Pacific Science Volume 48, Number 3, 1994
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Pacific Science is a quarterly publication devoted to the biological and physical sciences of the Pacific Region.
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ItemRatio of Energy and Nutrient Fluxes Regulates Symbiosis between Zooxanthellae and Corals(University of Hawaii Press, 1994-07)Ambient irradiance levels determine the rate of carbon influx into zooxanthellae at any given time, and thereby the energy available for the whole coral symbiotic association. Long-term photoacclimation of zooxanthellae to the time-averaged light regime at which the host coral grows results in optimization of light harvesting and utilization. Under high irradiance light harvesting is reduced, thereby avoiding photodynamic damage, whereas under low light, photon capture and quantum yield are maximized. Most of the photosynthate produced by the algae is respired. However, the capability of the zooxanthellae and the coral to retain carbon beyond that required to meet their respiratory needs depends on the availability of the commonly limiting nutrients, nitrogen and phosphorus. Therefore, the ratio of the flux of these nutrients into the colony to that of the photosynthetically driven carbon flux will regulate the growth of the zooxanthellae and of the animal. Nutrients acquired by predation of the coral on zooplankton are available first to the animal, whereas those absorbed by the zooxanthellae from seawater as inorganic compounds lead first to growth of the algae.
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ItemResource Partitioning by Reef Corals as Determined from Stable Isotope Composition II. 15N of Zooxanthellae and Animal Tissue versus Depth(University of Hawaii Press, 1994-07)The pattern of resource partitioning versus depth for corals collected in February, 1983, from Jamaica was investigated by analyzing their stable nitrogen isotope composition. Observations were made on isolated zooxanthellae and corresponding algae-free animal tissue from nine species of symbiotic corals at four depths over a 50-m bathymetric range, and from a nonsymbiotic coral at 1 m. 5 15N values versus depth ranged from +3.54 to -2.15 %0 for zooxanthellae and from +4.71 to +0.23 %0 for animal tissue. In those species that occurred over a 30- to 50-m depth range, both animal tissue and zooxanthellae tended to be depleted in 15N as depth increased to 30 m. In a few species animal tissue was enriched in 15N from 30 to 50 m. Depletion of 15N in zooxanthellae with increasing depth may be the result of depth-dependent differences in their nitrogen-specific growth rates. Animal tissue was consistently more depleted in 15N than for the nonsymbiotic coral Tubastrea coccinea (Ellis) at the same depth, but it was still slightly more enriched in 15N than corresponding zooxanthellae in 16 of 25 paired samples. The latter trend was not correlated with depth. A comparison of 5 13C and 5 15 N for zooxanthellae and animal tissue over 50 m revealed a tendency toward depletion of heavy isotopes as depth increases. Increased carbon fixation appears to be accompanied by decreased nitrogen fractionation.
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ItemEffects of Water Velocity on Respiration, Calcification, and Ammonium Uptake of a Porites compressa Community(University of Hawaii Press, 1994-07)Colonies of Porites compressa Dana were placed in a 10-m-long flume to form a community of coral. Ammonium uptake (N uptake) rate, respiration rate, and calcification rate were measured at different water velocities, ranging from 1 to 57 cm sec-1. N uptake was proportional to concentration from 20 to 0.15 uM N. The first-order rate constant for N uptake varied from 6.8 to 15.6 day-1, only an average of 2.1 times over a l0-fold change in water velocity. First-order rate constants for respiration were less than those for N uptake and ranged from 4.8 to 6.6 day-1. Respiration rate and calcification rate were not correlated with water velocity. The relative turnover of N compared with oxygen (O2) indicates that 94-98% of N flux must be retained within this coral community.
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ItemEffect of Ammonium-supplemented Seawater on Glutamine Synthetase and Glutamate Dehydrogenase Activities in Host Tissue and Zooxanthellae of Pocillopora damicornis and on Ammonium Uptake Rates of the Zooxanthellae(University of Hawaii Press, 1994-07)Host glutamine synthetase activity decreases in Pocillopora damicornis (Linnaeus) following exposure of the coral to seawater containing elevated ammonium (20 uM). Zooxanthellae isolated from these corals exhibited lower ammonium uptake capacity and glutamine synthetase activity compared with those from the control corals. Ammonium concentration of the surrounding seawater had no effect on the NADPH-dependent glutamate dehydrogenase activity in the host.
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ItemEffect of Ammonium Enrichment on Respiration, Zooxanthellar Densities, and Pigment Concentrations in Two Species of Hawaiian Corals(University of Hawaii Press, 1994-07)Small branch tips or "nubbins" of two species of Hawaiian corals, Pocillopora damicornis (Linnaeus) and Montipora verrucosa Vaughan, were exposed to four ammonium concentrations, ammonium-stripped < 2 uM), ambient (~2 uM), and two enriched (20 uM and 50 uM) in microcosm tanks. Nubbins represent replicates of a single coral colony. We examined the effect of ammonium enrichment on zooxanthellar densities, pigment concentrations, and respiration rates of the nubbins. Nubbins of both P. damicornis and M. verrucosa showed a trend of increased pigment concentration with elevated ammonium concentration. Pocillopora damicornis increased from 9.3 ug chlorophyll a cm-2 in the ammonium-stripped treatment to 24.8 ug cm-2 in the 50-uM ammonium treatment. Similarly, M. verrucosa increased from 1.9 to 19.4 ug chlorophyll a cm-2. There were no significant differences in algal densities, pigment concentrations per cell, pigment ratios, or respiration rates.