Distribution and Population Structure of Corallivorous Drupella Snails in the Coral Reefs of Kenting in Taiwan

The corallivorous Drupella snails are common predators of living hard corals in the Indo-Pacific Ocean, and they can significantly threaten coral reef ecosystems when outbreaks occur. In Taiwan, a Drupella outbreak, which resulted in the dramatic decline of Acropora and Montipora corals, was reported in Penghu in 2002-2009. However, the Drupella species involved was not identified, and no further research has been conducted. To obtain current knowledge on the predation pressure of corallivorous snails on hard corals, we investigated benthic communities and the distribution and population structure of Drupella snails in the coral reefs of Kenting, Taiwan. The composition of benthic communities revealed hard coral coverage ranging from 28.7 to 72.1% among the three surveyed sites at depths of 3-5 and 8-10 m. Drupella cornus (n = 326) and Drupella fragum (n = 6) had shell lengths of 13.6-40.1 and 8.0-17.8 mm, respectively. The density of Drupella snails among sites varied from 0.07 to 2.07 ind/m2, with no clear trend observed with water depth. Eight percent of the 1424 hard coral colonies contained Drupella snails; most patches only had one individual (48.2%). More snail patches were found in areas with more Montipora and Pocillopora colonies. Moreover, Porites corals were the avoided prey of Drupella snails. Although most Drupella snails formed a small patch (1-4 individuals) in this region, due to the current density being fi ve times higher than in 2013 (i.e., 0-0.37 ind/m2) and the existence of two Drupella species, we recommend broadening the survey areas better to understand the population dynamics of these corallivorous snails for local coral reef governance.