International Journal of Marine Science 2015, Vol.5, No.51: 1-11
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Table 1 Mean (±standard deviation) of environmental parameters
measured in paddy fields and channels in Maranchery Kole
wetlands during
Punja
crop season January -May 2011
Paddy fields
Channels
Depth(m)
0.31±0.11
1.1±0.28
Water temperature(ºC)
27.3±2.76
30.37±2.67
Sediment temperature(ºC)
23±0.46
24.15±0.18
Water pH
5.97±1.88
5.84±1.88
Sediment pH
5.5±0.18
5.38±0.14
Dissolved oxygen (mg/L)
6.65±0.66
6.16±0.113
Organic matter (%)
6.95±1.34
5.48±1.58
Clay (%)
25.079±3.16
25.87±5.02
Silt (%)
50.24±3.51
46.63±10.41
Sand (%)
24.67±3.51
27.49±13.02
Figure 2 Mean percentage composition of benthic fauna in
paddy fields and channels in Maranchery Kole wetlands
The most abundant benthic class was Oligochaeta
(56.72%) followed by Insecta (42.76%) while Gastropoda
(0.29%), Hirudinea (0.12%) and Crustacean (0.08%)
appeared occasionally with very low abundance. In
paddy fields insects (61%) were the most abundant
group followed by oligochaetes (37%). Gastropods
(1%) and crustaceans (1%) made a single appearance
in January 2011. Oligochaetes were the most abundant
in channels (60.39%) followed by insects (39.30%).
Gastropod (0.15%) and Hirudinae (0.15%) were
present in February and April 2011 respectively. A
total of fifteen oligochaete species were collected
from the samples (Table 2). Among them eleven
species belonged to the family naididae, three species
belonged to the family tubificidae and one species to
the family lumbriculidae. In terms of percentage
abundance, the species of the family naididae had the
highest contribution (56%) followed by tubificidae
(43%) and lumbriculidae (1%). Seven taxa,
Aulodrilus
pluriseta, Aulodrilus
sp
., Aulodrilus piguiti, Branchiodrilus
semperi, Stephensonia trivandriana, Pristinella
minuta, Pristinella jenkinae
were recorded both in the
paddy fields and channels. Six species,
Allonais
gwaliorensis, Allonais paraguensis, Dero zeylanica,
Pristinella accuminata, Pristina menoni, Lumbriculus
variegates
were exclusively found in the channels and
two taxa,
Branchiodrilus hortensis
,
Homochaeta
sp
.
,
exclusively in the paddy fields. Among the species
exclusively present in channels,
Allonais gwaliorensis,
Allonais paraguensis, Dero zeylanica
were observed
only once in the sample, during an unusual abundance
observed in May 2011. The most abundant species in
the paddy fields was
Aulodrilus
sp. (23%) closely
followed by
Aulodrilus pluriseta
(20%), whereas
Aulodrilus pluriseta
(49%) was the most abundant in
the channels. The analysis of oligochaete community
composition using ANOSIM revealed the absence of a
significant difference in oligochaete composition
between the paddy fields and channels (Global
R=0.19, p> 0.05).
Pattern of faunal abundance
The monthly variation in mean numerical abundance
of oligochaetes showed a slight zigzag pattern throughout
the crop season, decreasing from January 2011 (14%)
to February (6%), increasing in March (8%), again
decreasing in April (4%) and showed a sharp increase
in May 2011 (68%) (Figure 3). When the mean
numerical abundance of oligochaetes in the paddy
fields was considered, the maximum abundance was
observed in March 2011 (36%) and minimum in
February (6%). The channels showed the minimum
abundance in April 2011 (3%). In May 2011, an
unusually high abundance of 71% (4355 ind./m
2
) was
observed in channels. There existed a significant
difference in numerical abundance of oligochaetes
among the paddy fields and channels (ANOVA
F
1,
24
=6.02, p<0.05). Abundance of oligochaetes was high
in the channels than the paddy fields throughout the
crop season.
Oligochaete community structure
Though a significant difference in numerical abundance
was observed between the paddy fields and the
channels, the species diversity (Shannon wiener index)
and richness (Margalef’s index) showed no significant
variation among them. Evenness (Pielou's index)
showed a significant variation (ANOVA,
F
1, 8
=10.40,
p<0.05). A higher diversity was recorded in channels
