Metabolism of a tide-dominated reef platform subject to extreme diel temperature and oxygen variations

Benthic dissolved oxygen fluxes were measured on the reef flat of Tallon Island, an intertidal reef platform in the Kimberley region of northwestern Australia, for periods of 2 weeks in the wet and dry seasons. This reef flat is strongly tidally forced by semidiurnal tides (spring range > 8 m) and experiences highly asymmetric water level variability, with ebb durations lasting similar to 10 h; this results in diel variations in water temperature and dissolved oxygen (DO) concentration (up to similar to 11 degrees C and 440 mu M, respectively) that are among the most extreme recorded for reefs worldwide. Given the consistent tidal flow patterns, a one-dimensional control volume approach was used to make continuous Eulerian measurements of net production and community respiration from observed changes in DO within two zones: an inner zone dominated by seagrass and an outer zone dominated by macroalgae. Community respiration (R) was controlled primarily by DO concentration; however, fluxes approached the limits of DO mass transfer at low flow speeds. Estimates of gross primary production (P) suggested that reef communities were able to fix carbon at rates comparable to other tropical seagrass and mixed reef flat communities despite short-term (similar to hours) extremes in light (up to 1800 mu mol m(-2) s(-1)) and temperature (> 35 degrees C). Daily net community production fluctuated between net autotrophy and heterotrophy over a similar to 15 d period depending on the phase difference between the solar and tidal cycles but was nonetheless metabolically balanced on time scales greater than weeks (P : R = 1.0-1.1).