Diversity of microcrustacea (Crustacea: Branchiopoda) of Loktak Lake, a Ramsar site, Manipur, India
B.K. Sharma 1 & SumitaSharma 2
1 Department of Zoology, North-Eastern Hill University, Permanent
Campus, Umshing, Shillong,
Meghalaya 793022, India
2 Eastern Regional Station, Zoological Survey of India, Fruit
Gardens, Risa Colony, Shillong,
Meghalaya 793003, India
Email: 1 bksharma@nehu.ac.in; 2 sumitazsi@hotmail.com
Date
of publication (online): 26 November 2009
Date of
publication (print): 26 November 2009
ISSN 0974-7907
(online) | 0974-7893 (print)
Editor: M.M. Saxena
Manuscript
details:
Ms # o2231
Received 08 June
2009
Finally accepted
03 November 2009
Citation: Sharma, B.K.
& S. Sharma (2009). Diversity of microcrustacea (Crustacea: Branchiopoda) of Loktak Lake, a Ramsar site, Manipur, India. Journal
of Threatened Taxa 1(11): 541-548.
Copyright: © B.K. Sharma
& Sumita Sharma 2009. Creative Commons
Attribution 3.0 Unported License. JoTTallows unrestricted use of this article in any medium for non-profit purposes,
reproduction and distribution by providing adequate credit to the authors and
the source of publication.
Author Details: Both the
authors specialize in biodiversity and ecology of freshwater zooplankton and
have made significant contributions in the fields of their expertise.
Author
Contribution:The present study is the result of collaborative work undertaken by the
authors, mainly at the research laboratory of the senior author.
Acknowledgments:This study formed a part of the “Potential for Excellence Program
(Focused Area: Biosciences)” of North-Eastern Hill University, Shillong. The first author is thankful to G.B. Pant
Institute of Himalayan Environmental Development, Almorafor a research grant. Thanks are due to the Head, Department of Zoology,
North-Eastern Hill University, Shillongfor laboratory facilities. The second author is thankful to the Director,
Zoological Survey of India, Kolkata.
Abstract:Microcrustacea of LoktakLake (collected during Nov. 2002-Oct. 2004) reveal 57 species and show
qualitative dominance of Cladocera (51 species). They indicate monthly richness ranging
between 33±6 and 32±6 species, record 51.7-82.3 and 53.6-90.0% community
similarities during two years respectively, and follow trimodalannual patterns with peaks during winter. The microcrustaceans (112±17 and 124±13 n/l)
form an important quantitative component (45.7±4.9 and 43.3±3.7 %) of
zooplankton and show broadly trimodal annual patterns
with peak abundance during winter. Cladocera > Copepoda mainly
contribute to their quantitative variations. ANOVA registers significant monthly variations of microcrustacearichness and significant annual and monthly variations of their abundance. Richness is positively correlated with
dissolved oxygen and is negatively correlated with rainfall, hardness, chloride
and total dissolved solids while abundance is negatively correlated with pH
only. Multiple regressions indicate
higher cumulative effect of 15 abiotic factors on
richness and abundance. Our results
indicate no definite periodicity of richness and abundance of microcrustacea or their constituent groups during two
annual cycles and are characterized by their higher species diversity, higher
evenness and lower dominance.
Keywords:Abundance, dominance, ecology, equitability, LoktakLake, microcrustacea, Ramsarsite, richness, species diversity.
For Figures
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Introduction
Microcrustaceainclude various groups of brachiopod crustaceans which colonize the littoral
and limnetic regions of different freshwater
ecosystems. They comprise an integral
link of aquatic food-web, form important component of metazooplanktonand contribute notably to biological productivity in freshwaters. Though microcrustaceaoften form part of zooplankton studies from different parts of India, there are
yet limited studies on their ecosystem diversity and role in aquatic
productivity in freshwater environs of this country in general and the
floodplain lakes in particular (Sharma & Sharma 2009) because of inadequate
community analysis and incomplete species inventories. The related information from the floodplains
of northeastern India is so far limited to the works of Sharma & Hussain (2001) and Sharma & Sharma (2008, 2009).
