Tropical Ecology 52(3): 293-302, 2011
© International Society for Tropical Ecology
www.tropecol.com
ISSN 0564-3295
Zooplankton communities of Deepor Beel (a Ramsar site), Assam
(N. E. India): ecology, richness, and abundance
*
B. K. SHARMA
Department of Zoology, North Eastern Hill University, Permanent Campus, Umshing,
Shillong 793022, Meghalaya, 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 lakes 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, influenciada 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: bksharma@nehu.ac.in, profbksharma@gmail.com
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
Freshwater ecosystems are colonized by a
diverse array of aquatic organisms. Amongst
these, zooplankton, which function as primary
consumers, comprise an integral component of
aquatic food-webs and contribute significantly to
biological productivity. Inspite of several studies
from fresh-water environs of India, there is still
little information on the ecology and role of
zooplankton in the aquatic productivity of the
Indian floodplain lakes (Sharma & Sharma 2008).
Studies of zooplankton ecology from the floodplains of North-eastern India have so far been
restricted to the reports of Sharma & Hussain
(2001) and Sharma & Sharma (2008); in addition,
Sharma & Sharma (2001, 2005) and Sharma
(2005, 2009a, 2009b) dealt with Rotifera diversity.
Thus, in view of the paucity of works from
India, the present study of zooplankton communities of Deepor Beel, a Ramsar Site and an important floodplain lake of the Brahmaputra river
basin of Assam, assumes special importance. This
report presents information on zooplankton richness, community similarities and abundance, and
the constituent zooplankton groups at two sampling stations. Analysis includes the temporal
variation of species diversity, dominant groups,
and the influence of seventeen abiotic parameters
on zooplankton richness and abundance.
Materials and methods
Limnological investigations were undertaken
during November 2002 - October 2003 in Deepor
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
(Nov 02 - Oct 03) (Mean ± SD).
Factors
Rainfall (mm)
Water temperature (0C)
pH
Transparency (cm)
Specific Conductivity
(µS cm-1)
Dissolved oxygen (mg l-1)
Free CO2 (mg l-1)
Alkalinity (mg l-1)
Hardness (mg l-1)
Chloride (mg l-1)
Phosphate (mg l-1)
Sulphate (mg l-1)
Nitrate (mg l-1)
Silicate (mg l-1)
B.O.D5 (mg l-1)
Dissolved organic
matter (mg l-1)
Station I
204.5 ± 160.4
27.2 ± 4.6
6.89 ± 0.18
51.9 ± 26.2
99.2 ± 13.2
Station II
204.5 ± 160.4
27.4 ± 5.1
6.93 ± 0.21
52.7 ± 25.3
96.8 ± 15.5
6.7 ± 1.6
7.2 ± 2.1
66.3 ± 12.1
62.1 ± 9.9
34.6 ± 5.2
0.18 ± 0.07
10.2 ± 3.2
0.72 ± 0.12
3.02± 1.02
3.11 ± 0.59
3.84 ± 0.80
7.0 ± 1.1
6.8 ± 1.9
68.9 ± 10.3
61.2 ± 12.3
35.1 ± 5.0
0.19 ± 0.10
9.9 ± 3.4
0.74 ± 0.14
3.10 ± 1.27
3.21 ± 0.46
3.90 ± 0.64
Total dissolved solids (mg l-1) 2.37 ± 0.29
2.57 ± 0.30
- 26º 11′ N; area: 40 km2; altitude: 42 m above sea
level) in the Kamrup district of lower Assam, N. E.
India (Fig. 1 A & B). Various aquatic macrophytes,
namely Hydrilla verticellata, Eichhornia crassipes,
Vallisnaria spiralis, Utricularia flexuosa, Trapa
bispinosa, Euryale ferox, Najas indica, Monochoria
hastaefolia, Ipomoea fistulosa, Hygroryza aristata,
Polygonum hydropiper, and Limnophila sp., cover
this floodplain lake.
