Tropical Ecology 52(3): 293-302, 2011 ISSN 0564-3295 © International Society for Tropical Ecology www.tropecol.com

Zooplankton communities of Deepor Beel (a Ramsar site), (N. E. ): ecology, richness, and abundance

B. K. SHARMA*

Department of Zoology, North Eastern Hill University, Permanent Campus, Umshing, 793022, , India

Abstract: Limnological studies undertaken at two sampling stations of Deepor Beel (91º 35′ - 91º 43′ E, 26º 05′ - 260 11′ N) revealed the presence of 171 and 160 species of zooplankton at stations I and II, respectively. Species richness in different months ranged between 96 ± 11 and 97 ± 13 (mean ± SD) and community similarities across months between 48.9 - 88.1 % and 53.1 - 89.7 % at stations I and II, respectively. Richness, which was mainly influenced by Rotifera (110 species) and Cladocera (45 species), showed significant variations between months but not between stations. Zooplankton (475 ± 114, 459 ± 128 n l-1 at stations I and II, respectively) formed an important quantitative component of the net plankton. Rotifera and Cladocera dominated quantitatively, Copepoda and Rhizopoda formed sub-dominant groups, and Ostracoda and Conchostraca had very low densities. Zooplankton abundance varied significantly between both months and stations. At both stations, richness and abundance inversely correlated with water temperature and rainfall, and positively with specific conductivity and dissolved oxygen. While at station II both richness and abundance also positively correlated with transparency, alkalinity, and hardness, at station I, abundance positively correlated with free CO2. Finally, zooplankton richness and abundance oscillated with annual frequency but showed winter peaks, was not quantitatively dominated by any individual species, and was characterized by higher species diversity with equitable abundance of various species. In view of the paucity of works from the floodplain of India, this study provides important information on zooplankton diversity and ecology of the sampled Ramsar site.

Resumen: Estudios limnológicos realizados en dos estaciones de muestreo de Deepor Beel (91º 35′ - 91º 43′ E, 26º 05′ - 26º 11′ N) revelaron la presencia de 171 y 160 especies de zooplancton en las estaciones I y II, respectivamente. La riqueza de especies en diferentes meses varió entre 96 ± 11 y 97 ± 13 (media ± SD), y las similitudes a nivel de comunidad entre meses fluctuaron entre 48.9 - 88.1 % y 53.1 - 89.7 % en las Estaciones I y II, respectivamente. La riqueza, influen- ciada principalmente por Rotifera (110 especies) y Cladocera (45 especies), mostró variaciones significativas entre meses pero no entre estaciones. El zooplancton (475 ± 114, 459 ± 128 n l -1 en las Estaciones I y II, respectivamente) conformó un componente cuantitativamente importante del plancton. Rotifera y Cladocera dominaron cuantita-tivamente, Copepoda y Rhizopoda formaron grupos subdominantes, y Ostracoda y Conchostraca tuvieron densidades muy bajas. La abundancia del zooplancton varió significativamente tanto entre meses como entre estaciones. En ambas estaciones, la riqueza y la abundancia se correlacionaron inversamente con la temperatura del agua y la precipitación, y positivamente con la conductividad específica y el oxígeno disuelto. Mientras que en la Estación Ii tanto la riqueza como la abundancia también estuvieron correlacionados positivamente con la trans-parencia, la alcalinidad y la dureza, en la Estación I la abundancia se correlacionó positivamente con el CO2 libre. Finalmente, la riqueza y la abundancia del zooplancton oscilaron con una frecuencia anual pero mostraron picos de invierno, no estuvieron dominadas cuantitativamente por ninguna especie particular, y

N * Corresponding Author; e-mail: [email protected], [email protected] 294 ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL

estuvieron caracterizadas por una diversidad de especies más alta con una abundancia equitativa de varias especies. En virtud de la pobreza de trabajos de los lagos de planicie de inundación en la India, este estudio brinda información importante sobre la diversidad de zooplancton y la ecología del sitio Ramsar muestreado.

