46
Reef Environments
the surrounding ocean usually happens to be very low. Most often it drops
below a level that limits the growth of phytoplankton «0.5 ~ mol N03 and
0.2 ~ mol P04). Moreover, the level of primary production of reef-bottom
autotrophs actually does not depend much upon the level of standing stocks
of inorganic nutrients in reef waters (Kinsey 1977, 1983; Sorokin 1977a,
1984b; Wiebe 1985; Atkinson 1988). It seems that rich reef benthic
communities have to lose the nutrients as salts and also as organic forms,
being readily flushed out by blue oligotrophic waters. The outflow of organic
detritus and plankton driven out by currents from the reefs was also proved
(d. Sect. 2.3). But the very existence of the coral reef ecosystems a priori
needs the positive balance of nutrients. While they actually exist and
flourish, a positive balance of nutrients in their exchange between the reef
and the ocean should be axiomatic. Thus we need not even prove it, but we
do have to understand its mechanisms. Already a first approach to the
problem proves that these mechanisms should be mostly biological rather
than physical, e.g., such as are controlling the input of nutrients to the
euphotic zone in the pelagic communities.
At present, we also know in general the biological mechanisms which
govern the input and the turnover of nutrients and provide for their positive
balance in the reef ecosystems (Wiebe 1985; Sorokin 1986b, 1990b). The
level of their content in waters over the reef is also well known (D'Elia
1978; Crossland 1983), but data on the stock of their organic forms in
organic matter and in the biomass of organisms are still scarce (Hatcher
1985; Crossland et al. 1991). Probably, in some reef areas, iron could also
be a limiting element, besides Nand P (Entsch et al. 1983).
2.2.1 Ambient Concentration in Waters
Basic data are available mostly for the reefs of the Pacific basin: the Great
Barrier Reef (Relevante and Gilmartin 1982; Andrews 1983b; Crossland
and Barnes 1983; Crossland 1983; Hatcher 1985; Sorokin 1989, 1990a;
Furnas et al. 1990), French Polynesia (Sournia and Ricard 1976b; Ricard
1977c, 1981; Salvat 1981b), some atolls (Johannes et al. 1972; Pilson and
Betzer 1973; Wiebe et al. 1975; Marshall et al. 1975; Smith and Jokiel 1975;
Kimmerer and Walsh 1981; Charpy and Charpy-Ronband 1988), Hawaiian
reefs (Gilmartin and Relevante 1974; Henderson 1981; Atkinson 1981b,
1983), and high latitude reefs of Abrolhos (Crossland et al. 1984). The
ranges of corresponding data are summarized in Table 2.1, which shows that
the level of the standing stock of nutrients is equally low up the reefs,
situated in waters of a very diffent level of planktonic productivity, and even
up polluted reefs (Hawaii). This leads to the conclusion that the ambient
concentrations of inorganic nutrients in waters over the reef, being values in
equilibrium, reflect only the direction of the turnover but say nothing about
the flow rates or about the real size of its pool in the system. Thus, they
Reef Environments
the surrounding ocean usually happens to be very low. Most often it drops
below a level that limits the growth of phytoplankton «0.5 ~ mol N03 and
0.2 ~ mol P04). Moreover, the level of primary production of reef-bottom
autotrophs actually does not depend much upon the level of standing stocks
of inorganic nutrients in reef waters (Kinsey 1977, 1983; Sorokin 1977a,
1984b; Wiebe 1985; Atkinson 1988). It seems that rich reef benthic
communities have to lose the nutrients as salts and also as organic forms,
being readily flushed out by blue oligotrophic waters. The outflow of organic
detritus and plankton driven out by currents from the reefs was also proved
(d. Sect. 2.3). But the very existence of the coral reef ecosystems a priori
needs the positive balance of nutrients. While they actually exist and
flourish, a positive balance of nutrients in their exchange between the reef
and the ocean should be axiomatic. Thus we need not even prove it, but we
do have to understand its mechanisms. Already a first approach to the
problem proves that these mechanisms should be mostly biological rather
than physical, e.g., such as are controlling the input of nutrients to the
euphotic zone in the pelagic communities.
At present, we also know in general the biological mechanisms which
govern the input and the turnover of nutrients and provide for their positive
balance in the reef ecosystems (Wiebe 1985; Sorokin 1986b, 1990b). The
level of their content in waters over the reef is also well known (D'Elia
1978; Crossland 1983), but data on the stock of their organic forms in
organic matter and in the biomass of organisms are still scarce (Hatcher
1985; Crossland et al. 1991). Probably, in some reef areas, iron could also
be a limiting element, besides Nand P (Entsch et al. 1983).
2.2.1 Ambient Concentration in Waters
Basic data are available mostly for the reefs of the Pacific basin: the Great
Barrier Reef (Relevante and Gilmartin 1982; Andrews 1983b; Crossland
and Barnes 1983; Crossland 1983; Hatcher 1985; Sorokin 1989, 1990a;
Furnas et al. 1990), French Polynesia (Sournia and Ricard 1976b; Ricard
1977c, 1981; Salvat 1981b), some atolls (Johannes et al. 1972; Pilson and
Betzer 1973; Wiebe et al. 1975; Marshall et al. 1975; Smith and Jokiel 1975;
Kimmerer and Walsh 1981; Charpy and Charpy-Ronband 1988), Hawaiian
reefs (Gilmartin and Relevante 1974; Henderson 1981; Atkinson 1981b,
1983), and high latitude reefs of Abrolhos (Crossland et al. 1984). The
ranges of corresponding data are summarized in Table 2.1, which shows that
the level of the standing stock of nutrients is equally low up the reefs,
situated in waters of a very diffent level of planktonic productivity, and even
up polluted reefs (Hawaii). This leads to the conclusion that the ambient
concentrations of inorganic nutrients in waters over the reef, being values in
equilibrium, reflect only the direction of the turnover but say nothing about
the flow rates or about the real size of its pool in the system. Thus, they