Basic HTML Version
International Journal of Marine Science 2014, Vol.4, No.1, 1-15
http://ijms.sophiapublisher.com
7
Table 1 Summary of the carbon metabolisms of gross production, 24-hour respiration and calcification in the sand (SD), seagrass
(SG), coral-seagrass (SC), coral (CR), and sand-acorn worm (AC) habitats. Different letters in each column indicate a significant
difference between habitats (Tukey-Kramer HSD, P<0.05)
Habitat
Photosynthesis–Respiration (mmol m
–2
d
–1
)
Calcification (mmol m
–2
d
–1
)
P
gross
R
24h
P
gross
/R
24h
G
light
G
dark
G
net
SD
57.9±0.89
c
64.1±11.1
c
0.95±0.14
ab
3.6±1.1
c
-
3.1±1.0
b
0.5±1.7
c
SG
296.9±16.7
a
267.4±15.3
a
1.11±0.02
a
2.4±0.6
c
-
15.0±3.0
c
-
12.5±2.5
c
CS
252.5±14.4
ab
227.4±7.0
ab
1.11±0.07
a
38.9±5.6
b
-
1.7±2.6
b
37.2±7.9
b
CR
223.1±3.5
b
219.7±5.3
b
1.02±0.03
a
80.4±5.1
a
9.2±1.5
a
89.6±6.6
a
AC
53.2±1.2
c
83.2±1.4
c
0.64±0.02
b
-
6.9±1.0
c
-
9.1±0.6
bc
-
16.0±1.3
c
3.4 Nitrate and nitrite flux
Nitrate and nitrite (NO
x
) uptake rate in each habitat
was linearly correlated with NO
x
concentration with a
relatively strong relationship ranging from R
2
=0.40 in
the SG habitat to 0.83 in the AC habitat (Figure 6).
The higher concentrations corresponded to low tide.
The NO
x
concentration in each habitat was
significantly higher during low tide (n=18) than high
tide (n=15) (Student’s t-test; p<0.01). However there
was no evidence of a strong relationship between the
NO
x
uptake rates and photon fluxes in each habitat,
ranging from R
2
=0.09 in the AC to 0.17 in the SG.
These data clearly suggest that the NO
x
uptake rate in
each habitat is highly dependent on the NO
x
concentration. The AC habitat showed the highest
uptake rate of 906 µmol m
–2
h
–1
due to the high NO
x
concentration of 32 µmol l
–1
. Since the NO
x
concentration was different among all habitats, we
used the uptake rate constant to compare NO
x
acquisition ability. Figure 8a shows
the NO
x
uptake
rate constant
derived from the slope of the regression
line in Figure 6. The estimated rate constant in the CS
habitat was the highest and significantly different
from all other habitats (ANCOVA; p<0.05) except for
the coral habitat.
3.5 Ammonium flux
Figure 7 shows the relationship between the NH
4
+
uptake rate and concentration with the regression line
at each habitat. The correlations were relatively high
in the SD (R
2
=0.37), SG (R
2
=0.47), and AC (R
2
=0.81)
habitats while they were lower in the CS and CR
habitats. The NH
4
+
concentration in each habitat was
significantly higher during low tide (n=18) than high
tide (n=15) (Student’s t-test; p<0.01) although the
differences of the averaged concentration between low
and high tide were very small, ranging from 0.17 in
the SG to 0.32 µmol l
–1
in the AC habitat. These
results indicate that the ammonium concentrations in
Bise moat are likely affected by tidally-driven
groundwater inflow and the uptake rate is primarily
controlled by the concentration. In the SD and AC
habitats, there was no relationship between the
concentration and photon flux (R
2
=0.12 and 0.01,
respectively). More than half of the uptake rate data in
the CR habitat were negative, demonstrating the
release of NH
4
+
from coral. This caused a low
correlation between the uptake rate and concentration
of NH
4
+
in both the CR and CS habitats. Figure 8b
shows the uptake rate constants for NH
4
+
in all the
habitats. Although there were no significant
differences between them, the rate constant tended to
be the highest in the SG habitat. The lack of a
significant difference by ANCOVA statistics is likely
due to the low correlation in the CS and CR habitats
shown in Figure 7.
4 Discussions
4.1 Carbon production
In the sand habitat, the organic carbon production (OP)
was low (Figure 4). This suggests that the amount of
phytoplankton in the benthos and water column in the
Bise area is also low. Conversely, the OP in the coral
and seagrass habitats was higher in comparison to the
sand habitat. The OP was correlated with photon flux
in the seagrass, coral-seagrass and coral habitats (R
2
=
0.72, 0.70, and 0.85, respectively). Similar to previous
studies which have reported a photosynthesis-
respiration vs irradiance curve (P-I curve) (e.g.
Gattuso et al., 1999), our study also supports this
relationship. In addition, the carbon production of
coral and seagrass in the present study were within the
range of the metabolic data of macroalgal-dominated
coral reef community as shown in Bensoussan and
Gattuso (2007), although the photosynthetic gross
production and respiration rates in the seagrass habitat
were higher than in the other habitats in the Bise area
(Table 1).