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Enhancement of Grazing Gastropod Populations as a Coral Reef Restoration Tool: Predation Effects and Related Applied Implications
Authors:Ronald D Villanueva  Alasdair J Edwards  Johann D Bell
Institution:1. The Marine Science Institute, College of Science, University of the Philippines, Diliman, 1101 Quezon City, Philippines;2. School of Biology, Ridley Building, Newcastle University, Newcastle upon Tyne NE1 7RU, U.K.;3. The WorldFish Center, Jalan Batu Maung, Batu Maung, 11960 Bayan Lepas, Penang, Malaysia;4. Present address: Secretariat of the Pacific Community, BP D5 98848 Nouméa Cedex, New Caledonia
Abstract:We aimed to evaluate the efficacy of the gastropod grazer Trochus niloticus in controlling epilithic algae and enhancing coral recruitment on artificial substrata on coral reefs where the biomass of herbivorous fishes was low due to heavy fishing pressure. Hatchery‐reared, subadult trochus were stocked onto pallet balls (small artificial reefs composed of concrete and limestone aggregate) at a density of approximately four individuals per square meter (external surface area). This density was re‐established with releases of new trochus each month for 6 months. At the end of the experiment, there were no significant differences in algal biomass, cover and community composition, or the density of coral recruits on substrata with and without trochus. High monthly attrition of stocked trochus on the pallet balls, apparently due mainly to predation by octopus, did not allow the evaluation of the efficiency of the trochus enhancement, at the desired density, as a restoration tool. However, at the lower trochus densities (circa 1 m?2), which occurred as a result of predation in this study, no apparent enhancement of algal grazing or coral recruitment were observed. The surprisingly high predation of stocked trochus in a heavily fished and gleaned reef site stresses the importance of understanding all the factors affecting the survival of stocked animals. To help mitigate predation of trochus, artificial habitat with refuge spaces that allow the grazers to escape predation could be provided and individuals of a larger size could be released.
Keywords:coral recruitment  coral reef restoration  coral transplantation  grazing  herbivore predation  trochus
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