Organic Matter in Reef Waters
65
Crossland 1983). In any case, the fact of a permanently high primary
antotrophic production on reefs existing in the flow of oligotrophic oceanic
waters proves that the annual balance of nutrients in the system "reefocean" should be positive. That is to say, the input of the main limiting
nutrient, phosphorus in its organic and inorganic forms from oceanic waters,
exceeds its loss from reef to ocean. Its key role as limiting nutrient is clearly
seen in its regulatory function of community structure in reef benthic
macrophytes (Littler et al. 1991). The problems of the dynamics of nutrients
in reef ecosystems need further attention. It should be important to
accumulate more data on their flows in the food-chains and in the
regenerative systems with the use of isotopic techniques. This kind of
information is extremely important for the monitoring of coral reef
environments in areas of pollution and eutrophication.
2.3 Organic Matter in Reef Waters
A large part of the organic matter produced in coastal marine communities
by benthic plants, and on reefs also by symbiotic animals, is introduced into
the food-web via the "detritus chain", i.e., dead organic matter (Darnell
1967). In coral reef ecosystems, even at their high level of direct grazing of
plants and corals, which has been evaluated as within 50% (Hatcher 1983b),
more than 80% of organic matter would pass via the "detritus chain", if the
assimilability of plant materials by animals is 30-40%. This part of primary
plant production enters into the food chain as suspended, and also as
dissolved, organic matter. The latter is produced largely through its direct
excretion by plants and by corals, which comprise up to 20-30% of their
primary production. The suspended organic matter is formed from the
disintegrated faeces of phytophages, from the crushed talloms of dead
macrophytes, as well as from the microbial and algal biomass washed out
from bottom sediments and periphyton by surf. The importance of this stock
of organic matter in reef trophodynamics was stressed also by the first
investigators of this problem (Odum and Odum 1955; Bakus 1967). They
pointed out the abundance of filter feeders in reef benthic communities and
the domination of the detrital mass in their guts. These conclusions drew
attention to the study of suspended organic matter and organic aggregates in
reef waters (Johannes 1967; Klim 1969; Marshall 1968; Coles and
Strathmann 1973; Quasim and Sankaranarayanan 1970; Gordon 1971;
Gerber and Marshall 1974; Le Borgne et al. 1989).
As regards the stock of dissolved organic matter, data are still scarce
(Westrum and Meyers 1978) perhaps mostly because of methodological
obstacles. For example, the most widespread wet combustion persulfate
method after Menzel-Vaccaro underestimates it 1.5-2 times. Moreover, the
informative value of data on its total stock is limited because 70-80% of it is
65
Crossland 1983). In any case, the fact of a permanently high primary
antotrophic production on reefs existing in the flow of oligotrophic oceanic
waters proves that the annual balance of nutrients in the system "reefocean" should be positive. That is to say, the input of the main limiting
nutrient, phosphorus in its organic and inorganic forms from oceanic waters,
exceeds its loss from reef to ocean. Its key role as limiting nutrient is clearly
seen in its regulatory function of community structure in reef benthic
macrophytes (Littler et al. 1991). The problems of the dynamics of nutrients
in reef ecosystems need further attention. It should be important to
accumulate more data on their flows in the food-chains and in the
regenerative systems with the use of isotopic techniques. This kind of
information is extremely important for the monitoring of coral reef
environments in areas of pollution and eutrophication.
2.3 Organic Matter in Reef Waters
A large part of the organic matter produced in coastal marine communities
by benthic plants, and on reefs also by symbiotic animals, is introduced into
the food-web via the "detritus chain", i.e., dead organic matter (Darnell
1967). In coral reef ecosystems, even at their high level of direct grazing of
plants and corals, which has been evaluated as within 50% (Hatcher 1983b),
more than 80% of organic matter would pass via the "detritus chain", if the
assimilability of plant materials by animals is 30-40%. This part of primary
plant production enters into the food chain as suspended, and also as
dissolved, organic matter. The latter is produced largely through its direct
excretion by plants and by corals, which comprise up to 20-30% of their
primary production. The suspended organic matter is formed from the
disintegrated faeces of phytophages, from the crushed talloms of dead
macrophytes, as well as from the microbial and algal biomass washed out
from bottom sediments and periphyton by surf. The importance of this stock
of organic matter in reef trophodynamics was stressed also by the first
investigators of this problem (Odum and Odum 1955; Bakus 1967). They
pointed out the abundance of filter feeders in reef benthic communities and
the domination of the detrital mass in their guts. These conclusions drew
attention to the study of suspended organic matter and organic aggregates in
reef waters (Johannes 1967; Klim 1969; Marshall 1968; Coles and
Strathmann 1973; Quasim and Sankaranarayanan 1970; Gordon 1971;
Gerber and Marshall 1974; Le Borgne et al. 1989).
As regards the stock of dissolved organic matter, data are still scarce
(Westrum and Meyers 1978) perhaps mostly because of methodological
obstacles. For example, the most widespread wet combustion persulfate
method after Menzel-Vaccaro underestimates it 1.5-2 times. Moreover, the
informative value of data on its total stock is limited because 70-80% of it is