Pleistocene to Recent Environments and Species Distributions on the California Coast

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This project will take advantage of the exceptional fossil record of coastal California to examine the distributions of living mollusk species over the past ~125,000 years and, using geochemical analysis of their shells, reconstruct the environmental conditions where these species lived. This approach will make it possible to determine if the ancient distributions of species are consistent with their modern environmental ranges (implying stability) or if some species once lived outside their present-day environmental ranges (implying evolution). This work will contribute to an understanding of the stability of species' ranges in the face of environmental change, and will provide new data on how the environments and species compositions of economically important coastal ecosystems have varied through time.The primary goal of the proposed work is to determine whether the thermal niches of northeastern Pacific coastal mollusk species have evolved since the Late Pleistocene, and to test the performance of ecological niche models in hindcasting Late Pleistocene distributions. Reliable paleoenvironmental data are essential to this task, and a large number of stable isotope profiles and clumped isotope measurements for fossil and modern shells of the common gastropod Callianax biplicata will be generated to reconstruct environmental conditions along the California coast. At each of approximately 20 localities, isotope profiles from recent individuals will be compared with profiles from individuals that lived in the same area during different stages of the last interglacial complex and subsequent highstands (Marine Isotope Stages 5 and 3). Reconstructed temperature and salinity ranges and other paleoenvironmental data will be used to determine whether the mollusk species occurring at each fossil site were occupying environmental conditions similar to those of the geographic regions they now occupy. This work will result in an improved understanding of the determinants of species distributions in space and time, a more detailed reconstruction of California coastal environments during the last interglacial complex, and improved forecasting models for projecting species distributions in an economically critical ecosystem.