Surfing in the sandy-beach whelk Bullia digitalis (Dillwyn)

Abstract

A brief, integrated summary is presented of published and unpublished work relevant to surfing (swash riding) in intertidal members of the genus Bullia (Caenogastropoda), together with previously unreported investigations of the specific gravity of B. digitalis and the directional control exercised by the whelk during surfing. Specific gravity is higher than previously reported and is higher than that of B. rhodostoma, a factor in the more efficient surfing of the latter. B. digitalis surfs at an angle to the flow of the swash and tacks in a zigzag trajectory towards a food item. It usually requires several swash events for the animal to reach its food.