The Impacts of an Outbreak of Coral-Feeding Gastropods on Hong Kong's Corals  

Project Title: The Impacts of an Outbreak of Coral-Feeding Gastropods on Hong Kong's Corals

Applicant: The Swire Institute of Marine Science

Total Approved Grant: $533,025 (ECF&WWGF: 50/50)

Duration: 16/12/98 to 30/04/00

Project Status/Remarks: Completed

Scope: To study the impact of two species of coral - feeding snails, namely Drupella rugosa and Cronia margariticola, on Hong Kong corals.

Summary of the Findings/Outcomes: A 1997 report suggested that Hong Kong's corals were being consumed by an outbreak of coral-eating snails: Drupella and Cronia. This study investigated this observation and showed that such snails are widespread in Hong Kong and, they eat a wide variety of corals related to the occurrence and distribution of the latter at various locations. In laboratory experiments, Drupella, the only obligate corallivore, fed preferentically upon Acropora and Montipora and not other corals. Cronia is an opportunistic consumer of coral tissue facilitated by Drupella attacks. Surprisingly, it was shown that Drupella does not consume all coral tissues and the latter can survive an attack by the former and regrow. Thus, the main conclusion from the study is that Drupella and Cronia do not constitute a severe threat to Hong Kong's coral and that the large aggregations earlier reported upon in summer are probably a response to the coral's stress from other sources, e.g., pollution. The Government was advised, based on this study, that only monitoring of the snails is necessary during summer months (the peak feeding time) so that any outbreaks over the above naturally-defined levels identified in this study are monitored so that further action can be planned.