Resumo: Os estudos limnológicos levados a efeito em duas estações amostra em Deepor Beel (91º 35’ - 91º 43’ E, 26º 05’ - 26º 11’ N) revelou a presença de 171 e 160 espécies de zooplâncton nas Estações I e II, respectivamente. A riqueza específica nos diferentes meses oscilou entre 96 ± 11 e 97 ± 13 (média ± DP) e as semelhanças de comunidade ao longo dos meses situou-se entre os 48,9 - 88,1 % e os 53,1 - 89,7 % nas Estações I e II, respectivamente. A riqueza, que era principalmente influenciada pela Rotifera (110 espécies) e a Cladocera (45 espécies), mostrou variações significativas entre meses mas não entre Estações. O zooplâncton (475 ± 114,459, 459 ± 128 n ℓ-1 nas estações I e II, respectivamente) forma uma componente quantitativa importante do plâncton líquido. Os Rotifera e Cladocera dominavam quantitativamente, os Copepoda e Rhizopoda formam os subgrupos dominantes, apresentando os Ostracoda e os Conchostraca densidades muito baixas. A abundância do zooplâncton variou significativamente quer entre meses e quer entre estações. Em ambas as Estações, a riqueza e abundância estavam inversamente correlacionadas com a temperatura e a queda pluviométrica, e positivamente com a condutividade específica e o oxigénio dissolvido. Enquanto na Estação II, quer a riqueza, quer a abundância estavam também positivamente correlacionadas com a transparência, alcalinidade e dureza, já na Estação I, a abundância estava positivamente correlacionada com o CO2 livre. Finalmente, a riqueza e abundância do zooplâncton oscilaram com uma frequência anual mas mostraram picos no inverno que não estavam quantitativamente dominados por nenhuma espécie individual, e estava caracterizado por elevada diversidade de espécies com abundância equivalente das várias espécies. Com vista à insuficiência de trabalhos nos lagos de encharcamento da Índia, este estudo proporciona informação importante sobre a diversidade do zooplâncton e ecologia do sítio Ramsar amostrado.

Key words: Abundance, Ramsar site, richness, synecology, zooplankton.

Introduction Thus, in view of the paucity of works from India, the present study of zooplankton commu- Freshwater ecosystems are colonized by a nities of Deepor Beel, a Ramsar Site and an impor- diverse array of aquatic organisms. Amongst tant floodplain of the these, zooplankton, which function as primary basin of Assam, assumes special importance. This consumers, comprise an integral component of report presents information on zooplankton rich- aquatic food-webs and contribute significantly to ness, community similarities and abundance, and biological productivity. Inspite of several studies the constituent zooplankton groups at two samp- from fresh-water environs of India, there is still ling stations. Analysis includes the temporal little information on the ecology and role of variation of species diversity, dominant groups, zooplankton in the aquatic productivity of the and the influence of seventeen abiotic parameters Indian floodplain lakes (Sharma & Sharma 2008). on zooplankton richness and abundance. Studies of zooplankton ecology from the flood- plains of North-eastern India have so far been Materials and methods restricted to the reports of Sharma & Hussain (2001) and Sharma & Sharma (2008); in addition, Limnological investigations were undertaken Sharma & Sharma (2001, 2005) and Sharma during November 2002 - October 2003 in Deepor (2005, 2009a, 2009b) dealt with Rotifera diversity. Beel (longitude: 91º 35′ - 91º 43′ E, latitude: 26º 05′

SHARMA 295

Fig. 1. A-Map of India indicating location of Assam state and map of Assam indicating location of Deepor beel; B- Map of Deepor beel indicating the sampling stations I and II.

Table 1. Abiotic factors studied at Deepor Beel - 26º 11′ N; area: 40 km2; altitude: 42 m above sea (Nov 02 - Oct 03) (Mean ± SD). level) in the Kamrup district of lower Assam, N. E. India (Fig. 1 A & B). Various aquatic macrophytes, Factors Station I Station II namely Hydrilla verticellata, Eichhornia crassipes, Rainfall (mm) 204.5 ± 160.4 204.5 ± 160.4 Vallisnaria spiralis, Utricularia flexuosa, Trapa Water temperature (0C) 27.2 ± 4.6 27.4 ± 5.1 bispinosa, Euryale ferox, Najas indica, Monochoria pH 6.89 ± 0.18 6.93 ± 0.21 hastaefolia, Ipomoea fistulosa, Hygroryza aristata, Transparency (cm) 51.9 ± 26.2 52.7 ± 25.3 Polygonum hydropiper, and Limnophila sp., cover Specific Conductivity 99.2 ± 13.2 96.8 ± 15.5 this floodplain lake. (µS cm-1) Due to local constraints, the observations for Dissolved oxygen (mg l-1) 6.7 ± 1.6 7.0 ± 1.1 this study were limited (November 2002 - October Free CO2 (mg l-1) 7.2 ± 2.1 6.8 ± 1.9 2003) to two sampling stations (I and II). The Alkalinity (mg l-1) 66.3 ± 12.1 68.9 ± 10.3 sampled sites were characterized by common Hardness (mg l-1) 62.1 ± 9.9 61.2 ± 12.3 occurrence of H. verticellata, E. crassipes, U. flexuosa, Chloride (mg l-1) 34.6 ± 5.2 35.1 ± 5.0 T. bispinosa, E. ferox, N. indica, and P. hydro- Phosphate (mg l-1) 0.18 ± 0.07 0.19 ± 0.10 piper. Station II, however, differed from the former Sulphate (mg l-1) 10.2 ± 3.2 9.9 ± 3.4 in occasional (temporal) lack of the rest of the Nitrate (mg l-1) 0.72 ± 0.12 0.74 ± 0.14 observed macrophyte species, namely V. spiralis, Silicate (mg l-1) 3.02± 1.02 3.10 ± 1.27 M. hastaefolia, I. fistulosa, H. aristata, and B.O.D5 (mg l-1) 3.11 ± 0.59 3.21 ± 0.46 Limnophila sp.. Though there is no official moni- Dissolved organic 3.84 ± 0.80 3.90 ± 0.64 toring of water table of this floodplain lake, general -1 matter (mg l ) minimum and maximum water levels were obser- Total dissolved solids (mg l-1) 2.37 ± 0.29 2.57 ± 0.30 ved in Deepor beel during April 2003 and August

