Since 1998 the coral community on a 150-m artificial limestone quay at Eilat, Israel, constructed in the mid-1980s was monitored, annually. Between 1999 and 2000, large numbers of the corallivorous snail Drupella cornus appeared following coral mortality at the time of siltation stress. Numbers increased dramatically in the subsequent years, and by July 2004, there were more than 200 Drupella on each, 30-cm diameter colony of several branching coral species (Fig. 1a, b). Earlier research by Gur (1988) had found Drupella mainly on Acropora sp. and at lower density on other branching species (1–50 snails per colony). All coral colonies at the southern end of the quay died within 2 years. The Drupella then ‘moved’ to the northern end. At first, the Drupella fed only on branching coral species (Fig. 1a, b), but as these were killed, the snails were found on massive and encrusting species, including Turbinaria mesenterina (Fig. 1c), Pavona cactus, Millepora dichotoma (Fig. 1d), and Porites lutea (Fig. 1e).

Fig. 1
figure 1

Prey shift for Drupella. (a) Hundreds of Drupella feed on a 25-cm diameter Pocillopora damicornis colony. (b–e) Drupella snails feed on: (b) Acropora sp., (c) Turbinaria mesenterina, (d) Millepora dichotoma, (e) Porites lutea. (f) A young Stylophora pistillata colony recruited to the Drupella denuded area

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Drupella predators, including the fish Coris aygula, are rarely seen in this area. This lack of ‘top-down’ control may explain the behavior of medium sized (2–3 cm) snails that foraged during the daytime on the top surfaces of branching species and on exposed massive/encrusting corals (Fig. 1c–e). On the southern coast of Eilat, similar sized snails have not been seen exposed to predation during daytime (Gur 1988).

During the June 2005 survey, there were less than 10 intact branching colonies on the quay, and the dense population of Drupella had declined. By July 2006 and again in July 2007 new coral recruits were found (Fig. 1f) in the previously denuded areas.