Project Title: Species identification, ecology and biological control of apple snails in Hong Kong

Applicant: The Hong Kong Baptist University

Project Proponent: Dr. Jian-Wen Qiu

Total Approved Grant: $421,502.63 

Duration: 01/06/2006 to 31/05/2008

Project Status/Remarks: Completed

Scope:
This project aims to:

  • conduct an up-to-date and comprehensive survey of apple snails to determine the number of species present in Hong Kong, their distribution and environmental characteristics;
  • study the population dynamics of apple snails in different types of habitats;
  • determine their preference for local vegetables and natural hydrophytes, and the association between food preference and feeding rate, growth and reproduction;
  • assess the effects of apple snails on other freshwater gastropods; and 
  • explore the use of a biological method in apple snail control.

Summary of Findings/Outcomes:
During the two-year project period, we have completed the first proposed tasks. There is only one species of apple snail (Pomacea canaliculata) Hong Kong. Its distribution center is still in the New Territories, but its local range has expended as compared to 20 years ago, and has approached the edge of Lautau Island. Apple snail production was high and varied with habitat types. Apple snails collected from sites with different macrophytic coverage have very similar gut contents, with detritus and macrophytes as the dominant food items. Cultivated macrophytes are in general more desirable for the apple snail due to a higher nutritional value and lower physical and chemical defences. Snail feeding rate is negatively correlated to phenolics and growth rate is positively correlated with nitrogen and phosphorus. Egg production rate is significantly correlated with sodium, nitrogen and phosphorus. Apple snails devour heavily the eggs and neonates of five freshwater snails, but the predation rate on the adults depends on the shell harness and shell structure. Common carp can effectively remove apple snails, thus has the potential for use as a biological control agent for apple snails. However, care should be exercised because it also feeds on other freshwater snails.