Estimation of Age in the Sex-Changing, Coral-Inhabiting Snail Coralliophila Violacea from the Growth Striae on Opercula and a Mark–recapture Experiment

Change of sex in the coral-inhabiting snail Coralliophila violacea (Lamarck) may occur in a wide range of sizes in the field. One proposed explanation for this is that the snails change their sex at a certain age and that individuals have different growth rates caused by microhabitat differences. In this study, we attempt to establish a method to determine the age of this snail and age at sex change. The growth striae on the operculum were studied and compared to the age estimated by the Gompertz growth function based on growth data obtained from mark–recapture experiments in southern Taiwan. There is a significant correlation between the number of striae on the operculum and the age estimated from the Gompertz growth function, and the relationship is 1:1. These results suggest that the number of striae on the operculum can be used as an age index, with each stria representing 1 year of age. The age of sex change of this snail, according to our estimates by both stria number and aperture-length inferences, occurs between 4 and 6 years old. Growth rates of the snails are negatively correlated to size. Furthermore, individuals undergoing sex-change grow faster than males and females.