Strange Snails Indeed: Swash-Surfers, Self-Mutilators, Wave-Combers and Cannibals that Dominate Panamic Sandy Beaches

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Presentation Date


Conference Name

7th Congress of the European Malacological Societies

Conference Location

University of Cambridge, Cambridge, UK

Peer Review



The intertidal macrofauna of many sandy beaches in the Panamic faunal province (American west coast from Baja California to North Peru) is numerically dominated by a small number of olivid species (families Olividae and Olivellidae, Caenogastropoda) which exhibit a fascinating multitude of unique behavioural and morphological adaptations to their demanding habitat. Olivella semistriata and O. columellari, sister species that have been confused in all (!) papers addressing their ecology so far, have powerful appendages of the propodium which deploy and suspend mucus sheets to capture particles from the backwash. As the backwash zone moves with the tides, so do the snails, using parts of their body as underwater sails. O. semistriata is the main prey of Agaronia propatula which is aptly described as an Oliva adapted to life in the intertidal. Being a swash-surfer itself, A. propatula leaves its intertidal hunting grounds with sunset, probably to avoid a yet unidentified predator that also may be the evolutionary driving force behind the snail's habit of shedding parts of its foot when irritated (autotomy). A. propatula is the quintessential opportunistic predator, and is not shy of attacking artificial objects or human fingers. It will happily prey on conspecifics; since the success of cannibalistic attacks strictly depends on the size ratio between cannibal and conspecific prey, A., propatula forms size-structured populations in which size classes function as 'ecological species' with distinct trophic roles. On the other hand, O. semistriata applies various unusual modes of locomotion to escape aggressive A., propatula, including serial jumps on exposed sediment and active swimming when submerged. We will present the various types of behaviour - most of them for the first time - in movies taken in the wild, and discuss their evolution and ecological function. As a result, we will criticize and question established wisdom about swash-surfing snails, specifically the notions (1) that tidal migration is the main purpose of and context in which swash-surfing evolved, (2) that swash-surfers steer towards resources guided by olfactory clues, and (3) that swash-surfers would benefit and therefore can be expected to possess biological clocks aligned with the tidal cycle.



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