The invention relates to a method for production of biogas comprising anaerobic digestion of water living organisms from the group Ascidiacea. The invention also relates to culture and harvest of ascidians before anaerobic digestion. Further comprised is an integrated culture of ascidians and macroalgae before anaerobic digestion. The invention also comprises utilization of solid and fluid digestate from the anaerobic digestion for production of fertilizer. The invention also comprises a method for artificial seeding of ascidians in larval stage and anaerobically digested biomass obtained by anaerobic digestion of ascidians.
