Macroalgae detritus accelerates degradation of recalcitrant organic matter in coastal marine sediments

) between sediment and bottom water in macroalgae-amended and unamended sediment cores showed a clear impact of macroalgae additions, with elevated carbon (C) turnover in these cores. The differences in total DIC release between unamended cores and macroalgae-amended cores were more than 100% and up to 298% of the added macroalgae C. The macroalgae addition, therefore accelerated the degradation of pre-existing organic matter in the sediment. This observation, known as a "priming effect," is well described in soils and freshwater systems but has only recently been considered in marine systems. Results from this experiment suggest that short term priming (<three months) did not depend on the macroalgae species added to the sediment, nor nutrient enrichment of the added tissue. The modification of organic matter in marine sediments, driven by secondary production from degrading macroalgal detritus, as well as the conditions that promote this priming, are poorly understood. These uncertain features of the C cycle are critical for understanding overall C turnover and assessing the C mitigation potential of both cultivated and natural macroalgae populations.