphere reserves or conservation areas of India.