Alpha-L-rhamnosidase involved in ulvan degradation. Ulvan is the main polysaccharide component of the Ulvales (green seaweed) cell wall. It is composed of disaccharide building blocks comprising 3-sulfated rhamnose (Rha3S) linked to D-glucuronic acid (GlcA), L-iduronic acid (IduA), or D-xylose (Xyl). The enzyme is able to degrade p-nitrophenyl-alpha-L-rhamnopyranoside (PNP-Rha) in vitro. Incubating the enzyme with the products obtained after degradation with ulvan lyase and beta-glucuronyl hydrolase (i.e. the trisaccharides beta-alpha-L-Rha3S-IduA-Rha3S and beta-alpha-L-Rha3S-GlcA-Rha3S) showed no degradation, suggesting that the enzyme is active on neutral rhamnose and that desulfation of the oligosaccharide must be achieved before cleavage of rhamnose. Hydrolysis of terminal non-reducing alpha-L-rhamnose residues in alpha-L-rhamnosides. Belongs to the glycosyl hydrolase 78 family.