The present study on microcrustacea of Loktak - a Ramsar site, an important floodplain lake of South Asia and
one of the largest natural freshwater lakes of eastern India, assumes special limnological importance in view of the stated lacunae. The observations are made on qualitative and
quantitative analysis of the microcrustaceancommunities of this wetland with special reference to their richness, community
similarities, abundance, species diversity, evenness and dominance as well as
their constituent groups during two years of the study period. In addition, the
influence of abiotic parameters on their richness and
abundance are analyzed to understand ecological correlations.
Materials
and Methods
This study is a
part of limnological survey undertaken (Nov. 2002 -
Oct. 2004) in Loktak Lake (93046’-93055’E
& 24025’-24042’N) located in Bishnupur/ Imphal districts of Manipur (northeastern
India). This floodplain lake is
characterized by floating mats of vegetation called “phumdi”
which are inhabited by the threatened Brow-antlered Deer (Rucervus eldii eldii). The common aquatic plants of this wetland
include Eichhornia crassipes,Hydrilla verticellata,
Euryale ferox, Vallisnaria spiralis, Utricularia flexuosa, Trapa natans, Lemna trisula,Pistia striates, Salviniasp. Nymphaea spp., Nymphoides spp., Nelumbo mucifera,Potamageton spp. and Azolla pinnata.
The observations
were undertaken at monthly intervals, during the study period, at one selected
sampling site at Sendra (93047’45.61”E
& 24030’56.75”N). Water
samples collected were analyzed for various abioticfactors following APHA (1992) while water temperature, specific conductivity,
pH and dissolved oxygen were recorded by the field probes. Qualitative (by towing) and quantitative (by
filtering 25l water each) net plankton samples were collected by nylobolt plankton net (No. 25) and were preserved in 5%
formalin. The former were screened and
different species were identified following the works of Smirnov (1971, 1976,
1992, 1996), Michael & Sharma (1988), Korovchinsky (1992), Sharma & Sharma (1999, 2008) and Orlova-Bienkowskaja (2001). Quantitative samples were analyzed for abundance of Microcrustaceaand their constituent groups using Sedgwick-Rafter counting cell. Community similarities (Sorensen’s index),
species diversity (Shannon’s index), dominance (Berger-Parker’s index) and
evenness (Pileou’s index) were calculated following
Ludwig & Reynolds (1988) and Magurran (1988).
Significance of temporal variations of biotic parameters was ascertained by
ANOVA (two-way). Ecological correlations
between abiotic and biotic parameters were determined
by simple correlation coefficients (r). Multiple regression (R2) was used to ascertain cumulative
effect of 15 abiotic factors (water temperature,
rainfall, pH, specific conductivity, dissolved oxygen, free carbon dioxide,
alkalinity, hardness, phosphate, nitrate, sulphate,
silicate, chloride, dissolved organic matter and total dissolved solids) on
biotic factors.
Results and Discussion
Abiotic parameters
Mean water
temperature affirms sub-tropical range of LoktakLake. Specific conductivity indicates
low ionic concentration (Table 1) and, hence, warrants inclusion of this Ramsar site under ‘Class I’
category of Talling & Talling(1965). Slightly acidic and soft waters
of this floodplain lake depict moderate dissolved O2, low free CO2,
low concentration of micronutrients and other abioticfactors.
Richness and
community similarities
Plankton samples
examined from Loktak Lake reveal 57 species of microcrustacea,indicate highly speciose and diverse biocoenosis and, in turn, reflect greater environmental
heterogeneity of this Ramsar site. The richness exceeds the highest Indian
report of 51 species (Sharma & Sharma 2009) known from Deepor beel - another Ramsar site
and an important floodplain lake of northeastern India. All the examined species are observed during
first year while 53 species are noticed during the succeeding year of the study
period. Microcrustacea(Table 2) contribute notably (33±6, 32±6 species) to qualitative variations of
zooplankton of Loktak Lake (r = 0.746). Their richness registers significant temporal
differences between months (F11, 23. = 25.347, P < 0.005) but
shows insignificant annual variations. It follows trimodal and broadly concurrent
annual patterns (Fig. 1) with peaks during winter (December) and minima during
monsoon (July). Qualitative importance of micro-crustaceans, their trimodal patterns and winter peaks correspond with the
results of Deepor beel(Sharma & Sharma 2009) while our results deviate from the later in their
monsoon minima. Richness records
significant negative correlations with rainfall (r = -0.467), hardness (r =
-0.560), chloride (r = -0.684) and total dissolved solids (r = -0.552) and it is
positively correlated with dissolved oxygen (r = 0.538). Multiple regression indicates higher
cumulative effect of 15 abiotic factors on Microcrustacea richness (R2 = 0.743).
