On a rusting hulk of a ship half sunk near a remote reef in the South China Sea, the great geopolitical game for the future of Asia is being waged. And hardly anyone is paying attention.Earlier this month, while everyone was watching Ukraine, China made its move. For the first time in 15 years, Chinese coast guard ships prevented the Philippines from resupplying the handful of lonely soldiers who keep watch from the rusting deck of the Sierra Madre. The Philippine navy ran the old ship aground on Second Thomas shoal (“Ayungin” to the Philippines), in 1999 in retaliation for China’s occupation of a nearby reef a few years earlier. The two countries have stood guard, warily watching and waiting ever since. For the most part they leave each other alone. A New York Times reporter who visited the ship and its Filipino guards last year observed two Chinese ships as they circled like sharks; the message, he wrote, was clear: “We see you, we’ve got our eye on you, we are here.”Beijing sent a more direct message on March 9. Claiming that the Philippines’ ships were “loaded with construction materials” intended to build up a more solid position on Ayungin, the Chinese coast guard stopped the resupply mission. The Philippines retorted that it was sending provisions to the marines “to improve the conditions there,” and promptly sent aircraft to drop the supplies onto the Sierra Madre instead. Those airdrops will continue, the government said. “It is but our duty to provide for our own troops,” one official told the Philippine Star. “These are Filipino settlements.”Technically, China preventing the Philippines’ resupply ships violates the 2002 Declaration on the Conduct of Parties in the South China Sea, which China signed. Both Manila and Washington reacted angrily: “This is a provocative move that raises tensions,” said a State Department spokeswoman. “Our 62-year alliance with the Philippines remains key to our efforts to ensure the stability and prosperity of the Western Pacific,” declared the commander of the US Pacific forces.Though Ayungin is basically uninhabited and can hardly even be called a landmass, its importance in the geopolitical competition between China and its neighbors shouldn’t be understated. It lies at the center of the most hotly contested group of islands and reefs in the South China Sea, and the Sierra Madre is an important emblem of the Philippines’ resistance against China: the minnow against the shark. This is not the last time China will attempt to dislodge the minnow.