Metals and metalloids in corals from the Western Indian Ocean

Abstract

Coral reefs are one of the most species diverse biomes on earth. One of the many dangers that coral reefs face because of anthropogenic activities is the accumulation of metals and metalloids in skeleton and tissues of the colonies. No knowledge exists on the state of metal and metalloid contamination in corals from the Western Indian Ocean (WIO). Fragments of four soft- and five hard coral genera were collected from five sites in the WIO. Sodwana and Aliwal Shoal constituted the coastal sampling localities from South Africa. Three Mauritian outer-islands in the Mascarene basin– Agalega, Rodrigues, and St Brandon’s Atoll– were the selected oceanic sampling sites. A total of 81 coral fragments were collected and analysed for 31 metallic elements using ICP-MS analysis. The corals collected from South Africa contained a higher concentration of most of the metals that were analysed compared with the Mascarene Island samples. Corals without symbiotic algae could only be collected from the South African reefs, and contained the highest concentration of metalloids. Soft corals exhibited a different accumulation pattern of metals than hard corals. Alkaline earth metals, Fe, and U predominated in the hard corals. Soft corals contained a higher concentration of most of the post-transitional metals that were analysed. Sinularia is the coral with the most elements of the highest concentration. Pocillopora from SBR had very high concentrations of Fe and Cr present, possibly due to several shallow shipwrecks in the atoll. Most of the elements tested had lower concentrations in the WIO than in certain regions of the Great Barrier Reef and the Red Sea. Iron was consistently higher in all corals collected during this study than in corals from other studies. Some metals, such as Cu, Ni, and Cd inhibit fertilization success of corals. The reported decline of Sinularia cover in Sodwana during the last decade may be attributable to very high concentrations of Ni found. As ocean temperature rises and ocean acidification increases, metals can become more bioavailable to corals. Conservation efforts and legislation need to address these factors in order to effectively promote the conservation of coral reefs