Cladocera (51 species),
main qualitative component, are represented by 51 and 47 species respectively during
two years (Table 2). The present study
indicates the richest diversity of this group so far known from any floodplain
lake, Ramsar site and any aquatic ecosystem of
India. Their richness exceeds previous
highest Indian record of 45 species from Deepor Beel, another Ramsar site (Sharma
& Sharma 2008). The cladoceran richness merits special biodiversity interest in
context of a conservative estimate (Fernando & Kanduru1984; Sharma & Michael 1987) of occurrence of up to 60-65 species of this
group from tropical and subtropical parts of India. The present report shows a significant
departure from only nine cladoceran species listed
earlier from Loktak Lake (Singh 1991) while it is
also higher than our report of 21-39 species known from 15 floodplain lakes of
the Brahmaputra river basin (Sharma & Sharma 2008). Monthly richness of Cladocera(29±5 and 28±5 species) exhibits identical annual ranges and mean values and,
follows trimodal annual patterns identical with that
of Microcrustacea. Winter peaks of Loktak Cladoceraconcur with those of Deepor Beel(Sharma & Sharma 2008). ANOVA
registers significant temporal variations in richness between months (F11,
23 = 43.304, p < 0.005) but records insignificant annual
variations. Cladocerarichness is negatively correlated with water temperature (r = -0.512), rainfall
(r = -0.562), pH (r = -0.504), hardness (r = -0.658), nitrate (r = -0.564),
chloride (r = -0.627) and total dissolved solids (r = -0.785) while it is
positively correlated with dissolved oxygen (r = 0.443). Multiple regression
registers moderately higher cumulative influence of 15 abioticfactors (R2 = 0.703) on their richness.
Microcrustacea community
similarities (Tables 3 & 4) range between 51.8-87.3% during first year but depict
marginally higher range (54.2-90.9%) in the following year; the stated
variations, however, broadly concur with the results of Deepor beel (Sharma & Sharma 2009). Higher values (70-80%) are noticed in 53.0
and 40.9% instances while 31.8 and 33.3% instance indicated in the matrices
record 60-70% similarity respectively during two years of the study period. The
cluster analysis shows (Figs. 2 & 3) distinct variations in the patterns of
monthly groupings, thereby, indicating notable differences in their faunal
composition during two years. Higher
closeness is noticed between of microcrustaceacommunities during November-December-October-September in general and between
November-December (peak similarity) in particular during first year. On the other hand, the samples collected
during March-July in general and during June and July in particular exhibit
greater divergence in their composition during this year. Higher closeness is noticed between
March-April (peak similarity) and again between August-September in the
following year while the samples collected during January, February and
November exhibit distinct differences in their composition.
Microcrustacea (112±17 &
124±13 n/l) form an important quantitative component (45.7±4.9 & 43.3±3.7%)
of zooplankton during the study period. They register significant density variations between months (F11,
23 = 10.462, P < 0.005) as well as years (F1, 23 = 5.342, P
> 0.005). Abundance exhibits trimodal annual
patterns (Fig. 3 and 4), shows peaks during winter (December) but exhibits
minima during monsoon (August 1st year and September 2ndyear). It is negatively correlated with
pH (r = -0.544) only while multiple regression indicates
significantly higher cumulative effect of 15 abioticfactors on their abundance (R2 = 0.816). In general, lower abundance of the microcrustaceans of Loktak Lake
and limited influence of abiotic factors are in
contrast to the findings of Deepor beel (Sharma & Sharma 2009).
Cladocera (66±20 &
79±9 n/l) form dominant quantitative group (Table 2) of microcrustacea(56.8±14.0 & 64.7±7.3%), register significant annual variations in
abundance (F1, 23 = 7.927, P < 0.02) and influence temporal
variations of the latter (r = 0.514). In addition, they form sub-dominant
constituent (27.1±6.6 & 27.8±18.4%) of zooplankton and also influence their
density variations (r = 0.595) during the study
period. The observed abundance is higher
than the reports of Khan (1987), Yadava et al.
