Coral death from sewage and phosphate pollution at Aqaba,Red Sea

Localized pollution of coral reef areas is occurring at Aqaba, Red Sea, as a result of sewage discharge, and as a result of spillage of phosphate dust during loading of phosphate mineral onto ships. The rate of death of colonies of the coral Stylophora pistillata was found to be 4–5 times as great in the polluted area as in a control area. Coral damage in the control area is generally caused by grazing or by extreme low tide, but the cause of coral death in the polluted area was not readily apparent. The growth of algae, both on the damaged corals, and on glass slides placed out in the reef, was greatly stimulated in the polluted area, but it appeared that such algal growth was not the direct cause of coral death. Corals in the polluted area may be under stress because of reduced light intensity, inhibition of calcification by excess phosphate, and increased sediment load. It was found that in the polluted area there was a greater weight of sediment settling on the glass slides for a given weight of algae. But in addition, since algal growth was faster in the polluted area, the sediment load was increased by the sediment trapping capacity of the enhanced algal growth. Thus it is suggested that increased algal growth stimulated by increased nutrient concentrations may be important in greatly increasing the sediment load experienced by corals.