296 ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL

Table 2. Temporal variation of zooplankton at Deepor Beel (Nov 02 - Oct 03) (Range, Mean ± SD).

Qualitative Station I Station II Zooplankton Total richness 171 species 160 species Monthly richness 68 - 112 96 ± 11 68 - 113 97 ± 13 Community similarity (%) 48.9 - 88.1 53.1 - 89.7 Rotifera Total richness 110 species 100 species Monthly richness 43 - 65 56 ± 6 38 - 60 52 ± 7 Cladocera Total richness 45 species 43 species Monthly richness 17 - 41 29 ± 6 20 - 41 32 ± 6 Quantitative Net Plankton (n l-1) 708 - 961 812 ± 80 696 - 1058 801 ± 123 Zooplankton (n l-1) 239 - 657 475 ± 114 255 - 687 459 ± 128 Percentage 33.2 - 68.4 57.9 ± 9.0 35.4 - 66.9 56.5 ± 8.8 Species Diversity 3.548 - 4.229 3.991 ± 0.181 3.529 - 4.219 3.973 ± 0.193 Different Groups Rotifera (n l-1) 105 - 318 231 ± 60 106 - 325 198 ± 70 Percentage 42.8 - 65.2 48.7 ± 6.1 37.9 - 49.6 42.5 ± 4.1 Cladocera (n l-1 ) 43 - 252 142 ± 59 56 - 233 142 ± 48 Percentage 14.6 - 38.3 28.7 ± 7.0 22.0 - 37.6 30.6 ± 4.9 Copepoda (n l-1) 49 - 95 66 ± 17 66 - 101 81 ± 13 Percentage 7.6 - 31.4 15.1 ± 6.5 11.9 - 29.-0 18.7 ± 4.9 Rhizopoda (n l-1) 7 - 41 29 ± 14 5 - 66 35 ± 18 Ostracoda (n l-1) 2 - 10 6 ± 3 2 - 10 5 ± 2 Conchostraca (n l-1) 0 - 4 0 - 2

2003, respectively; the water levels were identical Quantitative samples were analyzed for abun- at both the stations. Further, the two sampling dance of net plankton (phyto- and zooplankton), stations experienced similar inputs of rainwater zooplankton, and zooplankton constituent groups. and floods. Community similarity (Sorensen’s index) and species Water samples were collected monthly from diversity (Shannon’s index) were calculated follo- the selected sampling sites and were analyzed for wing Ludwig & Reynolds (1988) and Magurran the following abiotic factors: water temperature, (1988). ANOVA was used to analyse the signi- rainfall, pH, transparency, specific conductivity, ficance of temporal variation of the biotic commu- dissolved oxygen, free CO2, alkalinity, hardness, nities. Simple correlation coefficients (r1 and r2, chloride, phosphate, sulphate, nitrate, silicate, respectively for stations I and II) were calculated BOD5, dissolved organic matter, and total dissol- between all abiotic and biotic parameters. ved solids. Water temperature, specific conductivity, and pH were recorded through field probes, trans- Results and discussion parency was noted with a Secchi disc, dissolved oxygen was estimated by Winkler’s method, and Water samples analyzed from Deepor Beel are the other parameters were analyzed following characterized by low ionic concentrations (Table 1) APHA (1992). Three qualitative (by towing) and and, thus, warrant the inclusion of this Ramsar quantitative plankton (by filtering 25 l water each) site under the ‘Class I’ category of trophic classi- samples were collected monthly at each station fication following Talling & Talling (1965). Mean using a nylobolt plankton net (No. 25). Zoo- water temperature confirms the tropical range plankton samples were preserved in 5 % formalin, concurrent with the lake’s geographical location. screened, and then identified following Koste The nearly neutral and marginally hard waters of (1978), Michael & Sharma (1988), Sharma (1998) this floodplain lake show moderate values for and Sharma & Sharma (1999a, 1999b, 2000, 2008). dissolved oxygen, low free CO2, and low concen- SHARMA 297

methodology) from 15 other floodplain lakes of the Brahmaputra river basin of Assam (102 - 156 spe- cies) underlines the relatively high species diver- sity of Deepor Beel. As in the findings of Sharma & Sharma (2008) and Sharma (2009a), zooplankton forms the domi- nant qualitative component (phytoplankton + zoo- plankton = 230 species) of the net plankton in Deepor Beel. These results, in turn, differ from the

higher phytoplankton richness reported in certain

other floodplain lakes from (Baruah et al.

