Flora and Fauna of the Oki Islands | Unique Ecosystem | Oki Islands UNESCO Global Geopark

Unique Creatures Found in the Oki Islands

Oki became islands about 10,000 years ago, but this is still a short period of time when compared with Sado Island and Tsushima Island, which are also located in the Sea of Japan. Unique creatures whose evolutionary process can be observed live here in Oki, the "young islands."

Oki Salamander

Oki salamander (Hynobius okiensis) is a small endemic salamander, found only on Dōgo Island.
It is an endemic species with rare and unique features.

Nature Site: Oki Salamander Habitat, Nakatani

Oki Dandelion

Oki dandelion (Taraxacum maruyamanum) is one of the endemic species that can be seen in many places on the Oki Islands. It is one of the endemic dandelions of Japan, and it can be distinguished from the common dandelion by looking at the calyx (sepal).

Oki Islands Treasure: Oki Dandelion

Japanese Dormouse

The Japanese dormouse (Glirulus japonicus), which lives in the mountains on Dōgo Island, is a small mammal which is designated as a Natural Monument of Japan. It is known for its unusual feature of hibernation by lowering its body temperature to almost the same as the temperature of the air outside its nest.

Unique Vegetation of the Oki Islands

There is no need to visit special locations; you can observe mysterious vegetation right along the coastal paths on the islands. For example, rugosa rose (Rosa rugosa) from the north, Nagoran orchid (Sedirea japonica) from the south, the alpine plant Japanese thuja (Thuja standishii), and the Asian fawnlily (Erythronium japonicum) from the ice age coexist harmoniously along the shore.
Here are a few notable locations where the mysterious plant distribution can be observed.

Vegetation at Kasuganohama Beach

The characteristic features of the Oki Islands' vegetation distribution can be observed near Kasuganohama Beach in the Fuse area, which is located in the northeast of Dōgo Island. Plants originally inhabiting very different habitats can be seen growing in the same place.

The southern Nagoran orchid (Sedirea japonica) can be seen growing on the Japanese black pines (Pinus thunbergii) on the grounds of Kasuga Shrine, which is located near the shore. Shrubs of the montane plant Oki rhododendron (Rhododendron japonoheptamerum var. okiense) are growing near the lower trunks of the black pines. In addition, the northern rugosa rose (Rosa rugosa) and continental climate plants such as tōteiran speedwell (Veronica ornata), mitsuba-iwagasa meadowsweet (Spiraea blumei var. obtusa), and bitchiu viburnum (Viburnum carlesii var. bitchiuense) can be seen growing naturally along the coast, just across the road.

Vegetation Along the Kumi Coast

The mysterious distribution of plants can be observed in two locations here at Kumi Coast; at the riverbank (Funaoroshi) which is just outside the village and at the observation deck of Rōsoku-jima (Candle Island). At Funaoroshi, subalpine plants such as Japanese thuja (Thuja standishii), fringed galax (Schizocodon soldanelloides var. soldanelloides), the montane plant mizunara oak (Quercus crispula), the northern mono maple (Acer pictum subsp. mono), the southern Japanese cheesewood (Pittosporum tobira), the continental climate plant mitsuba-iwagasa meadowsweet (Spiraea blumei var. obtusa), and yokoguranoki tree (Berchemiella berchemiaefolia) can be observed growing closely together.
In addition, oriental chive (Allium schoenoprasum var. orientale), a plant that survived the ice age, grows naturally in the area along with other plants such as the southern Yeddo hawthorn (Rhaphiolepis umbellata), Japanese cheesewood (Pittosporum tobira), and the continental climate plant seashore spatulate aster (Aster spathulifolius).

Oki Islands Treasure: Plants at Kumi Coast

Vegetation Along the Okutsudo Coast

At Okutsudo Coast, which is located in the southwest of Dōgo Island, the mysterious mixture of plants growing together can be easily be observed, such as the northern mono maple (Acer pictum subsp. mono), Japanese lime (Tilia japonica), the yuzuriha shrub (Daphniphyllum macropodum), the southern Japanese cheesewood (Pittosporum tobira), the subalpine fringed galax (Schizocodon soldanelloides var. soldanelloides), the continental climate plant seashore spatulate aster (Aster spathulifolius), and mitsuba-iwagasa meadowsweet (Spiraea blumei var. obtusa). The reason behind such distribution is yet to be fully explained. Since there are a few examples where plant distribution of such a characteristic manner can be observed in locations where alkali rhyolite is distributed, geological factors may also be playing an important role.

