Bacterio Plankton
83
in aggregates are of 3-10 ~ sizes. Experiments with reef water samples
filtered through the 1-~ filter to keep out particles and aggregates showed
that in the presence of an inhibitor of microbial growth the aggregates did
not form even in the presence of coral mucus, added as homogeneous
prefiltered solution. But without inhibitor these aggregates formed readily,
especially in samples enriched with glucose, which enhances microbial
growth (Sorokin 1978b). The effect of stimulating their formation by coral
mucus was detected only after 5 days of exposure. Mucus flakes gradually
became inhabited by bacteria, which used them also as a source of nutrition
(Duck low and Mitchell 1979b; Rublee et al. 1980; Paul et al. 1986).
Nevertheless, the formation of aggregates is an immanent feature of
microbial growth and proceeds also without suspended particles or mucus,
which were supposed to be the centers of microbial growth. The aggregates
grew well even in prefiltered water. The aggregation of a significant part of
bacterioplankton makes it accessible for grazing by crude filterers and even
by seizers.
It was shown above that the microbial biomass and production in waters
over the reefs are several times greater than in the surrounding oceanic
waters, especially in oligotrophic regions. The influence of large reefs upon
the abundance of bacterioplankton in oceanic waters was detectable at a
distance of 10-12 km, as it could be seem from Fig. 3.3. The microbial
biomass and also its production will gradually decrease within this interval to
a very low level, but the specific production rates (PIB) will increase. The
latter is connected with the enhanced trophodynamics in pelagic ecosystems
of tropical ocean, as well as with the absence of an additional input of inert
microbial biomass from the sediments, which happens in waters over the
reefs. The enrichments of oceanic waters, in contact with reefs, by the dissolved organic matter could be seen from the elevated values of the potential
microbial production, which is an indirect indicator of the relative abundance
of labile organic matter in sea water. For example, at the cross section from
the Tarawa atoll to the open ocean elevated values of potential microbial
production - up to 83 mg C m -3 - were found at a distance of over 6 km
from the atoll. Further, it decreases to 9 mg C m -3 at a distance of 17 km
(Sorokin 1973c). We may conclude that the highly productive reef ecosystems enrich waters of the surrounding oceanic and shelf waters with
bacterioplankton and with labile organic matter, thus increasing their food
sources, which are used by fish.
3.1.2 Bacteria as Food for Coral Reef Animals
Coral reefs are inhabited by an abundant filtering fauna. Being an important
component of the plankton in reef waters, the bacterioplankton was
supposed to be an important source for its feeding. This was proved
experimentally by Di Salvo (1971b, 1973). He placed dead coral heads
83
in aggregates are of 3-10 ~ sizes. Experiments with reef water samples
filtered through the 1-~ filter to keep out particles and aggregates showed
that in the presence of an inhibitor of microbial growth the aggregates did
not form even in the presence of coral mucus, added as homogeneous
prefiltered solution. But without inhibitor these aggregates formed readily,
especially in samples enriched with glucose, which enhances microbial
growth (Sorokin 1978b). The effect of stimulating their formation by coral
mucus was detected only after 5 days of exposure. Mucus flakes gradually
became inhabited by bacteria, which used them also as a source of nutrition
(Duck low and Mitchell 1979b; Rublee et al. 1980; Paul et al. 1986).
Nevertheless, the formation of aggregates is an immanent feature of
microbial growth and proceeds also without suspended particles or mucus,
which were supposed to be the centers of microbial growth. The aggregates
grew well even in prefiltered water. The aggregation of a significant part of
bacterioplankton makes it accessible for grazing by crude filterers and even
by seizers.
It was shown above that the microbial biomass and production in waters
over the reefs are several times greater than in the surrounding oceanic
waters, especially in oligotrophic regions. The influence of large reefs upon
the abundance of bacterioplankton in oceanic waters was detectable at a
distance of 10-12 km, as it could be seem from Fig. 3.3. The microbial
biomass and also its production will gradually decrease within this interval to
a very low level, but the specific production rates (PIB) will increase. The
latter is connected with the enhanced trophodynamics in pelagic ecosystems
of tropical ocean, as well as with the absence of an additional input of inert
microbial biomass from the sediments, which happens in waters over the
reefs. The enrichments of oceanic waters, in contact with reefs, by the dissolved organic matter could be seen from the elevated values of the potential
microbial production, which is an indirect indicator of the relative abundance
of labile organic matter in sea water. For example, at the cross section from
the Tarawa atoll to the open ocean elevated values of potential microbial
production - up to 83 mg C m -3 - were found at a distance of over 6 km
from the atoll. Further, it decreases to 9 mg C m -3 at a distance of 17 km
(Sorokin 1973c). We may conclude that the highly productive reef ecosystems enrich waters of the surrounding oceanic and shelf waters with
bacterioplankton and with labile organic matter, thus increasing their food
sources, which are used by fish.
3.1.2 Bacteria as Food for Coral Reef Animals
Coral reefs are inhabited by an abundant filtering fauna. Being an important
component of the plankton in reef waters, the bacterioplankton was
supposed to be an important source for its feeding. This was proved
experimentally by Di Salvo (1971b, 1973). He placed dead coral heads