THE SEA AND JAPAN: CORAL, CURRENTS AND KELP

JAPAN AND THE SEA

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Hokkaido beach Japan has a small land mass but its surrounding waters are vast. Japan ranks sixth in the world in terms of combined areas of its territorial waters, exclusive economic zones and continental shelf. In these waters are large deposits of hydrothermal ores and rich biological resources. Natural gas and possibly oil lie in waters contested by Japan and China.

The concept of “ satoumi “ — the belief that human intervention in the ecology of coastal waters can lead to greater biodiversity — is gaining popularity in Japan with people doing things like pulling up sea cabbage so eel grasses, which host a variety of sea creatures, grows better. Some feel the movement is bringing back a link between the people and seas that existed for a long time in Japan but has been lost in recent decades.

In October 2008, Japan aimed to dramatically expand the amount of ocean under its control by applying to the United Nations for the right to claim areas designated as Japan’s continental shelves. The five areas — including waters in the Shikoku Oceanic base, the Kyushu-Palau ridge and the Ogasawara Oceanic Plateau — that Japan is claiming in the Pacific Ocean to the south and southeast of Japan have a combined area almost equal to that of Japan itself and are thought to contain resources that one day might be mined.

Studies by the Meteorological Research of Institute shows that waters off Japan are getting more acidic. Between 1983 and 2008 the pH of water off the Kii Peninsula in Japan decreased from 8.18 to 8.13. The lower the pH the more acidic something is.

In August 2012, Jiji Press reported: “Japan has been given a score of 69 out of 100 in terms of ocean health, an international group of researchers said. Jarvis Island, an uninhabited U.S. coral island located south of Hawaii near the equator in the Pacific Ocean, received the highest rating for its ocean quality with 86 points. The lowest score, 36, was given to Sierra Leone in West Africa, according to the researchers, who evaluated the health of oceans for 171 countries and regions worldwide using the Ocean Health Index. The average score was 60. The Ocean Health Index is a composite measure comprising 10 different indexes that rate the oceanic health of a country or region's exclusive economic zone in terms of biodiversity, artisanal opportunities such as commercial fishing, tourism and other aspects. The research was published in the online version of British scientific journal Nature. [Source: Jiji Press, August 17, 2012]

Good Websites and Sources: Japanese Society of Oceanic Studies jsos.net Japan Agency for Marine Earth Science and Technology jamstec.go.jp ; ; National Geographic on Giant Squids nationalgeographic.com ; Sea-Related Activities in Japan Outdoor Japan Outdoor Japan Diving and Snorkeling PADI International Website: PADI ; Dive Japan Dive Japan ; Dive Centers in Japan Dive Centers.net ; Okinawa Diving: Dive Bum Okinawa Dive Bum Oki ;Dive Sites Reef Encounters ; Aquariums Osaka and Okinawa have famous aquariums with whale sharks. Also Check Out: Shinagawa Aquarium at Japan Guidebook site apike.ca Aburatsubo Marine Park (Misaki area in Miura, Kanagawa Prefecture) features a huge tank with tuna swimming around at high speed.

Japan’s Oceanic Environment

Juli Berwald wrote in National Geographic:’sunlight streams between cracks in the ice. Thicker chunks glow emerald green, bejeweled by algae. The characters of this frosty realm begin to appear: a translucent, blue swimming snail, a pink fish with a tail like a geisha's fan, a bright orange lumpsucker that looks as if it leaped out of a Pokémon cartoon.”[Source: Juli Berwald, National Geographic, November 2010]

Most people think of Japan as a compact collection of large islands, but a map of the country shows otherwise. Japan stretches over 1,500 miles and includes more than 5,000 islands. As land mingles with sea over these vast distances, it embraces at least three distinct ecosystems. In the frigid north, sea-eagles, with their seven-foot wingspans, and king crabs frequent the ice-covered seas off the remote Shiretoko Peninsula. In the mild central waters of the Izu Peninsula and Toyama Bay, a few hours' drive from the skyscrapers of Tokyo, firefly squid swarm, and soft coral forests grow. In the balmy south, delicate butterflyfish and huge sand tiger sharks share coral reefs in the Bonin Islands, a collection of 30 or more islands about 500 miles south of Tokyo.

Ocean currents are key to the marine diversity, bathing Japan's shores in temperatures of water that range from around 30̊F to 85̊F. The currents also bring the country a couple of world records. The powerful Kuroshio shoots warm water northward, allowing coral reefs to thrive where they would not normally be found. The East Sakhalin Current draws cold water down toward Japan, helping make the Shiretoko Peninsula the southernmost spot with winter sea ice.

These currents control more than water temperature. They transport distant marine life as well. Inlets pockmark Japan's volcanic shoreline, explains Florida Institute of Technology professor Robert van Woesik. On islands surrounded by coral reefs, the lagoons "act like baseball mitts catching coral and fish larvae." As in so much of the world's oceans, these ecosystems are at risk. Japan is filling in lagoons to create more land to build upon. When this happens, fish, coral, and crab larvae glide past without settling down.