1993; Sinha et al. 1994) and Assam (Sharma & Hussain 2001). Rotifera (110 species) and Cladocera (45 species) contribute the most to zooplankton richness. The micro-faunal diversity of these two groups in Deepor Beel, as well as their nature and

composition, were discussed in Sharma & Sharma (2005, 2008). Fig. 2. Monthly variations in zooplankton richness Zooplankton richness in Deepor Beel shows of Deepor Beel (Nov 02 - Oct 03). little annual variation between station I (171 species) and station II (160 species). Comparisons tration of micronutrients. In general, the ranges of between sampling stations indicate broadly similar most abiotic factors show insignificant differences monthly ranges, mean values, and standard devi- at the two stations and broadly agree with earlier ations of zooplankton richness (68 - 112, 96 ± 11 reports from other floodplain lakes of Assam species; 68 - 115, 97 ± 13 species). On the other hand, (Sharma & Sharma 2001, 2008; Sharma 2005). significant monthly variation (F11, 23 = 23.966, P < Plankton samples from Deepor Beel show 0.005) occurred in zooplankton composition. This (Table 2) the existence of a speciose and diverse statement holds valid for the present stations and zooplankton biocoenosis (171 species) and, thus, may not reflect the general environmental hetero- reflect the overall environmental heterogeneity geneity of Deepor Beel unless ascertained by ana- and habitat diversity of this Ramsar site. Total lysis of collections from other parts of this Ramsar zooplankton richness (171 species), the second site. Richness (Fig. 2) oscillates with annual highest known from any floodplain lake or indi- frequency with winter peaks in February (station vidual aquatic ecosystem in India, follows that of I) or December (station II) and minima in summer 212 species for Loktak Lake (Sharma 2009a & b) - (April). While the peaks concur with luxuriant another important Ramsar site and floodplain lake winter growth of aquatic macrophytes, the latter located in N. E. India. Richness in Deepor Beel is, coincides with the lowest water level. Lack of however, distinctly more than that reported from information on the seasonal variation in zooplank- several other floodplain lakes of India: 51 species ton richness in other Indian floodplain lakes prohi- from Trigamasar and Naranbagh lakes (Khan bits comparison of this study with other areas, but 1987), and 26 species from Mirgund winter peaks concur with the author’s observations (Yousuf et al. 1986) of Kashmir; 19 (Baruah et al. in Loktak Lake (Sharma unpublished). 1993) and 31 species (Sanjer & Sharma 1995) from Rotifera species (56 ± 6, 52 ± 7 species) form the Kawar Lake, Bihar; 49 species from Samuajan main qualitative component of zooplankton at both Beel, Upper Assam (Sharma & Hussain 2001); and stations and exert the dominant influence on zoo- 71 species from Beri Gopalpur and Sosadanga, plankton temporal variation (monthly zooplankton (Khan 2003). Though Deepor Beel is richness and Rotifera richness, r1 = 0.969, r2 = in fact more species rich, the differences between 0.918). Additionally, Cladocera (34 ± 6, 38 ± 6 this study and other studies may result also from species) contributes significantly to the zooplank- incomplete species inventories, inadequate samp- ton richness (r1 = 0.923, r2 = 0.966). The qualitative ling, and overlooking identification of smaller importance of Rotifera in Deepor Beel agrees with species. Nevertheless, a comparison with the zoo- that reported for several other floodplain lakes plankton species richness reported by the author (Khan 2002, 2003; Sharma 2000, 2005, 2009a, b; in Sharma & Sharma (2008) (which used similar Sharma & Sharma 2001, 2008). 298 ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL

Table 3. Zooplankton community similarities (%) at station I (Nov 02 - Oct 03).

Nov Dec Jan Feb March Apr May June July Aug Sep Oct Nov - 66.7 73.0 88.1 80.7 51.0 85.7 65.5 78.0 73.4 76.4 74.1 Dec - 76.2 74.6 66.7 66.7 60.7 69.0 67.8 77.2 69.1 66.7 Jan - 77.4 76.7 59.3 71.2 72.1 77.4 76.7 75.9 66.7 Feb - 85.7 56.0 80.0 63.2 82.8 82.1 81.5 79.2 March - 62.5 64.1 61.8 75.0 66.7 76.9 70.6 April - 55.3 65.3 56.0 58.3 65.2 48.9 May - 66.7 72.7 71.7 70.6 68.0 June - 63.2 69.1 60.4 61.5 July - 85.7 74.1 75.5 Aug - 73.1 74.5 Sept - 57.1 Oct -

Table 4. Zooplankton community similarities (%) at station II (Nov 02 - Oct 03).

