Composition,
abundance and ecology of phytoplankton communities of LoktakLake, Manipur, India
B.K. Sharma
Department of Zoology, North-Eastern Hill University, Permanent
campus, Umshing, Shillong,
Meghalaya 793022, India
Email:bksharma@nehu.ac.in
Date of publication (online): 26
August 2009
Date of publication (print): 26
August 2009
ISSN 0974-7907 (online) |
0974-7893 (print)
Editor: R. Jindal
Manuscript details:
Ms # o2193
Received 04 May 2009
Final received 30 June 2009
Finally accepted 28 July 2009
Citation: Sharma, B.K.
(2009). Composition, abundance and ecology of phytoplankton communities of Loktak Lake, Manipur, India. Journal of Threatened Taxa1(8): 401-410.
Copyright: © B.K. Sharma
2009. Creative Commons Attribution 3.0 UnportedLicense. JoTT allows 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: B.K. Sharma is a Professor in
Department of Zoology and Dean, School of Life Sciences and is a specialist in
the fields of limnology and acquatic biodiversity.
Acknowledgement: This study is
undertaken under the “Potential for Excellence Program (Focused Area:
Biosciences) of North-Eastern Hill University, Shillong. The author is thankful to the G.B. Pant
Institute of Himalayan Environmental Development, Almorafor a research grant during which plankton samples for this study were collected. Thanks are due to the Head, Department of
Zoology, North-Eastern Hill University, Shillong for
necessary laboratory facilities.
Abstract: Phytoplankton
communities of Loktak Lake (a Ramsarsite), studied during November 2002-October 2004, reveal the occurrence of 75
and 71 species, indicate monthly richness ranging between 47±6 and 49±3 species
and record 50.0-83.2 and 64.5-84.0 % community similarities during two annual
cycles respectively. Chlorophyta (33±5 and 35±5
species) show qualitative dominance and importance of Closterium > Cosmarium > Staurastrum > Micrasterias > Gonatozygonspecies. Phytoplankton (206±58 and
220±53 n/l) comprise between 45.1±6.5 and 42.9±5.8 % of net plankton abundance,
indicate trimodal annual patterns and record peak
abundance during winter. Chlorophyta (111±20 and
119±15 n/l), the dominant quantitative component, indicate winter peaks; Closterium > Staurastrum> Gonatozygon > Micrasterias species contribute significantly
to their abundance. Ceratium hirudinella (43±52 and 39±37 n/l) is the sole important
individual species of phytoplankton. Dinophyta > Bacillariophyta are sub-dominant groups and Euglenophyta > Cyanophyta> Chrysophyta show very low densities. Phytoplankton communities are characterized
by higher species diversity, higher evenness and lower dominance. Abiotic factors register limited influence on richness and
abundance of phytoplankton and on abundance of constituent groups. Multiple
regression indicates relatively lower influence of fifteen abioticfactors on richness of phytoplankton and higher cumulative influence on
abundance of phytoplankton, Chlorophyta, Dinophyta and Bacillariophyta.
Keywords:Composition, Floodplain Lake, Loktak, Phytoplankton, Ramsar site, synecology
For Figure, Image & Table
– click here
Introduction
The floodplain
lakes cover a water spread area of about 0.12 million ha in northeastern India,
are mainly located in the states of Assam and Manipur and exhibit significant
fishery production potential (Sugunan 1997). Little is, however, known so far about their
biological productivity in general and about composition, abundance and ecology
of phytoplankton in particular. Investigations on the latter from northeastern region are confined to
fewer preliminary publications from Assam (Yadava et
al. 1987; Baruah & Das 1997; Goswami& Goswami 2001) indicating poor ecological data
due to inadequate species determination. On the other hand, Sharma (2004) gave useful information on
phytoplankton ecology of a floodplain lake of upper Assam while Sharma (in
press) analyzed phytoplankton communities of Deepor Beel - a Ramsar site and an
important floodplain lake of Assam.
This study on
the composition and synecology of phytoplankton of Loktak Lake, a Ramsar site, an
important floodplain lake of northeastern India and the largest freshwater
wetland of India, is of ecological
importance. Observations were made on monthly variations in richness, abundance of phytoplankton, their
constituent groups, community similarities, species diversity, dominance and
evenness for two annual cycles. Remarks are made on the influence of abiotic factors on richness and abundance of phytoplankton
communities.