Japanese Ocean Currents

The Kuroshio Current (also known as the Japan Current) off the east coast of Japan is the Pacific’s answer to the Gulf Stream. Flowing northward and a little towards the east along the east coat of Japan, it brings warm water up from the Philippines in the south and like the Gulf Stream in the Atlantic is part of clockwise gyre that in the case of the Kuroshio Current embraces almost all of the perimeter of the northern Pacific. Waters from the Kuroshio and a branch current called the Tsushima Current mix with waters from the Oyashio Current, a cold water current that flows southward along the Kuril Islands and the Pacific coasts of Hokkaido and northern Honshu. Kuroshio means “Black Tide.” The Tsushima Current is a less powerful than the Kuroshio Current and flows northward and a little towards the east along the west coat of Japan. See the map above.

The Kuroshio Current has produced the northernmost colony of table coral off the southern coast of Wakayama Prefecture. Kushimoto Marine Park in this area contains 120 species of coral and a great variety of fish normally associated with more southern seas. The current has only been flowing to this area since 1990.

The Oyashio current brings cold water from the north. It affects the Pacific Ocean side of Hokkaido. The sea of Okhotsk north of Hokkaido is also very cold and becomes completely covered by pack ice in the winter. Among the cold-water species of fish that thrive in these waters are halibut, cod, salmon and Atka mackeral. Describing the watery world between ice floes in the Sea of Okhotsk, bordering the Shiretoko Peninsula in northern Hokkaido.

The migration of marine life is often tied with the currents. Squid and fish such as bonito, horse mackerel move northward with Kuroshio while cold water species such as cod, halibut and Alaska pollack move south with the Oyashio. In 2009 and 2010 a number oarfish — strange ribbon-like creatures that normally live at depths between 200 meters and meters and aren’t seem near the surface — were seen in coastal waters in the Sea of Japan. They were most often spotted when strong winds blew from the sea.

Coral in Japan

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Okinawa coral The are large coral reefs around Okinawa and other tropical islands Japan. Indigenous stony coral has been found growing in Tokyo Bay. Roughly 200 species for non-reefal communities from Tanegashima to the Kii Peninsula have been counted and roughly 55 species for outlying coral communities (from the Izu Peninsula to Tokyo Bay).

The northern limits of table coral and expanding northward as ocean waters warm. A piece of coral taken from Kagoshima prefecture has survived on land for more than 20 years in the garden of man who watered the coral occasionally. The coral even began sprouting branches.

Coral poaching is a problem in Japan. According to one survey 45 of 75 pet shops contacted were selling coral collected from Japanese waters. The coral sold for prices ranging from ¥2,000 to ¥4,000. See Below. Coral-eating crown of thorns starfish is a problem in some of the reefs around Okinawa. Damage to reefs is also caused by divers and sewage released from boats with tourists and divers.

Baby coral transplanted onto the Sekisei coral-reef lagoon — Japan’s largest coral reef — in Okinawa Prefecture is growing fast. Scientists working on the project implant fertilized corals eggs into ceramic beds and once the eggs grow into larvae one centimeter to two centimeters they are attached to rock in the seabed.

Coral Bleaching in Japan

Coral reefs especially around Okinawa have been damaged by coral bleaching. Particularly worrisome is the presence of bleached coral around Ishigakijima, which boasts Japan’s largest coral reef. Much of the damage has been blamed on unusually high water temperatures — temperatures above 30 degrees for extended periods, usually in July and August — in recent years. Soil erosion that washed into the sea from construction sites and farms is blamed from contributing to the problem by clouding up the water.

Coral bleaching occurred four times in the 1990s ad 2000s — in 1998, 2001, 2003 and 2007 — in Okinawa Prefecture. In 1998 around 40 percent of the coral around Ishigakijima died. In 2007 large swaths of bleached coral were found in eight locations around Ishigakijima and off Sesokojima Island off Okinawa. Most of the reef stretching from Yonehara beach on Ishigakajima out into the sea had turned completely white. That year water temperatures were high in July.

Coral bleaching caused by an unknown disease has been occurring off the coast of Miyazaki and has been found as far north as the Kochi Prefecture coast. Coral has also been severely damaged by Acanthaster starfish.

