Combating the problem of corallivorous Drupella snails has been something we have focused on at the NHRCP since 2010. This month we are proud to announce a new publication based on our research work, written by Dr. Bert Hoeksmea of the Department of Marine Zoology at the Naturalis Biodiversity Center in Holland, and Chad Scott of the New Heaven Reef Conservation Program on Koh Tao.
The paper outlines a shift in diet of the coral eating snails following the mass bleaching event of 2010. Previous to that event, Drupella snails where seen aggregating on some branching and tabulate corals (of the families called Acropora and Pocilliopora). As far back as 2007 our team was removing them from areas such as the Taa Chaa Biorock Project. By early 2010 we had become concerned with the number of drupella around, and began collecting them to reduce the amount of coral being eaten. Then during the 2010 bleaching, around 70% of the branching and tabulate corals in Chalok Ban Kao died, so the abundance of the preferred prey species for the Drupella snails was greatly reduced.
With their preferred coral food types gone, the Drupella snails then moved onto to start eating other species of corals on the reef, which they would not normally have consumed, including mushroom corals (of the family Fungia). This was the first time that mushroom corals had been observed to be a prey species for Drupella snails, and indicates that they may have a wider range of diet than previously thought, and thus are quite dangerous for the health of coral reefs in areas where outbreaks occur.
The full article published in the scientific journal Coral Reefs is titled “Dietary shift in corallivorous Drupella snails following a major bleaching event at Koh Tao, Gulf of Thailand” (Hoeskema et al., 2013). And can be downloaded from SpringerLink.
Outbreaks, or population explosions, of Drupella snails have been observed in many locations around the globe since about the early 1980’s, including Kenya, Hong Kong, and the Red Sea. In most of the cases, the snails restricted their feeding to a narrow range of corals species, and in some cases completely removed those species from the reef, causing long-term decreases in abundance and biodiversity of corals and their related reef organisms.
These outbreaks are generally thought to be caused by an increase in nutrients in shallow seas, where the planktonic Drupella larvae reside. It may also be greatly compounded by over-fishing and the removal of snappers and wrasses that would normally eat the larvae or juvenile snails.
In addition to researching the problems caused by Drupella snails around our island, we are also actively involved in the management of Drupella snail populations. When we perform our restoration work, we always remove any Drupella snails from our nurseries, artificial reefs, or other restoration zones. Between late 2010 and early 2011, students in our program kept data on a few of the Drupella collection dives, and found that we collected well over 15,000 Drupella snails, in about 41 dive hours.
There is still much more work to be done here to solve this problem, and still much more that we can learn about these very interesting, but destructive snails.
Find many more articles and scientific papers published by our staff or students at our Publications & Student Papers page.