Drupella, Thiele, 1925

Scott, C. M., Mehrotra, R., Hein, M. Y., Moerland, M. S. & Hoeksema, B. W., 2017, Population dynamics of corallivores (Drupella and Acanthaster) on coral reefs of Koh Tao, a diving destination in the Gulf of Thailand, Raffles Bulletin of Zoology 65, pp. 68-79 : 76

Drupella and Acanthaster abundance relative to previous local studies. Drupella and Acanthaster abundances showed no significant correlation to diver impact levels of reefs around Koh Tao as compared to those determined in 2010 by Weterings (2011), which is in contrast with results on Drupella in the northern Red Sea ( Guzner et al., 2010). When coral predator abundance was compared to the combined stress model of Weterings (2011), there were no significant correlations. It should be noted however that the location lacks effective control sites as in the study by Guzner et al. (2010), and even those sites not listed by Weterings (2011) as ‘highly impacted’ by divers are still dived on.

The relative abundance of Drupella showed no significant correlation to the observations of coral health and disease by Lamb et al. (2014). Little is understood about the causes and implications of Drupella snail population increases, except that multiple factors interact to create the conditions for outbreaks ( McClanahan, 1994), and more robust data and studies are needed to fully understand these interactions. Drupella snails have been shown to be a highly effective transmission vector for Brown Band Disease, as well as white syndromes and SEB and Black Band Disease ( Antonius & Riegl, 1998; Nicolet et al., 2013). It is currently unclear whether Drupella snails promote coral disease outbreaks or are merely attracted to them.

When the abundance of Drupella snails was plotted against the descriptions of high- and low-use sites as designated by Hein et al. (2015), the abundance of Drupella snails did not show significant differences, which does not agree with results from Eilat, Gulf of Aqaba, where higher abundances were found in high-use than in low-use areas ( Guzner et al., 2010). A study by Turner (1994) found higher abundances of Drupella snails in non-protected reef sites than in protected ones, but when Drupella abundance on Koh Tao was averaged according to MPA vs. non-MPA status, no significant difference was found. As the MPAs were only designated in 2012, more long-term monitoring is needed to evaluate their effectiveness ( Hein et al., 2015). Acanthaster abundance also did not show significant differences between low- and high-use sites, despite the regular collection of the sea star by concerned local divers.