Corallivory plays a limited role in the mortality of new coral recruits in Hong Kong marginal coral communities

Coral recruitment plays a vital role in mediating adult coral population structure as well as in promoting coral reef recovery after disturbances. As one of the most delicate life stages of coral, coral recruits were reported to be sensitive to several environmental, physical and biological stresses. This study aimed to examine the effects of Drupella corallivory on coral recruits of the massive Platygyra acuta and branching Acropora pruinosa in Hong Kong. Coral recruits were induced to settle on settlement tiles (R tiles). These tiles, alongside with tiles without coral recruits (NR tiles) and brand new tiles (NE tiles), were used in the prey-choice experiment to test the attractiveness of coral recruits to Drupella. The overall attractiveness of different types of tiles to the snails was low, and more Drupella snails were found on NR tiles instead of the R tiles. Effect of Drupella corallivory was also evaluated by counting the number of recruits lost after a movement experiment. The results revealed that only <10% of coral recruits were removed by Drupella, and similar outcomes were also obtained when herbivorous gastropods Tectus pyramis and Euplica scripta were used. This suggested that the loss of coral recruits due to corallivorous gastropods was not any greater than that due to the herbivores. All these results indicate that coral recruits were not attractive to Drupella, and the effect posed by this corallivore gastropod on the survival of coral recruits was limited.