International Journal of Marine Science 2015, Vol.5, No.23 1-13
4
Diversity indices such as, Shannon-Wiener diversity (H’),
Margalef’s richness index (d) and Pielou’s evenness
index (J’) were computed using PRIMER Vs. 6.0
(Clarke and Gorley, 2006). Multidimensional scaling
(MDS) was used to graphically display the
two-dimensional ordination plots showing differences of
organization of the fish abundance. A stress value of
<
0.2 gives a useful representation of results (Clarke and
Warwick, 2001). Species numeric abundance in relation
to environmental variables was analysed using the
canonical correspondence analysis (CCA). It is an
example of direct gradient analysis, where the gradient in
environmental variables is known a prior and the species
abundances (or presence/absences) are considered to be a
response to this gradient. This ordination method was
used to detect patterns of species association directly
related to environmental variables. A perpendicular line
is traced between the species and environmental vector,
that represents the relation between the species and the
factor (Ter Braak and Verdonschot, 1995).
2 Results
2.1 Physico -Chemical characteristics
The depth of the estuary ranged between1.4 to 8.5m
with an average of 3.93 ± 1.93m. Seasonal average
values of major physico-chemical parameters are
given in Table 1. The lowest temperature of 28ºC was
observed in Station 1, Station 2, Station3 and Station 4
and maximum of 33ºC in Station 9 and Station 10.
The pre monsoon season (31.03 ±1.14 ºC) showed the
maximum temperature as compared to post monsoon
(31.4 ± 0.68 ºC) and monsoon (30.25 ± 1 ºC). The
average minimum temperature of 29.2 ±0.95 ºC was
recorded during February 2012 and maximum 32.05 ±
0.64 ºC during April 2012. The ANOVA of
temperature showed that variation between seasons
was significant (F= 11.08, p < 0.01). The transparency
value ranged between 0.25m (March, 2012, Station 3)
to 2.25m (December 2012, Station 6) with an average
of 1.74m. The pH varied from 6.25 (August 2012,
Station 1) to 10.02 (March 2012, Station 4). The mean
pH of the estuarine system during the study period
was 7.06 ±0.56. The lowest mean value was recorded
in August 2012 (6.37 ± 0.98), while highest in
February 2012 (8.39 ± 0.66). Generally alkaline
condition was observed in the northern sector of the
estuary. On an average, pH of the study stations in the
southern sector was 7.06, whereas that of the northern
sector was 7.2. Compared to pre monsoon and post
monsoon, a relatively low alkaline condition was
observed during monsoon (6.72 ±0.24). The ANOVA
of pH showed that the variation between seasons were
significant (F= 17.24, p < 0.01). The dissolved oxygen
ranged from 4mg/l, recorded during November 2012
at station 1 and 2 to 9.6 mg/l, recorded during June at
Station 2 and 8 with mean value of 6.8 ± 1.2 mg/l.
When compared to stations of southern sector (6.78 ±
0.28 mg/l), higher dissolved oxygen values were
observed in stations of northern sector (6.92 ± 0.14
mg/l). Maximum dissolved oxygen concentration was
observed during monsoon (7.6 ± 1.3 mg/l) followed
by pre monsoon (6.8 ± 1.1 mg/l) and post monsoon
period (6.1 ± 0.87 mg/l). The ANOVA showed that
seasonal variation of dissolved oxygen was significant
(F= 16.57, p < 0.01).
Table 1 Seasonal average values of physico-chemical variables in Vembanad estuarine system [Depth (m), Temperature (
0
C), Salinity
(ppt), Dissolved oxygen (mg/l)]
Parameter
Premonsoon
Monsoon
Postmonsoon
Range
Depth
4.06±2.03
3.82±1.88
3.93±1.9
1.4 – 8.5
Temp
31.03±1.45
30.25±1
31.44±0.68
28 – 33
pH
7.4±0.69
6.72±0.24
7.06±0.41
6.25 – 10.02
DO
6.85±1.06
7.6±1.23
6.14±0.88
4 – 9.6
Salinity
7.58±8.16
1.38±2.1
7.89±1.15
0.1 – 33
Parameter
Premonsoon
Monsoon
Postmonsoon
Range
Depth
4.06±2.03
3.82±1.88
3.93±1.9
1.4 – 8.5
Temp
31.03±1.45
30.25±1
31.44±0.68
28 – 33
pH
7.4±0.69
6.72±0.24
7.06±0.41
6.25 – 10.02
DO
6.85±1.06
7.6±1.23
6.14±0.88
4 – 9.6
Salinity
7.58±8.16
1.38±2.1
7.89±1.15
0.1 – 33
Parameter
Premonsoon
Monsoon
Postmonsoon
Range
Depth
4.06±2.03
3.82±1.88
3.93±1.9
1.4 – 8.5
Temp
31.03±1.45
30.25±1
31.44±0.68
28 – 33
pH
7.4±0.69
6.72±0.24
7.06±0.41
6.25 – 10.02
DO
6.85±1.06
7.6±1.23
6.14±0.88
4 – 9.6
Salinity
7.58±8.16
1.38±2.1
7.89±1.15
0.1 – 33