(1987), Baruah et al. (1993), Sinhaet al. (1994), and Sharma & Hussain (2001), while
it is relatively lower than the results of Sanjer& Sharma (1995), and Sharma & Sharma (2009). Cladocera exhibit
bimodal and multimodal patterns of quantitative variations respectively with
annual peaks during winter (December) and summer minima (May) during both
years. The recorded maxima and minima,
however, concur with the results in Deepor Beel (Sharma & Sharma 2009) but the former differ from
summer maxima reported by Sanjer & Sharma (1995),
and Sharma & Hussain (2001) while comparisons
with other studies in the Indian floodplains are not possible because of lack
of definite information. Cladocera abundance is negatively correlated with water
temperature (r = -0.467), hardness (r = -0.571), nitrate (r = -0.534), chloride
(r = -0.421) and total dissolved solids (r = 0.560). Multiple regression registers relatively
lower cumulative effect of 15 abiotic factors on
their abundance (R2= 0.696).
The cladocerans depict quantitative importance of the littoral-periphytonic / facultative planktonicspecies in general and members of the family Chydoridae(34±11 & 39±7 n/l) in particular. This salient feature concurs with the results in Deepor Beel (Sharma & Sharma 2009) while it is in
contrast to lack of any such aspect noticed in several other Indian floodplain
lakes (Khan 1987; Sanjer & Sharma 1995; Sharma
& Hussain 2001; Khan 2003). The chydorids,
however, show insignificant density variations between months as well as years.
They contribute significantly to abundance of Cladocera(r = 0.825) and also exhibit significant positive correlation with their
richness (r = 0.637). They follow
multimodal and trimodal patterns of temporal
variations during two years respectively but show winter peaks (December)
during both years. The chydorids register inverse correlations with hardness (r =
-0.424), nitrate (r = -0.433) and total dissolved solids (r = -0.430) in this
study.
Daphniidae(14±6 & 26±5 n/l), another family of Cladocera,
registers distinct quantitative variations between months (F11, 23 =
125.270, p < 0.005) as well as years (F1, 23 = 27.417, p <
0.005). They follow trimodalannual patterns and record peak abundance during winter (December &
January) during both years; this trend is supported by their inverse
correlation with water temperature (r1 = -0.582). The Daphniidae exhibit inverse correlations with pH (r =
-0.419), free CO2 (r = -0.542), hardness (r = -0.529), nitrate (r =
-0.573) and total dissolved solids (r = -0.481) in Loktak. Sidiidae, third notable family, record relatively lower
abundance (12±4 & 11±3 n/l) and register insignificant density variations
between months and years during this study.
Copepoda (48±21 &
44±11 n/l) form another important group (Table 2) of microcrustacea(41.3±15.8 & 34.9±6.8%) as well as sub-dominant component of zooplankton
(19.7±8.8 & 15.3±4.1%) during both years respectively. The last feature is in contrast to their
dominant role noticed by Yadava et al. (1987), Baruah et al. (1993), Sharma & Hussain(2001), and Khan (2003). Their abundance
in Loktak Lake, however, is lower than the reports of
Khan (1987), Sinha et al. (1994), Sharma & Hussain (2001), Khan (1987), Sharma& Sharma (2009). The copepods exhibit trimodalpatterns of temporal variations and show summer peaks (May) during both annual
cycles; they register only significant monthly variations (F11, 23 =
3.110, P < 0.05). The stated patterns
differ from bimodal variations reported by Sharma & Hussain(2001) but concur with the later with respect to higher densities during summer
and monsoon seasons. Amongst the abiotic factors, Copepoda exhibit
significant inverse relationship only with sodium (r = -0.530) while
multiple regression registers relatively lower cumulative effect of 15 abiotic factors on their abundance (R2 = 0.723).
