3 Plankton in Coral-Reef Waters
For a long time an absolute predomination of bottom communities in
functioning coral-reef ecosystems has been accepted axiomatically (Odum
and Odum 1955; Johannes et al. 1970). But this opinion contradicted
observations of the obvious abundance of planktonovore animals in reef
communities. In fact, about half of the reef benthic animals are the filterers,
or the sedimentary feeders, which feed on plankton. Among them are
bivalves, some gastropods, sedentary pelychaetes, brittle stars and crinoids,
many crustaceans, bryozoans, tunicates, and also corals, hydroids, and
zoantharians. The zooplankton is a main source of food for the pelagic
larvae of most bottom animals, of fish larvae, and of a dense population of
such common reef planktonovore fish like Alanetta, Chromis, Caesio.
Nevertheless, the plankton of coral-reef waters has been studied less than
that of oceanic waters. Its real quantitative studies have started
comparatively recently in 1968-72, and those of the microzooplankton only
in 1981. The data, which we now have, are still scarce and patchy, and not
only on metereotrophic microplankton but also on the traditional objects of
plankton studies, phytoplankton and zoo-plankton. Still, even so we can
also recognize that plankton in reef-waters is abundant, has high specific
productivity and plays a sighificant role in reef trophodynamics and
metabolism.
3.1 Bacterioplankton
3.1.1 Biomass and Production
The organic primary production of reef is extremely large. Being as high as
30-80 g m -2 of wet biomass per day, it cannot be grazed directly by
phytovores. The nongrazed organic matter enters the water c'olumn and
bottom sediments as detritus. The enrichment of reef waters with dissolved
organic matter, organic aggregates and detritus is well known (Gerber and
Marshall 1974). It can enter the reef food-web mainly via the microbial link,
and so bacteria should be a priori a key component in reef trophodymanics.
This opionion was expressed by Odum and Odum (1955) long ago, but at
that time corresponding quantitative evaluations were lacking (Wood 1960).
For a long time an absolute predomination of bottom communities in
functioning coral-reef ecosystems has been accepted axiomatically (Odum
and Odum 1955; Johannes et al. 1970). But this opinion contradicted
observations of the obvious abundance of planktonovore animals in reef
communities. In fact, about half of the reef benthic animals are the filterers,
or the sedimentary feeders, which feed on plankton. Among them are
bivalves, some gastropods, sedentary pelychaetes, brittle stars and crinoids,
many crustaceans, bryozoans, tunicates, and also corals, hydroids, and
zoantharians. The zooplankton is a main source of food for the pelagic
larvae of most bottom animals, of fish larvae, and of a dense population of
such common reef planktonovore fish like Alanetta, Chromis, Caesio.
Nevertheless, the plankton of coral-reef waters has been studied less than
that of oceanic waters. Its real quantitative studies have started
comparatively recently in 1968-72, and those of the microzooplankton only
in 1981. The data, which we now have, are still scarce and patchy, and not
only on metereotrophic microplankton but also on the traditional objects of
plankton studies, phytoplankton and zoo-plankton. Still, even so we can
also recognize that plankton in reef-waters is abundant, has high specific
productivity and plays a sighificant role in reef trophodynamics and
metabolism.
3.1 Bacterioplankton
3.1.1 Biomass and Production
The organic primary production of reef is extremely large. Being as high as
30-80 g m -2 of wet biomass per day, it cannot be grazed directly by
phytovores. The nongrazed organic matter enters the water c'olumn and
bottom sediments as detritus. The enrichment of reef waters with dissolved
organic matter, organic aggregates and detritus is well known (Gerber and
Marshall 1974). It can enter the reef food-web mainly via the microbial link,
and so bacteria should be a priori a key component in reef trophodymanics.
This opionion was expressed by Odum and Odum (1955) long ago, but at
that time corresponding quantitative evaluations were lacking (Wood 1960).