Basic HTML Version
International Journal of Marine Science 2014, Vol.4, No.47, 1-11
http://ijms.biopublisher.ca
7
environmental variables and the sediment textural
changes in different seasons. The distribution and
abundance of benthic fauna are attributed to the
impact of localized environmental and biotic factors,
which are site specific and play an important role in an
ecosystem (Ajmal Khan et al., 2004; Saravanakumar
et al., 2007; Kundu et al., 2010), this statement was
relatively evident to the present observation.
There were 53 species of infaunal macrobenthos as
against 43 species (Ajmal Khan et al., 1975), 73
species (Chandran et al., 1982), 38 species (Fernando,
1987) and 54 species (Murugasan et al., 2007). The
difference in the number of species may be attributed
to the sampling effort. With the respect to the
population density of macrobenthos in transect I, it
was lower compared to previous investigation by
Ajmal Khan et al. (1975) and Murugasan et al. (2007).
This might be due to either the preponderance of
crustaceans
Apseudes
spp. and
Tanaeus
spp. in
transect I (Ajmal Khan et al., 1975), or polychaetes
(Fernando, 1987; Murugasan et al., 2007), while in the
present study gastropods topped the list in terms of
abundance. It was quite evident in the earlier study of
Chandran et al. (1982). In terms of number of species
in polychaetes recorded maximum (21species)
followed by crustaceans (13 species). Similarly, in the
previous investigations 25 species of polychaetes and
10 species of crustaceans have been reported by Ajmal
Khan et al. (1975), 33 polychaete and 11 crustacean
species have been reported by Chandran et al. (1982),
10 polychaete species have been found by Fernando
(1987), and 33 species of polychaetes and 10 species
of crustaceans have been observed by Murugasan et al.
(2007). In the present investigation, gastropod
Cerethedia
spp. was the most abundant throughout the
study area constituting 42.68% of total macrobenthic
abundance. Similarly, Fernando (1987) has reported
Cerethedia
spp. as the most dominant and contributed
31.58% of total macrobenthic density.
Species diversity is a simple and useful measure of a
biological system (Redding and Cory, 1975).
He
found a high level of agreement between species
diversity and the nature of the environment and hence,
regarded the measure of species diversity as an
ecologically powerful tool.
Generally, in a healthy
environment diversity indices are high (Clarke and
Warwick, 1994).
Species diversity in the present study
varied from
1.945
(monsoon) to 2.746 (summer)
between transects and seasons. The similar pattern of
variability in species diversity with of lower
valuesduring monsoon season and higher diversity
values in summer has been recorded in the study area
previously
(Ajmal Khan et al., 1975; Chandran et al.,
1982; Murugasan et al., 2007).
In contrast, the maximum values of species richness of
infaunal macrobenthos were recorded during the
summer season that was significantly higher those
found previously (Ajmal Khan et al., 1975; Murugasan
et al., 2007; Table 4). It was comparatively very high
to the earlier observation (Ajmal Khan et al., 1975 –
1.95; Murugasan et al., 2007 – 2.56). A similar
observation was reported by Kumar (1995) in
Cochin
backwaters and Kundu et al. (2010) in Parangipettai
waters. The low species richness recorded in this
study during monsoon might be due to the freshwater
flow, which induced low saline conditions, which in
turn affected the distribution of benthos. Maximum
diversity and species richness recorded during summer
in the studied area might be due to stable
environmental factors during summer period (e.g.
salinity), which play an important role in faunal
distribution.
In this consequence the present study made and find
out the influences of the environmental variables on
macrobenthic density from Vellar estuary using simple
correlation analysis. It was positively correlated with
salinity, pH, sandy nature of sediment (P > 0.05)
temperature, organic carbon (P > 0.001) and negatively
correlated with dissolved oxygen and clay content
(P > 0.001). For the consideration of number of
individuals and number of species were analyzed
against transects and seasons using two-way ANOVA,
the results was not statistically significant. At this
point of view, the multivariate analysis was carried
and realizes the influence of environmental variables
and the infaunal macrobenthic abundance of the
present study. BEST BIO-ENV procedure, dissolved
oxygen concentration is manifested as the best
matching variable with biological entities. The
rho
value was greater than 0.6 in all the combinations.
Generally if the value is more than 0.6, it indicates the
best matching variables defining faunal distribution
(Clarke and Anisworth, 1993). The present
investigation observed there are changes in the species