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International Journal of Marine Science 2013, Vol.3, No.36, 285-294
http://ijms.sophiapublisher.com
290
estuary were lower than those collected from the
marine area. The mean
δ
15
N value of zooplankton was
lower during the rainy season (+5.2
±
07‰) compared
with those collected during the 1
st
(+8.0
±
1.5‰) and
2
nd
dry (8.1
±
1.4‰) seasons. The mean
δ
15
N values
of zooplankton were always higher than corals even
though it is not significantly different.
3.5
Δδ
13
C and
Δδ
15
N
Figure 2 shows the
Δδ
13
C (
δ
13
C difference between
coral tissue and zooxanthellae) and
Δδ
15
N (
δ
15
N
difference between coral tissue and zooxanthellae) for
each genus during the three seasons at the three
localities. The mean
Δδ
13
C of
Porites
was positive
during every season and at every locality, ranging
from 0.6‰ to 2.2‰. The values of
Seriatopora
showed only a small variation from –0.4‰ to +0.8‰.
The majority of
Δδ
13
C values were positive for
Stylophora,
ranging from –0.4‰ to +1.9‰.
Figure 2 Mean
Δδ
13
C (open bar) and
Δδ
15
N (filled bar) values
of the differences between coral tissues and zooxanthellae for
three genera during three seasons at the three localities
Note: Mean
Δδ
13
C and
Δδ
15
N values for genera were
significantly different; while seasonally only mean
Δδ
15
N was
different
The mean
Δδ
15
N values exhibited a different trend
from
Δδ
13
C. The
Δδ
15
N values of
Porites
were
positive during the 1
st
and 2
nd
dry seasons (0.0‰ to
0.7‰) but negative during the rainy season (–1.2‰ to
–0.5‰). There were similar trends were also observed
in the
Seriatopora
and
Stylophora
where the mean
Δδ
15
N values during the 1
st
and 2
nd
dry seasons were
higher in general than those of rainy season
.
3.6 Multivariate analysis of variance (MANOVA)
Table 3 shows the results of the statistical analysis
using a generalized linear model for MANOVA.
Partial eta squared values indicate the proportion of
variance in the dependent variables that was explained
by the independent variables. Pallant (2005) categorized
eta squared values as follows: 0.01=small effect; 0.06 =
moderate effect; 0.14=large effect.
Analysis of the
δ
13
C values indicated that all factors
had significant effects on coral tissues and
zooxanthellae. Genus differences had significant
effects on the
δ
13
C values of coral tissue,
zooxanthellae and the
Δδ
13
C values. Seasonal, locality
and depth differences had moderate effects on the
δ
13
C values of coral tissue and zooxanthellae.
Genus differences had significant effects on the
Δδ
15
N
values but not coral tissue or zooxanthellae. Seasonal
differences had large significant effects on the
δ
15
N
values of coral tissue, zooxanthellae and the
Δδ
15
N
values. The analysis did not indicate significant
differences in
δ
15
N values for locality and depth.
4 Discussion
Isotope values of pool nitrogen were high in the study
area implied to the small of mean C-N ratio (4-6)
compare to the other tropical and temperate areas with
C-N ratio of the dry season was lower rainy season.
The C-N ratio of coral tissue in the Red Sea coral
Stylophora pistillata
ranged from 4.86 to 6.26
(Muscatine et al., 1989). In this study, mean C-N ratio
coral tissue (5.23) was slightly higher than C-N ratio
zooxanthellae (4.95). Lamb and Swart (2008)
remarked specifically that lower C-N ratios were
measured in the Florida Keys during dry season of
September – October.
Environmental factors such as depth, light, turbidity,
salinity, pH, and nutrient availability are known to
affect coral reef distribution (Sorokin, 1993). In this