Muricid gastropods in the genus Drupella are found on coral reefs throughout the tropical and subtropical shallow waters of the Indo-Pacific. They are corallivorous and prey almost exclusively on living coral tissues. Over the past decade there have been reports of population outbreaks of Drupell on several reefs in the tropical Indo-West Pacific region (Japan, the Philippines, the Marshall Islands, Western Australia). These high densities of snails appear to have been responsible for extensive and significant coral mortality on a scale which has previously only been documented for the crown-of-thorns starfish Acanthaster planci. At Ningaloo Reef, Western Australia, where the outbreak has been on a greater temporal and spatial scale than has so far been documented elsewhere in the Indo-Pacific region, it is estimated that live coral cover in the back-reef areas may have been reduced by more than 75%. The implications of such extensive coral mortality for the reefs population, community and ecosystem structure and function, and the ramifications of such changes in ecological, evolutionary and geomorphological terms are unknown. The available information regarding the reproduction, early life history, feeding biology, growth and longevity, mortality and population genetics of Drupella is reviewed and areas where further research is required are identified. The history of the outbreaks is reviewed, and the possible causes examined. Both anthropogenic (increased terrestrial run-off, over-fishing and increased reef damage) and natural (variable larval recruitment) causes have been proposed to explain the outbreaks. There is insufficient information available at present to enable any of the alternative hypotheses to be objectively assessed. Information on the effects of Drupella outbreaks on coral reefs and reef recovery following outbreaks are described and the management issues associated with these outbreaks are discussed. There are conflicting views regarding the significance of outbreaks of Drupella, and consequently, the desirability and feasibility of implementing appropriate management responses.
