132
Benthic Microflora, Periphyton and Plant Associations
reef sediments is by about an order more than in silts of temperate coasts
(Sorokin 1978b). These extremely abundant populations of bacteria in reef
sediments could be supported only by their high production and metabolism
based energetically on a high flow-rate of suspened organic matter, which
settles a from the water column (cf. Sect. 2.3). In fact, the production of
bacteria in them is very high. As estimated by different methods, it was 10
to 70llgCg-I day-I. That is, within an active layer 2-3m thick it would be
0.2-2gCg- 2 day-lor 1-lOgm- 2 of wet microbial biomass. According to
Moriarty et al. (1985b), production of bacteria, estimated by the thymidine
method in coral sands of Lizard Island ranged in summer within 0.120.37 g C g-2 day-I, comprising 30-40% of the gross photosynthesis production of their microphytobenthos. Taking the total stock of microbial
biomass as 10-50g m- 2 , the coefficients of specific production of benthic
bacteria (PIB) could be estimated within 0.1-0.2 per day. That means that
the turnover time of the stock of microbial biomass in coral sands should be
rather short: 5-10 days.
The abundance of microbial populations in coral sands appears to be
dependent upon the density of coral growth (Table 4.2). The largest
numbers of microbial biomass were found in sands of reefs with a rich or
medium coral cover, and the smaller in sands of "algal" reefs, where the
living corals were rear ones, such as the reefs of New Hebrides and some
reefs of the Lau archipelago. These data prove that the mucus shed by
corals is a most important source of energy, which supports a rich microbial
population in reef sediments (Rublee et al. 1980; Pascal and Vacelet 1981;
Paul et al. 1986; Sorokin 1986a; Wahbeh and Mahasnen 1988). The mucus
enriched with settled particulated matter, when shed by corals, accumulates
at the bottom under thickets of living corals and forms there downy mucous
sediments, which are especially peculiar to the patch-free areas of some
Pacific atolls (Sorokin 1973a). The density of microflora in them was about
as high as in the detrital sediments (Tables 4.1-4.3). The rate of microbial
respiration in these sediments was so high that also at depths of 1-2 cm on
vertical profiles the Eh dropped to 100 mv, and at depths 10-15 cm dropped
below 200 mv (Fig. 4.2), but what was very curious was that it happened
without any sign of sulfate reduction in them (see below). A high microbial
biomass (0.3-1 mg C g-l) was also found in silted coral sands of the fringing
reefs off the coast of central Vietnam (Table 4.3), and in the reef areas of
the GBR covered with seagrasses (Moriarty and Pollard 1982). In coral
sands of Vietnamese reefs in the open South China Sea it was 5 -10 times
less: 0.02-0.15mgCg- 1 . Extremely high values of microbial biomass, as
measured with the use of the ATP-method, reported by Burns et al. (1984),
were surely overestimates because this method counted together with
bacteria also all other living components of the present in the sediment
samples. In total, the density of microbial populations in coral-reef
sediments is usually by 1-2 orders more than in the upper layer of silts of
temperate coasts (Sorokin 1978a).
Benthic Microflora, Periphyton and Plant Associations
reef sediments is by about an order more than in silts of temperate coasts
(Sorokin 1978b). These extremely abundant populations of bacteria in reef
sediments could be supported only by their high production and metabolism
based energetically on a high flow-rate of suspened organic matter, which
settles a from the water column (cf. Sect. 2.3). In fact, the production of
bacteria in them is very high. As estimated by different methods, it was 10
to 70llgCg-I day-I. That is, within an active layer 2-3m thick it would be
0.2-2gCg- 2 day-lor 1-lOgm- 2 of wet microbial biomass. According to
Moriarty et al. (1985b), production of bacteria, estimated by the thymidine
method in coral sands of Lizard Island ranged in summer within 0.120.37 g C g-2 day-I, comprising 30-40% of the gross photosynthesis production of their microphytobenthos. Taking the total stock of microbial
biomass as 10-50g m- 2 , the coefficients of specific production of benthic
bacteria (PIB) could be estimated within 0.1-0.2 per day. That means that
the turnover time of the stock of microbial biomass in coral sands should be
rather short: 5-10 days.
The abundance of microbial populations in coral sands appears to be
dependent upon the density of coral growth (Table 4.2). The largest
numbers of microbial biomass were found in sands of reefs with a rich or
medium coral cover, and the smaller in sands of "algal" reefs, where the
living corals were rear ones, such as the reefs of New Hebrides and some
reefs of the Lau archipelago. These data prove that the mucus shed by
corals is a most important source of energy, which supports a rich microbial
population in reef sediments (Rublee et al. 1980; Pascal and Vacelet 1981;
Paul et al. 1986; Sorokin 1986a; Wahbeh and Mahasnen 1988). The mucus
enriched with settled particulated matter, when shed by corals, accumulates
at the bottom under thickets of living corals and forms there downy mucous
sediments, which are especially peculiar to the patch-free areas of some
Pacific atolls (Sorokin 1973a). The density of microflora in them was about
as high as in the detrital sediments (Tables 4.1-4.3). The rate of microbial
respiration in these sediments was so high that also at depths of 1-2 cm on
vertical profiles the Eh dropped to 100 mv, and at depths 10-15 cm dropped
below 200 mv (Fig. 4.2), but what was very curious was that it happened
without any sign of sulfate reduction in them (see below). A high microbial
biomass (0.3-1 mg C g-l) was also found in silted coral sands of the fringing
reefs off the coast of central Vietnam (Table 4.3), and in the reef areas of
the GBR covered with seagrasses (Moriarty and Pollard 1982). In coral
sands of Vietnamese reefs in the open South China Sea it was 5 -10 times
less: 0.02-0.15mgCg- 1 . Extremely high values of microbial biomass, as
measured with the use of the ATP-method, reported by Burns et al. (1984),
were surely overestimates because this method counted together with
bacteria also all other living components of the present in the sediment
samples. In total, the density of microbial populations in coral-reef
sediments is usually by 1-2 orders more than in the upper layer of silts of
temperate coasts (Sorokin 1978a).