Nutrients
45
the sea-level in the vicinity of reefs bring about the elevation of deep
oceanic waters rich in nutrients to the surface (Wolanski 1982). It proceeds
not only via formation of eddies and divergences of current after these
interactions, but also by the driving up of waters from deeper layers by
strong tidal currents. The possibility of this increases in regions of barrier
reefs subject to the influence of large vertical movements of the upper
boundary of the thermocline caused by long-period barotrophic shelfinternal waves. For example, the amplitude of vertical shift of the
thermocline boundary off the outer edge of the GBR up to the depth of
300m could be 100m (Wolanski and Pickard 1983b). The input of nutrients
through the hydrodynamic processes of advection of deep waters in the
vicinity of reefs is one of the important factors supporting high plankton
productivity in reef waters (cf. Sect. 3.2.2). Interaction of the ring reef with
incoming oceanic current results in the formation of a series of rings. When
going downstream their diameter increases. They cease at a distance 10-15
times exceeding the diameter of the ring reef itself (Fig. 2.4). The formation
of these rings supports the development of plankton and influences the
distribution of pelagic fish in shelf areas off atolls and small high islands
(Alldredge and Hamner 1980; Hamner and Hauri 1981).
The oceanic currents as well as the local tidal- and wind-driven surface
currents support a permanent flow of plankton over and through the
communities of benthic planktonovorous animals including corals and
planktonovorous fish, being thus one of the most important factors of
trophodynamics in the reef ecosystem (Williams et al. 1984). The back-andforth tidal currents accelerate the exchange of the dissolved and particulated
organic matter between the reef ecosystems and the pelagic ecosystems of
the surrounding ocean (Le Borgne et al. 1989). Transporting and
redistributing the organic matter and plankton inside the reef system,
currents provide energy interconnections between different biotopes and
different sites of the reef ecosystem, thus uniting it as a whole (Sorokin
1977a).
2.2 Nutrients
Ever since Charles Darwin the enigma of the existence of a rich life on coral
reefs surrounded by surface oligotrophic oceanic waters depleted of
nutrients became a point of heated discussions and investigations (Stoddard
1969; Andrews and Gentien 1982; Crossland 1983; Atkinson 1983; Wiebe
1985). And, in fact, the photosynthetic primary production of the powerful
reef autotrophic associations of plants and symbiotic animals approaches the
highest level known for marine and terrestrial ecosystems: 5lOgCm- 2 day-1, and sometimes even more, while the ambient
concentrations of inorganic nutrients (NO)", NOi, NHt, PO~-) in waters of
45
the sea-level in the vicinity of reefs bring about the elevation of deep
oceanic waters rich in nutrients to the surface (Wolanski 1982). It proceeds
not only via formation of eddies and divergences of current after these
interactions, but also by the driving up of waters from deeper layers by
strong tidal currents. The possibility of this increases in regions of barrier
reefs subject to the influence of large vertical movements of the upper
boundary of the thermocline caused by long-period barotrophic shelfinternal waves. For example, the amplitude of vertical shift of the
thermocline boundary off the outer edge of the GBR up to the depth of
300m could be 100m (Wolanski and Pickard 1983b). The input of nutrients
through the hydrodynamic processes of advection of deep waters in the
vicinity of reefs is one of the important factors supporting high plankton
productivity in reef waters (cf. Sect. 3.2.2). Interaction of the ring reef with
incoming oceanic current results in the formation of a series of rings. When
going downstream their diameter increases. They cease at a distance 10-15
times exceeding the diameter of the ring reef itself (Fig. 2.4). The formation
of these rings supports the development of plankton and influences the
distribution of pelagic fish in shelf areas off atolls and small high islands
(Alldredge and Hamner 1980; Hamner and Hauri 1981).
The oceanic currents as well as the local tidal- and wind-driven surface
currents support a permanent flow of plankton over and through the
communities of benthic planktonovorous animals including corals and
planktonovorous fish, being thus one of the most important factors of
trophodynamics in the reef ecosystem (Williams et al. 1984). The back-andforth tidal currents accelerate the exchange of the dissolved and particulated
organic matter between the reef ecosystems and the pelagic ecosystems of
the surrounding ocean (Le Borgne et al. 1989). Transporting and
redistributing the organic matter and plankton inside the reef system,
currents provide energy interconnections between different biotopes and
different sites of the reef ecosystem, thus uniting it as a whole (Sorokin
1977a).
2.2 Nutrients
Ever since Charles Darwin the enigma of the existence of a rich life on coral
reefs surrounded by surface oligotrophic oceanic waters depleted of
nutrients became a point of heated discussions and investigations (Stoddard
1969; Andrews and Gentien 1982; Crossland 1983; Atkinson 1983; Wiebe
1985). And, in fact, the photosynthetic primary production of the powerful
reef autotrophic associations of plants and symbiotic animals approaches the
highest level known for marine and terrestrial ecosystems: 5lOgCm- 2 day-1, and sometimes even more, while the ambient
concentrations of inorganic nutrients (NO)", NOi, NHt, PO~-) in waters of