Rhodolith Beach on Udo Island, Jeju

Along the northern coast of Jeju Island, sandy beaches and dunes composed mostly of shell sand are found in many locations. However, the beach on Udo Island in Jeju City is made up not of shell sand but of rhodolith sand, or rhodoliths, nodules formed by coralline red algae, giving it very important academic value. The rhodoliths that make up the Udo beach vary greatly in diameter, ranging from around 1cm to 5–8cm. The rhodolith beach that has developed along the Udo coastline is about 300m long and 15m wide, and it presents a striking contrast with the black basalt found in the area. It was formerly mistakenly known as a "coral sand beach", but it has recently been established that the sediment making up the beach consists of rhodoliths. The red algae living along the Udo coast are a type of calcareous algae that photosynthesise and deposit calcium carbonate in and between their cell walls; they are usually 4–5cm in diameter, generally spherical in shape, with an uneven, bumpy surface. The internal tissue and reproductive organs of the rhodoliths are usually well preserved. Overseas, rhodoliths have been reported in various regions, including Florida and the Bahamas in the United States, and are mainly observed around reefs. However, cases in which rhodoliths form the main constituent sediment of a beach, as at Udo, are very rare, giving the site high academic value.

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Where it is

Region

Jeju City, Jeju

Designation

Natural Monument · 천연기념물