Drupella is a snail alike thing that eat coral and damage the corals. Their favourite 'home' is staghorn and also table corals, you can find a lots of them when you diving or snorkeling and you will only see them if you see through those corals really really carefully as they are very small.
Adults are identified by a robust snail shell (5 cm long) and are covered with small cones or spikes. The shell is completely overgrown with calcareous algae. This gives the animal a rather rough and corrugated look with a deep purple colour. Juvenile shells are white and vary in size from 0.5 to 1cm. Just imagine these small things able to 'kill' the beautiful corals.
Drupella uses specialised mouth parts or a radula and feeds on living coral tissue. It leaves white scars on affected corals, if you find out some corals turn into white colour while you snorkeling or diving, have a futher inspection and you most probably will see some Drupellas has their own colony inside those corals and feeding on them !! I ever found more than 30 of them in a small part of the staghorn coral during the snorkeling clean up !! How scary is that !!
Bubbles Dive Resort do organise some underwater clean up project every year such as Earth day on the 22nd April and also some Project Aware, we do the underwater clean up during diving and also snorkeling, and we educated tourist about the importance of the corals, fishes, turtles and stuffs about the ocean. Please fell free to ask me any questions and join our projects !! :D