Due to local constraints, the observations for
this study were limited (November 2002 - October
2003) to two sampling stations (I and II). The
sampled sites were characterized by common
occurrence of H. verticellata, E. crassipes, U. flexuosa,
T. bispinosa, E. ferox, N. indica, and P. hydropiper. Station II, however, differed from the former
in occasional (temporal) lack of the rest of the
observed macrophyte species, namely V. spiralis,
M. hastaefolia, I. fistulosa, H. aristata, and
Limnophila sp.. Though there is no official monitoring of water table of this floodplain lake, general
minimum and maximum water levels were observed 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
Zooplankton Total richness
Monthly richness
Community similarity (%)
Station I
Station II
171 species
68 - 112 96 ± 11
48.9 - 88.1
160 species
68 - 113 97 ± 13
53.1 - 89.7
Rotifera
Total richness
Monthly richness
110 species
43 - 65 56 ± 6
100 species
38 - 60 52 ± 7
Cladocera
Total richness
Monthly richness
45 species
17 - 41 29 ± 6
43 species
20 - 41 32 ± 6
Quantitative
Net Plankton (n l-1)
708 - 961
Zooplankton (n l-1)
Percentage
Species Diversity
239 - 657
33.2 - 68.4
3.548 - 4.229
812 ± 80
696 - 1058
475 ± 114
57.9 ± 9.0
3.991 ± 0.181
801 ± 123
255 - 687
35.4 - 66.9
3.529 - 4.219
459 ± 128
56.5 ± 8.8
3.973 ± 0.193
Different Groups
Rotifera
(n l-1)
Percentage
105 - 318 231 ± 60
42.8 - 65.2 48.7 ± 6.1
106 - 325 198 ± 70
37.9 - 49.6 42.5 ± 4.1
Cladocera (n l-1 )
Percentage
43 - 252 142 ± 59
14.6 - 38.3 28.7 ± 7.0
56 - 233 142 ± 48
22.0 - 37.6 30.6 ± 4.9
Copepoda (n l-1)
Percentage
49 - 95 66 ± 17
7.6 - 31.4 15.1 ± 6.5
66 - 101 81 ± 13
11.9 - 29.-0 18.7 ± 4.9
Rhizopoda (n l-1)
7 - 41 29 ± 14
5 - 66 35 ± 18
Ostracoda (n
l-1)
Conchostraca (n l-1)
2 - 10
6±3
0-4
2003, respectively; the water levels were identical
at both the stations. Further, the two sampling
stations experienced similar inputs of rainwater
and floods.
Water samples were collected monthly from
the selected sampling sites and were analyzed for
the following abiotic factors: water temperature,
rainfall, pH, transparency, specific conductivity,
dissolved oxygen, free CO2, alkalinity, hardness,
chloride, phosphate, sulphate, nitrate, silicate,
BOD5, dissolved organic matter, and total dissolved solids. Water temperature, specific conductivity,
and pH were recorded through field probes, transparency was noted with a Secchi disc, dissolved
oxygen was estimated by Winkler’s method, and
the other parameters were analyzed following
APHA (1992). Three qualitative (by towing) and
quantitative plankton (by filtering 25 l water each)
samples were collected monthly at each station
using a nylobolt plankton net (No. 25). Zooplankton samples were preserved in 5 % formalin,
screened, and then identified following Koste
(1978), Michael & Sharma (1988), Sharma (1998)
and Sharma & Sharma (1999a, 1999b, 2000, 2008).
2 - 10
5±2
0-2
Quantitative samples were analyzed for abundance of net plankton (phyto- and zooplankton),
zooplankton, and zooplankton constituent groups.
Community similarity (Sorensen’s index) and species
diversity (Shannon’s index) were calculated following Ludwig & Reynolds (1988) and Magurran
(1988). ANOVA was used to analyse the significance of temporal variation of the biotic communities. Simple correlation coefficients (r1 and r2,
respectively for stations I and II) were calculated
between all abiotic and biotic parameters.
Results and discussion
Water samples analyzed from Deepor Beel are
characterized by low ionic concentrations (Table 1)
and, thus, warrant the inclusion of this Ramsar
site under the ‘Class I’ category of trophic classification following Talling & Talling (1965). Mean
water temperature confirms the tropical range
concurrent with the lake’s geographical location.
The nearly neutral and marginally hard waters of
this floodplain lake show moderate values for
dissolved oxygen, low free CO2, and low concen-
SHARMA
Fig. 2. Monthly variations in zooplankton richness
of Deepor Beel (Nov 02 - Oct 03).
tration of micronutrients. In general, the ranges of
most abiotic factors show insignificant differences
at the two stations and broadly agree with earlier
reports from other floodplain lakes of Assam
(Sharma & Sharma 2001, 2008; Sharma 2005).
