64
Reef Environments
proceed mainly through the functioning of biological mechanisms based of
trophodymanics within the reef biota (Crossland 1980, 1983). The same
mechanisms drive the flows of nutrients inside the planktonic and the
benthic communities as well as between them via consumption an excretion
of their mainly organic forms within the food-webs (cf. scheme, Fig. 2.12).
Therefore, the measurements of standing stocks and flows of only their
inorganic forms cannot give correct information even on their direction, let
alone their size. The domination of flows of organic nutrients inside reefbottom communities over the flows of their inorganic forms is a consequence
of the abundance of compartments in them with semi-closed nutrients
cycles, as in corals and periphyton (Yonge and Nicholls 1931; Lewis 1973;
Pomeroy et al. 1974). The processes of nutrients regeneration in the reef
ecosystem are accomplished mostly by planktonic and benthic animals
(Ikeda et al. 1982) as well as by fish, with a minor participation of bacteria,
which largely rather consume than regenerate them. Their role in inorganic
nutrients regeneration from organic forms can be seen mainly in the
consumption of dissolved organic phosphorus from the oceanic waters
passing over the reef. They take it up into their biomass and thus into the
food-web. Being grazed by fiiter-, detritus- and periphyton-eaters, these
nutrients consumed by bacteria are finally mineralizing. Bacteria participate
also in the mobilization of the stock of organic nutrients in the so-called
regenerative sediments which consist of detritus (Di Salvo and Gundersen
1971). But the final regeneration of nutrients is accomplished mainly by
animals and among them by the benthic fiiterers and detritovores as well as
by reef fish (Webb et al. 1977; Meyer et al. 1983). In accordance with the
data of the latter authors, the rate of N-regeneration by reef zoobenthos
attains around 75mgm- 2 day-l. Fish, having an average biomass of about
70gm- 2 , could excrete some 30mgm- 2 of NH 4 day-l, and also the
zooplankton according to Ikeda et al. (1982) should excrete at least 15 mg
NH4 m -2 day-I. Thus the total regeneration rate could be evaluated to be
within 115 mg N m -2. At an average depth of waters of 5 m over the reef it
will be around 1.5 ~ moll-I. This rate of regeneration might then provide
the turnover time of N in reef waters as around 2 days. As for phosphorus,
regeneration could be estimated as 20 mg m- 2 day-I, which is around
0.15 ~ mol, which means the same 2 days of turnover time.
With reference to the scheme (Fig. 2.12) it can be seen that while the
nutrients stocks are permanently and many times recycled inside the reef
communities and are also kept in pools of living biomass, detritus and
sediments, reef autotrophic communities should not suffer nutrients
limitations even when flushed by the depleted oligotrophic oceanic waters
(Pilson and Betzer 1973; Wiebe 1985; Atkinson 1988). A large storage
capacity of the coral reef ecosystems in relation to nutrients enables them to
build up their stock during the periods of their extensive input with drainage
(Marsh 1977) or deep oceanic waters, and then use this stock in periods of
when their supply is poor (Tsuda 1974; Kimmerer and Walsh 1981;
Reef Environments
proceed mainly through the functioning of biological mechanisms based of
trophodymanics within the reef biota (Crossland 1980, 1983). The same
mechanisms drive the flows of nutrients inside the planktonic and the
benthic communities as well as between them via consumption an excretion
of their mainly organic forms within the food-webs (cf. scheme, Fig. 2.12).
Therefore, the measurements of standing stocks and flows of only their
inorganic forms cannot give correct information even on their direction, let
alone their size. The domination of flows of organic nutrients inside reefbottom communities over the flows of their inorganic forms is a consequence
of the abundance of compartments in them with semi-closed nutrients
cycles, as in corals and periphyton (Yonge and Nicholls 1931; Lewis 1973;
Pomeroy et al. 1974). The processes of nutrients regeneration in the reef
ecosystem are accomplished mostly by planktonic and benthic animals
(Ikeda et al. 1982) as well as by fish, with a minor participation of bacteria,
which largely rather consume than regenerate them. Their role in inorganic
nutrients regeneration from organic forms can be seen mainly in the
consumption of dissolved organic phosphorus from the oceanic waters
passing over the reef. They take it up into their biomass and thus into the
food-web. Being grazed by fiiter-, detritus- and periphyton-eaters, these
nutrients consumed by bacteria are finally mineralizing. Bacteria participate
also in the mobilization of the stock of organic nutrients in the so-called
regenerative sediments which consist of detritus (Di Salvo and Gundersen
1971). But the final regeneration of nutrients is accomplished mainly by
animals and among them by the benthic fiiterers and detritovores as well as
by reef fish (Webb et al. 1977; Meyer et al. 1983). In accordance with the
data of the latter authors, the rate of N-regeneration by reef zoobenthos
attains around 75mgm- 2 day-l. Fish, having an average biomass of about
70gm- 2 , could excrete some 30mgm- 2 of NH 4 day-l, and also the
zooplankton according to Ikeda et al. (1982) should excrete at least 15 mg
NH4 m -2 day-I. Thus the total regeneration rate could be evaluated to be
within 115 mg N m -2. At an average depth of waters of 5 m over the reef it
will be around 1.5 ~ moll-I. This rate of regeneration might then provide
the turnover time of N in reef waters as around 2 days. As for phosphorus,
regeneration could be estimated as 20 mg m- 2 day-I, which is around
0.15 ~ mol, which means the same 2 days of turnover time.
With reference to the scheme (Fig. 2.12) it can be seen that while the
nutrients stocks are permanently and many times recycled inside the reef
communities and are also kept in pools of living biomass, detritus and
sediments, reef autotrophic communities should not suffer nutrients
limitations even when flushed by the depleted oligotrophic oceanic waters
(Pilson and Betzer 1973; Wiebe 1985; Atkinson 1988). A large storage
capacity of the coral reef ecosystems in relation to nutrients enables them to
build up their stock during the periods of their extensive input with drainage
(Marsh 1977) or deep oceanic waters, and then use this stock in periods of
when their supply is poor (Tsuda 1974; Kimmerer and Walsh 1981;