Internal bioerosion by macroborers in Pocillopora spp. in the tropical eastern Pacific

 Bioerosion of branched corals was assessed in a fringing reef (Playa Blanca) and a patch reef (Gorgonilla) of Gorgona Island in the tropical eastern Pacific. Cylinder-shaped experimental units (EUs), made from branches of Pocillopora spp., were set 50 cm above the sea bottom for 6, 12 and 18 mo in Playa Blanca (4 zones: Back Reef, Reef-Flat Crest, Reef Front and Reef Slope) and the Gorgonilla patch reef. Borers were represented by bivalves Lithophaga spp. and Gastrochaena ovata, polychaetes, sipunculids and cirripeds (order Acrothoracica). Lithophaga spp. were the main borers and cirripeds were abundant mainly during the first period of exposure. The highest bioerosion rates were recorded in the Gorgonilla patch reef and the Reef Front of Playa Blanca (2.03 and 1.52 kg CaCO 3 m –2 yr –1 , respectively), while the lowest (0.76 kg CaCO 3 m–2 yr–1 ) were in the Back Reef of Playa Blanca. Bioerosion increased rapidly during the first 12 mo and remained constant thereafter. EU mass was rapidly reduced by 50%.