Oxygen metabolism of intertidal oyster reefs measured by aquatic eddy covariance

Oyster reef restoration is pursued at numerous places worldwide, yet little is known about how ecosystem function changes as these reefs develop. In this study, we used the noninvasive aquatic eddy covariance technique to measure the in situ oxygen flux of 4 intertidal sites on the Virginia (USA) coast: a natural oyster reef, 2 restoration reefs, and a mudflat. Oyster densities of the 3 reefs were 350, 295, and 186 oysters m(-2). Mean summer values of nighttime oxygen flux (FluxDARK) were -488,-428,-300, and-56 mmol m(-2) d(-1) over the natural reef, 2 restoration reefs, and mudflat, respectively. All 4 sites had smaller daytime vs. nighttime oxygen uptake, with mean summer differences between FluxDARK and FluxLIGHT of 360, 250, 239, and 27 mmol m(-2) d(-1). Light was an important short-term driver of daytime reef oxygen flux due to its effect on microalgal photosynthesis. All 3 oyster reefs were significantly heterotrophic, with summer net ecosystem metabolism values ranging from -157 to -298 mmol m(-2) d(-1). FluxDARK values were similar across the 3 reefs when normalized by density, with values between -1.8 and -2.3 mmol m(-2) d(-1) oyster(-1). This study represents the most detailed measurements to date of in situ oyster reef oxygen flux, and shows that benthic microalgae can significantly impact reef oxygen dynamics. FluxDARK values scale with oyster density, and consequently can be used as a metric for reef restoration success.