In 2017, a bout 70 per cent of the Sekisei Lagoon coral reef in Okinawa Prefecture — the largest such reef in Japan — was bleached according to the Environment Ministry. Higher ocean temperatures stemming from global warming and other factors are believed to be the cause. The ministry called it “an extremely serious situation in recent years.” When the ocean temperature reaches about 30 C, it becomes easy for coral bleaching to occur, in which plankton that lives symbiotically with coral leaves the coral. If this continues for a long period, the coral will die from poor nutrition. [Source: The Japan News/ANN, January 11, 2017]

Coral Colonies Depleted in Okinawa

Yomiuri Shimbun reported: “On the famous coral reefs off Ishigakijima island, Okinawa Prefecture, the size of coral colonies has sharply decreased to about a quarter of their size about 10 years ago, according to research by a national environment institute. The National Institute for Environmental Studies in Tsukuba, Ibaraki Prefecture, an independent administrative institution, conducted the research off the island's Shiraho beach. The institute believes the decrease is caused by "coral bleaching," a phenomenon in which rising seawater temperatures kill coral; poor behavior by careless tourists who damage coral; and an inflow of red soil erosion into the ocean. [Source: Yomiuri Shimbun, October 20, 2011]

“According to the research, the percentage of coral per square meter dropped from 11.9 percent in 1998 to 3.1 percent in 2010. Some stony corals, known in Japanese as midori-ishi (acropora coral) and komon-sango (montipora coral), are particularly prone to environmental changes, and have decreased drastically to one-hundredth of former levels in some places, according to the institute. Coral bleaching has been observed for more than 10 years. But, red soil erosion from sugarcane and pineapple farms is also contributing to the decrease.

“Additionally, the number of tourists visiting the island has increased, rising to about 873,000 last year, or 1.2 times the number from 10 years ago. Many tourists have stepped on or otherwise damaged the coral off Shiraho beach while scuba diving. Ishigakijima island is home to a number of popular diving spots.

Chinese Coral Poachers in Japanese Water

In the early 2010s coral poaching by Chinese vessels in Japanese waters was so rampant that it damaged diplomatic relations between Tokyo and Beijing. Takahiro Suzuki wrote in the Yomiuri Shimbun: “It is well known among fishermen that there is good-quality red coral in waters around the Ogasawara Islands. Among coral used to make jewelry, red coral is designated by the Chinese government as a top-tier protected animal species, like the giant panda, whose protection is prioritized under its wildlife conservation law. Collecting the species is prohibited by law. [Source: Takahiro Suzuki, Yomiuri Shimbun, November 1, 2014]

Many of the Chinese fishing boats that poach scarce coral, dubbed “jewelry coral,” in waters around the Ogasawara Islands in Tokyo cast off from Xiapu County in Fujian Province, The “It seems those fishermen, in the belief that Japanese coral commands high prices, are repeatedly setting sail and poaching coral near Japanese waters with the dream of striking it rich. As word spreads of a ship owner said to have made about ¥350 million in just one month last year, the number of ships involved in coral poaching is reportedly on the rise.

“Another fisherman, 56, said that he had been hired by a Taiwan boat and engaged in red coral poaching off Okinawa Prefecture about 10 years ago. As Japanese aircraft had been flying over the area on alert, they poached the coral covertly during the night, the man recalled. “Red coral from Japanese waters sells at a very high price,” he added.

“In China, jewelry coral enjoys high popularity for accessories, and red coral especially is prized as a luxury. At a red coral jewelry store in Shanghai, coral is processed into necklaces and pendants, which are on display priced at more than ¥1 million. Items made from Japanese red corals are especially popular and are known as “Aka,” which means red in Japanese. Larger red coral with a darker color is said to be more expensive, and they are mainly purchased by the wealthy. According to this store, high-quality red coral was sold at about ¥35,000 per gram five years ago, but the price has more than quadrupled to about ¥150,000. Saying the store buys its red coral from Japan and Taiwan, staff added that it is becoming harder to buy. “The price of Aka will rise further,” they said.

Kelp Forest

Kelp often grows in huge masses called forests. Kelp forests are found off the coast of New Zealand, Japan and California. A number of fish and other aquatic species are unique to kelp forests.

Kelp is a kind of seaweed that grows in long strips that hold onto rocks on the sea bottom with a claw-like fastener that serves only as an anchor and provides no root like functions. Kelp needs to be anchored to the bottom of the sea in some way or it will be washed away. Kelp are designed to live offshore in places with crashing surf. The have inflatable bladders that keep them afloat and flexible leaves that move in the moving water without breaking. Some have a slippery mucous coating to protect them from exposure to sun and air.

Kelps dominates reefs in cool seas. Relatively little is known of their origins. Some think they originated 5 to 10 million years ago in the Northern Hemisphere when the northern seas were cool and full of nutrients. This theory is hard to prove because the soft tissues of kelps don’t mineralize into fossils very well. Studies of large abalone shells that feed primarily on kelp suggest that kelp first appeared in large amounts in the Northern Hemisphere about 5 million years ago.

Last updated March 2025

Image Sources: 1) Ray Kinnane 2) 6) Greenpeace 3) 5) Japan-Animals blog 4) Hector Garcia 7) 8) exorsyst blog, Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, Daily Yomiuri, Yomiuri Shimbun, Japan National Tourist Organization (JNTO), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated March 2025