The contribution of macroalgae to the coastal dissolved organic matter pool

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 excitation–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.