Ryukyu Islands ecology
The Ryukyu Islands, also known as the Nansei Shoto, comprise a subtropical archipelago that stretches approximately 621 miles from Kyushu, Japan, to Taiwan. This region is characterized by diverse climates, with northern islands experiencing temperate conditions and southern islands, including the Yaeyama Islands, situated in a tropical zone. The unique geography of these islands, featuring both coral and volcanic formations, supports a rich array of subtropical vegetation, including mangrove forests and alpine habitats.
Biodiversity in the Ryukyu Islands is notable, with many endemic species such as the Habu snake, Okinawa rail, and Amami rabbit, the latter representing a "living fossil" with a genetic lineage dating back millions of years. The region is also crucial for migratory species, including various birds and nesting sea turtles. However, the ecosystems face significant threats from human activities, climate change, and environmental degradation. These challenges include coral reef damage from sedimentation and nutrient overload, habitat loss due to urbanization, and increased vulnerability of wildlife to invasive species. Conservation efforts are essential to protect the unique ecological heritage of the Ryukyu Islands, which encompasses both land and marine environments.
Subject Terms
Ryukyu Islands ecology
Category: Marine and Oceanic Biomes.
Geographic Location: Pacific Ocean.
Summary: The Ryukyu Archipelago is a biodiversity hot spot, rich in threatened endemic species and abounding in coral reefs.
The Ryukyu Archipelago is a chain of subtropical islands, also known as Nansei Shoto, that runs along the oceanic trench of the same name, and extends for approximately 621 miles (1,000 kilometers) from Kyushu in Japan to the eastern coast of Taiwan. This region, belonging to the Japanese Kagoshima prefecture, is divided into the Satsunan Islands in the north and the Ryukyu Shoto in the south. Amami-oshima and Okinawa-jima are the largest islands of these respective areas.
The climate of the Ryukyu Archipelago is considerably warmer than that of mainland Japan. However, due to the latitudinal gradient separating the islands, differences can be observed. The Satsunan Islands traverse a climatic cutoff, with the northern islands exposed to a temperate climate and the Amami islands subjected to a clear subtropical climate. Similarly, most of the Ryukyu Shoto exhibit subtropical flora, but the southwestern part, encompassing the Yaeyama Islands, is located in a tropical climatic zone.
Yakushima Island here, one of the wettest places on Earth with rainfall totalling as much as 394 inches (10,000 millimeters) per year, exhibits a variety of the climate and flora evident in the Ryukyus. While typical subtropical forests populate the lower slopes of the island, deciduous and coniferous forests such as the millennial yakusugi are located at higher altitudes, and in the surroundings of the Miyanoura-dake peak, reaching 6,348 feet (1,935 meters), alpine habitats can be covered by snow in winter. Overall, the general weather in the Ryukyus is marked by mild winters and hot summers, with high average precipitation. Extreme meteorological conditions can be recorded during the rainy season and the subsequent arrival of typhoons from July to September.
Biodiversity
Most of the 200 islands forming the Ryukyu archipelago are made from coral, and some of them are volcanic, such as Iwo-tori-shima and Suwanose-jima. Their geography is variable, but most of them are hilly or mountainous and covered with dense subtropical vegetation, including mangrove forests in some coastal areas. This allows abundant and diverse wildlife to flourish. The Ryukyus have become an evolutionary shelter for many species. Nowadays, the shelters are home to a large number of endemic (found only here) animals, including the venomous Habu snake, the threatened Okinawa rail, Amami jay, Ryukyu tip-nosed frog, and Ryukyu flying fox.
Moreover, the islands are a natural haven for numerous migratory species. Of the birds found here, 80 percent are non-resident varieties. Ryukyu’s birds include the Amami woodcock, Izu thrush, Japanese paradise flycatcher, Narcissus flycatcher, Okinawa rail, ruddy turnstone, Ryukyu kingfisher, minivet, robin, and Scops owl.
Endangered loggerhead and green turtles use the islands, from which their migration starts, as nesting sites. About half of the island chain’s amphibians are endemic to the islands, including the sword-tail and Anderson’s crocodile newt; and such frogs as Holst’s, Otton, Ishikawa’s, Ryukyu tip-nosed, Namiye’s, and the Kampira Falls frogs. Among the local lizards are Kishinoue’s giant skink and Kuroiwa’s ground gecko.
Living Fossils
Certain animals, such as the Okinawa woodpecker and the Ryukyu long-tailed giant rat, are emblematic of the Ryukyu Islands. The most fascinating ones are probably the so-called living fossils. This oxymoronic term, coined by Charles Darwin, designates a living species that appears similar to one that otherwise is known only from fossils and has no close living relatives. Living fossils typically have endured through the millennia because of their confinement in an area with reduced competition for resources, and they represent unique remnants of the past.
The Amami rabbit is the most renowned illustration of a living fossil in this part of the world, and has become the symbol of the eponymous region. This species is notable for its small ears and sounds it makes to call its extended family members, features that are the result of 10–20 million years of genetic isolation. Although extremely furtive, this dark-furred, short-legged rabbit can be spotted at night on rare occasions. During the day, it sleeps in burrows or caves, making it particularly vulnerable to human activities such as deforestation.
Human activity and other factors, such as road kills, habitat fragmentation, and predation by feral cats and introduced mongooses, have contributed to population declines—leading to the classification of this species as endangered by the International Union for Conservation of Nature.
Environmental Threats
The biota of the Ryukyu Islands is already deeply endangered as much in the coastal waters as on land. The abundant coral reefs, which are part of the World Wildlife Fund’s Global 200 ecoregions, feature the largest colony of blue corals in the world, and are prey to sedimentation and eutrophication, or nutrient-overload and oxygen depletion. While the islands have a low human population and are poorly developed, local agriculture and fisheries, as well as increasing urbanization, have been putting the ecosystems under stress and causing devastating effects on wildlife.
As an island chain, climate change with its associated warming seawater and heavier storms has started delivering detrimental effects on the coral reefs. The prospect for continually rising sea levels, meanwhile, is leading to great concern over flooding and erosion of shoreline habitats. Scientists have been taking steps to prepare for the inevitable effects of climate change by studying how the region’s coral reefs react to warmer ocean temperatures.
Bibliography
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Kerr, George H. Okinawa: The History of an Island People. North Clarendon, VT: Tuttle Publishing, 2000.
Pearson, Richard J. Archaeology of the Ryukyu Islands: A Regional Chronology from 3000 B.C. to the Historic Period. Honolulu: University of Hawaii Press, 1969.
Røkkum, Arne. Nature, Ritual, and Society in Japan’s Ryukyu Islands (Japan Anthropology Workshop Series). London: Routledge, 2006.