Basic HTML Version
International Journal of Marine Science 2014, Vol.4, No.47, 1-11
http://ijms.biopublisher.ca
3
Abott and Dance (1982), Pinn (1990); Subba Rao et al.
(1991; 1992), Subba Rao and Dey (2000); Amphipods:
Lincoln (1979); Lyla et al. (1999)). The data were
compared with earlier investigations of this estuary in
1974 by Ajmal Khan et al. (1975), in 1977 (Chandran
et al., 1982), in 1977-78 (Fernando, 1987), as well as
with recent study in the marine zone in 2000 between
transects I and II of the present study (Murugasan et
al., 2007). The above investigations were based on
monthly collections for a period of one year.
1.3 Data analysis
Biodiversity measures
(Shannon Wiener diversity -
H′log
2
, Margalef’s species richness - d, Pielou’s
evenness - J′ and Simpson dominance index -
l-Lambda′) were calculated,
and the multivariate
analysis consisted of estimating Bray-Curtis similarity
of sample abundance data. The similarity matrix was
subjected to both clustering (hierarchical agglomerative
method using group-average linking) and ordination
(non-metric multidimensional scaling, MDS).
Seasonal variation of physico-chemical variables were
analysed using
Principal Component Analysis (PCA).
The r
elationship between the distribution of
macrobenthos and physico-chemical variables were
analysed using comparative (Mantel-type) tests on
similarity matrices and rank correlations between the
similarity matrix derived from the species abundance
data and matrix derive from subset of environmental
variables to define suites of variables which best
explain the biotic structure. Analysis of uni- and
multivariate statistics were performed using the PC
software packages PRIMER version 6 (Clarke
and
Gorley, 2006) and PAST version 1.93 (Hammer et
al., 2001).
2 Results
2.1 Abiotic variables
Abiotic variables such as temperature, salinity, pH and
organic carbon were found to be decreased with
increasing distance from estuarine mouth, whereas the
dissolved oxygen showed the opposite trend (Table 1).
Seasonally, maxima of bottom water temperature,
salinity and pH were observed in summer, and
minimum values of these variables were observed in
monsoon period, whereas the reverse trend was noted
in dissolved oxygen concentrations. The highest
organic carbon content (12.59±0.7 mg g
-1
)
was
observed during premonsoon period, and lowest
content (1.99±0.3 mg g
-1
) was found in monsoon in
2007) (Table 1). In the sandy nature of sediments were
observed more during all the seasons while the
monsoon season clay content was high. The sandy
nature of sediments noted with the highest percentage
in transect I (estuarine mouth), while the silt content
showed maximum in transects II (mangrove
environment) and transect III (oyster bed), and the
clay content observed is higher in the transect IV due
to freshwater inflow during the all the seasons (Table 1).
2.2 Species composition of macrofauna
Over 6426 individual of macrobenthic organisms were
collected belonging to 53 species under four major
groups (polychaetes, gastropod, bivalves and
amphipods). Gastropods contributed 81.6% followed
by polychaetes (7.7%), bivalves (5.5%) and amphipods
(5.2%). Infaunal macrobenthic abundance observed
decrease with increasing distance from estuarine
mouth. The macrobenthic abundance (Mean ± SD)
recorded 1742±196, 2470±148, 1254±154 and 960±112
individuals m
-2
from transect I, II, III and IV,
respectively (Figure 2A). Seasonally, infaunal
macrobenthic abundance varied from 2060±282
individuals m
-2
in summer to 1098±236 individuals
m
-2
during monsoon period (Figure 2B).
Among gastropods,
Cerethedia cingulata
(Gmelin,
1791),
Cerethedia obtuse
(Lamarck, 1822) and
Umbonium vestiarium
(Linnaeus, 1758) were the
dominant species observed in all transects as well all
seasons. Polychaetes were second dominant group and
the species represented
Diapatra neopolitana
(Delle
Chiaje, 1841),
Prionospio saldanha
(Day, 1961) and
Glycera longipinnis
(Grube, 1878). Bivalves were
next dominant group observed in the present study,
Crassostrea madrasensis
(Preston, 1908),
Saccostrea
cucullata
(Born, 1778),
Meretrix meretrix
(Linnaeus,
1758) and
Meretrix casta
(Chemnitz, 1782) were most
dominant species in all seasons. Amphipods were
present throughout the year in all transects and the
species such as
Amphitho eramondi
(Audouin, 1826),
Grandidierella gravipes
(Barnard, 1935) and
Photis
digitata
(Barnard, 1935) were the most abundant.
2.3 Diversity indices
The calculated diversity values are shown in Table 2.
The univariate methods (Shannon diversity, Margalef’s
richness and Simpson dominance index) showed
decrease with increasing distance from estuarine
mouth, while the Pielou’s evenness index showed a reverse