FURTHER STABLE ISOTOPIC EVIDENCE FOR OMNIVORY WITHIN THE NATICIDAE

Further stable isotopic evidence for omnivory within the Naticidae

By Patrick M. Schneider, Abram Z. Jeremenko, Laurel M. Lenz, Zoe M. Lueba, and Michelle M. Casey

The fossil record of drill holes represents an important source of information on trends in predator-prey interactions through time. Therefore, it is important to constrain the diet of extant drilling gastropods to provide context for interpreting drill hole derived patterns in deep time. Predatory gastropods belonging to the family Naticidae are thought to be carnivorous, feeding primarily on bivalves. Recently, stable isotopic analysis of Neverita duplicata called this diet into question. Laboratory testing and field investigation of N. duplicata from Long Island Sound confirmed that individuals fed exclusively bivalves had higher nitrogen signatures than their wild counterparts, indicating that the low nitrogen signatures of wild-caught individuals were not the result of an unusual nitrogen fractionation factor (Casey et al., 2014). Casey et al. (2014) used this evidence to suggest that N. duplicata is an omnivore consuming a diet of infaunal bivalves and littoral plant material. To better assess the prevalence of omnivory within the Naticidae we conducted a stable isotopic diet analysis on two naticid species from Baymouth Bar, Alligator Harbor, FL (Neverita delessertiana formerly part of Neverita duplicata) and Sinum perspectivum. Animals were live collected, frozen, dissected, dried and ground for whole body, bulk analysis of δ¹³C and δ¹⁵N. Samples were lipid corrected using a mathematical model after Post et al. (2007). Trophic position (TP) was estimated using a two end-member mixing model and proxies for the isotopic baseline (pelagic = Crassostrea virginica, littoral = Turbo castanea). S. perspectivum’s isotopic signatures show considerable overlap with those of N. delessertiana, indicating similar diets for both species with Neverita exhibiting greater intraspecific diet variation. Both naticid species yield TP estimates consistent with omnivory (<3.0), though S. perspectivum has a slightly higher average TP (avg. TP_Sinum = 2.6, avg. TP_Neverita = 2.4). These findings are consistent with the same mixed diet of bivalves and littoral plants suggested for N. duplicata and indicate that omnivory may be common within naticids.