The marine Flavobacterium Formosa agariphila KMM 3901T is able to use a broad range of different carbohydrates as growth substrates. This is reflected in the strain’s repertoire of 13 polysaccharide utilization loci (PUL) in total. One PUL – termed as PUL H – is responsible for ulvan degradation, which is a widely distributed, algal-derived polysaccharide. The PUL comprises almost 40 genes, coding for transporters, lyases, glycoside hydrolases or sulfatases, among others. These proteins catalyse the breakdown of ulvan or the uptake of degradation products. A combined application of isotope labeling, subcellular protein fractionation and quantitative proteomics revealed that corresponding PUL encoded proteins were substrate specific up-regulated in ulvan-cultivated cells. The sulphated polysaccharide ulvan also induced the specific expression of proteins necessary for subsequent monosaccharide degradation. Compared to a control (fructose-cultivated cells), expression of PUL H additionally responded to rhamnose, a basic component of ulvan, indicating that this monosaccharide might signal ulvan availability in the environment. Our proteome analyses proofed a substrate specific expression of proteins involved in ulvan utilization and allowed us to deduce a comprehensive degradation pathway for this complex marine polysaccharide.