Plankton samples from Deepor Beel show
(Table 2) the existence of a speciose and diverse
zooplankton biocoenosis (171 species) and, thus,
reflect the overall environmental heterogeneity
and habitat diversity of this Ramsar site. Total
zooplankton richness (171 species), the second
highest known from any floodplain lake or individual aquatic ecosystem in India, follows that of
212 species for Loktak Lake (Sharma 2009a & b) another important Ramsar site and floodplain lake
located in N. E. India. Richness in Deepor Beel is,
however, distinctly more than that reported from
several other floodplain lakes of India: 51 species
from Trigamasar and Naranbagh lakes (Khan
1987), and 26 species from Mirgund Wetland
(Yousuf et al. 1986) of Kashmir; 19 (Baruah et al.
1993) and 31 species (Sanjer & Sharma 1995) from
Kawar Lake, Bihar; 49 species from Samuajan
Beel, Upper Assam (Sharma & Hussain 2001); and
71 species from Beri Gopalpur and Sosadanga,
West Bengal (Khan 2003). Though Deepor Beel is
in fact more species rich, the differences between
this study and other studies may result also from
incomplete species inventories, inadequate sampling, and overlooking identification of smaller
species. Nevertheless, a comparison with the zooplankton species richness reported by the author
in Sharma & Sharma (2008) (which used similar
297
methodology) from 15 other floodplain lakes of the
Brahmaputra river basin of Assam (102 - 156 species) underlines the relatively high species diversity of Deepor Beel.
As in the findings of Sharma & Sharma (2008)
and Sharma (2009a), zooplankton forms the dominant qualitative component (phytoplankton + zooplankton = 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 Bihar (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).
Zooplankton richness in Deepor Beel shows
little annual variation between station I (171
species) and station II (160 species). Comparisons
between sampling stations indicate broadly similar
monthly ranges, mean values, and standard deviations of zooplankton richness (68 - 112, 96 ± 11
species; 68 - 115, 97 ± 13 species). On the other hand,
significant monthly variation (F11, 23 = 23.966, P <
0.005) occurred in zooplankton composition. This
statement holds valid for the present stations and
may not reflect the general environmental heterogeneity of Deepor Beel unless ascertained by analysis of collections from other parts of this Ramsar
site. Richness (Fig. 2) oscillates with annual
frequency with winter peaks in February (station
I) or December (station II) and minima in summer
(April). While the peaks concur with luxuriant
winter growth of aquatic macrophytes, the latter
coincides with the lowest water level. Lack of
information on the seasonal variation in zooplankton richness in other Indian floodplain lakes prohibits comparison of this study with other areas, but
winter peaks concur with the author’s observations
in Loktak Lake (Sharma unpublished).
Rotifera species (56 ± 6, 52 ± 7 species) form the
main qualitative component of zooplankton at both
stations and exert the dominant influence on zooplankton temporal variation (monthly zooplankton
richness and Rotifera richness, r1 = 0.969, r2 =
0.918). Additionally, Cladocera (34 ± 6, 38 ± 6
species) contributes significantly to the zooplankton richness (r1 = 0.923, r2 = 0.966). The qualitative
importance of Rotifera in Deepor Beel agrees with
that reported for several other floodplain lakes
(Khan 2002, 2003; Sharma 2000, 2005, 2009a, b;
Sharma & Sharma 2001, 2008).
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ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL
Table 3. Zooplankton community similarities (%) at station I (Nov 02 - Oct 03).
Nov
Dec
Jan
Feb
March
April
May
June
July
Aug
Sept
Oct
Nov
-
Dec
66.7
-
Jan
73.0
76.2
-
Feb
88.1
74.6
77.4
-
March
80.7
66.7
76.7
85.7
-
Apr
51.0
66.7
59.3
56.0
62.5
-
May
85.7
60.7
71.2
80.0
64.1
55.3
-
June
65.5
69.0
72.1
63.2
61.8
65.3
66.7
-
July
78.0
67.8
77.4
82.8
75.0
56.0
72.7
63.2
-
Aug
73.4
77.2
76.7
82.1
66.7
58.3
71.7
69.1
85.7
-
Sep
76.4
69.1
75.9
81.5
76.9
65.2
70.6
60.4
74.1
73.1
-
Oct
74.1
66.7
66.7
79.2
70.6
48.9
68.0
61.5
75.5
74.5
57.1
-
July
71.2
69.1
71.7
80.8
74.5
66.7
66.7
76.0
-
Aug
76.2
78.0
77.2
71.4
58.2
53.1
65.4
70.4
66.7
-
Sep
76.7
82.1
77.9
79.2
73.1
65.2
69.2
72,7
70.6
69.1
-
Oct
74.6
72.7
75.5
84.6
74.5
66.7
66.7
60.0
72.0
70.4
78.4
-
Table 4. Zooplankton community similarities (%) at station II (Nov 02 - Oct 03).
