Ballast Island (Japan)
![Small boats near the coast of a sandy islet](http://upload.wikimedia.org/wikipedia/commons/thumb/b/bb/%E3%83%90%E3%83%A9%E3%82%B9%E5%B3%B6_-_panoramio.jpg/220px-%E3%83%90%E3%83%A9%E3%82%B9%E5%B3%B6_-_panoramio.jpg)
Ballast Island, also known as Barasu Island (Japanese: バラス島, romanized: Barasu-shima), is a small uninhabited coral island or cay in the Yaeyama chain off the coast of mainland Japan, located between the islands of Iriomote and Hatoma. The island sits at the center of a coral reef composed primarily of species of the stony coral genus Acropora, most numerously Acropora muricata. At least four goby species have been found at the island, as well as a specimen of the moray eel Gymnothorax ryukyuensis.
Two small islets on the site had formed by the 1960s. A mass bleaching of the reef's corals from July to September 1998 led to the merging of the two islets, accelerated by the impact of several typhoons in 1998 and 1999. Ballast Island reached a maximum land area of around 10,000–20,000 square metres (2.5–4.9 acres) in late 1999, before steadily declining over the following years. As of 2016[update], the island had a surface area of around 2,000–2,400 square metres (0.5–0.6 acres), a size it has maintained since 2009. While uninhabited, the island is visited on snorkeling tours departing from Iriomote, allowing access to the surrounding coral reefs.
Geography
[edit]![An underwater photograph of spiky branched coral](http://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Acropora_muricata_%28formosa%29.jpg/220px-Acropora_muricata_%28formosa%29.jpg)
Ballast Island is a small cay in the Yaeyama Islands, lying at the center of an isolated coral reef. The island measures approximately 200 meters (660 ft) in length, and ranges between 20–30 meters (66–98 ft) in width. The island lies south of Hatoma and approximately 2.5 kilometres (1.6 mi) northeast of the coast of Iriomote.[1][2] As of 2016, the island measures 2,000–2,400 square metres (0.5–0.6 acres) in area.[3]
Biology
[edit]Coral
[edit]The island is primarily composed of more than 90% coral gravel, mainly branch particulates from the stony coral genus Acropora, with fragments reaching sizes of up to 10 centimetres (4 in). The reef on which Ballast Island sits, described as "butterfly-shaped", stretches 300–600 meters (980–1,970 ft) from Ballast Island's shoreline. The edges of the reef have the greatest density of coral, featuring various Acropora species. On the eastern side of the reef, Acropora muricata covers around 40% of the surface, with smaller amounts covered by the species A. hyacinthus, A. cytherea, and A. intermedia. On the western side of the reef, A. intermedia, A. muricata, and A. aspera make up the majority of reef cover.[4]
Fish
[edit]Multiple species of fish are known from Ballast Island. A holotype and several paratypes of the goby Gobiodon aoyagii were collected at the island throughout the 1990s, alongside specimens of Gobiodon erythrospilus and Cabillus pexus.[5][6] A paratype of Eviota filamentosa, the threadfin dwarfgoby, was found at the eastern reef.[7] An individual of the moray eel species Gymnothorax ryukyuensis was found at Ballast Island in 1982.[8]
History
[edit]![The end of a long sandy cay, with a seaplane parked nearby](http://upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Barasu_Island_near_Iriomote_Island_2.jpg/220px-Barasu_Island_near_Iriomote_Island_2.jpg)
Local accounts describe islands existing at its present location since at least the 1960s, although subject to considerable changes in shape and terrain due to typhoons and the yearly monsoons.[1] Ballast Island was initially divided into two smaller islets in an east–west arrangement, with a combined land area ranging from 470–2,700 square metres (5,100–29,100 sq ft).[4] The name Ballast Island refers to the island's gravelly composition, resembling ships' ballast.[9]
A large-scale bleaching event struck the reef's corals from July to September 1998, leading to the accumulation of dead coral over the following seasons. The land area above water rose sharply by early 1999 as two smaller islets coalesced to form Ballast Island. Three typhoons in 1998 and 1999 may have contributed to the rapid accumulation of coral on the island. The island reached its largest size in November 1999, around 10,000–20,000 square metres (2.5–4.9 acres), before steadily declining in area over the following years.[10] The island had declined to around 5,400–7,700 square metres (1.3–1.9 acres) by 2001, likely due to sediment dispersal in the surrounding water. It maintained an area ranging from 4,700–7,700 square metres (1.2–1.9 acres) throughout the 2000s, before declining to 2,000–2,400 square metres (0.5–0.6 acres) in 2009, remaining around this size since.[3]
Snorkeling tours, departing from Iriomote, take place around Ballast Island and Hatoma.[11]
References
[edit]![](http://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
Citations
[edit]- ^ a b Kayanne et al. 2016, p. 85.
