68
Reef Environments
3
1,0
0,75
2
0,25
o
Fig. 2.13. Content of suspended organic matter in waters of the open ocean 6 km (1) and
1 km (2) off the windward fiat of the Kawaratti atoll, as well as in waters over the reef fiat
(3) and in the lagoon (4). (After Quasim and Sankaranrayanan 1970)
high stock of LOM is maintained chiefly by its excretion by phytoplankton.
In reef areas the oceanic waters, which pass over the reef-flat, get a new
input from plants and symbiotic animals. It is clearly reflected by a drastic
increase in DOM and LOM contents (Fig. 2.13). Larger contents of LOM
were recorded up the coastal or leeward reefs and reef flats. The percentage
of LOM in total DOM in reef waters is much higher than in oceanic waters,
comprising 30-40%, as against 15-25% in the latter. This also reflects the
immediate enrichment with LOM of waters in contact with the reef benthic
communities.
The LOM excreted by benthic autotrophes and thus introduced into the
water column is then consumed by planktonic, periphytonic and benthic
heterotrophic microflora. The rates of its consumption by benthic microflora
are difficult to measure because of the reciprocal process of its excretion.
But estimations of the use of LOM by planktonic microbial communities
could be done by measuring their respiration rates. They are usually very
high in reef waters: 0.2-0.6Ilg 0 2 1- 1 day-1 (Table 2.9). The turnover time
of LOM, which was estimated by taking into account only its consumption
in the water column, was at most of the reefs investigated rather short: 2 to
8 days. Its real value was more than 10 days. Moreover, a real LOM
turnover time should be even shorter if it could be possible to take into
account in its estimation also the LOM consumption by· benthic and
periphytonic microflora. An extremely quick turnover time of LOM stock in
reef waters reflects high metabolic rates of their planktonic communities.
Data on the composition of DOM in reef waters are scarce (Meyer et al.
1978; Fontaine et al. 1981). But if we agree that it might not be very
different from the composition of DOM in oceanic waters, it should contain
20-30% of peptides and amino acids, 15-30% of carbohydrates and 10-
Reef Environments
3
1,0
0,75
2
0,25
o
Fig. 2.13. Content of suspended organic matter in waters of the open ocean 6 km (1) and
1 km (2) off the windward fiat of the Kawaratti atoll, as well as in waters over the reef fiat
(3) and in the lagoon (4). (After Quasim and Sankaranrayanan 1970)
high stock of LOM is maintained chiefly by its excretion by phytoplankton.
In reef areas the oceanic waters, which pass over the reef-flat, get a new
input from plants and symbiotic animals. It is clearly reflected by a drastic
increase in DOM and LOM contents (Fig. 2.13). Larger contents of LOM
were recorded up the coastal or leeward reefs and reef flats. The percentage
of LOM in total DOM in reef waters is much higher than in oceanic waters,
comprising 30-40%, as against 15-25% in the latter. This also reflects the
immediate enrichment with LOM of waters in contact with the reef benthic
communities.
The LOM excreted by benthic autotrophes and thus introduced into the
water column is then consumed by planktonic, periphytonic and benthic
heterotrophic microflora. The rates of its consumption by benthic microflora
are difficult to measure because of the reciprocal process of its excretion.
But estimations of the use of LOM by planktonic microbial communities
could be done by measuring their respiration rates. They are usually very
high in reef waters: 0.2-0.6Ilg 0 2 1- 1 day-1 (Table 2.9). The turnover time
of LOM, which was estimated by taking into account only its consumption
in the water column, was at most of the reefs investigated rather short: 2 to
8 days. Its real value was more than 10 days. Moreover, a real LOM
turnover time should be even shorter if it could be possible to take into
account in its estimation also the LOM consumption by· benthic and
periphytonic microflora. An extremely quick turnover time of LOM stock in
reef waters reflects high metabolic rates of their planktonic communities.
Data on the composition of DOM in reef waters are scarce (Meyer et al.
1978; Fontaine et al. 1981). But if we agree that it might not be very
different from the composition of DOM in oceanic waters, it should contain
20-30% of peptides and amino acids, 15-30% of carbohydrates and 10-