Two coral colonies were found near a protective bank under construction in the Henoko district of Nago, Okinawa Prefecture. (The Asahi Shimbun)

The Defense Ministry has found itself fighting on another front in Okinawa Prefecture, where it already faces stiff opposition to a proposed offshore U.S. military base.

Coral experts are taking issue with the ministry's argument that two colonies found at the land reclamation site do not meet conditions to be transplanted for protection.

The central government is forging ahead with its plan to relocate the U.S. Marine Corps Air Station Futenma in Ginowan, Okinawa Prefecture, to the Henoko district of Nago in the same prefecture.

The Defense Ministry commissioned Tokyo-based construction consultant Ecoh Corp. to examine the coral after The Asahi Shimbun reported in June on the existence of those colonies near a protective bank under construction at the tip of Cape Henoko.

According to a report submitted by Ecoh to the ministry the following month, the base of one of the coral communities measures up to 1.6 meters, and a species called Porites tenuis was discovered on one side. It also said the base of the other is up to 2.9 meters long and a type of coral known as Pavona decussata was found on one side.

The ministry's stated policy is that small, large or rare coral at the land reclamation site will be transplanted for protection if they meet certain conditions. Large coral colonies are covered by the preservation program if “a single colony is larger than 1 meter.”

Referring to the two cases, the report concluded that “no single colony larger than 1 meter was identified.”

It said the Porites tenuis comprises four or more coral colonies, each with a maximum length of 90 centimeters, and that the Pavona decussata “spreads in a band on one side of the base.”

Michio Hidaka, professor emeritus of coral biology at the University of the Ryukyus, said he believes that the Porites tenuis was originally a large single colony and appears to have divided when some tissue died.

Hidaka, who serves as president of the Japanese Coral Reef Society, said coral is normally deemed as belonging to a single colony if the same external skeleton is shared.

Nobuyuki Hori, professor emeritus of geography at Tokyo Metropolitan University, who is knowledgeable about the features of coral reefs, also said the Pavona decussata “obviously forms a single large colony, fulfilling the transplantation conditions.”

Twenty-two large coral colonies discovered on the Oura Bay side of the landfill site have been covered by the ministry’s preservation program.

Nami Okubo, an associate professor of coral biology at Tokyo Keizai University, argued that the two cases should be treated in the same way.

“The Defense Ministry confirmed that some of the coral (to be transplanted) form single colonies, including dead parts, just like the Porites tenuis in question,” Okubo said. “The two colonies should be transplanted based on the same criteria.”

The ministry insists the survey was "properly conducted,” but it has not released details of the research.

Hori noted that coral reefs form and spread by settling on dead parts.

“The (two) cases should be regarded as single colonies like those on the Oura Bay side, even though they include dead parts,” Hori said.

While the Porites tenuis inhabits the water channel linking the southern coast of Henoko and Oura Bay, the Pavona decussata lives in another waterway branching off from the channel.

“The coral will die out completely if the flow of water is cut by the protective bank and the supply of food is suspended over a prolonged period,” said Hori.