Nov
Dec
Jan
Feb
March
April
May
June
July
Aug
Sept
Oct
Nov
-
Dec
71.9
-
Jan
71.0
89.7
-
Feb
75.4
73.7
80.0
-
March
76.7
60.7
70.4
75.5
-
At both stations, zooplankton richness is negatively correlated with water temperature (r1 =
- 0.705, r2 = -0.776) and rainfall (r1 = -0.523, r2 =
- 0.654) but positively correlated with specific conductivity (r1 = 0.497, r2 = 0.647) and dissolved
oxygen (r1 = 0.501, r2 = 0.764). Richness is also
positively correlated with transparency (r2 = 0.650),
alkalinity (r2 = 0.608), and hardness (r2 = 0.632) at
station II.
At stations I and II respectively, this study
found 48.9 - 88.1 % and 53.1 - 89.7 % similarity in
zooplankton community across monthly samples
(Tables 3 & 4). Further, 34.8 and 33.3 % instances
in the matrices indicate 60 - 70 % similarity and an
additional 40.9 and 54.5 % of instances at the two
stations respectively indicate 70 - 80 % similarity.
In summary, the majority (75 - 88 %) of instances
show 60 - 80 % similarity. This generally high level
of similarity suggests limited monthly variations
in species composition contrasted by lower simila-
Apr
63.0
56.0
62.5
68.1
73.9
-
May
70.0
64.3
63.0
71.7
76.9
69.6
-
June
67.8
65.4
71.7
65.4
70.6
66.7
70.6
-
rities, due to decreased species richness, during the
four month summer period (March - June). At
stations I and II, respectively, peak similarity values
occurred between November - February and December - February and minima were recorded in AprilOctober and April - August. Zooplankton composition
shows closeness between November - February and
July - August at station I and between DecemberJanuary and February - October at station II. At
both stations, and apparently due to the fewer
number of species present in April, the samples
collected in April exhibit the greatest divergence in
their composition.
Zooplankton (239 - 657, 475 ± 114 n l-1 and 255
- 687, 459 ± 128 n l-1) forms the main quantitative
component of net plankton of Deepor Beel (33.2 68.4, 57.9 ± 9.0 % 35.4 - 66.9, 56.5 ± 8.8 %, at the
two stations respectively), thus, significantly
contributing to net planktons’ temporal variation
(monthly net plankton abundance and zooplankton
SHARMA
Fig. 3. Monthly variations of zooplankton abundance
of Deepor Beel (Nov 02 - Oct 03).
Fig. 4. Monthly variations of zooplankton species
diversity of Deepor Beel (Nov 02 - Oct 03).
abundance, r1 = 0.906, r2 = 0.919). The lowest
percentage composition was recorded in April. At
both stations, in the six months of November
through February and July through August,
zooplankton contributed more than 60.0 % of the
net plankton abundance.
In general, quantitative dominance of zooplankton agrees with earlier reports from Assam
(Sharma & Hussain 2001). However, such patterns
299
contrast with the higher phytoplankton abundance
noticed in some floodplain lakes and wetlands 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 December at station I and January at station II. Density
registers significant monthly variation (F11, 23 =
24.386, P < 0.005) but insignificant variation
between stations. This study shows no definite
seasonal periodicity other than higher winter densities. The high winter densities at both stations
reflect a significant negative correlation of zooplankton 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, abundance 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 &
Sharma 2008) and, at both stations, show broadly
identical values. The zooplankton community
shows significant monthly variation (F11, 23 =
15.185, P < 0.005) but insignificant variation
between stations. In general, at station I, relatively high diversities (more than 4.0) are observed
in January through February and July through
October and, at station II, from January through
March and July through December. Zooplankton
diversity follows oscillating annual patterns at both
stations, peaking in July at station I and October
at station II. Both have April minima (Fig. 4).
300
ZOOPLANKTON COMMUNITIES OF DEEPOR BEEL
Fig. 5. Monthly variations of zooplankton groups’
abundance of Deepor Beel (Nov 02 - Oct 03) at
station I.
