Okinawa

Okinawa (The Ryukyu islands) is located on the southwestern-most tip of Japan and consists of 160 islands which enjoy the only subtropical oceanic climate in Japan.

Seagrass flora in Japan differs distinctly between the subtropical south-western Islands and the temperate coasts of the main islands. Sixteen seagrass species, including seven temperate species and nine tropical species occur on the coasts of Japan. The tropical species are restricted to the south-western islands (Ryukyu and Amami Islands), except for Halophila ovalis. The temperate species are restricted to the larger main islands, with the exception of Zostera japonica which is found in the Ryukyu Islands.

The area of seagrass meadows in Japan, especially the temperate meadows of Zostera marina, have declined since the 1960s, mainly the result of land reclamation and industrial development in the coastal regions of Japan. The Environment Agency of Japan surveyed the status of seagrass meadows along most of the coastal areas of Japan in 1978 and again in 1991 and reported a loss of approximately 4%. Although these losses were generally confined to the larger islands of Japan, the losses had serious effects on coastal fisheries. The area of seagrass for Japan in 1991 was estimated at 495km2.

In multispecific meadows in the Ryukyu Islands, Halodule pinifolia, Cymodocea rotundata and Thalassia hemprichii are dominant in the intertidal to upper subtidal zone, while Cymodocea serrulata and Enhalus acoroides are more abundant in the deeper subtidal zone. Among the tropical seagrass species, Enhalus acoroides and Halophila decipiens are found only in limited localities in the Ryukyu Islands and they have ben listed as Vulnerable in the Red Data Book of threatened Japanese plant species.

In the Ryukyu Islands where large investments have been made toward rapid modernisation, the coastline has been damaged by land reclamation and port construction. The natural ecosystems of coral reefs and lagoons are greatly impacted.

Dugongs inhabit several seagrass meadows in the north eastern coast of Okinawa Island, which is the northern limit of global distribution of this threatened marine mammal. In Okinawa (Japan), seagrass on which dugongs feed is called Jangusa (literally means dugong-grass) and seagrass meadows are called Jangusanumi (sea of Jangusa).

Unfortunately, Okinawa's seagrass meadows are currently facing the greatest threats by the proposed construction of a U.S. military airport and/or reclamation. The Nature Conservation Society of Japan has therefore decided to launch a community-based Seagrass-Watch monitoring program by conducting “Okinawa Jangusa-Watch”.

Kayo

Principal watchers: Masahito Yoshida (Nature Conservation Society of Japan), Masahiro Nakaoka (Chiba University) and Naoko Kochi (Hokkaido University)
Occasional and past watchers: Hokkaido University students
Location: The seagrass meadow at Kayo is easily accessed by foot from the beach.
Site code:
Issues:
Comments: Monitoring of the seagrass meadows is conducted every three month since July 2002, along line transects (five, each 200m long perpendicular to shore each 50m apart). Five to ten quadrats were set randomly at each study point using standard Seagrass-Watch quadrat measures.

Status:

Seven species of seagrasses as well as dugong feeding trails can be observed.
Meadow around Kayo is relatively unfragmented
The highest percentage cover was observed closer to shore, but at 200m and beyond, cover percentage decreased. Thalassia hemprichii had a broad distribution and was found throughout the entire survey range, whereas Syringodium isoetifolium was restricted to shallow water. Halophilia ovalis was abundant in deep depths and on intertidal sandbanks. Dugong feeding trails were sited in Kayo during all of the surveys.

Henoko

Principal watchers: Masahito Yoshida (Nature Conservation Society of Japan), Masahiro Nakaoka (Chiba University) and Naoko Kochi (Hokkaido University)
Occasional and past watchers: Hokkaido University students
Location: Henoko Cape-Camp Schwab area
Site code:
Issues: airport construction plan for the US marine corps
Comments: Monitoring is conducted by free diving using a grid survey technique instead of line transects. Grid is horizontal and rectangular lines every 200 m apart. A total of 60 to 70 study points were designed at the intersection of two sets of lines. Every study point was approached by boat with a help of GPS unit.

