The present invention notably relates to ulvan lyases, to nucleic acid sequences coding for these ulvan lyases, to vectors comprising these coding sequences, to a method of manufacturing these ulvan lyases, as well as to a method of degrading ulvans using these ulvan lyases and applicable applications to the degradation products of the ulvans. The ulvan lyases of the present invention, or ulvanolytic protein, are notably defined as proteins of 30 or 46 kD comprising the following four sequences in their peptide sequence: PNDPNLK, LLEVGNTGTFGSTGS, DLANPDNV and WNLPE.