GASTROPOD OPERCULA AS NEAR-TIME PALEOECOLOGICAL ARCHIVES: A STABLE ISOTOPE APPROACH

The biosphere is changing in response to natural processes and human activities, but the extent of change is, in most cases, unknown. Paleontological investigations have provided valuable insight into ecosystem condition and function over millennial to million-year time scales while ecological investigations have produced robust data sets collected across annual and decadal scales. However, human impact can drive change on centennial scales, which are frequently overlooked. Historical collections contain biological specimens that could be used to investigate changes in food webs throughout this critical temporal gap. To address this issue in marine gastropods, we investigated trophic ecology of the long-lived predatory gastropod Triplofusus giganteus (horse conch) using compound-specific and bulk nitrogen (δ¹⁵N) stable isotopes collected from an ontogenetic time series of the operculum, one of the only organic structures typically preserved in older historical collections. Annual increments of the operculum were identified and compared to an independent time series derived from shell isotope sclerochronology (δ¹⁸O). Both age models suggested the animal lived approximately eight years, with δ¹⁵N recording changes in diet, nutrient sources, and trophic level throughout ontogeny. This research establishes methods for using gastropod opercula in historical collections as a source of ecological information and paves the way for future investigations.