Materials and Methods
The present study is a part of limnological survey (undertaken during November, 2002 -
October, 2003) in Loktak Lake (93046’-93055’E
& 24025’-24042’N; area: 286km2; max.
depth: 4.58m, mean depth: 2.07m; altitude: 768.5m) located in Bishnupur / Imphal districts of
Manipur. This large natural freshwater
wetland is characterized by floating mats of vegetation called as “Phumdi” which are inhabited by the Critically Endangered
Brow-antlered Deer (Cervus eldi eldi). Common aquatic plants of this floodplain lake
include Eichhornia crassipes,Hydrilla verticellata,
Euryale ferox, Vallisnaria spiralis, Utricularia flexuosa, Trapa natans, Lemna trisula,Pistia striates, Salvinia, Nymphaea spp., Nymphoides spp.,Nelumbo mucifera, Potamageton spp., Azolla pinnata, Sagittaria spp, and Cyperus spp. etc.
The present observations were undertaken
at regular monthly intervals at one selected sampling site at Sendra (93047’45.61’’E & 24030’56.75”N). Water samples collected monthly were analyzed
for various abiotic factors following APHA (1992)
while water temperature, specific conductivity, pH and dissolved oxygen were
recorded by the field probes. Monthly
qualitative and quantitative net plankton samples were collected by nylobolt plankton net (No. 25) and were preserved in 5%
formalin. The former were screened and
phytoplankton taxa were identified following Needham
& Needham (1962), Islam & Haroon (1980), Adoni et al. (1985) and Fitter & Manuel (1986). Quantitative plankton samples were analyzed
for abundance (n/l) of net plankton, phytoplankton and constituent groups.
Sorensen’s index, Shannon’s indices,
Berger-Parker’s index and 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
phytoplankton and their groups.
Results and Discussion
Abiotic parameters
Water
temperature indicates sub-tropical nature of LoktakLake. Specific conductivity exhibits low ionic concentrations (Table 1) of thisRamsar site and, hence, warrants its inclusion under
‘Class I’ category of trophic classification vide Talling & Talling(1965). Slightly acidic and soft waters
of this floodplain lake depict moderate dissolved oxygen, low free CO2,
low concentration of micro-nutrients and other abioticfactors. In general, the abiotic factors differ from Deepor Beel (Sharma in press),
distinctly in the recorded ranges of pH, alkalinity and hardness.
Phytoplankton composition, richness and
community similarities
Seventy-five species of phytoplankton
(Table 2), belonging to six groups, documented from Loktakexhibit their speciose and diverse nature and, hence,
reflect greater environmental heterogeneity of this Ramsarsite. Total richness is distinctly
higher than only 33 species examined earlier in an unpublished report (Bhatia
1979) from this wetland as well as than 59 species reported from Deepor Beel (Sharma in
press). The present collections are
characterized by qualitative dominance of Chlorophyta(56 species) and distinct qualitative importance of species of five desmid genera (64.3%) namely Closterium(11 spp.) > Cosmarium (7 spp.) = Staurastrum (7 spp.) > Micrasterias(6 spp.) > Gonatozygon (5 spp.). Desmid diversity is
considered to be an indicator of slightly acidic, Calcium-poor waters with low
ionic concentrations (Payne 1986), this interesting generalization is confirmed
by the salient features of water quality of LoktakLake. Further, higher desmid richness is concurrent with phytoplankton
communities of various (sub)tropical aquatic environs of northeastern India
(Sharma unpublished). The species and
generic diversity of Loktak phytoplankton distinctly
outnumbers the earlier records of Baruah et al.
(1993), Acharjee et al. (1995), Sanjer& Sharma (1995), Goswami & Goswami (2001), and Sharma (2004). The general qualitative dominance of the Chlorophyta observed in this study corresponds with the
results of Goswami & Goswami(2001) and Sharma (in press) but differs from the greater diatom richness
reported by Baruah et al. (1993) and Sharma (2004).
Phytoplankton richness varies between
37-57 (47±6) species and 45-54 (49±3) species during two annual cycles
respectively (Table 2); it records significant monthly variations (F11, 23= 4.821, P < 0.005) but shows insignificant annual variations. Richness shows (Fig. 1) peaks during
post-monsoon (October) and higher species number during winter (December)
during both years and lowest richness is noticed during January (first year)
and March (second year). The present
study, however, exhibits no definite pattern of periodicity of richness of any
group or species of phytoplankton. This
generalization concurs with the author’s earlier remarks in two floodplain
lakes of Assam (Sharma 2004, in press) while Loktakphytoplankton reflect higher range of richness variations. Further, the richness exhibits limited
influence of individual abiotic factors and indicates
significant negative correlations with nitrate (r = -0.458), sulphate (r = -0.569) and silicate (r = -0.415). Multiple regression also registers relatively
lower cumulative influence of 15 abiotic factors on phytoplankton richness (R2 =0.579).
