Population Dynamics of Symbiotic Zooxanthellae in the Coral Pocillopora damicornis Exposed to Elevated Ammonium [(NH4)2 SO4] Concentrations
Population Dynamics of Symbiotic Zooxanthellae in the Coral Pocillopora damicornis Exposed to Elevated Ammonium [(NH4)2 SO4] Concentrations
Date
1994-07
Authors
Hoegh-Guldberg, Ove
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University of Hawaii Press
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Abstract
Division synchrony and growth rate of symbiotic zooxanthellae
was investigated for populations living in colonies of the reef-building coral
Pocillopora damicornis (Linnaeus) exposed to different concentrations of ammonium
[(NH4)2S04] in seawater. Presence of low concentrations of ammonium
(0.2 uM) did not affect (compared with corals growing in ammoniumstripped
seawater) either division synchrony or growth rate. Exposure to higher
concentrations of ammonium (20 or 50 uM), however, affected the population
dynamics of the zooxanthellae residing in P. damicornis. Zooxanthellae in
corals exposed to 20 uM ammonium had mitotic indices (percentage of total
cells dividing) that were two to three times higher than mitotic indices of
zooxanthellae in control (0.2 uM) corals. Although division of zooxanthellae
was still phased in corals exposed to 20 uM ammonium, there were many more
cells dividing out of phase compared with control corals. Division of zooxanthellae
in corals exposed to 50 uM was not phased. Calculated growth rates
of zooxanthellae exposed to 20 or 50 uM ammonium were higher than those
representative of zooxanthellae living in control corals, although growth rate of
both carbon and nitrogen pools was lower in 50 uM as compared with 20 uM
ammonium. These data support the conclusion that the population dynamics of
symbiotic zooxanthellae within P. damicornis are affected by concentrations of
ammonium in seawater that are equal to or higher than 20 uM and that 50 uM
ammonium concentrations may be toxic to some extent. These data taken in
isolation, however, do not constitute an effective test of the hypothesis that
zooxanthellae are limited by the supply of ammonium under ambient conditions
and further emphasize the importance of enrichment studies concentrating
on growth and nitrogen incorporation rates measured for the entire
symbiotic association.
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Hoegh-Guldberg O. 1994. Population dynamics of symbiotic zooxanthellae in the coral Pocillopora damicornis exposed to elevated ammonium [(NH4)2 SO4] concentrations. Pac Sci 48(3): 263-272.
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