Basic HTML Version
International Journal of Marine Science 2014, Vol.4, No.1, 1-15
http://ijms.sophiapublisher.com
9
Figure 8 Uptake rate constants of NO
x
(A) and NH
4
+
(B) in
the sand (SD), seagrass (SG), coral-seagrass (CS), coral
(CR), and sand-acorn worm (AC) habitats. * indicates a
significant difference between habitats (ANCOVA,
Bonferroni adjustment, p<0.05). There are no significant
differences among the NH
4
+
rate constants
Using the P
gross
and R
24h
values calculated from the
sand, coral, and seagrass habitats respectively, we
can calculate the expected P
gross
and R
24h
values in
the coral-seagrass mixed habitat based on the
sand:coral:seagrass ratio found in the chambers. By
applying this ratio (5% sand + 45% coral + 50%
seagrass) and summing each parameter, the values
are 251.7 for P
gross
and 235.8 for R
24h
, respectively.
These values were similar to the measured
photosynthesis and respiration rates in the
coral-seagrass habitat (t-test: p = 0.97 and 0.41
respectively). If a synergistic effect were present,
we would expect the observed rates to be higher
than those calculated in the coral-seagrass habitat.
Therefore, there was no synergistic effect of
photosynthesis and respiration processes in the
coral-seagrass habitat and hence no beneficial
relationship
between
seagrass
and
coral
co-inhabitation with respect to the organic carbon
metabolism in the Bise reef moat.
In comparison to the other habitats, the P
gross
/R
24h
ratio in the acorn worm habitat had a lower ratio,
indicating a higher respiration rate was found in the
acorn worm community (Table 1). As bioturbating
organisms often create a more oxic environment due
to their burrowing activities (Kogure and Wada,
2005), it is possible that the oxygen consumption of
microorganisms living in the burrowed layer
affected the incubation water as well as respiration
of the acorn worm. This is further confirmed in a
study conducted by Papaspyrou et al. (2007) which
showed that the bioturbating polychaete,
Arenicola
marina
positively affected the O
2
flux in the
sediment-water interface. In the case of the acorn
worm, previous research has stated that the species,
Ptychodera flava
shows an increase in respiratory
activity in response to lowered salinity (Azariah et
al., 1975). Therefore, it is possible that both the
bioturbation activity and the influx of groundwater
in the acorn worm habitat concurrently contribute to
the higher respiration rate. Our results also indicate
that bioturbation of sediments leads to increased
dissolution rates. It was considered that more
advection of seawater into sediments drives faster
rates of dissolution (Rao et al., 2012; Cyronak et al.,
2013).
With the exception of the acorn worm habitat,
P
gross
/R
24h
ratios were 1.0±0.1 which indicates no
net production or net consumption, and that the
community is slightly autotrophic (Table 1). As the
acorn worm habitat is limited to a narrow area along
the coastal beach (~10% of the total reef area), the
net organic carbon produced by seagrass seems to
sustain the nutritional needs of the acorn worm
habitat and balances the overall reef ecosystem.
This is in agreement with Kinsey (1985) that
reported the value of a whole reef system was ~1.0
even if the P
gross
/R
24h
ratio varied in different
benthic reef environments.
In the sand habitat, the inorganic carbon production
(IP) was also low (Figure 5). This suggests that the
contribution of micro-calcifying organisms, i.e.
foraminiferans or coccolithophorids, to inorganic
production in this area is consequently small. In
contrast, the coral-seagrass and coral habitats
demonstrated that IP was correlated with the photon
flux (R
2
= 0.70 and 0.76, respectively, Figure 5)
which is consistent with the light-enhanced
calcification theory of coral reviewed in Gattuso et