Page 12 - IJMS-2014v4n46

International Journal of Marine Science 2014, Vol.4, No.47, 1-11
http://ijms.biopublisher.ca
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Table 4 Comparison of environmental variables, macrofaunal abundance, species composition and diversity between present and
previous investigations
Abiotic variables Ajmal Khan et al.
1975
Chandran et al.
1982
Fernando 1987 Murugasan et al.
2007
Present study
2007-2008
Temperature (℃) 26- 32 24- 31 24 – 36 26- 32 21.4-38.2
Salinity (psu) 28- 32 20- 35 4 -32 28- 32 2.6- 40.2
Dissolved oxygen (ml/l) 4.6- 5.5 3.3- 7.6 3.4- 5.5 4.5- 5.3 4 -4.7
pH 7.6- 8.2 6.7- 8.1 7.2- 8.3 7.6- 8.2 7.6- 8.6
Organic carbon (mg/g) - 1.8- 14.1 0.14-10.49 - 1.99-12.59
No. of organisms 16- 18128 58- 1121 112- 3897 298-5125 960–2470
No. of species 43 73 38 54 53
Shannon – Wiener diversity 0.41-3.55 0.23- 2.28 0.98-2.54 2.32- 4.10 1.945- 2.746
Higher values in summer could be attributed to faster
evaporation and lower salinity was observed in
monsoon probably due to freshwater runoff and
rainfall. Temperature and salinity both are integral
variables in intertidal environment, globally those are
significantly inter-related when one variable increase
another one also increase viz. Similarly the present
study proved the inter-relationship between
temperature and salinity (Table 1).
In the present investigation, dissolved oxygen was
high during the monsoon season in transect IV
(4.7±0.7 ml l-1), which might be due to the cumulative
effect of higher wind velocity coupled with heavy
rainfall and the resultant freshwater mixing. Relatively
lower values were observed during summer season
(4±0.4 ml L-1) in transect I, which could be mainly
due to reduced agitation and turbulence. These
dissolved oxygen concentration was lower compared
to the previous studies in this estuary (Table 4). De
Souza and Gupta (1986), Zingde et al. (1987) and
Vijayakumar et al. (2000) have attributed seasonal
variations in dissolved oxygen mainly to the
freshwater influx and ferruginous impact of sediments.
Hydrogen ion concentration (pH) in sediment surface
waters remained alkaline at all transects throughout
the study period, with the maximum value during
summer season (8.6±0.1) and the minimum during
monsoon season (7.6±0.2 ) and the previous
investigations of this estuary found to be similar in
Vellar estuary (Table 4) and in Parangipettai waters
(Kundu et al., 2010). Generally, fluctuations in pH
values during different seasons of the year are
attributed to factors like removal of CO2 by
photosynthesis through bicarbonate degradation,
dilution of seawater by freshwater influx, reduction of
salinity and temperature, and decomposition of
organic matter (Ragothaman and Patil, 1995;
Upadhyay, 1988).
Sediment composition showed maximum sand content
in the estuarine mouth (transect I). It may the reason
of interaction between sea water and fresh water,
while the river debouch sediment and mixing with
beach sand reporting more sand content from this
transect I. Similar findings were reported previously
in this estuary (Murugasan et al., 2007; Kundu et al.,
2010). Silty nature of sediments found more in
artificial mangrove environment (transect II) and
oyster bed (transect III) in this study because
settlement of sand and silty nature of sediments
mixture in mangrove roots. Generally, mangrove areas
are mainly dominated in silty sediments (Kathiresan et
al., 1996; Ajmal Khan et al., 2004) with higher
amount of organic carbon content (Ansari et al., 2014).
Clay nature of sediments was found more in the
present study in partially fresh water region (transect
IV) probably due to terrestrial input from Parangipettai
town.
The present study obtained that intertidal
macrobenthic abundance was highest in transect II,
and lowest in transect IV. The number of individuals
recorded in this study was comparatively higher than
those found by Chandran et al. (1982) and
Murugasan et al. (2007), but lower than it has been
found by Ajmal Khan et al. (1975) in Vellar estuary.
These variations in the number of individuals at all
transects may be the reason for influences of