388
Biogeochemical Metabolism and Energy Flows in Reef Ecosystems
care of largely by microflora, which in the model was absent as a functional
component. Equally absent was the detritus food chain, which had been
proved to be important in real systems (Peres and Pickard 1969; Gerber and
Marshall 1974; Chardy et al. 1988). Finally, as a real reef ecosystem is
actually an open system, it should not be internally balanced as it has been
asserted, in the model, this being one of its basic principles. For example,
the reef biofilter consumes a significant portion of energy from the passing
oceanic waters.
Concluding the analysis of the ECOPATH model, it could be assumed
that the simplification of the coral reef ecosystem postulated in it, which, in
fact, has made possible its very creation, at the same time deprirved it of the
necessary adequacy, and thus of serious scientific value. While any model
represents actually only a hypothesis, it should not ignore also established
facts. So we have to recognize that the reef ecosystem seems to be too
complex to be managed in this way by imitation modeng. However, there is
a rather realistic way to generalize also established data regarding the
functioning of coral reef communities at the level of a whole ecosystem, i.e.,
the composition of the above-mentioned schemes of energy flows. An
example of such a scheme is given in Fig. 10.7. The basic data used in it are
given in corresponding chapters of this book.
According to the scheme, the basis of energy metabolism in a reef
ecosystem is composed of the detritus pool. It is represented by the
permanently regenerating stock of dissolved and particulated organic
matter. The scheme includes values of the production of the food rations, of
subsequent links in the food web, and of non assimilated and nonconsumed
food. All these values are expressed in kcalm- 2 day-l. The main flows of
energy are expressed by thick arrows. The energy input into the reef
ecosystem is composed of bottom plants from internal sources of antotrophic
production of planktonic algae, and of symbiotic algae, as well as coming
from its external sources, like plankton and organic matter of the oceanic
waters utilized by reef biota. On barrier and fringing reefs a significant
portion of external organic matter reaches the reef systems from the land
and from mangroves. This external organic matter enters into its detritus
pool and is then incorporated into the food web via the intermedial
participation of bacteria. Despite the abundance of herbivores in reef
communities, a large portion of autotrophic production created by benthic
plants enters the food web via the detritus pool ~ bacteria. The flow of
energy from the bottom plant and coral communities via the dt.!tritus pool to
the reef fauna is, according to this scheme, a main way of using autotrophic
production in heterotrophic processes. This was proved by field studies
(Chardy et al. 1988). By its size the second energy flow passes
intraorganismically from symbiotic zooxanthellae to animal tissues of their
hosts - corals, clams and forams. These organisms, especially corals and
Tridacna clams, excrete a large portion of this translocated autotrophic
production as mucus and DOM, which then enter the detritus pool and are
Biogeochemical Metabolism and Energy Flows in Reef Ecosystems
care of largely by microflora, which in the model was absent as a functional
component. Equally absent was the detritus food chain, which had been
proved to be important in real systems (Peres and Pickard 1969; Gerber and
Marshall 1974; Chardy et al. 1988). Finally, as a real reef ecosystem is
actually an open system, it should not be internally balanced as it has been
asserted, in the model, this being one of its basic principles. For example,
the reef biofilter consumes a significant portion of energy from the passing
oceanic waters.
Concluding the analysis of the ECOPATH model, it could be assumed
that the simplification of the coral reef ecosystem postulated in it, which, in
fact, has made possible its very creation, at the same time deprirved it of the
necessary adequacy, and thus of serious scientific value. While any model
represents actually only a hypothesis, it should not ignore also established
facts. So we have to recognize that the reef ecosystem seems to be too
complex to be managed in this way by imitation modeng. However, there is
a rather realistic way to generalize also established data regarding the
functioning of coral reef communities at the level of a whole ecosystem, i.e.,
the composition of the above-mentioned schemes of energy flows. An
example of such a scheme is given in Fig. 10.7. The basic data used in it are
given in corresponding chapters of this book.
According to the scheme, the basis of energy metabolism in a reef
ecosystem is composed of the detritus pool. It is represented by the
permanently regenerating stock of dissolved and particulated organic
matter. The scheme includes values of the production of the food rations, of
subsequent links in the food web, and of non assimilated and nonconsumed
food. All these values are expressed in kcalm- 2 day-l. The main flows of
energy are expressed by thick arrows. The energy input into the reef
ecosystem is composed of bottom plants from internal sources of antotrophic
production of planktonic algae, and of symbiotic algae, as well as coming
from its external sources, like plankton and organic matter of the oceanic
waters utilized by reef biota. On barrier and fringing reefs a significant
portion of external organic matter reaches the reef systems from the land
and from mangroves. This external organic matter enters into its detritus
pool and is then incorporated into the food web via the intermedial
participation of bacteria. Despite the abundance of herbivores in reef
communities, a large portion of autotrophic production created by benthic
plants enters the food web via the detritus pool ~ bacteria. The flow of
energy from the bottom plant and coral communities via the dt.!tritus pool to
the reef fauna is, according to this scheme, a main way of using autotrophic
production in heterotrophic processes. This was proved by field studies
(Chardy et al. 1988). By its size the second energy flow passes
intraorganismically from symbiotic zooxanthellae to animal tissues of their
hosts - corals, clams and forams. These organisms, especially corals and
Tridacna clams, excrete a large portion of this translocated autotrophic
production as mucus and DOM, which then enter the detritus pool and are