Dastardly Drupella snails....
- Created: Wednesday, 03 April 2013 13:36
Drupella Snails can be responsible for extensive coral reef damage, once an outbreak occurs removal must take place for the balance to be restored. On Koh Tao in 2010 following a bleaching event we lost a significant amount of the Drupellas favourite dish - Acropora (staghorn) coral. As a result, the Drupella population well exceeds the Acropora cover, meaning goodbye to even more acropora colonies as they eat the remainders. Drupella snails use a special mouth 'radula' and feed off of living coral tissue, particular favourites being stag horn and plate coral colonies here on Koh Tao. The snails leave white tissue scars on affected coral and can usually be found congregated at the base or deep down in-between the coral branches. Adults have a robust looking shell, 2 to 3cm long, are covered in small cones/ spikes and are deep purple in colour due to their shells being cover in calcereous algae. Juveniles are usually 0.5 to 1cm long and are white in colour.
In an attempt to reestablish the balance between durpella and Ancropora populations, we must remove excess Drupella snails from the reef. It is important to make sure removal is of the snail's only and not the common hermit crab which also takes up residence in an empty Drupella snail's shell, some easy clues for checking are waving the shell (if they drop off immediately, they are hermit crabs), and also the hermit crab will re-emerge from its shell relatively quickly once removed and in your hand.
On our last trip we collected 313 snails! We saw 31 aggregations, and then the odd snail or two on its own. All in all a good trip (well...maybe not for the Drupella victims...).
If you are planning your own collection, be careful not to damage the coral colony you are collecting them from; there's no point 'helping the coral' by removing snails if you break the coral in order to do so.... we only remove the most easily accessible Drupella snails. Once we've removed what we can from a dive we place the snails in fresh water for 24hrs before then replacing the shells back onto the coral reef so the shell can then bio-degrade, this then enriches the water with calcium carbonate which other organisms will intern use to build their own exoskeleton (anything from coral, octopus, all marine shell's, cuttlefish, clams..etc).