Release and microbial degradation of dissolved organic matter (DOM) from the macroalgae Ulva prolifera

Release and microbial degradation of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) from the macroalgae Ulva prolifera were studied in laboratory incubation experiments. The release of DOM and CDOM from Ulva prolifera was a rapid process, and hydrolysis played an important role in the initial leaching of the organic compounds from the algae. Bacterial activity enhanced the release of DOM and CDOM during degradation of the algae and utilization of the released organic compounds. It is calculated that 43 ± 2% of the C and 63 ± 3% of the N from Ulva prolifera's biomass were released during the 20-day incubation, and 65 ± 3% of the released C and 87 ± 4% of the released N were utilized by bacteria. In comparison, only 18 ± 1% of the algae's C and 17 ± 1% of its N were released when bacterial activities were inhibited. The fluorescence characteristics of the CDOM indicate that protein-like DOM was the major organic component released from Ulva prolifera that was highly labile and biodegradable. Bacteria played an important role in regulating the chemical composition and fluorescence characteristics of the DOM. Our study suggests that the release of DOM from Ulva prolifera provides not only major sources of organic C and N, but also important food sources to microbial communities in coastal waters.