Phytoplankton of LoktakLake indicate community similarities (vide Sorenson’s index) ranging between
50.0-84.0% with marginal variations during two successive years of the study
period i.e., 50.0-83.2 % (Table 3) and 64.5-84.0 % (Table 4) respectively. The recorded values differ from wider
similarity ranges noticed by Sharma (2004, in press). The similarity, however, varies between 70-80
% in majority of instances (72%) included in the matrix during the second year
while only 31.2% instances belong to the stated range and 48.5% instances
indicate 60-70 % similarity during the first year. Hierarchical cluster analysis shows notable
differences in clusters groupings during the study period. It registers higher associations among
phytoplankton communities during December-September-August-November-October and
exhibits more differences in January-July-June during the first year (Fig.
2). On the other hand, higher
associations are observed during January-September-December and more
differences are apparent during March-July-February in the following year (Fig.
3).
Chlorophyta, the most speciose component of phytoplankton, include 56 and 51
species during two annual cycles respectively and significantly influence
temporal variations of richness of the latter (r = 0.913). Richness of this group registers
insignificant monthly and annual variations. It follows (Fig. 4) relatively wider range of variations during first
year (20-40, 33±5 species) than in the succeeding year (30-42, 35±3 species)
and exhibits an indefinite pattern of temporal periodicity with peaks during
post-monsoon (October) during both years but shows minima during January, 2002
and February, 2003. The Chlorophyta richness registers no significant
correlation with any individual abiotic factor, while multiple regression registers higher
commutative influence (R2 = 0.829) of 15 abioticfactors.
Phytoplankton abundance
Phytoplankton
form a sub-dominant quantitative component of net plankton (44.1±6.3 %),
following zooplankton, throughout the study period except only during January
(1st year) and January-February (2nd year). The stated trend corresponds with the results
of Sharma (2004, in press) and Sharma & Sharma (2008) while it is in
contrast to phytoplankton dominance reported from the floodplain lakes from Kashmir (Kaul& Pandit 1982), Bihar (Rai& Dutta - Munshi 1982; Baruah et al. 1993; Sinha et al.
1994; Sanjer & Sharma 1995), West Bengal (Sugunan 1989), Assam (Yadava et al. 1987; Baruah& Das 1997; Goswami & Goswami2001), Kerala (Krishnan et al. 1999) and
Maharashtra (Patil 2002).
Phytoplankton
abundance (Table 2) ranges between 155-369 (206±58 n/l) and 158-323 (220±53 n/l)
during the two years respectively; it exhibits significant monthly (F11.
23 = 15.026, P < 0.005) but insignificant annual variations. Abundance
follows (Fig. 5) broadly identical trimodal yearly
patterns with higher densities during winter season and peaks during January,
maxima during post-monsoon (September), a small maxima during June and minima
during July. The present results differ
from multimodal patterns noticed in Deepor Beel (Sharma in press) and also from the bimodal
periodicity reported by Yadava et al. (1987)
and Sanjer & Sharma (1995). On the other hand, the peak density noticed
presently during winter concurs with the results of Yadavaet al. (1987) and Sanjer & Sharma (1995) while it
differs from early summer maxima reported by Sharma (2004). Phytoplankton abundance in Loktak Lake is yet lower than that from Deepor Beel (Sharma in press), while it is marginally higher
than in Samuajan Beel(Sharma 2004). In addition, the density
is distinctly lower than the reports from certain beelsof West Bengal (Sugunan 1989; Vass 1989) and Bihar (Baruah et al. 1993; Sanjer &
Sharma 1995); these differences are attributed to soft nature of water of Loktak with low ionic concentrations and resulting in lower
general biological productivity.
Of the recorded
parameters, phytoplankton abundance is inversely correlated with water
temperature (r = -0.795), free carbon dioxide (r = -0.568), silicate (r =
-0.490) and total dissolved solids (r1 = -0.465). On the contrary, fifteen abioticfactors exert significantly higher cumulative influence (R2 =
0.952). Further, the present results
record insignificant positive correlation between abundance of phytoplankton
and zooplankton. This aspect is in
contrast to significant positive correlations between the two communities
recorded earlier by Yadava et al. (1987) and Sharma
(2004, in press).
