Continuous measurements of net production over a shallow reef community using a modified Eulerian approach

We made continuous measurements of the flux of dissolved oxygen over an algal-dominated reef flat community on the Kaneohe Bay Barrier Reef, Hawaii as a proxy for the net production (NP) of organic carbon. Fluxes were calculated from measurements of dissolved oxygen and current profiles taken from moored oxygen sensors and acoustic Doppler current profilers (ADCPs) located at points defining the vertices of a triangular control volume 250 m in length on each side. Surface cruciform drifters as well as dye patches were tracked across the control volume to get independent measurements of Lagrangian currents. While the dye patch speeds were highly correlated with the depth-averaged current speeds calculated from ADCP data on a 1: 1 basis (r(2) = 0.86, n = 24), drifter speeds exceeded both dye and calculated current speeds by 30-100% on average. Measurements of dissolved oxygen sampled within the dye patches as it propagated across the study site were used to calculate NP following a Lagrangian approach. Lagrangian estimates of NP were highly correlated with Eulerian estimates of NP on a 1: 1 basis (r(2) = 0.81, n = 7). Ratios of community production and community respiration varied from 0.7 to 1.4 on a daily basis, but approached a value of 1.0 when integrated over the entire data record.