96
Plankton in Coral-Reef Waters
Data on the phytoplankton of Atlantic reefs are still scarce (Glynn 1973;
Hargraves 1982). The latter author colected phytoplankton samples with the
aid of a plankton net 10 and 6011 mesh and recorded in waters up the barrier
reef Belize 73 species of algae. Among them the most numerous were the
diatoms Chaetoceros (16 species) Rhyzosolenia (10 species), Coscinodiscus
(7 species), and the dinoflagellate Triceratium sp.
Thus, an analysis of the taxonomic composition of plankton in reef waters
shows that it is formed by three main components. One is comprised of the
mostly common oceanic or neritic diatom species. Being opportunistic, they
adapt to new reefal environments and start to grow there. This could be
proved by data showing an increase of phytoplankton density in the vicinity
of reefs or in the lagoons (Angot 1968; Sournia and Ricard 1975a).
Sometimes the growth of diatoms in these waters attains a level of
"blooms", as it was found in waters off the reefs of Socotra, the Seychelles
and Kargados-Karahos I. (cf. Table 3.11), and in lagoons of some Pacific
atolls (Michel et al. 1972). The second important contribution to the reefal
phytoplankton is comprised by the periphytonic and benthic microalgae
washed out by waves and tidal currents from bottom biotopes. From this
source it is enriched with large benthic diatoms, filamentous blue-green
algae, and even with fragments of red algae (Glynn 1973a). This washout of
benthic algoflora is a significant phenomenon from the point of view of reef
trophodynamics because it makes available a part of the production of
bottom micro algae for being directly consumed by the benthic filter-feeders
and by zooplankton. Together with the algae there are washings out also of
fregments of filamentous algae and detritus - forming thus the
"pseudoplankton". Its biomass in turbulent zones of reef may exceed the
biomass of the phytoplankton itself (Quasim and Sankaranarayanan 1970;
Johannes and Gerber 1974; Sournia 1977). The pseudoplankton itself .often
prevails in the guts of filtering zooplankters (Gerber and Marshall 1974),
being ingested even by the polyps of corals (Lewis 1977a). Finally, the third
component of the phytoplankton is the wind-driven blue-green algae
mentioned above. It is especially important for such areas as the Coral Sea,
the Timor Sea and other Indonesian seas, the South China Sea, and many
reefs of the western Indian Ocean, where the blooms of Trichodesmium are
an ordinary phenomenon (Chindambaram and Mukundan 1944; Quasim
1970).
3.2.2 Biomass, Production, Chlorophyll
Data on the biomass of phytoplankton in water over the reefs are still
scarce. Most researchers gave their quantitative data in number of cells, but
rarely estimated the biomass of the phytoplankton. Moreover, as mentioned
above, the use of ordinary Utromol sedimentation method leads to the
underestimation of up to 50 or more. As regards the separate groups of the
Plankton in Coral-Reef Waters
Data on the phytoplankton of Atlantic reefs are still scarce (Glynn 1973;
Hargraves 1982). The latter author colected phytoplankton samples with the
aid of a plankton net 10 and 6011 mesh and recorded in waters up the barrier
reef Belize 73 species of algae. Among them the most numerous were the
diatoms Chaetoceros (16 species) Rhyzosolenia (10 species), Coscinodiscus
(7 species), and the dinoflagellate Triceratium sp.
Thus, an analysis of the taxonomic composition of plankton in reef waters
shows that it is formed by three main components. One is comprised of the
mostly common oceanic or neritic diatom species. Being opportunistic, they
adapt to new reefal environments and start to grow there. This could be
proved by data showing an increase of phytoplankton density in the vicinity
of reefs or in the lagoons (Angot 1968; Sournia and Ricard 1975a).
Sometimes the growth of diatoms in these waters attains a level of
"blooms", as it was found in waters off the reefs of Socotra, the Seychelles
and Kargados-Karahos I. (cf. Table 3.11), and in lagoons of some Pacific
atolls (Michel et al. 1972). The second important contribution to the reefal
phytoplankton is comprised by the periphytonic and benthic microalgae
washed out by waves and tidal currents from bottom biotopes. From this
source it is enriched with large benthic diatoms, filamentous blue-green
algae, and even with fragments of red algae (Glynn 1973a). This washout of
benthic algoflora is a significant phenomenon from the point of view of reef
trophodynamics because it makes available a part of the production of
bottom micro algae for being directly consumed by the benthic filter-feeders
and by zooplankton. Together with the algae there are washings out also of
fregments of filamentous algae and detritus - forming thus the
"pseudoplankton". Its biomass in turbulent zones of reef may exceed the
biomass of the phytoplankton itself (Quasim and Sankaranarayanan 1970;
Johannes and Gerber 1974; Sournia 1977). The pseudoplankton itself .often
prevails in the guts of filtering zooplankters (Gerber and Marshall 1974),
being ingested even by the polyps of corals (Lewis 1977a). Finally, the third
component of the phytoplankton is the wind-driven blue-green algae
mentioned above. It is especially important for such areas as the Coral Sea,
the Timor Sea and other Indonesian seas, the South China Sea, and many
reefs of the western Indian Ocean, where the blooms of Trichodesmium are
an ordinary phenomenon (Chindambaram and Mukundan 1944; Quasim
1970).
3.2.2 Biomass, Production, Chlorophyll
Data on the biomass of phytoplankton in water over the reefs are still
scarce. Most researchers gave their quantitative data in number of cells, but
rarely estimated the biomass of the phytoplankton. Moreover, as mentioned
above, the use of ordinary Utromol sedimentation method leads to the
underestimation of up to 50 or more. As regards the separate groups of the