Refractory and labile organic carbon in coral reef seawater

Abstract

Coral reef seawater samples from Bora Bay off Miyako Island in Okinawa, Japan were incubated with an initial volume of 20 liters. The degradation of organic carbon in this seawater was monitored for more than three months in dark, unstirred polycarbonate vessels by measuring the concentration of organic carbon in the seawater. The concentration of organic carbon gradually decreased to the background level of the refractory organic matter. The ratio of labile organic carbon to total organic carbon was about 30% in the water within the reef, and 10% in the water outside. The concentration of inorganic nutrients gradually increased with the degradation of the organic matter. In terms of the cell density and cell biomass of bacteria, the doubling rate was initially about twice a day and then declined during the incubation. Rate of degradation of labile organic carbon was about 20mmol C/m2/day in the reef. It was much smaller than the respiration rate reported for the whole coral reef community. This indicates that benthos like corals plays a major role in carbon dynamics in the coral reef. The result that the refractory organic concentration in the reef is lower than that in the outer sea indicates that the coral reef has the role of carbon sink in that organic carbon might be absorbed to the sedimentation particle.