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International Journal of Marine Science 2013, Vol.3, No.36, 285-294
http://ijms.sophiapublisher.com
291
Table 3 Partial eta squared values by general linear model of multivariate analysis of variance using
δ
13
C and
δ
15
N values of coral
tissue and zooxanthellae
δ
13
C (‰)
δ
15
N (‰)
Coral tissue
Zooxanthellae
Δ
Coral tissue
Zooxanthellae
Δ
Genera
0.610 *
0.397 *
0.151 *
0.063
0.061
0.157
Season
0.130 *
0.102 *
0.006
0.330 *
0.280 *
0.227
Locality
0.112 *
0.118 *
0.015
0.033
0.007
0.033
Depth
0.100 *
0.060 *
0.003
0.014
0.012
0.001
Note: *Significant at p = 0.05
study, we focused on employing analyses of carbon
and nitrogen isotope for detecting relationship
between coral and zooxanthellae in localities with
different depth, sedimentation rate as different
distances from river mouth, and nutrient availability
as different season. Furthermore, this study examined
relationships among three genera of different
branching corals. Our results showed that the
δ
13
C
values of coral tissue and zooxanthellae were affected
by differences in genera, seasons, localities, and depth,
whereas the
δ
15
N values varied significantly with
seasons alone. Of the three branching corals, the
δ
13
C
values of
Seriatopora
were lower than
Porites
and
Stylophora
. The
δ
13
C values of
Seriatopora
were
closer to the
δ
13
C value of POM, which may be due to
them utilizing food more actively from surrounding
areas rather than depending on nutrients derived from
zooxanthellae. Such a clear seasonal variation in the
δ
15
N between coral and zooxanthellae was observed in
a Florida reef tract (Swart et al., 2005).
The
δ
15
N values of consumer tissues are known to be
correlated with their diet (Peterson and Fry, 1987;
Yamamuro et al., 1995). Different
δ
15
N values
between coral tissue and zooxanthellae are expected to
be good indicators of nutrient transfer from
zooxanthellae to coral tissue (Muscatine and Kaplan,
1994). During the 1
st
and 2
nd
dry seasons, most coral
tissue samples had higher
δ
15
N values compared with
zooxanthellae, indicating that zooxanthellae were the
main source of nutrients for corals. In contrast, the
δ
15
N values of corals collected during the rainy season
were not always higher than those of zooxanthellae,
and the
Δδ
15
N values were negative. This finding
suggests that corals utilize food sources other than
nutrients from zooxanthellae during the rainy season
(Muscatine and Kaplan 1994, Susanto et al., 2009).
The
δ
15
N values of coral tissues during the dry
seasons were lower than zooplankton and POM,
indicating that corals did not utilize zooplankton and
POM during those times. Indeed, the
δ
15
N values of
zooplankton were higher than those of corals in all
seasons, which implied that coral did not depend on
zooplankton as a food source. Thus, corals are likely
to have utilized POM as a nutrient source because the
δ
15
N values of POMs were lower than those of corals
during the rainy season. Heikoop et al (2000b) also
noted that a seasonal variation in nutrient sources
affected
δ
15
N records in coral tissues.
Therefore, the results of this study suggest that,
although corals depend on zooxanthellae alone during
the dry season, they were also able to utilize POM,
which was probably produced by algal blooms during
the rainy season in November 2007. November is the
beginning of the rainy season and algal blooms occur
at this time, so corals were likely to be using POM as
their main source of organic matter. In addition, the
source of dissolved inorganic nitrogen available for
zooxanthellae changed during the rainy season, and
corals are not yet in isotopic equilibrium with
internal inorganic nitrogen pool. NOAA-ERDDAP
data on primary productivity in the study area also
showed that net primary productivity during rainy
season was higher than other two dry seasons (see
http://coastwatch.pfeg.noaa.gov/ erddap/index.html).
The different nutritional modes found in corals
suggest that they may be adaptively polytrophic and
opportunistic feeders (Muller-Parker and D’Elia,
1997). Polytrophism seems to account for their ability
to thrive in low nutrient environments. However, there