International Journal of Marine Science 2015, Vol.5, No.51: 1-11
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Table 3 BIOENV results showing the spearman correlation coefficient (ρ) for correlation with oligochaete abundance in paddy fields
and channels in Maranchery Kole wetlands
Paddy fields
Channels
Sl no. variables
variables selected
BEST Correlation
value (Rho)
variables selected
BEST Correlation
value (Rho)
1
depth
dissolved oxygen, clay
0.29
dissolved oxygen, clay, silt 0.28
2
sediment temperature dissolved oxygen
0.17
silt
0.2
3
moisture content
depth, dissolved oxygen
0.17
clay, silt
0.16
4
organic matter
organic matter, clay
0.17
dissolved oxygen,
clay, sand
0.16
5
dissolved oxygen
depth, dissolved oxygen, clay 0.17
depth, silt
0.13
6
sediment pH
silt
0.05
moisture content,
dissolved oxygen, silt
0.13
7
clay
depth, sediment temperature,
clay
0.05
depth, dissolved
oxygen, clay
0.10
8
silt
depth, organic matter, clay
0.05
clay, silt, sand
0.10
9
sand
depth, sediment pH, clay
0.05
dissolved oxygen, silt
0.09
sediment temperature,
dissolved oxygen, clay
0.05
depth, dissolved
oxygen, clay, silt
0.09
in an environment where oxygen deficiency and high
silt loads combine to kill most of the fauna. But in this
study, in May 2011, all the environmental parameters
analyzed, especially oxygen, organic matter and silt
content remained similar to the other samples. Further
though tubificids dominated (61%), naidids also
showed a good abundance (39%) in the particular
samples. Along with oligochaetes in the benthic
sample, insect larvae especially chironomids also
showed an unusually high abundance comparable to
that of oligochaetes. Both Wishner et al., (1990) and
Brinkhurst (1996) emphasized the significance of the
abundance of food source for the unusual benthic
abundance. The organic matter in the present study
was higher throughout the study period, ensuring a
food source for benthos. Apart from the quantity of
organic matter, the nutritional quality is also important
in determining benthic abundance (Neira 2011). The
abundance of good quality food would have favored
the unusual benthic abundance in May 2011. Or some
specific, localized condition would have resulted in
the patchy distribution of the fauna in channels as
suggested by Verdonschot et al., (2011).
The average numerical abundance of oligochaetes was
less in this study when compared to similar studies.
Roger (1996) and Simson et al., (1993) recorded
tubificid populations of about 10,000 and 40,000
ind.m
-2
in Japan and Philippines paddy fields
respectively. Ojha et al., (2010) observed 178 ind.m
-2
from Chapra, Bihar. Along with the difference in
zoogeographic factors, the difference in sampling
methods also would have contributed to the difference.
Community structure
There were two contradictory possibilities about the
presence of oligochaetes in the paddy fields. The
reduced habitable area due to paddy plantation would
have reduced the number of oligochaetes in paddy
fields. On the contrary, due to the same reason the
oligochaetes would have utilized the available
habitable open areas as a refuge, thus ensuring a fairly
high diversity and richness in areas free from paddy
roots. This could be viewed analogous to the increased
benthic richness observed in available water patches,
when the rest of the substratum are dry, due to the use
of the water patches as refuge by the benthic
organisms (Sommer and Horwitz 2009). Though the
numerical abundance varied significantly between
channels and paddy fields, comparable species
richness and diversity was maintained throughout the
study period in the paddy fields which could be due to
the usage of the available habitable area by the
oligochaetes in the restricted habitat. Though the
species number in the paddy fields was less than that
of the channels, the species diversity and richness was
comparable among them. A study on benthic
invertebrates in paddy fields and channels in Italy
