Dissolved organic matter (DOM) in coastal environments has various origins; one of the most intensely
studied sources is terrestrial DOM input via rivers. On the other hand, contributions from other significant
DOM sources, such as macroalgae, to the coastal DOM pool have not been extensively studied. The
present study quantified the contribution of macroalgae to the DOM pool in the coastal environment
using, firstly, a bag-covering experiment on a brown alga, Ecklonia cava, and identifying fluorescent DOM
components by parallel factor analysis of three-dimensional excitatione emission matrix spectra. Using
the fluorescent DOM as an indicator, we evaluated the horizontal distribution of macroalgal DOM in the
coastal area, showing that the fluorescent DOM component had a synchronous gradient with dissolved
organic carbon (DOC) concentrations along the transect line from the coast to offshore. On the basis of
the correlation between DOC and fluorescent DOM, we evaluated concentrations of DOC originating from
macroalgae, accounting for up to 20% of total DOC concentrations. This implies that in contrast to previous
studies, macroalgae do make a measurable contribution to the coastal DOM pool.