Chlorophyta, the sole
dominant quantitative component, notably influence temporal variations of
phytoplankton (r = 0.547) of Loktak Lake and, hence,
concur with earlier reports of Yadava et al. (1987), Choudhary & Singh (2001), Goswami& Goswami (2001) and Sharma (in press). The dominance pattern, however, differs from
the predominance of the diatoms over the green algae noticed by Baruah et al. (1993) and Krishnan et al. (1999) as well as
from nearly equal importance of the two groups reported by Sharma (2004). Chlorophytaabundance (Table 2) ranges between 78-155 (115±18) n/l and comprises between
56.2±10.5 % of phytoplankton. ANOVA registers significant monthly (F11. 23=3.084, P <0. 005) and insignificant annual variations in their
abundance. The green-algae follow (Fig.
6) trimodal but marginally different annual patterns
with higher abundance during winter (December-January), peaks during December
and minima during July and June respectively during two years. The present study shows notably higher
abundance of this group than the earlier report from Samuajan beel (Sharma 2004), while the density broadly
corresponds with the report from Deepor Beel (Sharma in press) but differs distinctly from the same
in their higher percentage contributions. Amongst the recorded abiotic factors, Chlorophytaabundance is inversely correlated with water temperature (r = -
0.585), free CO2 (r = - 0.412), hardness (r =
- 0.553), nitrate (r = - 0.473), silicate (r = - 0.565),
chloride (r = - 0.559) and total dissolved solids (r = -
0.710), while multiple regression registers higher cumulative influence (R2=0.825) of 15 abiotic factors.
Chlorophyta are
characterized by quantitative importance of certain desmid taxa (Figs. 7-8) namely Closterium spp. (25±9 n/l) > Staurastrumspp. (18±6 n/l) > Gonatozygon spp. (15±6
n/l) while Micrasterias spp. (10±6 n/l)
and Cosmarium spp. (6±2 n/l) also
deserve mention. This salient feature is
in contrast to lack of any such dominance pattern noticed in Samuajan (Sharma 2004) and Deepor(Sharma in press) beels of Assam. The stated taxa,
however, exhibit lack of definite temporal periodicity. Of these, only Closterium spp., and Gonatozygon spp. exhibit
significant annual (F1. 23 = 16.209, P < 0.005; F1. 23= 7.663, P < 0.001) and monthly (F11. 23 = 4.335, P < 0.01; F11.
23 = 6.511, P < 0.002) variations and register negative correlations
with water temperature (r = - 0.525, r = - 0.456).
Dinophyta (13-193, 51±43
n/l, 22.0±11.8%), a sub-dominant quantitative component of phytoplankton of Loktak Lake, follow wider range of abundance and record
only significant monthly temporal variations (F11. 23 = 7.068, P
< 0.001). This group exhibits (Fig.
9) distinctly higher abundance (peaks) during winter (February/January) in both
years and notably contributes to higher winter densities of phytoplankton
during this period in particular. These
interesting features are supported by their inverse correlation with water
temperature (r = -0663). Besides, this
group is inversely correlated with free CO2 (r = -0.490), while 15 abiotic factors exercise higher cumulative influence (R2=0.839) on their quantitative variations. Ceratium hirudinella(4-193, 41±45 n/l), the sole important individual phytoplankton species
observed in Loktak Lake, exhibits broadly bimodal
periodicity with distinct annual peaks during winter. This species is solely responsible for Dinophyta periodicity as well as for contributing to
phytoplankton abundance during winter. ANOVA affirms significant monthly (F11. 23 = 7.991, P <
0.005) density variations of C. hirudinella. The present observations broadly conform with
the results in Deepor Beel(Sharma in press) relating to sub-dominant role of Dinophytaand quantitative significance of C. hirudinellabut differ from the latter in broader range of variations and winter dominance
patterns. These results are, however, in
contrast to very poor abundance of this group noticed in Samuajan Beel (Sharma 2004).
Bacillariophyta (35±11 n/l;
16.3±3.5%) form another sub-dominant component of phytoplankton and exhibit
significant annual (F1. 23 = 6.369, P > 0.02) and monthly (F11.
23 = 4.559, P > 0.005) quantitative variations. The abundance of this
group is lower than earlier reports of Sharma (2004, in press). The diatoms follow (Fig. 10) multimodal and trimodal annual patters during two years respectively and
record higher abundance during winter with peaks in January. The last feature is supported by their
inverse correlation with water temperature (r = -0.627). Further, winter peaks observed in this study
are in contrast to their summer peaks reported in Deepor Beel (Sharma in press). Besides, Bacillariophytaare inversely correlated with free CO2 (r = -0.427) and silicate (r
= -0.627), while multiple regression registers moderately higher influence (R2= 0.774) of 15 abiotic factors.
