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International Journal of Marine Science 2014, Vol.4, No.42, 1-11
http://ijms.biopublisher.ca
8
not significantly different at the study stations (ANOVA,
F = 0.790,
p >
0.05).
2.6 Relationship between chl-a and faunal variables
Spearman's correlations between chl-a and faunal
attributes in the study area (Table 4) indicated that
there was significant and positive correlation between
density (
r
s
= 1;
p
< 0.01), diversity (
r
s
= 1;
p
< 0.01)
and chl-a in water. However, there was negative
correlation between density (
r
s
= 0.43;
p
> 0.01),
diversity (
r
s
= 0.45;
p
> 0.01) and chl-a in sediment.
Among the physical factors studied, only transparency
of water correlated positively and significantly with
chl-a in sediment (
r
s
=1;
p
< 0.01) and chl-a in water
(
r
s
= 0.8; p <0.01). Turbidity and depth of water
related negatively but significantly with chl-a in water
and sediment. In general, the result of this study
demonstrated that chl-a composition affected the
faunal variables while physical attributes investigated
had major influence on chl-a concentration.
Table 4 Spearman's correlations between chl-a and environmental
parameters in the study area; +: positive correlation; -: negative
correlation; ns: no significant correlation;
p
> 0.01; *: significant
correlation;
p
< 0.01
Environmental
Parameter
Chl-a in sediment Chl-a in water
Physical attribute
Transparency
+*
+*
Turbidity
-
ns
-
ns
Depth
-
ns
-
ns
Faunal variables
Density
-
ns;
+*
Diversity
-
ns
+*
3 Discussion
Overall trends in physical variables were similar to
those previously recorded for the Lagos Lagoon and
some estuarine water bodies in Nigeria (Brown, 2000;
Ogunwemo and Osuala, 2004). The result of the
correlation analyses between physical factors and
chl-a concentration revealed the interplay of factors
that may have determined the overall pattern in the
results obtained. Transparency related positively and
significantly with chl-a in water and sediment, while
turbidity and depth correlated negatively with chl-a in
water and sediment. These observations are in
agreement with the report of earlier workers (Marra,
1978; Platt
et al
. 1980; Pinckney and Zingmark, 1993;
MacIntyre and Cullen, 1995). According to Marra
(1978), primary production by phytoplankton is
known to be influenced by transparency of water,
turbidity and depth. Variability in these factors may be
due to several factors such as, the daily and seasonal
cycles of incident irradiance and interactive changes
in biological and physical characteristics of the water
column.
The effects of turbidity and transparency of water on
chl-a in estuarine ecosystems have been widely
studied (Jennes and Duineveld, 1985). The effect of
turbidity on chl-a is more of a shorter time-scales than
the effect of the externally imposed daily changes in
transparency of water (Garrad and Hey, 1987). The
magnitude of the effect of changes depend on the
mechanisms that drive them, and their effect on
overall rates of primary production depends on the
degree to which, they influence the co-occurrence of
chl-a and light. Turbidity in estuarine waters is
determined largely by the concentration of suspended
sediments (Cloern, 1987) and can change with tidal
frequency, either because of advection of water
masses with differing loads of seston or because
changes in current velocity cause alternating episodes
of suspension and deposition of sediment (Cloern,
1987). Resuspension is also caused by wind-driven
mixing (Cloern, 1987) and by boat traffic (Garrad and
Hey, 1987) which is a common activity in the study
area. The frequency with which water clarity varies
may be tidal or sub-tidal, depending on the relative
influence of tides and winds. This variability is
superimposed on the day/night cycle in determining
the amount of light to which phytoplankton suspended
in the water column are exposed (Marra, 1978; Baillie
and Welsh, 1980).
Variability in the concentration of chl-a may be due to
advection of patchily distributed populations, resuspension
of benthic assemblages and/or changes in the balance
between growth and grazing. Resuspension of benthic
microalgae has been identified as the major cause of
the variability in chl-a concentration in shallow
estuaries (Sullivan and Moncrieff, 1988; de Jonge and
van Beusekom, 1992). Productivity in the water
column of turbid estuaries may even be dominated by
resuspended benthic algae (Shaffer and Onuf, 1985,
de Jonge and van Beusekom, 1992). Further
variability in suspended chl-a on diel time-scales may