Nov Dec Jan Feb March Apr May June July Aug Sep Oct Nov - 71.9 71.0 75.4 76.7 63.0 70.0 67.8 71.2 76.2 76.7 74.6 Dec - 89.7 73.7 60.7 56.0 64.3 65.4 69.1 78.0 82.1 72.7 Jan - 80.0 70.4 62.5 63.0 71.7 71.7 77.2 77.9 75.5 Feb - 75.5 68.1 71.7 65.4 80.8 71.4 79.2 84.6 March - 73.9 76.9 70.6 74.5 58.2 73.1 74.5 April - 69.6 66.7 66.7 53.1 65.2 66.7 May - 70.6 66.7 65.4 69.2 66.7 June - 76.0 70.4 72,7 60.0 July - 66.7 70.6 72.0 Aug - 69.1 70.4 Sept - 78.4 Oct -

At both stations, zooplankton richness is nega- rities, due to decreased species richness, during the tively correlated with water temperature (r1 = four month summer period (March - June). At - 0.705, r2 = -0.776) and rainfall (r1 = -0.523, r2 = stations I and II, respectively, peak similarity values - 0.654) but positively correlated with specific con- occurred between November - February and Decem- ductivity (r1 = 0.497, r2 = 0.647) and dissolved ber - February and minima were recorded in April- oxygen (r1 = 0.501, r2 = 0.764). Richness is also October and April - August. Zooplankton composition positively correlated with transparency (r2 = 0.650), shows closeness between November - February and alkalinity (r2 = 0.608), and hardness (r2 = 0.632) at July - August at station I and between December- station II. January and February - October at station II. At At stations I and II respectively, this study both stations, and apparently due to the fewer found 48.9 - 88.1 % and 53.1 - 89.7 % similarity in number of species present in April, the samples zooplankton community across monthly samples collected in April exhibit the greatest divergence in (Tables 3 & 4). Further, 34.8 and 33.3 % instances their composition. in the matrices indicate 60 - 70 % similarity and an Zooplankton (239 - 657, 475 ± 114 n l-1 and 255 additional 40.9 and 54.5 % of instances at the two - 687, 459 ± 128 n l-1) forms the main quantitative stations respectively indicate 70 - 80 % similarity. component of net plankton of Deepor Beel (33.2 - In summary, the majority (75 - 88 %) of instances 68.4, 57.9 ± 9.0 % 35.4 - 66.9, 56.5 ± 8.8 %, at the show 60 - 80 % similarity. This generally high level two stations respectively), thus, significantly of similarity suggests limited monthly variations contributing to net planktons’ temporal variation in species composition contrasted by lower simila- (monthly net plankton abundance and zooplankton SHARMA 299

contrast with the higher phytoplankton abundance noticed in some floodplain lakes and of Kashmir (Kaul & Pandit 1982), Bihar (Baruah et al. 1993; Rai & Dutta-Munshi 1982; Sanjer & Sharma 1995), and West Bengal (Sugunan 1989; Vass 1989). Generally, zooplankton abundance of Deepor Beel is higher than that reported from Kawar wetland of Bihar (Baruah et al. 1993) and certain beels of Assam (Sharma & Hussain 2001;

