374
Biogeochemical Metabolism and Energy Flows in Reef Ecosystems
O2 ,------------------------------,
70
8
2 O~----~~------~----~----~
v
72
18
2/f
TimPly the dafll hours
Fig. 10.3. Diurnal changes in dissolved oxygen contents (02 , mgl- 1 ) in waters over the
Lizard I. reef (1) and over the Kauai I. reef, Hawaii. (Data by Kohn and Helfrich 1957;
Sournia 1976b)
O 2
Ni,pht resJlirutiOIJ
112
]Jail time photosynthesis
g
ft.JOpm
!lt8
70 t4" pm
7
g
[
Ii
01
IJ
tlJOam
72afl7
.70
7
'00
200
.JIJIJ
0
TIJO
200
JIJIJ t,m
Fig. 10.4. Changes in dissolved oxygen content (02mgl-1) in waters over the leeward
reef off Koetivi I., Seychelles at the cross-section from the shore; L distance from the
shore, m. (Data by the author)
the latter is the carbon flow from water to bottom communities through
calcification, and the rest of 70-90% - through its photosynthetic
assimilation by benthic autotrophs (Atkinson and Grigg 1984; Kinsey 1985b;
Crossland et al. 1991). The level of the total carbon flow in coral-reef
ecosystems is close to its maximum known in the natural biota. Moreover,
the values of Pt , for example, recorded in the reef systems were sometimes
close to their theoretically possible upper level in nature. The latter, in
communities of ramose corals with 100% bottom cover has been evaluated
to be about 60gCm- 2 day-l (Odum and Odum 1955), in communities of
aquatic plants 40 g, and in those of dry-land plants 8 g (Larkum 1983).
Maximal PI values actually recorded on reefs in biotopes dominated by
corals were as high as 34 g C m -2 day-I, and in those dominated by