Bacterial decomposition of coral mucus as evaluated by long-term and quantitative observation

Coral mucus released from Acropora formosa and Montipora digitata was incubated with bacteria under dark conditions for 1 year to evaluate the quantitative degradability. All the mucus samples showed a similar decomposition pattern: about 80% of total organic carbon (TOC) in the mucus was mineralized within 1 month, while some mucus was slowly decomposed over the 1 year. Regression analysis using an exponential curve considering three degradability pools (labile, semilabile, and refractory) fitted the changes of the TOC concentrations very well (r (2) > 0.99). Compiling the data on the two coral species, the labile organic C in the coral mucus had mineralization rates of 10-18% d(-1) and accounted for 79-87% of the initial TOC in the mucus. Semilabile organic C had mineralization rates of 0.3-1.6% d(-1) and accounted for 11-18% of the initial TOC. Refractory organic C accounted for 6% at most. These results suggest that not all coral mucus is rapidly decomposed by bacteria but some mucus remains as semilabile and refractory organic matter for several months.