Sharma & Sharma 2008). On the other hand,

abundance is lower than that reported from

various floodplain lakes of Bihar (Rai & Dutta - Munshi 1982; Sanjer & Sharma 1995), Kashmir (Khan 1987) and West Bengal (Khan 2002; Sugunan 1989; Vaas 1989). At both stations, zooplankton abundance (Fig. 3) oscillates with annual frequency with a rather halting general increase to winter peaks in Decem- ber at station I and January at station II. Density Fig. 3. Monthly variations of zooplankton abundance registers significant monthly variation (F11, 23 = of Deepor Beel (Nov 02 - Oct 03). 24.386, P < 0.005) but insignificant variation between stations. This study shows no definite seasonal periodicity other than higher winter den- sities. The high winter densities at both stations reflect a significant negative correlation of zoo- plankton abundance with water temperature (r1 = - 0.782, r2 = -0.876). Abundance at both stations is also negatively correlated with rainfall (r1 = -0.573, r2 = -0.647) and positively correlated with dissolved oxygen (r1 = 0.662, r2 = 0.712), transparency (r1 = 0.609, r2 = 0.605), and specific conductivity (r1 = 0.474, r2 = 0.640). In addition at station II, abun- dance is negatively correlated with free CO2 (r2 = -0.470) and positively correlated with alkalinity (r2 = 0.545) and hardness (r2 = 0.598). At both stations, zooplankton abundance is also positively correlated with its richness (r1 = 0.863, r2 = 0.889). Zooplankton communities of Deepor Beel are characterized by higher species diversity (3.548 - 4.238, 3.991 ± 0.181 and 3.529 - 4.219, 3.973 ± 0.192) than other beels of Assam (Sharma & Fig. 4. Monthly variations of zooplankton species Sharma 2008) and, at both stations, show broadly diversity of Deepor Beel (Nov 02 - Oct 03). identical values. The zooplankton community shows significant monthly variation (F11, 23 = abundance, r1 = 0.906, r2 = 0.919). The lowest 15.185, P < 0.005) but insignificant variation percentage composition was recorded in April. At between stations. In general, at station I, relati- both stations, in the six months of November vely high diversities (more than 4.0) are observed through February and July through August, in January through February and July through zooplankton contributed more than 60.0 % of the October and, at station II, from January through net plankton abundance. March and July through December. Zooplankton In general, quantitative dominance of zoo- diversity follows oscillating annual patterns at both plankton agrees with earlier reports from Assam stations, peaking in July at station I and October (Sharma & Hussain 2001). However, such patterns at station II. Both have April minima (Fig. 4).

300 ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL

(2008). This interesting feature (mainly influenced by higher Rotifera diversity) also concurs with the results of Dumont & Segers (1996) in a tropical lake with developed weedy littoral. At both sta- tions, zooplankton species diversity is positively correlated with richness of zooplankton (r1 = 0.656, r2 = 0.610), Rotifera (r1 = 0.571, r2 = 0.623) and Cladocera (r1 = 0.590, r2 = 0.575) and, at station I, is significantly correlated with zooplankton abun- dance (r1 = 0.467). At both stations, Rotifera (231 ± 60 and 198 ± 90 n l-1) constitute the dominant quantitative group (48.7 ± 6.1 % and 42.5 ± 4.1 %) of zooplankton, thus, significantly contributing to the overall temporal variation (r1 = 0.896, r2 = 0.970). At both stations and in accordance with the results of Khan (1987), Sanjer & Sharma (1995), Sharma & Sharma (2001, 2008) and Sharma (2005, 2009a), rotifers reveal