Status:

Henoko has the largest seagrass meadow on Okinawa Island.
Seven seagrass species grow in this region and feeding trails of the dugong and sea turtle were found. Thalassia hemprichii had a broad distribution throughout the entire survey range, whereas Syringodium isoetifolium was restricted to shallow water. Halophila ovalis showed significant growth after the big typhoon in October 2002 when tide and waves disturbed seagrass colonies. Halophila shows characteristics of pioneer species that the first ones to come back after disturbance.
From aerial photographs, the seagrass meadow seemed to reach only 500m from shore; however, the survey revealed that it actually extends to 1000m from shore. Dense colonies of S. isoetifolium and C. serrulata were found in shallow waters, while T. hemprichii and H. ovalis occur in patchy colonies 400-1000m from shore.
These findings are important, as a report published by the Defense Facilities Administration Agency (DFAA) of Japan included only seagrass of greater than 25% in it's distribution map around the Henoko. In contrast, the seagrass meadow actually extends outside of the distribution range indicated by the agency. Dugong feeding trails were found where percentage cover less than 25%. As dugongs prefer less dense patches such as of H. ovalis rather than dense patches, an environmental impact assessment of the proposed airport construction plan, which will begin soon, will need to incorporate the studies and predictions of changes in the distribution of seagrass patches with percentage cover less than 25% that reflect the effects of the construction on ocean current pattern and sea floor.
The Naha Bureau of DFAA, on November 17 2004, launched the drilling survey at the dugong habitat in Henoko, without waiting the completion of EIA. IUCN - the World Conservation Union adopted a recommendation, on November 25, at its third World Conservation Congress held in Thailand to request the Government of Japan to conduct an EIA with overall study including comparisons with alternative sites or zero construction option and study of impacts from drilling survey.

Update

U.S. and Japan had intensive negotiations to find a solution to relocate a present U.S. Marine Corps Futenma Air Station based in Ginowan, Okinawa before President Bush's visit to Japan in November 2005.

During the negotiations from September to October, Japan insisted on constructing an airport inland from Camp Schwab, Nago, Okinawa, the U.S. refused to this, insisting on constructing a shorter runway (1,300 to 1,500 m) than the one planned (2,600 m) inside Henoko Reef, and offshore of Camp Schwab. (See Fig 1 below).

The U.S. supported the shorter runway option because they believed the plan would minimize the impact on coral reef.

However Okinawa Janguwa (seagrass)-Watch, revealed that the shorter runway option still has a serious impact on the largest seagrass meadow in Okinawa and integrity of Henoko reef.

The Nature Conservation Society of Japan (NACS-J) sent a statement of opposition to U.S. Secretary of Defense, Secretary of State, Japanese Minister of Defense and the Minister of Foreign Affairs on October 6.

Because of opposition from conservation organizations and local government, Japan proposed an alternative site to construct an airport with a 1800 m runway, by reclaiming the coast of Oura Bay. Japan and U.S. agreed to this option on October 26.

However, this area is home to a new type of Halophila that was found during the last Jangusa Watch held in September 2005.

Though Halophila ovalis is widely distributed and H. decipiens is found deeper waters of Okinawa, this new type of Halophila was found in medium (7-8 mtr) depth, and has comparatively long leaves, resembling H. hawaiiana. Further investigations will be needed to determine the taxonomy of the new Halophila, and to elucidate environmental and ecological factors responsible for its limited distribution in Oura Bay.

Besides seagrass, stands of the coral Porites cylindrica (home to anemone fish) and Oulastrea crispata (a parasite on a kind of seashell Strombus canarium turtulella) were found in the Oura Bay. Construction works of airport may risk rich biodiversity of Oura Bay.

NACS-J will conduct another field survey in January 2006 to investigate a possible impact of the airport on integrated system of Oura Bay.