Bacteria and Microalgae in Reef Bottom Sediments
135
sulfide thus formed (Fig. 4.3). Studies of sulfate reduction in sediments of
the Kaneohe bay, the Majuro atoll, and off the coast of Vietnam showed
that this process is most intensive in sediments of reefs subjected to
pollution or to terrigenous siltation. It was quite odd that sulfate reduction
was absent in the "mucous" coral sands mentioned above, which accumulate
under the thickets of living corals; nevertheless, the Eh dropped below
100 mv also at 2-4 cm under the bottom surface. But the sulfate reduction in
the same sediments occurred in polluted areas close to the village. In silty
coral sands off the Vietnam coast, influenced by the terrigenous input of
organic matter, sulfate reduction is widespread. This process appears to be
an important ecological factor there. It causes the intoxication of benthic
fauna and of fish feeding on benthos, and lead to the development of oxygen
deficiency in near-bottom layers (Sorokin et al. 1982). In the lagoon of
Lizard Island influenced by terrigenous outflow of detritus, sulfate reduction
proceeds actively in coral sands at depths of only 1-2 cm below the surface.
The maxima of sulfide content within the sediments were found at depths
3-4cm, and maximum rates of S04 2 reduction by bacteria at 2-3 cm
below the bottom surface (Skyring and Chambers 1976; Skyring 1985). This
process was also discovered within the column of lime rock at depths of
2- 3 m under the bottom surface of fringing reefs in the Kaneohe bay,
Hawaii (Tribble et al. 1988).
White coral sands harbor dense populations of micro-algae which exhibit
high phothosynthesis rates (Sorokin 1971a; Gribb 1973). The chlorophyll
content in them reaches hundreds of mgm- 2 (Sournia 1976b). Thus, besides
their function in the heterotrophic production and in nutrients regeneration,
soft bottom sediments are the sites of an intensive primary production,
which attains there 1-3gCm- 2 day-l. The micro-algae are living in the
mucous micro-habitats around and within the porous sand graines (Fig. 4.1).
In calm places they form a kind of greenish-brown algal mats over the sand
bottom surface. These communities of microphytobenthos contain various
benthic diatoms, cyanobacteria and zooxanthellae living within their
symbiotic foraminiferans (Plante-Guny 1973; Gribb 1973; Sournia 1976b,
1977; Miller et al. 1977). The diatoms are represented by their genera
Navicula, Nitzschia, Surirella, Acanthes, Cocconeis, Amphora, Gyrosigma,
Diploneis, Bacillaria, Donkinya. Some of them are attached to the surface
of sand graines (Acanthes, Cocconeis). Others are moving between them
(Nitzschia, Navicula, Gyrosigma). Their number attains 0.5 x 10 6 cells g-l.
Among the cyanobacteria the genera Schizotrix, Calotrix, Rivularia,
Oscillatoria, Chroococcus, and Lyngbia are the most numerous. In coarse
coral sands of turbulent zones, on reef shallows or in channels the symbiotic
foraminifera harboring zooxanthellae are responsible for the larger part of
photosynthesis production, not just the free living micro-algae (Plante-Cuny
1973; Sournia 1976b). The content of chlorophyll a in the upper layer of
coral sands is usually 1.5 - 5 mg g -1. The biomass of algae in sands comprises
about 1-2% of their total organic matter which is at a level of 0.4-1.3 mg
135
sulfide thus formed (Fig. 4.3). Studies of sulfate reduction in sediments of
the Kaneohe bay, the Majuro atoll, and off the coast of Vietnam showed
that this process is most intensive in sediments of reefs subjected to
pollution or to terrigenous siltation. It was quite odd that sulfate reduction
was absent in the "mucous" coral sands mentioned above, which accumulate
under the thickets of living corals; nevertheless, the Eh dropped below
100 mv also at 2-4 cm under the bottom surface. But the sulfate reduction in
the same sediments occurred in polluted areas close to the village. In silty
coral sands off the Vietnam coast, influenced by the terrigenous input of
organic matter, sulfate reduction is widespread. This process appears to be
an important ecological factor there. It causes the intoxication of benthic
fauna and of fish feeding on benthos, and lead to the development of oxygen
deficiency in near-bottom layers (Sorokin et al. 1982). In the lagoon of
Lizard Island influenced by terrigenous outflow of detritus, sulfate reduction
proceeds actively in coral sands at depths of only 1-2 cm below the surface.
The maxima of sulfide content within the sediments were found at depths
3-4cm, and maximum rates of S04 2 reduction by bacteria at 2-3 cm
below the bottom surface (Skyring and Chambers 1976; Skyring 1985). This
process was also discovered within the column of lime rock at depths of
2- 3 m under the bottom surface of fringing reefs in the Kaneohe bay,
Hawaii (Tribble et al. 1988).
White coral sands harbor dense populations of micro-algae which exhibit
high phothosynthesis rates (Sorokin 1971a; Gribb 1973). The chlorophyll
content in them reaches hundreds of mgm- 2 (Sournia 1976b). Thus, besides
their function in the heterotrophic production and in nutrients regeneration,
soft bottom sediments are the sites of an intensive primary production,
which attains there 1-3gCm- 2 day-l. The micro-algae are living in the
mucous micro-habitats around and within the porous sand graines (Fig. 4.1).
In calm places they form a kind of greenish-brown algal mats over the sand
bottom surface. These communities of microphytobenthos contain various
benthic diatoms, cyanobacteria and zooxanthellae living within their
symbiotic foraminiferans (Plante-Guny 1973; Gribb 1973; Sournia 1976b,
1977; Miller et al. 1977). The diatoms are represented by their genera
Navicula, Nitzschia, Surirella, Acanthes, Cocconeis, Amphora, Gyrosigma,
Diploneis, Bacillaria, Donkinya. Some of them are attached to the surface
of sand graines (Acanthes, Cocconeis). Others are moving between them
(Nitzschia, Navicula, Gyrosigma). Their number attains 0.5 x 10 6 cells g-l.
Among the cyanobacteria the genera Schizotrix, Calotrix, Rivularia,
Oscillatoria, Chroococcus, and Lyngbia are the most numerous. In coarse
coral sands of turbulent zones, on reef shallows or in channels the symbiotic
foraminifera harboring zooxanthellae are responsible for the larger part of
photosynthesis production, not just the free living micro-algae (Plante-Cuny
1973; Sournia 1976b). The content of chlorophyll a in the upper layer of
coral sands is usually 1.5 - 5 mg g -1. The biomass of algae in sands comprises
about 1-2% of their total organic matter which is at a level of 0.4-1.3 mg