- ^ Tajima 2018, p. 1.
- ^ a b Kayanne et al. 2016, pp. 90–91.
- ^ a b Kayanne et al. 2016, p. 87.
- ^ Shibukawa, Suzuki & Aizawa 2013, pp. 147–150.
- ^ Shibukawa & Aizawa 2013, p. 141.
- ^ Suzuki & Greenfield 2014, pp. 36–37.
- ^ Hatooka 2003, p. 8.
- ^ "エメラルドグリーンの海に浮かぶ、地図にない"幻の島"へ――沖縄、バラス島". JAL Skyward Plus (in Japanese). July 30, 2021. Archived from the original on February 29, 2024. Retrieved February 28, 2024.
ちなみに「バラス」というのは船や気球の重心を安定させるために積む砂利などの重しや、線路の枕木の安定のために敷く小石などを指す「バラスト」から転じた言葉で、砂利や砕石の呼び名。
- ^ Kayanne et al. 2016, pp. 89–90.
- ^ Ichihashi, Aya (October 2, 2019). "Treasures on land, in sea make inhabited Okinawan island of Iriomote a rare jewel". Stars and Stripes. Archived from the original on March 3, 2024. Retrieved March 3, 2024.
Bibliography
[edit]- Kayanne, Hajime; Aoki, Kenji; Suzuki, Takuya; Hongo, Chuki; Yamano, Hiroya; Ide, Yoichi; Iwatsuka, Yuudai; Takahashi, Kenya; Katayama, Hiroyuki; Sekimoto, Tsunehiro; Isobe, Masahiko (14 July 2016). "Eco-geomorphic processes that maintain a small coral reef island: Ballast Island in the Ryukyu Islands, Japan". Geomorphology. 271: 84–93. Bibcode:2016Geomo.271...84K. doi:10.1016/j.geomorph.2016.07.021. Archived from the original on 27 February 2024. Retrieved 27 February 2024 – via ScienceDirect.
- Tajima, Yoshimitsu (2018). "Numerical Study on Accumulation Mechanism on Coral Gravels Around Ballast Island, the Coral Cay off the Coast of Iriomote Island". Coastal Engineering. 1 (36): 93. doi:10.9753/icce.v36.sediment.93. Archived from the original on 2024-02-27. Retrieved 2024-02-27.
- Suzuki, Toshiyuki; Greenfield, David W. (2014). "Two new dwarfgobies from the Ryukyu Islands, Japan: Eviota shibukawai and Eviota filamentosa (Teleostei: Gobiidae)" (PDF). Journal of the Ocean Science Foundation. 11. Archived (PDF) from the original on 2023-12-24. Retrieved 2024-03-03.
- Shibukawa, Koichi; Suzuki, Toshiyuki; Aizawa, Masahiro (August 22, 2013). "Gobiodon aoyagii, a New Coral Goby (Actinopterygii, Gobiidae, Gobiinae) from the West Pacific, with Redescription of a Similarly-colored Congener Gobiodon erythrospilus Bleeker, 1875" (PDF). Bulletin of the National Museum of Nature and Science Series A. 39 (3). Archived (PDF) from the original on June 16, 2022. Retrieved March 3, 2024.
- Shibukawa, Koichi; Aizawa, Masahiro (August 22, 2013). "Cabillus pexus, a New Marine Goby (Teleostei, Gobiidae) from Amami-oshima Island, Ryukyu Islands, Japan" (PDF). Bulletin of the National Museum of Nature and Science Series A. 39 (3). Archived (PDF) from the original on March 3, 2024. Retrieved March 3, 2024.
- Hatooka, Kiyotaka (March 31, 2003). "A new moray eel, Gymnothorax ryukyuensis, from the Western Pacific Ocean (Anguilliformes: Muraenidae)" (PDF). Bulletin of the Osaka Museum of Natural History (57). Archived (PDF) from the original on March 3, 2024. Retrieved March 3, 2024.