ARE FEEDING SCARS PRESERVED ON THE SHELL OF THE GASTROPOD FASCIOLARIA A GOOD PROXY FOR THE RELATIVE ABUNDANCE OF BIVALVE VS. NON-BIVALVE PREY IN ITS ENVIRONMENT?

When attacking bivalve prey, the tulip snail, Fasciolaria lilium hunteria, wedges the prey’s valves apart using its apertural lip, sometimes breaking its own shell and resulting in repair scars. Wedging behavior is not used when feeding on gastropods. The frequency of repair scars on Fasciolaria is thus a potentially useful proxy in the fossil record for assessing the relative proportion of bivalve to non-bivalve prey in Fasciolaria’s diet in space and time. Wells (1958) observed a preference hierarchy (gastropod prey over oysters), which complicates simple extrapolation analyses of the frequency of feeding scars to estimate relative abundances of prey types available to Fasciolaria. In this study, we reevaluate the robustness of Wells’ preference hierarchy for Fasciolaria.

We collected nine Fasciolaria from a shelly, sandy mudflat with patchily distributed oyster clumps in Masonboro Sound, North Carolina. One snail, between 70 and 86 mm, was placed in each of nine 38-liter aquaria. Observations were conducted throughout April 2009. An oyster-only treatment containing five Crassostrea virginica, a gastropod prey-only treatment containing five Urosalpinx cinerea, and a mixed treatment containing five Crassostrea and five Urosalpinx were used. Consumed prey were replaced daily. A total of seven Crassostrea and 60 Urosalpinx were consumed by Fasciolaria over the 25-day observation period. Consumed prey biomass was estimated by regressing ash free dry mass (AFDM) on shell size for both prey species. Whereas the average number of Urosalpinx consumed (2.4/day) was greater than the number of oysters consumed (0.28/day), in terms of biomass this pattern was reversed (1.09g AFDM/day for Urosalpinx and 3.57g AFDM/day for oysters).

Further tests using a simple Y-shaped flow table to evaluate prey preference directly using prey effluent plumes yielded choices of 50% oysters and 50% Urosalpinx among trials. Treatments using live and crushed prey both yielded 50:50 preference ratios over 10 runs.

These results do not support Wells’ prey preference hierarchy, suggesting that variation in scarring frequencies in space and time reflect variation in the relative abundances of bivalve and non-bivalve prey available to F. lilium hunteria.