Fig. 6. Monthly variations of zooplankton groups’
abundance of Deepor Beel (Nov 02 - Oct 03) at
station II.
The high species diversity of zooplankton in
Deepor beel, characterized by low densities of
majority of species of different groups, may be
ascribed to fine niche partitioning amongst species
in combination with high micro- and macro-scale
habitat heterogeneity in this Ramsar site with a
well developed littoral profile and occurrence of
various macrophytes as hypothesized by Segers
(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 stations, 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 abundance (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
January (winter) peaks. Throughout the study
period and at both sites, species of Brachionidae
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 considerably
influencing
zooplankton
temporal
variation (monthly zooplankton abundance and
Cladocera abundance). At both stations respectively, 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
largely influenced by species of Chydoridae and
Daphniidae. As with Rotifera, only a few cladoceran species show relatively high individual
densities but no individual species shows any
distinct dominant role.
At the two stations respectively, Copepoda
abundance ranges between 66 ± 17 n l-1 and 81
± 13 n l-1 comprising 15.1 ± 6.5 % and 18.7 ± 4.9 %
of zooplankton. Copepoda abundance oscillates
with annual frequency peaking in May (station
I) and February and September (station II)
SHARMA
with minima in October (both stations) (Figs. 5 &
6). The sub-dominant role of Copepoda in this
study contradicts their dominant role reported
earlier in certain floodplain lakes of Bihar (Baruah
et al. 1993), Assam (Sharma & Hussain 2001), and
West Bengal (Khan 2003). At both stations,
cyclopoids play a dominant role and nauplii occur
throughout the whole study period indicating an
active reproductive phase of this group. Another
sub-dominant group is Rhizopoda; at stations I
and II, abundances range respectively, between 29
± 14 n l-1 and 35 ± 18 n l-1 (Figs. 5 & 6) and
comprise 5.9 ± 2.2 % and 7.3 ± 18 % of zooplankton
peaking in September at both stations. Other
zooplankton groups such as Ostracoda and Conchostraca have very poor abundance.
The paucity of detailed analysis of zooplankton
in the Indian floodplain lakes highlights the
importance of this study, which, in turn, indicates
the distinctly rich and diverse nature of zooplankton biocoenosis of Deepor Beel, the speciose
character of Rotifera and Cladocera, and the qualitative and quantitative predominance of zooplankton in net plankton communities. Zooplankton richness and abundance show winter peaks
that occur simultaneously with lower water
temperature. The lack of clear temporal patterns,
the different monthly trends, and certain other
variations noticed at the two sampling stations
need further confirmation. The present results
may not reflect holistic environmental heterogeneity of this Ramsar site unless extended to
more sampling stations with particular reference
to variations in the macrophyte associations. In
view of the existing lacunae, investigations have
since been initiated by the author.
Conclusions
Zooplankton comprises an important quantitative component of net plankton, showing a
diverse and speciose character, with a rich faunal
diversity and the quantitative dominance of Rotifera and Cladocera. In general, richness or abundance of zooplankton or its constituent groups is
found to oscillate with annual frequency but more
observations may be required to corroborate this
conclusively. Results show high species diversity
with relatively low densities and equitable abundance for the majority of species. Individual abiotic
factors have a limited influence on zooplankton
richness and abundance. The present results provide
useful information on zooplankton diversity
particularly in view of the paucity of a detailed
301
community analysis in the Indian floodplain lakes.
In order to acquire better understanding of holistic
environmental heterogeneity of this Ramsar site,
investigations, however, need to be extended to
more sampling stations with particular reference
to variations in the macrophyte associations.
Acknowledgements
This study is undertaken partly under the
“Potential for Excellence Program (Focus Area:
Biosciences) of North-Eastern Hill University,
Shillong. The author is thankful to the G. B. Pant
Institute of Himalayan Environmental Development, Almora, for a research grant during which
this study was initiated. The author is grateful to
Dr. (Mrs.) Sumita Sharma, North Eastern Regional Centre, Zoological Survey of India, Shillong, for
her useful comments. Thanks are also due to the
Head of the Department of Zoology, North-Eastern
Hill University, Shillong, for the necessary laboratory facilities. Finally, the author wishes to thank
an anonymous reviewer for critical comments and
constructive suggestions.
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(Received on 28.05.2009 and accepted after revisions, on 16.09.2010)