Euglenophyta > Cyanophyta > Chrysophytaindicate very low densities and contribute insignificant quantitative
components of phytoplankton of Loktak Lake. These remarks are in contrast to sub-dominant
role of the Cyanophyta and relatively higher
abundance of the other two groups noticed in Deepor Beel (Sharma in press).
Species
diversity, evenness and dominance
The present
results are characterized by higher species diversity of phytoplankton
(2.520-3.805, 3.404±0.329); the range may be misleading as its values are
higher (< 3.0) in major part of the study period except during winter
(January-February). Further, it follows
significant annual (F 1. 23 = 17.084, < 0.005) and monthly (F11.
23 = 8.861, P < 0.005) variations. The diversity (Fig. 11) does not
follow any definite annual and monthly patterns; peak values are recorded
during October (post-monsoon) and May (summer) while minima are noticed during
January and February (winter) during two years respectively. Species diversity is positively correlated
with richness of Phytoplankton (r = 0.645) and Chlorophyta(r = 0.633) and is negatively correlated with abundance of phytoplankton (r =
-0.623), Bacillariophyta (r = -0.440) and Dinophyta (r = -0.835). The present observations indicate higher species diversity than the
reports from Dighali Beel (Acharjee et al. 1995) and Samuajan Beel (Sharma 2004) of Assam while range and mean
value is also marginally higher than the report from Deepor Beel (Sharma in press). Further, indefinite annual periodicity and
summer peak noticed during second year of the present study concur with the
results of Deepor phytoplankton (Sharma in press).
Phytoplankton
dominance shows wider range (0.055-0.523, 0.180±0.118) and registers
significant monthly (F11. 23 = 9.298, P < 0.005) and
insignificant annual variations. It
follows (Fig. 12) trimodal and bimodal annual
patterns and shows generally low values during the study period except for
peaks in January and February during two years respectively. The later, in turn, correspond with peaks of Ceratium hirudinella- the sole dominant species observed in LoktakLake. Dominance is inversely correlated
with species diversity (r = -0.904), and richness of phytoplankton (r = -0.408)
and Chlorophyta (r = -0.442) while it is positively
correlated with abundance of phytoplankton (r = 0.853), Bacillariophyta(r = 0.590) and Dinophyta (r = 0.972). The salient
feature of low dominance though broadly corresponds with earlier reports of
Sharma (2004, in press) but differs from the same in the broad range observed
presently.
Phytoplankton
communities of Loktak Lake exhibit higher evenness
(0.698-0.956, 0.879±0.075) which, in turn, reflects equitable abundance of
various species; this statement holds valid during major part of the study
period except particularly during winter (January and February). Evenness follows (Fig. 13) trimodal and multimodal annual with peaks during October
and November and minima during January and February during two years
respectively; the last feature again corresponds with peaks of Ceratium hirudinella. Evenness is positively correlated with
species diversity (r = 0.975), and richness of Phytoplankton (r = 0.460) and Chlorophyta (r = 0.473). It is, however, inversely correlated dominance (r = -0.934), and
abundance of Phytoplankton (r = -0.730), Bacillariophyta(r = -0.494) and Dinophyta (r = -0.862). In general, higher evenness and lower
dominance broadly concur with earlier results of Sharma (2004, in press) in two
floodplain lakes of Assam as well as with phytoplankton communities of certain
other aquatic environments of northeastern India (Sharma 1995; Sharma & Lyngdoh 2003; Sharma & Lyngskor2003).
To sum up,
diverse and speciose phytoplankton communities of Loktak Lake are characterized by distinct qualitative
importance of Chlorophyta and the desmids. Phytoplankton and their individual groups
reflect lack of definite periodicity of richness. Chlorophyta show
quantitative dominance; Dinophyta > Bacillariophyta are sub-dominant groups; Ceratium hirudinellais the only quantitatively notable species while Closterium,Cosmarium, Staurastrum, Micrasterias, Gonatozygonspecies show importance. Phytoplankton
communities are characterized by higher diversity, lower dominance and higher
evenness. Individual abioticfactors depict little or limited influence on richness and abundance but
register higher cumulative influence. The present study limited to one sampling station, though provides
useful information on phytoplankton ecology of Loktak,
may not reflect full environmental heterogeneity of this interesting Ramsar site. Future
investigations on phytoplankton in different parts (pats) of Loktak basin with special focus on periphytonassociations with diverse aquatic macrophytes are
desired and have been initiated.
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