OBSERVATIONS OF FASCIOLARIA FEEDING BEHAVIOR AS A BASELINE FOR INTERPRETING THE TRACE FOSSIL RECORD OF PREDATION

Shells of the tulip snail Fasciolaria lilium hunteria often exhibit small (<1 cm), scallop-shaped repair scars parallel to the growth lines of the convex edge of the apertural lip. These scars have been assumed to be induced by the predators' own feeding behavior. Wells (1958) observed that, in attacking bivalves, Fasciolaria inserts the edge of its apertural lip between the prey's valves in order to wedge them apart, which may result in breakage to the predator's shell. This wedging behavior is not used in feeding on gastropods. Wells also observed a preference for gastropod prey over bivalves, perhaps because of the risk involved in attacking bivalves. In this study, we document whether the repair scars commonly found on the shell of tulip snails result from shell wedging and reevaluate Wells' observation of a preference for gastropod prey.

We collected 16 live F. lilium hunteria from a shelly, sandy-mudflat in Masonboro Sound, NC. Two tulip snails, ranging from 41 - 88 mm, were placed in eight 38-liter aquaria. Observations were conducted throughout July, 2008. Two prey treatments were used: 3 control tanks contained an oyster only treatment with a large clump of Crassostrea virginica (between 5 and 15 individuals, 10 – 110 mm in size); and 5 experimental tanks with a similar oyster clump plus an alternative gastropod prey, Urosalpinx cinerea (5 individuals, 10 – 25 mm in size). We observed that repair scars on the convex edge of the apertural lip of Fasciolaria are induced by attempts to wedge open tightly closing bivalves such as oysters. In contrast to Wells (1958), a feeding preference for gastropod prey by F. lilium hunteria was not supported. Preliminary analysis shows the mean daily number of oysters consumed in the absence of alternative gastropod prey (0.49 oysters/tank/day) was not significantly different from when Urosalpinx was present (0.46 oysters/tank/day); ANOVA; F(1, 6)= 0.03; p= 0.88).

Our observations confirm a feeding-induced origin for the scars on shells of F. lilium hunteria, which will enable interpretation of the history of the behavior in the fossil record. However, the lack of a clear preference for gastropod prey over bivalve prey complicates assessments of the importance of these components of Fasciolaria's diet from an analysis of the trace fossil record of feeding-induced scars alone.