Sulfatase involved in ulvan degradation (PubMed:31285597). 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) (Probable). The sulfatase is most active on ulvan polymers, particularly on xylose-rich ulvan. It can desulfate oligosaccharides containing the motif Rha3S-Xyl2S-Rha3S and thus likely proceeds in an endolytic mode of action, removing sulfates from xylose residues in periplasmic oligosaccharides (PubMed:31285597). Binds 1 Ca(2+) ion per subunit. By ulvan and rhamnose. The conversion to 3-oxoalanine (also known as C-formylglycine, FGly), of a serine or cysteine residue in prokaryotes and of a cysteine residue in eukaryotes, is critical for catalytic activity. This post-translational modification is severely defective in multiple sulfatase deficiency (MSD). Belongs to the sulfatase family. Truncated N-terminus.