Kurokizuta is a southern type of seaweed that is found in shallow water around the Oki Islands. It is named after the place it was first discovered by the botanist Kintaro Okamura in 1910. This was in the shallow water in front of Kurogi-gosho (Kurogi Imperial Residence) in Nishinoshima. At the time, the species had only been found in the Red Sea of the Arabian Peninsula and around the Dōzen Islands. In recognition of this, in 1992 kurokizuta habitats in Nishinoshima Town and Ama Town were designated Natural Monuments of Japan.
Later on, the species was also found in the tropical-subtropical areas of the Indian Ocean and the Atlantic Ocean, as well as around Aichi Prefecture and Kochi Prefecture in Japan. However, these days places it can be found in Japan are in decline due to environmental degradation.
Kurokizuta has been discovered in 13 different habitats around the coast of the Oki Islands. Out of 1,300 different species of seaweed, only the habitat of kurokizuta has been designated a Natural Monument of Japan.