International Journal of Marine Science 2015, Vol.5, No.51: 1-11
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highlighted significant differences between them, with
higher diversity observed in channels (Lupi et al., 2013).
Though the univariate indices such as richness,
species number and diversity showed no significant
variation between paddy fields and channels, evenness
varied significantly between paddy and channel.
According to Ma (2005), the individual diversity
components were found to respond independently to
different ecological factors. When the taxa and the
studied system was regulated more by dispersal and
migration, species richness was found to be more
sensitive. Oligochaetes are characterized by the
absence of a planktonic dispersal stage which limits
their dispersal, also as they are benthic crawlers, their
migration ability is also limited (Wiggins et al., 1980,
Levin et al., 1996) so the sensitivity of the richness
component would be limited. On the other hand,
evenness was found to be more sensitive to biotic
interactions (Ma 2005). Although biotic interactions
have not been analyzed in this study, previous studies
have proved that in the temporary wetlands, the biotic
interactions are important in structuring the communities
(Peltzer and Lajmanovich, 2004). Moreover, at small
and large spatial scales the importance of biotic
interactions in structuring communities have been
emphasized (Hildrew et al., 2004).
The number of oligochaete species recorded in this
study was more compared to similar studies from
India. A similar study from Chapra, Bihar revealed 4
oligochaete species (Ojha et al., 2010), whereas from
Dakshin Kannada revealed 3 oligochaete species
(Hegde and Sreepada, 2014
)
.
Relationship between biotic and environmental
patterns
The present study shows the importance of substrate
composition and dissolved oxygen in determining the
oligochaete pattern irrespective of paddy fields and
channels. The importance of substrate composition in
determining the oligochaete pattern in water bodies
was documented in previous studies by Stimpson et al.,
(1975). The present study showed that dissolved
oxygen was a major factor structuring oligochaete
communities. Generally, some pollution tolerant
oligochaete species such as L. hoffmeisteri, Tubifex
tubifex and Bothrioneurum vejdovskyanum were
reported to be able to tolerate extremely oxygen-
deficient environments (Brinkhurst, 1974), but they
were absent in Maranchery paddy fields.
Various studies revealed a variety of factors associated
with oligochaete distribution and abundance in water
bodies including substrate composition (Stimpson et
al., 1975), organic matter content (Lazim and Learner,
1987) sediment chemistry (Sarkka and Paasivirta,
1972) and fish predation (Kajak and Dusoge, 1971).
Previous studied showed that in paddy fields, the
species density showed positive correlation with nitrogen,
phosphorous and potassium. Further oligochaetes
were scarce or absent where algae were scarce,
pesticides and fertilizers were applied and farm
manure was not applied (Hedge and Sreepade, 2014).
Some factors which we have not directly measured
also would have played a major role in the distribution
of benthic fauna like the area of the habitable patch
available without paddy roots for the survival of
oligochaetes. The significance of the area of the
habitable patch in determining the benthic structure
was proved in previous studies (Fleishman et al., 2002).
Also predation by chironomids on oligochaetes
especially from the chironomids belonging to the
genus Tanypus, Procladius and Ablabesmyia were
reported (Loden, 1973; Arslan and Sahin, 2006). The
paddy fields were characterized by the abundance of
chironomids, this also would have played a key role in
determining the community structure.
The present study showed that irrespective of the
habitat alterations associated with the paddy cultivation,
the oligochaetes community remained healthy in Kole
fields implying its potential to harbor high
biodiversity. Most importantly, there was no usage of
agrochemicals during the study period, but further
researches are needed to evaluate its impacts.
Traditionally, the research on aquatic systems was
focused on permanent waters thereby ignoring
temporary waters like paddy fields which resulted in
fewer data bases of these unique habitats. Research on
oligochaetes in the paddy fields is significant when
the ill effects of chemical fertilizers and pesticides are
revealed gradually, since oligochaetes are known to
improve soil fertility and reduce weed formation.
Such baseline information from the field is essential
for management and conservation aspects.
