Effects of sand deposition on scleractinian and alcyonacean corals

The ability of corals to withstand experimental sand deposition was investigated for two experimental periods (17 hand 6 wk) in eight scleractinia (Favia favus, Favites pentagona, Platygyra daedalea, Gyrosmilia interrupta, Galaxeafascicularis, Cyphastrea chalcidicum, Favires abdita, Goniopora djiboutensis) and five alcyonacea (Lobophytum depressum, L. venustum, Sinularia dura, S. leptoclados, Sarcophyton glaucum) collected in 1992 from Natal, South Africa. Scleractinia were active sediment shedders, alcyonacea passive, relying on water motion and gravity. Short-term sand clearing efficiency was primarily dependent on corallum shape. Sand application led to hydrostatic inflation of polyps in scleractinia and the entire colony in alcyonacea as well as to increased tentacular action in the scleractinian Gyrosmilia interrupta. Under continuous sand application, inflation remained while other activities, such as tentacular motion, ceased completely. In scleractinia and alcyonacea, tissue necroses appeared after the first week of continuous sand application. Death of entire colonies and partial bleaching of continually sandcovered areas were observed in alcyonacea only. Different grain sizes of sand had no influence on clearing reaction or efficiencies.