(Figs. 5 & 6) an oscillating annual periodicity with Fig. 5. Monthly variations of zooplankton groups’ January (winter) peaks. Throughout the study abundance of Deepor Beel (Nov 02 - Oct 03) at period and at both sites, species of Brachionidae station I. and Lecanidae, in the stated order, constitute the major components of rotifer diversity. In contrast to Sharma (1992), no definite seasonal periodicity of abundance of loricate or illoricate rotifers was found. Furthermore, only a few rotifer species seem to be of relative quantitative importance but no individual species shows any distinct dominant role. Cladocera forms a second important group (142 ± 59 and 142 ± 48 n l-1), comprising 28.7 ± 7.0 % and 30.6 ± 4.9 % of general abundance, and consi- derably influencing zooplankton temporal variation (monthly zooplankton abundance and Cladocera abundance). At both stations respec- tively, Cladoceran density oscillates with annual frequency and shows (Figs. 5 & 6) peaks in winter (January and December) and minima during April (summer). Their abundance is higher than that reported in the floodplain lakes of Kashmir (Khan 1987), Bihar (Baruah et al. 1993; Sinha et al. 1994), and Assam (Sharma & Hussain 2001; Sharma & Sharma 2008). Cladocera abundance is Fig. 6. Monthly variations of zooplankton groups’ largely influenced by species of Chydoridae and abundance of Deepor Beel (Nov 02 - Oct 03) at Daphniidae. As with Rotifera, only a few clado- station II. ceran species show relatively high individual The high species diversity of zooplankton in densities but no individual species shows any Deepor beel, characterized by low densities of distinct dominant role. majority of species of different groups, may be At the two stations respectively, Copepoda ascribed to fine niche partitioning amongst species abundance ranges between 66 ± 17 n l-1 and 81 in combination with high micro- and macro-scale ± 13 n l-1 comprising 15.1 ± 6.5 % and 18.7 ± 4.9 % habitat heterogeneity in this Ramsar site with a of zooplankton. Copepoda abundance oscillates well developed littoral profile and occurrence of with annual frequency peaking in May (station various macrophytes as hypothesized by Segers I) and February and September (station II) SHARMA 301 with minima in October (both stations) (Figs. 5 & community analysis in the Indian floodplain lakes. 6). The sub-dominant role of Copepoda in this In order to acquire better understanding of holistic study contradicts their dominant role reported environmental heterogeneity of this Ramsar site, earlier in certain floodplain lakes of Bihar (Baruah investigations, however, need to be extended to et al. 1993), Assam (Sharma & Hussain 2001), and more sampling stations with particular reference West Bengal (Khan 2003). At both stations, to variations in the macrophyte associations. cyclopoids play a dominant role and nauplii occur throughout the whole study period indicating an Acknowledgements active reproductive phase of this group. Another sub-dominant group is Rhizopoda; at stations I This study is undertaken partly under the and II, abundances range respectively, between 29 “Potential for Excellence Program (Focus Area: ± 14 n l-1 and 35 ± 18 n l-1 (Figs. 5 & 6) and Biosciences) of North-Eastern Hill University, comprise 5.9 ± 2.2 % and 7.3 ± 18 % of zooplankton Shillong. The author is thankful to the G. B. Pant peaking in September at both stations. Other Institute of Himalayan Environmental Develop- zooplankton groups such as Ostracoda and Con- ment, Almora, for a research grant during which chostraca have very poor abundance. this study was initiated. The author is grateful to The paucity of detailed analysis of zooplankton Dr. (Mrs.) Sumita Sharma, North Eastern Regio- in the Indian floodplain lakes highlights the nal Centre, Zoological Survey of India, Shillong, for importance of this study, which, in turn, indicates her useful comments. Thanks are also due to the the distinctly rich and diverse nature of zooplank- Head of the Department of Zoology, North-Eastern ton biocoenosis of Deepor Beel, the speciose Hill University, Shillong, for the necessary labora- character of Rotifera and Cladocera, and the quali- tory facilities. Finally, the author wishes to thank tative and quantitative predominance of zoo- an anonymous reviewer for critical comments and plankton in net plankton communities. Zooplank- constructive suggestions. ton richness and abundance show winter peaks that occur simultaneously with lower water References temperature. The lack of clear temporal patterns, the different monthly trends, and certain other A. P. H. A. 1992. Standard Methods for the Exami- variations noticed at the two sampling stations nation of Water and Wastewater. 18th edn. Ameri- need further confirmation. The present results can Public Health Association, Washington D. C. may not reflect holistic environmental hetero- Baruah, A., A. K. Sinha & U. P. Sharma. 1993. Plank- geneity of this Ramsar site unless extended to ton variability of a tropical wetland, Kawar (Begu- more sampling stations with particular reference sarai), Bihar. Journal of Freshwater Biology 5: 27- to variations in the macrophyte associations. In 32. view of the existing lacunae, investigations have Dumont, H. J. & H. Segers. 1996. Estimating lacustrine since been initiated by the author. zooplankton species and complementarity. Hydro- biologia 341: 125-132. Conclusions Kaul, V. & A. K. Pandit. 1982. Biotic factors and food chain structure in some typical wetlands of Kash- Zooplankton comprises an important quanti- mir. Pollution Research 1: 49-54. tative component of net plankton, showing a Khan, M. A. 1987. Observations on zooplankton com- diverse and speciose character, with a rich faunal position, abundance and periodicity in two flood- diversity and the quantitative dominance of Roti- plain lakes of the Kashmir Himalayan valley. Acta fera and Cladocera. In general, richness or abun- Hydrochemica Hydrobiologica 15: 167-174. dance of zooplankton or its constituent groups is Khan, R. A. 2002. The ecology and faunal diversity of found to oscillate with annual frequency but more two floodplain Ox-bow lakes of South-Eastern West observations may be required to corroborate this Bengal. Records of the Zoological Survey of India, conclusively. Results show high species diversity Occasional Paper No. 195: 1-57. with relatively low densities and equitable abun- Khan, R. A. 2003. Faunal diversity of zooplankton in dance for the majority of species. Individual abiotic freshwater wetlands of Southeastern West Bengal. factors have a limited influence on zooplankton Records of the Zoological Survey of India, Occasio- richness and abundance. The present results provide nal Paper No. 204: 1-107. useful information on zooplankton diversity Koste, W. 1978. ROTATORIA. Die Rädertiere Mitte- particularly in view of the paucity of a detailed leuropas, begründet von Max Voigt. Überordnung 302 ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL

