Abstract: Heavy metal pollution provides potential risks to the growth and development of corals. In recent decades, the coral reefs of South China Sea have been degraded as a whole, but the research on heavy metal pollution in such areas is scarce. This study was based on the integrated scientific survey and sampling on the nine selected coral reef areas of South China Sea in the summer of 2015, including Huangyan Island of Zhongsha Islands, Yongxing Island, Seven Lantau Island, Dongdao Island, Langhua Reef, Beijiao Reef, Huaguang Reef, Panshi Island and Yuzhuo Reef of Xisha Islands, and then focused on the distribution of the heavy metals in the seawater of those reefs. Our results indicated that: 1) The average concentrations of heavy metals in the seawater of the nine coral reef areas were 1.309, 1.702, 2.831, 0.056, 0.204 and 0.272 μg/L, respectively, for Cu, Pb, Zn, Cd, Cr and As. It meant that the overall level of heavy metals was relatively low, and Zn, Pb and Cu were the main contents of the total heavy metals, whose amount could be up to 92%. Besides, in some part of the sites, the content of Pb was higher than those of the First-Classed Seawater Quality Standard of China. 2) Generally, the distribution of heavy metals at the eastern reefs was higher than that at the western reefs. Furthermore, the content of heavy metals differed in atoll lagoon and reef slope, and Cu, Pb, Zn and Cd at reef slope were higher than in atoll lagoon, while As lower. The difference might be related with the relatively closed water in atoll lagoon. 3) The environmental factors, which affected the distribution of heavy metals in seawater in the coral reef areas of Zhongsha and Xisha Islands, mainly included terrestrial input, atmospheric deposition, ocean currents and so on. Thereinto, the terrestrial input principally influenced the amount of Zn, and the effect of atmospheric deposition on Pb was obvious, and ocean currents affected the local level. 4) Water quality was evaluated by the method of weighting-factor modified Nemerow index, which turned out the seawater was clean in Zhongsha and Xisha Islands. The content of heavy metals in seawater was not up to the level of affecting the coral growth except Cu element.

Key words: the Zhongsha Islands, the Xisha Islands, coral reef area, surface sea water, heavy metal