POSSIBLE OMNIVORY IN THE MURICID GASTROPOD UROSALPINX CINEREA FROM LONG ISLAND SOUND, USA

A recent feeding experiment has confirmed the presence of trophic omnivory, or feeding from multiple trophic levels, in the naticid gastropod Neverita duplicata through the use of stable isotope analysis. This surprising result led researchers to question the predatory status of other drilling gastropods such as those within the family Muricidae. This preliminary study uses stable isotopic trophic methods to evaluate the trophic position and diet of the muricid gastropod Urosalpinx cinerea from Long Island Sound, USA to see if it too might demonstrate omnivory (i.e., feeds on both meat and plants). Whole body, soft tissue analysis of nitrogen and carbon was conducted on 25 U. cinerea individuals from 5 Long Island Sound localities including: Rye, NY; Bridgeport, CT; Milford, CT; Guildford, CT; and Westerly, RI. The isotopic baseline for each locality was quantified using proxy taxa: the grazing gastropod Littorina littorea for the littoral baseline and the filter-feeding mussel Mytilus edulis for the pelagic baseline. Trophic positions of U. cinerea range between 2.2 and 2.7. Like wild-caught N. duplicata, this number is low compared to a fully predatory trophic position of 3.0, suggesting omnivory. Unlike N. duplicata, there is no experimental evidence that can be used to exclude the possibility of a lower-than-average nitrogen discrimination factor which could explain these low trophic position estimates. Carbon signatures of U. cinerea are intermediate between pelagic and littoral signatures, or more similar to those of the pelagic baseline. These carbon signatures are consistent with a diet of primarily pelagic carbon sources (i.e., filter-feeding mussels and oysters) with a minimal reliance on littoral or pelagic primary producers. Additional information in the form of feeding experiments or compound-specific stable isotopic analysis will be necessary to refute one of these competing hypotheses. If confirmed, the widespread appearance of trophic omnivory within drilling gastropods should not be surprising given the increasing realization of the importance omnivory plays in numerous taxa within marine food webs. The confirmation of driller omnivory will have wide-ranging implications for the paleoecological studies of drillholes in the fossil record and their interpretations.