Nutrients
49
they release phosphates, which are driven out with groundwaters and thus
enrich the water column over the reef with phosphorus (Gordon et al.
1971). An important role in the mobilization of the nutrients deposited in
bottom sediments is their permanent resuspension by means of wave action
(Fanning et al. 1982; Entsch et al. 1983). In some reef areas a significant
input of nutrients is produced by accumulation of masses of the floating
wind-driven blue-green algae Trichodesmium (Sorokin et al. 1982).
The processes listed above provide a permanent flow of nutrients, both
inorganic and organic in their forms, from the external sources and from the
deposits within a coral reef ecosystem. The consumption of nutrients from
this flow, their retention and regeneration are accomplished by biological
mechanisms. One of them is the consumption of inorganic Nand P by
phytoplankton and bacterioplankton, which are present in coral-reef waters.
They consume P04-P in about the same proportion of 1-2% (by weight) to
their production in carbon units per day (Sorokin 1985, 1990a). Direct
estimations of its consumption by microplankton of coral-reef waters by the
use of labeled phosphate showed (Table 2.2) that it is quite significant:
0.03-0.15/l moll- I day-I. The microplankton, which consumes phosphorus
from sea water passing over the reef, is itself then grazed by reef filter
feeders. Thus, the nutrients of oceanic waters become included via the food
web into the nutrients pool of the reef ecosystem mainly in the form of
biomass and feces.
The nutrients in oceanic waters coming over the reef are also utilized by
benthic plant communities, such as periphyton, microphytobenthos and
seaweeds (Muscatine et al. 1979). The periphytonic associations include
numerous nitrogen-fixing bacteria and cyanobacteria which assimilate the
atmospheric nitrogen. They harbor also a rich heterotrophic microflora,
which uses for its growth mainly the dissolved organic matter taken straight
from the oceanic waters, and thus utilizes also the organic forms of Nand P
which it contains (ct. Table 2.1). The macrophytes consume inorganic
nutrients from oceanic waters by the surfaces of their thalloms (Pilson and
Betzer 1973; Nelson 1985) and may accumulate them as stock (Robishaux
1985). The seagrasses get nutrients mainly from the sediments through their
roots. But their leaves usually bring with them a lot of epiphytic macroalgae, which consume nutrients also from water columns (Short 1981).
The symbiotic animals, such as corals, gorgonaceans, tridacna clams, may
consume inorganic nutrients in their ambient concentration in waters passing
over the reef: 0.3-1/lmolP04' 0.4-2/lmolN03 and 0.8-5/lmolNH4 per
liter. The consumption of inorganic nutrients by these animals was
established by observations of the decrease in concentration in their
presence (Kawaguti 1953; Webb and Wiebe 1978; Muscatine and D'Elia
1978; Propp 1981; ct. Fig. 2.8), or by the measurements of consumption of
radiolabeled Nand P compounds (Pomeroy et al. 1974; Sorokin 1973c;
D'Elia 1977; Propp 1981; Burris 1983; Wafar et al. 1985; Atkinson and
Smith 1987). The ahermatypic corals, which do not have zooxanthellae, only
49
they release phosphates, which are driven out with groundwaters and thus
enrich the water column over the reef with phosphorus (Gordon et al.
1971). An important role in the mobilization of the nutrients deposited in
bottom sediments is their permanent resuspension by means of wave action
(Fanning et al. 1982; Entsch et al. 1983). In some reef areas a significant
input of nutrients is produced by accumulation of masses of the floating
wind-driven blue-green algae Trichodesmium (Sorokin et al. 1982).
The processes listed above provide a permanent flow of nutrients, both
inorganic and organic in their forms, from the external sources and from the
deposits within a coral reef ecosystem. The consumption of nutrients from
this flow, their retention and regeneration are accomplished by biological
mechanisms. One of them is the consumption of inorganic Nand P by
phytoplankton and bacterioplankton, which are present in coral-reef waters.
They consume P04-P in about the same proportion of 1-2% (by weight) to
their production in carbon units per day (Sorokin 1985, 1990a). Direct
estimations of its consumption by microplankton of coral-reef waters by the
use of labeled phosphate showed (Table 2.2) that it is quite significant:
0.03-0.15/l moll- I day-I. The microplankton, which consumes phosphorus
from sea water passing over the reef, is itself then grazed by reef filter
feeders. Thus, the nutrients of oceanic waters become included via the food
web into the nutrients pool of the reef ecosystem mainly in the form of
biomass and feces.
The nutrients in oceanic waters coming over the reef are also utilized by
benthic plant communities, such as periphyton, microphytobenthos and
seaweeds (Muscatine et al. 1979). The periphytonic associations include
numerous nitrogen-fixing bacteria and cyanobacteria which assimilate the
atmospheric nitrogen. They harbor also a rich heterotrophic microflora,
which uses for its growth mainly the dissolved organic matter taken straight
from the oceanic waters, and thus utilizes also the organic forms of Nand P
which it contains (ct. Table 2.1). The macrophytes consume inorganic
nutrients from oceanic waters by the surfaces of their thalloms (Pilson and
Betzer 1973; Nelson 1985) and may accumulate them as stock (Robishaux
1985). The seagrasses get nutrients mainly from the sediments through their
roots. But their leaves usually bring with them a lot of epiphytic macroalgae, which consume nutrients also from water columns (Short 1981).
The symbiotic animals, such as corals, gorgonaceans, tridacna clams, may
consume inorganic nutrients in their ambient concentration in waters passing
over the reef: 0.3-1/lmolP04' 0.4-2/lmolN03 and 0.8-5/lmolNH4 per
liter. The consumption of inorganic nutrients by these animals was
established by observations of the decrease in concentration in their
presence (Kawaguti 1953; Webb and Wiebe 1978; Muscatine and D'Elia
1978; Propp 1981; ct. Fig. 2.8), or by the measurements of consumption of
radiolabeled Nand P compounds (Pomeroy et al. 1974; Sorokin 1973c;
D'Elia 1977; Propp 1981; Burris 1983; Wafar et al. 1985; Atkinson and
Smith 1987). The ahermatypic corals, which do not have zooxanthellae, only