Enhancement of Grazing Gastropod Populations as a Coral Reef Restoration Tool: Predation Effects and Related Applied Implications uri icon

abstract

  • In this study, we aimed to evaluate the efficacy of adding T. niloticus to control epilithic algal biomass and enhance coral recruitment on artificial substrata at a heavily fished reef in northwestern Philippines. Our main hypothesis was that with addition of trochus, the growth of algae would be lower and the number of coral recruits would be higher. The reason for trying to control algal growth through trochus grazing was to reduce preemption of space for settlement of coral larvae. Trochus was used as a grazer because it can be cultured easily and released effectively, allowing the production of juveniles and subadults in adequate numbers for local stock enhancement. We also examined any interactions between the possible beneficial effects of trochus and â??seedingâ?� the substrate with small transplanted coral colonies to promote recruitment of coral and attract fishes and any effects of trochus on the survival of the transplanted coral colonies. Aside from assisting coral recruitment, grazing of benthic algae by trochus was expected to limit competitive effects of macroalgae on coral transplants because different functional groups of benthic algae can cause coral mortality by overgrowth, shading, abrasion, and allelopathy
  • 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.

publication date

  • 2010
  • 2010
  • 2010