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International Journal of Marine Science 2013, Vol.3, No.14, 111-120
http://ijms.sophiapublisher.com
115
Table 3 Percentage representation of molluscan species in the study stations
Study stations
1
2
3
4
5
6
7
8
Neritidae
Nertinaglabarata
10
sd
0.4
r
2.47
c
6.6
sd
3.8
c
7.9
sd
6
sd
9
sd
N. kuramoensis
2.75
c
0.2
r
2.47
c
2.7
c
6.2
sb
12.8
sd
6.4
sd
11.9
sd
Melaniidae
Pachymelaniaaurita
2.75
c
0.8
r
8.6
sd
38.3
d
50.1
d
52.4
d
67.5
d
37.6
d
P. fusca
var
quadrisiata
-
0.1
r
-
0.6
r
0.6
r
0.9
r
0.2
r
0.1
r
Gastropoda
Potamididae
Tympanotonusfusatus
0.92
r
1.0
c
3.7
c
1.7
c
3.8
c
0.2
r
1.9
c
2.9
c
T
.
fuscatus
var
radula
0.92
r
0.2
r
11.11
sd
8.2
sd
3.4
c
6.5
sb
1.3
c
1.3
c
Tellinidae
Macomacumana
56.9
d
88.4
d
50.6
d
40.3
d
30.5
d
2
c
12.4
sb
34.9
d
Tellinanymphalis
7.3
sd
2.2
c
14.8
sd
0.8
r
0.1
r
0.03
r
0.1
r
1.2
c
Avcidae
Mytilusedulis
-
-
-
-
-
-
0.6
r
-
Bivalvia
M. perna
-
-
-
-
-
-
0.9
r
-
Ostreidae
Crassostreagazar
-
-
-
-
-
-
1.1
c
-
Aloididae
Aloidistrigona
18.3
d
6.9
sd
6.2
sd
0.7
r
1.3
c
-
1.6
c
1.0
c
Note: ≥ 15% = dominant (d); ≥ 5 to < 15 % = sub-dominant (sd); ≥ 1% to < 5% = common (c); < 1% = Rare (r)
Figure 5 Hierarchical cluster analysis based on total mollusc
density in the study stations
1.4 Dominant, Subdominant, Occasional and Rare
Species
The species representation analysis of mollusc in the
study stations are presented in Table 3.
Macoma
cumana
and
A. trigona
were dominant in station 1,
while
N. glabarata
and
T. nymphalis
assumed
subdominant position. Other species recorded
occurred as common and rare species. In station 2 and
3,
M. cumana
was dominant, while
A. trigona
occurred as subdominant species in both stations.
Tympanotonus
fuscatus
var
radula
and
T. nymphalis
were recorded as subdominant species in station three.
Pachymelania aurita
and
M. cumana
(except in
stations 6 and 7) were dominant in stations 4~8.
Neritina glabarata
occurred as subdominant species in
stations 4, 6, 7 and 8, whereas
N. kuramoensis
was
recorded as subdominant species in stations 5, 6, 7 and
8. The overall species representation indicates that,
M.
cumana
and
P. aurita
were the dominant species in Epe
Lagoon while,
P. fusca
var
quadrisiata, M. edulis, M.
perna,
and
C. gazar
occurred as rare species.
1.5 Environmental influence on molluscs
Spearman's correlations between biotic and
environmental variables in the study area (Table 4)
indicates that water salinity correlated positively and
significantly with overall mollusc diversity (rs=0.0857,
p < 0.01) and gastropod density (rs = 0.762, p < 0.5).
Total organic content of sediment correlated
negatively and significantly with density of mollusc
(rs = 0.738, p < 0.5) and gastropod species richness
(rs = 0.756, p < 0.5). The amount of sand fractions in
sediment also correlated negatively and significantly
with density of bivalves (rs = 0.958, p < 0.01). In the
overall relationship, salinity, TOC and percentage of
sand in sediment had strong effects on the benthic
molluscan assemblage in the study stretch.