Nature Site: Fringed Galax Plant Group, Okutsudo Coast

Marine Life of the Oki Islands

Kurokizuta is a species of seaweed which is found distributed in the Red Sea, which is about 10,000 km away from Japan. This seaweed can be found in the sea of the Oki Islands, and is the only seaweed whose habitat is designated as a natural monument of Japan.
In addition, the Luna lionfish (Pterois lunulata) and the coral Alveopora japonica which inhabit the warm waters in the south, and a 1-meter-long starfish, which is thought to be a new species, can be observed here as well. Here is some of the unique marine life that calls the Oki Islands UNESCO Global Geopark home.

Kurokizuta (Caulerpa scalpelliformis)

Kurokizuta is a southern seaweed that can be found in the shallow waters around the Oki Islands. There are approximately 1300 known species of seaweed, and the habitat of kurokizuta is the only one that is designated as a natural monument of Japan.
A total of 13 locations have been confirmed as this seaweed's habitat along the coast of the Dōzen Islands and Dōgo Island.

Squid

Squid is one of the specialties of the Oki Islands.
The relationship between the people of the region and squid can be traced all the way back to the age of myths and legends.

Yurahime Shrine is located in an inlet on Nishinoshima Island in the Dōzen area. According to legend, a squid bit the hand of Yurahime-no-mikoto, the deity that is enshrined there, and shoals of squid are washed up on the shore next to the shrine every year since to repent its sin.
In fact, it has been recorded that squids (swordtip squids, Uroteuthis edulis) washed ashore every year during the festival period, and locals scooped them up by hand. Nowadays, once every few years, squid squads are washed up on the shore and locals will "pick" them up.

In addition, diamond squid (Thysanoteuthis rhombus), about 1 m in size, approach the shore every autumn to winter, so the islanders keep a sharp eye in order to catch them. The diamond squid would only approach two particular shores; there are two "squid shores," one on Nishinoshima Island and one on Dōgo Island. Both "squid shores" are located at the back of inlets facing the south to west, and the diamond squid in particular is known to migrate from the southern seas along the Tsushima Warm Current which flows from the southwest. Through this, we can see how the topography of the coast of the Oki Islands and the ecology of squids (migration route) are related.

Abortive Migration in Fish

The Tsushima Warm Current, the part of the Kuroshio Current that branches from Tsushima Strait, flows through the Sea of Japan along the Japanese archipelago. This current flows through the straits in the south and the north of Hokkaido and out into the Pacific Ocean and Bering Sea. As a result, the distribution of creatures living in waters warmer than the Pacific extends northwards.

Even with the warm current flowing throughout the year, the temperature in the Sea of Japan drops during winter. Therefore, the subtropical and tropical marine creatures that come with the warm current die without surviving winter. Such species are known as abortive migration fish. Abortive migration fish such as boxfish (Family Ostraciidae) and pearl-spot chromis (Chromis notata) can often be observed along the coast of the Oki Islands.

However, nothing goes to waste. With the increase in Earth's surface temperature, if the abortive migration fish can survive winter at their destination, they will be able to secure a new habitat before other marine creatures arrive. It is still unclear why this migration pattern occurs, but it is not an abnormal natural phenomenon; instead, it can be classified as part of nature's work.

The Relationship between Organisms and Geography

Living beings share habitats in many different ways; there is no such thing as a natural forest formed with only one type of tree, or a grassland inhabited by only one type of insect. Many creatures, large and small, live in one place, and create one ecosystem.

However, if the environment is different, then the members forming the ecosystem will change, too. The Japanese archipelago, stretching long from north to south, has a climate ranging from subarctic to subtropical. Due to its location on a mobile belt where collisions of tectonic plates occur, a rugged ladscape is formed, resulting in the formation of a variety of ecosystems and various habitat boundaries.

When looking at the distribution of terrestrial animals, the clearest distribution boundary line is a strait. At first glance, it seems there is no difference between the animals inhabiting Shimane Peninsula and the Oki Islands, the two separated by the Oki Strait. However, there are differences in the creatures which can be observed, such as the absence of large mammals in the Oki Islands, and the existence of endemic species.

Furthermore, even within the Oki Islands, there are also creatures that can only be seen on particular islands.

Here at the Oki Islands UNESCO Global Geopark, not only the organisms but also their habitat, the ecosystem is considered and introduced as a "geoheritage."

Ecosystem Flora and Fauna of the Oki Islands