International Journal of Marine Science 2015, Vol.5, No.51: 1-11
7
Figure 7 Two dimensional nMDS ordination of oligochaete
community structure in paddy fields and channels in
Maranchery wetlands
level might have reduced the organic matter in
channels due to dilution as observed by Ali et al.
(2002).
Paddy fields were characterized by emergent vegetation,
reduced water levels, compartmentalized benthic
habitat whereas channels were line shaped, deeper
open water habitats with submerged vegetation. In
spite of these differences, the oligochaete composition
did not show a significant difference between them.
The less prominent niche specialization of oligochaetes
proved by many studies could be a reason for this
(Verdonschot
and Higler, 1989; Verdonschot, 1999).
The paddy fields and the channels explored in this
study were very close to each other, separated by an
earthen bund, also until December 2010, both paddy
fields and channels were submerged thus were
connected to each other and behaved as the same
water body. Then the preparation for paddy cultivation
was carried out, which separated the area into paddy
fields and channels. Though the practices prior to
farming such as draining, ploughing etc. would have
disturbed the area, oligochaetes are known to survive the
unfavorable period by mechanisms such as diapausing
eggs; resistant cysts enclosing young, adults or
fragments of individuals (Williams, 1987). The
oligochaetes prevailed in the flooded period would
have survived in the area as dormant structures during
unfavorable period and became active once there was
sufficient water, which could be the probable reason
for the similar oligochaete composition in the paddy
fields and the channels.
Similar studies across the world revealed different
results on oligochaete composition of paddy fields. In
Philippines the oligochaete populations were dominated
by
Limnodrilus hoffmeisteri
and
Branchiodrilus
sowerbyi,
of the family tubificidae, the species
belonging to naidids, lumbriculids, and enchytraids
were also represented (Simpson et al., 1993). Heckman
(1974) and (1979) recorded oligochaete species
exclusively of the family naididae from the paddy
fields from Laos and Thailand respectively. According
to Senapati et al., (1991), the earthworm
Darwida
willsi
dominated the paddy fields in India. The families
aeolosomatidae, tubificidae and megascolecidae
constituted oligochaete fauna in Chapra, Bihar (Ojha
et al., 2010). A recent study from the paddy fields of
Dakshin Kannada revealed a very high density of
Aulophorus furcata
of the family naididae (Hegde and
Sreepada, 2014
)
.
Pattern of faunal abundance
The significant variation numerical abundance of
oligochaetes between paddy fields and channels could
be explained by the area of available habitat. The
increase in habitable area could result in an increase in
the number of organisms (Sommer and Horwitz,
2009). Unlike the bottom of the channel, bottom of the
paddy field was compartmented by paddy root
structures providing insufficient space for the proper
development of benthic fauna, could be a probable
reason as observed by Ojha et al., (2010). In this study,
on an average, the abundance of oligochaetes in paddy
fields was 8.7 times less than that of channels; a
similar report was from Chapra, Bihar where the total
average number of benthic macrofauna of paddy fields
was nearly eight times less in contrast to the benthos
from adjacent ponds (Ojha et al., 2010).
There was an unusually high abundance of oligochaetes
in May 2011 in the channels. The unusually high
benthic abundance was observed previously by
Wishner et al. (1990), the enriched sediment resulting
from reduced consumption and degradation of sinking
material which supply high food level, was the
suggested reason. According to Brinkhurst (1996), the
unusual abundance of oligochaetes especially
tubificids were clear indication of excess organic matter
