Johnson South Reef (Chinese: 赤瓜礁; pinyin: Chìguā Jiāo; Vietnamese: Đá Gạc Ma), also known as Chigua Reef, Yongshu reef, Gạc Ma Reef and Mabini reef is a reef in the Spratly Islands in the South China Sea controlled by the People's Republic of China (PRC), but whose ownership is disputed by the Philippines, Brunei, Taiwan, and Vietnam.