International Journal of Marine Science 2016, Vol.6, No.30, 1-8
4
Figure 3 Aggregation of
Acartia
species in Ashtamudi estuary during the study period (A, B&C. 4X, D. 10X)
The physico chemical characteristics of Ashtamudi estuary is presented in Table 1. Temperature in the water
column ranged from 28°C to 30°C; salinity from 20 ppt to 26 ppt and the pH from 5.1 to 6.8, that was slightly
acidic.
Table 1 Variations in physico chemical parameters in Ashtamudi estuary during the study period
Parameters
Ashramam
Kavanad
Ashtamudi
Water Temperature (
0
C)
30
28.5
28
pH
6.87
7.49
7.8
Salinity(ppt)
26
24
20
Carbon dioxide (mg.l
-1
)
17.6
13.2
18.7
Dissolved oxygen (mg.l
-1
)
5.8
6.8
5.1
Nitrate- nitrogen (µmol.l
-1
)
0.11
0.44
0.05
Nitrite- nitrogen (µmol.l
-1
)
0.16
0.02
1.27
Ammonia- nitrogen (µmol.l
-1
)
3.57
1.00
3.76
Phosphate-phosphorus (µmol.l
-1
)
0.63
1.48
1.93
Silicate- silicon (µmol.l
-1
)
3.59
7.45
6.69
4 Discussion
Aggregation of zooplankton mainly appears to be influenced by various factors. They can be passively
concentrated or actively motivated. When considering the nutrient profile, usually monsoon showers bring
nutrients from allochthonous sources into the systems enriching the phosphate, nitrate and silicate concentrations
in water (Bijoy Nandan 2008). Apart from nutrients, the present study revealed that salinity was the most
fluctuating factor recording maximum at the swarming area, Ashramam. Although most zooplankton species
survive under a wide range of environmental conditions, their growth and density depend on a number of
