Schematic outline of benthic zones classified in the surveys conducted at Koh Tao A fringing reef slope, usually near-shore B reef edge as determined by drastic reduction in reef-building scleractinian abundance, leading to zone of no stable substrate nor any Scleractinia C soft sediment habitats characterised by sand/silt dominated substrates and colonised by organisms absent/extremely rare in zones A and B. D Deepening of soft sediment slope resulting in a drastic reduction but not absence of soft-sediment colonisers. Illustrated by Pau Urgell Plaza.