Monogononta. Gebrüder Borntraeger, Berlin, Stutt- Assam (N. E. India). Ecology, Environment & gart. Conservation 7: 397-403. Ludwig, J. A. & J. F. Reynolds. 1988. Statistical Ecology: Sharma, B. K. & S. Sharma. 1999a. Freshwater a Primer on Methods and Computing. John Wiley & Rotifers (Rotifera : Eurotatoria). State Fauna Series: Sons, New York. Fauna of Meghalaya 4: 11-161. Zoological Survey of Magurran, A. E. 1988. Ecological Diversity and its Mea- India, Calcutta. surement. Croom Helm Limited, London. Sharma, B. K. & S. Sharma. 1999b. Freshwater Clado- Michael, R. G. & B. K. Sharma. 1988. Indian Cladocera cerans (Crustacea: Branchiopoda: Cladocera). State (Crustacea: Branchiopoda: Cladocera). Fauna of Fauna Series: Fauna of Meghalaya 4: 469-550. India and Adjacent Countries Series. Zoological Zoological Survey of India, Calcutta. Survey of India, Calcutta. Sharma, B. K. & S. Sharma. 2000. Freshwater Rotifers Rai, D. N. & J. M. Dutta-Munshi. 1982. Ecological cha- (Rotifera: Eurotatoria). State Fauna Series: Fauna racteristics of `Chaurs’ of North Bihar. pp. 89-95. of 7: 163-224. Zoological Survey of India, In: B. Gopal, R. E. Turner, R. G. Wetzel & D. F. Calcutta. Winghon (eds.) Wetlands - Ecology and Manage- Sharma, B. K. & S. Sharma. 2001. Biodiversity of Roti- ment. Vol. II. International Scientific Publications fera in some tropical floodplain lakes of the Brah- and National Institute of Ecology, Jaipur, India. maputra river basin, Assam (N. E. India). Hydro- Sanjer, L. R. & U. P. Sharma. 1995. Community struc- biologia 446 / 447: 305-313. ture of plankton in Kawar lake wetland, Begusarai, Sharma, B. K. & S. Sharma. 2005. Faunal diversity of Bihar: II. Zooplankton. Journal of Freshwater Biology Rotifers (Rotifera: Eurotatoria) of Deepor Beel, Assam (N. E. India)- a Ramsar site. Journal of the 7: 165-167. Bombay Natural History Society 102: 169-175. Segers, H. 2008. Global diversity of rotifers (Rotifera) in Sharma, B. K. & S. Sharma. 2008. Faunal diversity of freshwater. Hydrobiologia 595: 49-59. Cladocera (Crustacea: Branchiopoda) of Deepor Sharma, B. K. 1992. Systematics, distribution and eco- Beel, Assam ()- a Ramsar site. logy of freshwater rotifera in West Bengal. pp. 231 - Journal of the Bombay Natural History Society 105: 273. In: S. R. Mishra & D. N. Saksena (eds.) Recent 196-201. Advances in Aquatic Ecology. Ashish Publishing Sharma, S. & B. K. Sharma. 2008. Zooplankton diversity House, New Delhi. in floodplain lakes of Assam. Records of the Zoolo- Sharma, B. K. 1998. Freshwater rotifers (Rotifera: gical Survey of India, Occasional Paper No. 290: 1- Eurotatoria). Fauna of West Bengal State Fauna 307. Series 3: 341-461. Zoological Survey of India, Cal- Sinha, A. K., A. Baruah, D. K. Singh & U. P. Sharma. cutta. 1994. Biodiversity and pollution status in relation to Sharma, B. K. 2000. Synecology of rotifers in a tropical physico-chemical factors of Kawar lake (Begusarai), floodplain lake of Upper Assam (N. E. India). The North Bihar. Journal of Freshwater Biology 6: 309- Indian Journal of Animal Sciences 70: 880-885. 331. Sharma, B. K. 2005. Rotifer communities of floodplain Sugunan, V. V. 1989. Limnological features in beels: lakes of the Brahmaputra basin of lower Assam (N. Biotic factors. Bulletin of Central Inland Capture E. India): biodiversity, distribution and ecology. Research Institute, Barrackpore 63: 128- Hydrobiologia 533: 209-221. 135. Sharma, B. K. 2009a. Diversity of rotifers (Rotifera, Talling, J. F. & I. B. Talling. 1965. The chemical compo- Eurotatoria) of Loktak Lake, , North eas- sition of African lake waters. Internationale Revue tern India. Tropical Ecology 50: 277-285. Gesammten Hydrobiologia 50: 421-463. Sharma, B. K. 2009b. Rotifer communities of floodplain Vass, K. K. 1989. Beel fisheries resources in West lakes of Manipur (N. E. India): biodiversity, distri- Bengal. Bulletin of Central Inland Capture Fisheries bution and ecology. Journal of the Bombay Natural Research Institute, Barrackpore 63: 29-35. History Society 106: 45-56. Yousuf, A. R., G. Mustafa Shah & M. Y. Qadri. 1986. Sharma, B. K. & Md. Hussain. 2001. Abundance and Some limnological aspects of Mirgund wetland. ecology of zooplankton in a tropical floodplain lake, Geobios New Reports 5: 27-30.

(Received on 28.05.2009 and accepted after revisions, on 16.09.2010)