Measurement of oxygen metabolism in open-top aquatic mesocosms: application to a coral reef community

A new experimental and analytical protocol enabling the measurement of the metabolism of aquatic communities in open-top mesocosms is described. It in volves estimation of air-water gas exchange and use of a polynomial regress ion to estimate metabolic parameters from measurements of dissolved oxygen concentration. Sample data is provided for a coral reef community. Its majo r advantage compared to the standard respirometry technique is that the com munity is not subject to great variations of physical and chemical paramete rs such as dissolved oxygen concentration or pH during the experiment. Chan ges in the concentration of dissolved oxygen were measured over 24 h period s and used to derive community gross photosynthesis (P-g) and respiration ( R). Experiments performed on the same community with 2 differents light int ensities (360 and 250 mu mol m(-2) s(-1)) provided consistent estimates of P-g (208 +/- 50 and 73 +/- 20 mmol O-2 m(-2) d(-1)) and R (-219 +/- 55 and -79 +/- 29 mmol O-2 m(-2) d(-1)). The air-water oxygen transfer velocities, K-O2, varied between 34 +/- 5 and 84 +/- 12 cm h(-1). This approach provid ed estimates of community metabolism that are not significantly different f rom those obtained using the standard respirometry technique.