 Historically , Lihou was an important location for a commercially significant industry based around the harvesting of seaweed ( or <unk> in the local language , <unk> ) . Records suggest considerable activity as early as the beginning of the nineteenth century . The value of the seaweed as a fertiliser was so great that in 1815 <unk> Le Marchant , lieutenant bailiff of Guernsey and owner of Lihou , initiated a court case to prevent islanders from drying seaweed on the beaches of Lihou . The case eventually led to new regulations issued in 1818 by the Bailiwick legislature , known as the Chief Pleas at the time , based on a review of ancient royal decrees . However , the Royal Court of Guernsey ruled in favour of the islanders in 1821 , with the effect that permission to harvest seaweed on Lihou was granted to inhabitants of the parishes of St Peters and St <unk> . More than a century later , in 1927 , a factory was established on the island to produce iodine from the seaweed . 