The Cyclopoida form main quantitative component of Copepoda; their dominance corresponds with earlier reports
from the Indian floodplains by Khan (1987), Yadava et
al (1987), Sanjer & Sharma (1995), Sarma (2000), Sharma & Hussain(2001), Khan (2003), and Sharma & Sharma(2009). This generalization is also affirmed by lower
abundance of Calanoidea, represented by Heliodiaptomus spp. Cyclopoida exhibit
mean annual abundance of 26±12 and 23±7 n/l respectively in Loktakand follow trimodal and bimodal patterns of
quantitative variations which, in turn, are mainly influenced by Mesocyclops leuckarti (17±11,
16±8 n/l). The occurrence of nauplii throughout the study period indicates an active
continuous reproductive phase of the cyclopoidcopepods as also reported earlier by Yadava et al
(1987), Sharma & Hussain (2001) and Sharma &
Sharma (2009).
Species
diversity, Evenness and Dominance
The present
results record wider variations but marginally different mean values of species
diversity of microcrustacea i.e., between 2.305-3.331
(2.923±0.334) and 2.615-3.526 (2.903±0.246) during two years respectively
(Table 2). The diversity follows bimodal
and trimodal annual patterns, shows peaks during
autumn (November) during both annual cycles but indicates minima during summer
(May) during first year and during monsoon (August) in the following year. Further, it registers insignificant temporal
variations between months and years. Higher diversity values (> 3.0) are observed during November-February
and again during August-October during first annual cycle while such values are
noticed only during November and October in the succeeding annual cycle. The species diversity registers significant
positive correlations with richness of microcrustacea(r = 0.501) and Cladocera (r = 0.448) as well as with abundance of Cladocera(r = 0.557) while it is negatively correlated with Copepoda abundance (r = -0.689).
This study
indicates (Table 2) higher microcrustacea evenness
(0.746-0.983 & 0.832-0.999) which registers significant temporal variations
between months (F11, 23 = 3.033, P < 0. 05) and insignificant
annual variations; the last aspect is also endorsed by marginal differences in
mean values. Higher evenness reflects
equitable abundance of various species. It follows (Fig. 8) trimodal and multimodal
annual patterns with peaks during September and November respectively during
two annual cycles while minima are recorded during summer (May) during both
years of the study period. Evenness is
positively correlated with species diversity of microcrustacea(r = 0.884) and abundance of Cladocera(r = 0.484) while it is negatively correlated with abundance of Copepoda (r = -0.809).
Our results
indicate (Table 2) lower dominance of microcrustacea(0.083-0.344 & 0.111-0.193) which follows multimodal annual patterns during
both years and registers insignificant monthly and annual variations. In general, lower dominance confirms lack of
quantitative importance of individual species while it records marginally
higher values during March-June during first years of the study period.
Dominance is negatively correlated with species diversity (r = -0.625)
and evenness (r = -0.716) and abundance (r = -0.727)
of Cladocera while it is positively correlated with Copepoda abundance (r = 0.793).
The stated
features are endorsed (Table 2) by higher species diversity (2.875±0.212 &
2.904±0.273), higher evenness (0.914±0.043 & 0.909±0.042) and lower
dominance (0.137±0.028 & 0.147±0.048) of Cladocera. These generalizations concur with the results
of Sharma and Sharma (2009). These
parameters follow multimodal patterns of temporal periodicity during both years
and register insignificant monthly as well as annual variations during this
study. Higher evenness and lower
dominance of Cladocera affirm lower densities and
equitable abundance of majority of species of this important qualitative and
quantitative group of microcrustacea. The cladoceranspecies diversity registers significant direct correlation with their richness
(r = 0.865); dominance registers inverse correlations with richness (r =
-0.450) and species diversity (r = -0.492) while evenness registers a positive
correlation with diversity (r = 0.726) and an inverse relationship with
dominance (r = -0.446).
To sum up, microcrustacea of Loktak Lake
reflect rich and diverse biocoenosis; exhibit lack of
definite periodicity of their richness or abundance or of their constituent
groups; indicate lower densities of majority of species and lack of distinct
quantitative importance of any individual species. Both microcrustaceaand Cladocera are characterized by higher species
diversity, higher evenness and lower dominance. Abiotic parameters influence on their richness
and exhibit limited influence on their abundance but fifteen abiotic factors exert significant cumulative influence on
these two communities.
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