Abstract
Phosphate uptake (P-uptake) into coral reef communities has been hypothesized to be mass-transfer limited. One method of demonstrating mass-transfer limitation of P-uptake is to show dependence of P-uptake on water velocity. Water velocity across reef flats varies with tides and swell; thus, we measured P-uptake over the entire reef flat on eight different days, representing a range in water velocities. P-uptake was calculated from changes in P concentration of the water column. Changes in P concentration were measured by water sampling at six sites along a 300-m cross-reef transect while simultaneously measuring water velocity. To smooth the variability in phosphate concentrations, peristaltic pumps were used to get time-integrated water samples for 4–6 h at each site. Water velocities were measured in the middle of the transect using an acoustic Doppler current profiler and were averaged to match the time-integrated water sampling. Depth-averaged cross-reef water velocities were 0.031 ± 0.013 m s−1 (mean ± SD), while the root-mean-square water velocities, accounting for oscillatory flow, averaged 3.3 times higher, 0.101 ± 0.021 m s−1 (mean ± SD). Phosphate decreased along all transects. The first-order rate constant for P-uptake (S) was 8.5 ± 2.4 m d−1 (mean ± SD) and increased linearly with root-mean-square water velocity. The Stanton number derived from oscillatory flow, the ratio of the first-order rate constant for P-uptake to the root-mean-square water velocity (S/U rms), was (9.4 ± 1.2) × 10−4 (mean ± SD). P-uptake ranged from 0.2 to 1.1 mmol P m−2 d−1, demonstrating that P-uptake is variable on short time scales and is directly related to P concentration and water velocity.
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Acknowledgments
We acknowledge the Regional Council of La Réunion Island (ITUE Program) and the US National Science Foundation Award #: OCE04-53117. We also thank the RunSeaScience program, funded by European Union, for awarding a postdoctoral fellowship to E. Cordier.
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Communicated by Guest Editor Dr. Clifford Hearn
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Cuet, P., Pierret, C., Cordier, E. et al. Water velocity dependence of phosphate uptake on a coral-dominated fringing reef flat, La Réunion Island, Indian Ocean. Coral Reefs 30 (Suppl 1), 37–43 (2011). https://doi.org/10.1007/s00338-010-0712-4
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DOI: https://doi.org/10.1007/s00338-010-0712-4