The application of pH and pCO2 monitoring to estimating the rates of coral reef community metabolism

In the present study, the applicability of the continuous monitoring of pH and partial pressure of CO2 (pCO2) to the investigations of coral reef community metabolism was examined. Of the four measurable parameters of the aquatic carbonate system, pH, pCO2, total alkalinity (TA), and total inorganic carbon (TIC), only pH and pCO2 could be continuously monitoring. Although the values of TA and TIC calculated from the pH and pCO2 data were not more precise than direct measurements, the continuous monitoring data with high time-resolution were shown to provide good estimations of the changes in CO2-related variables using the least-squares method. A new equation for estimating inorganic carbon metabolism (precipitation and dissolution of CaCO3: g) with an initial value of TA and a simplified equation for estimating organic carbon metabolism (photosynthesis and respiration: p) also helped to minimize the uncertainty. A simulation analysis showed that the standard errors for the calculations of the rates of g and p were less than ±5μmol kg-1 h-1 when pH (±0.005unit) and pCO2 (±2μatm) were monitored at 1-min intervals for 1h; this error is comparable to that of the calculations made using direct measurements of TA (±4μmol kg-1) and TIC (±2μmol kg-1) at the start and end of monitoring. The pH and pCO2 monitoring, tested in the present study at the Shiraho coral reef (Ishigaki Island, Japan), resulted in estimates for g and p that were equivalent to those calculated from TA-TIC direct measurements. The continuous monitoring of pH and pCO2 has been shown both theoretically and experimentally to be adequate for the estimation of coral reef community metabolism.