The oxygen microenvironment adjacent to the tissue of the scleractinian Dichocoenia stokesii and its effects on symbiont metabolism |
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Authors: | D J Gardella P J Edmunds |
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Institution: | (1) Department of Biology, California State University, 1811 Nordhoff Street, Northridge, California 91330, USA Fax: 001 (0) 818 677-2034 e-mail: peter.edmunds@csun.edu, US |
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Abstract: | The biology of symbiotic scleractinians is profoundly influenced by their intracellular zooxanthellae, and many studies have
focused on the mechanistic basis of this influence. This has usually been accomplished by examining the metabolism of zooxanthellae
under physical conditions measured in the open reef and assumed to be similar to conditions in hospite. Recent advances in the measurement of conditions near and within coral tissue suggests that this assumption may result in
substantial errors. To address this possibility, the role of water flow in determining oxygen saturation adjacent to the tissue
of Dichocoenia stokesii was investigated, and the effect of these measured oxygen saturations on the respiration and photosynthesis of zooxanthellae
isolated from the same species was quantified. Using a microelectrode (700 μm diam), we measured oxygen saturations above
(≤4 mm) the tissue in two flow speeds over 24 h periods in a flume receiving sunlight at in situ levels. The results were
used as a proxy for ecologically relevant intracellular oxygen saturations, which were applied to zooxanthellae in vitro to
assess their effect on symbiont metabolism. Microenvironment oxygen saturations (% air saturation) ranged from 74–159% in
slow flow (2.7 cm s−1) to 88–110% in faster flow (7.5 cm s−1) over day–night cycles. Therefore, the metabolic rates of zooxanthellae were measured at 50 to 54% (hypoxia), 98 to 102%
(normoxia) and 146 to 150% (hyperoxia) oxygen saturation. Oxygen saturation significantly affected the metabolism of zooxanthellae,
with gross photosynthesis increasing 1.2-fold and dark respiration increasing 2-fold under hyperoxia compared to hypoxia.
These results suggest that the metabolism of zooxanthellae in hospite is affected markedly by their microenvironment which, in turn, is influenced by flow-mediated mass transfer.
Received: 13 July 1998 / Accepted: 30 April 1999 |
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