48
Reef Environments
produced is then oxidized to N03 by nitrifying microflora which is localized
in the upper layer of bottom sediments and in the periphytic overgrowth
(Webb and Wiebe 1975; Webb et al. 1975; Atkinson 1981b, 1983).
Ambient nutrients concentration in water is relatively stable up the
different reef biotopes (Odum and Odum 1955; Pilson and Betzer 1973). A
significant increase - up to 1 to 3!l mol of P04-P - was observed only in the
lagoons of barrier reefs due to the influence of the drainage of rivers during
the rainy season, and in lagoons of atolls situated in the equatorial upwelling
area (Ricard 1981; Kimmerer and Walsh 1981). Nutrients, and especially the
limiting one - phosphorus, are present in reef waters also in dissolved and
suspended organic matter in their organic forms. Oceanic surface waters
contain 0.1-0.2!l mol of dissolved organic phosphorus and 1-4 mol of
organic N (Table 2.1). In reef waters the content of P-org is about the same,
while the N-org content could be even more: 3-6!l mol. Making use of
organic nutrients proceeds in coral-reef ecosystems by the participation of
microbial communities and through the action of the coral-reef biofilter
(Sorokin 1978b, 1986; d. Sect. 3.1.2).
2.2.2 Mechanisms of External Input of Nutrients
The input of nutrients into the coral reef ecosystem, or the debit part of
their balance, is provided by several interacting physical and biological
mechanisms. The nutrients are brought to the reef with oceanic waters
driven up the reef by the wind and by the geostrophic currents (Johannes et
al. 1972; Kimmerer and Walsh 1981; Hatcher 1985). The importance of this
source of input increases in areas where the surface waters are enriched with
nutrients through their elevation from deeper layers in areas of quasipermanent upwellings and divergences in the equatorial zone. The same
happens in the vicinity of an island's systems interacting with the geostrophic
oceanic currents - so-called "island mass effect" (Gilmartin and Relevante
1974; Andrews and Gentien 1982). The nutrients of the deep oceanic water
may penetrate into the closed or semi-closed lagoon of the ring reef
traveling with the water that is filtering into it through its porous base during
high tide, when the level of water in the lagoon is lower than outside in the
ocean (Rougerie 1982, 1985). The waters of the barrier and fringing reefs off
the high islands and continental coasts get a significant input of nutrients
with the river and ground drainages (Marsh 1977; Johannes 1980; D'Elia et
al. 1981; Johannes and Hearth 1985). At atolls that are situated in
productive waters a significant nutrients input is provided by the sea birds,
which form there big colonies. The P04-P content in such reef areas could
be up to 1 !l moll-I. The ancient reefs off some islands contain large deposits
of phosphorite ores, which are 200-800 thousands of years old (Veeh 1985).
They were discovered at the Nauru and the Christmas Islands. On a smaller
scale phosphorites can be found in reef rocks of atolls. On being eroded
Reef Environments
produced is then oxidized to N03 by nitrifying microflora which is localized
in the upper layer of bottom sediments and in the periphytic overgrowth
(Webb and Wiebe 1975; Webb et al. 1975; Atkinson 1981b, 1983).
Ambient nutrients concentration in water is relatively stable up the
different reef biotopes (Odum and Odum 1955; Pilson and Betzer 1973). A
significant increase - up to 1 to 3!l mol of P04-P - was observed only in the
lagoons of barrier reefs due to the influence of the drainage of rivers during
the rainy season, and in lagoons of atolls situated in the equatorial upwelling
area (Ricard 1981; Kimmerer and Walsh 1981). Nutrients, and especially the
limiting one - phosphorus, are present in reef waters also in dissolved and
suspended organic matter in their organic forms. Oceanic surface waters
contain 0.1-0.2!l mol of dissolved organic phosphorus and 1-4 mol of
organic N (Table 2.1). In reef waters the content of P-org is about the same,
while the N-org content could be even more: 3-6!l mol. Making use of
organic nutrients proceeds in coral-reef ecosystems by the participation of
microbial communities and through the action of the coral-reef biofilter
(Sorokin 1978b, 1986; d. Sect. 3.1.2).
2.2.2 Mechanisms of External Input of Nutrients
The input of nutrients into the coral reef ecosystem, or the debit part of
their balance, is provided by several interacting physical and biological
mechanisms. The nutrients are brought to the reef with oceanic waters
driven up the reef by the wind and by the geostrophic currents (Johannes et
al. 1972; Kimmerer and Walsh 1981; Hatcher 1985). The importance of this
source of input increases in areas where the surface waters are enriched with
nutrients through their elevation from deeper layers in areas of quasipermanent upwellings and divergences in the equatorial zone. The same
happens in the vicinity of an island's systems interacting with the geostrophic
oceanic currents - so-called "island mass effect" (Gilmartin and Relevante
1974; Andrews and Gentien 1982). The nutrients of the deep oceanic water
may penetrate into the closed or semi-closed lagoon of the ring reef
traveling with the water that is filtering into it through its porous base during
high tide, when the level of water in the lagoon is lower than outside in the
ocean (Rougerie 1982, 1985). The waters of the barrier and fringing reefs off
the high islands and continental coasts get a significant input of nutrients
with the river and ground drainages (Marsh 1977; Johannes 1980; D'Elia et
al. 1981; Johannes and Hearth 1985). At atolls that are situated in
productive waters a significant nutrients input is provided by the sea birds,
which form there big colonies. The P04-P content in such reef areas could
be up to 1 !l moll-I. The ancient reefs off some islands contain large deposits
of phosphorite ores, which are 200-800 thousands of years old (Veeh 1985).
They were discovered at the Nauru and the Christmas Islands. On a smaller
scale phosphorites can be found in reef rocks of atolls. On being eroded