72
Reef Environments
usually extremely low (0.15-0.5%). Most of the organic matter produced by
autotrophs is consumed and oxidized in the water column where it is many
times resuspended. Its settled remains are consumed and decomposed by an
abundant benthic fauna and microflora. The biomass of bacteria alone in
coral sands might comprise up to 3-4% of the total organic matter which
they contain, and the turnover time of this living microbial biomass is only
4-5 days.
The organic matter suspended in reef waters has a high nutritional value
because of the abundance of microbial biomass and mucus in it. The
suspended matter is the source of feeding for corals (Johannes and Gerber
1974; Lewis and Price 1975), and zooplankton (Johannes 1967; Richman et
al. 1975; Sumner et al. 1975; Gerber and Gerber 1979; Gottfried and
Roman 1983; Le Borgne et al. 1989). The flakes of "marine snow" and of
aggregates are ingested by soft corals (Coffroth 1984) and even by fish
(Hiatt and Strasburg 1960; Benson and Muscatine 1974). The LOM and
DOM of reef waters are also readily used and not only by planktonic
periphytonic and benthic bacteria, but also directly by many planktonic and
benthic animals, which have the ciliated epithelium, like some larvae
(trochophores,echinocardium, veligers), and like benthic filterers: bivalves,
sponges, sedentary polychaetes, tunicates and corals. These animals, by
feeding on LOM in concentration close to that of the ambient sphere, could
compensate by its direct assimilation for 10-30% of their energy
expenditures (Sorokin 1968, 1978b, 1984a, 1986a; see Tables 9.17-9.19).
The stocks of LOM and SOM in the water column over the reef being
mobile and moving to and fro, driven by tidal currents, act as an energy
interconnection link between the reef biotopes and, before all, between the
biotopes of the windward flat where the autotrophic production
predominates, and of the lagoon where the heterotrophic processes are
more active (Johannes et al. 1972; Smith and Marsh 1973; Sorokin 1971b,
1978b, 1986a,b). The flows of detrital suspended matter and LOM connect
the biotopes of flats with planktonic and benthic communities of the outer
reef slope (Hubbard et al. 1981) and of the surrounding ocean (Marshall
1965; Coles and Strathmann 1973; Zieman et al. 1979; Darnell and Soniat
1979; Sorokin et al. 1982, 1983; Barnes et al. 1976).
Reef Environments
usually extremely low (0.15-0.5%). Most of the organic matter produced by
autotrophs is consumed and oxidized in the water column where it is many
times resuspended. Its settled remains are consumed and decomposed by an
abundant benthic fauna and microflora. The biomass of bacteria alone in
coral sands might comprise up to 3-4% of the total organic matter which
they contain, and the turnover time of this living microbial biomass is only
4-5 days.
The organic matter suspended in reef waters has a high nutritional value
because of the abundance of microbial biomass and mucus in it. The
suspended matter is the source of feeding for corals (Johannes and Gerber
1974; Lewis and Price 1975), and zooplankton (Johannes 1967; Richman et
al. 1975; Sumner et al. 1975; Gerber and Gerber 1979; Gottfried and
Roman 1983; Le Borgne et al. 1989). The flakes of "marine snow" and of
aggregates are ingested by soft corals (Coffroth 1984) and even by fish
(Hiatt and Strasburg 1960; Benson and Muscatine 1974). The LOM and
DOM of reef waters are also readily used and not only by planktonic
periphytonic and benthic bacteria, but also directly by many planktonic and
benthic animals, which have the ciliated epithelium, like some larvae
(trochophores,echinocardium, veligers), and like benthic filterers: bivalves,
sponges, sedentary polychaetes, tunicates and corals. These animals, by
feeding on LOM in concentration close to that of the ambient sphere, could
compensate by its direct assimilation for 10-30% of their energy
expenditures (Sorokin 1968, 1978b, 1984a, 1986a; see Tables 9.17-9.19).
The stocks of LOM and SOM in the water column over the reef being
mobile and moving to and fro, driven by tidal currents, act as an energy
interconnection link between the reef biotopes and, before all, between the
biotopes of the windward flat where the autotrophic production
predominates, and of the lagoon where the heterotrophic processes are
more active (Johannes et al. 1972; Smith and Marsh 1973; Sorokin 1971b,
1978b, 1986a,b). The flows of detrital suspended matter and LOM connect
the biotopes of flats with planktonic and benthic communities of the outer
reef slope (Hubbard et al. 1981) and of the surrounding ocean (Marshall
1965; Coles and Strathmann 1973; Zieman et al. 1979; Darnell and Soniat
1979; Sorokin et al. 1982, 1983; Barnes et al. 1976).