Postdoctoral Fellowship: OCE-PRF: Do dead shells make good homes? Assessing the Development, Stability, and Evolution of Shell Gravel Habitats Across Space and Time

The aim of this project is to assess the coevolution of benthic invertebrate communities and shell gravel habitats along a latitudinal gradient. Benthic communities directly modify their physical habitat as the skeletal debris (shells, bones, sclerites, etc.) of dead organisms over many generations accumulate in the sediment, creating patches of coarse substrates upon which epibenthic (surface-living) organisms can colonize. Despite being rare on modern continental shelfs, shell gravel habitats are hotspots for biodiversity and perhaps the best modern analogs of early fossil assemblages from before the onset of pervasive soft-sediment infaunal communities (> 65 million years ago). Further, while the evolutionary origins and ecological consequences of the global latitudinal gradient have been rigorously assessed to explain both modern and deep-time biodiversity, we still know little about latitudinal variation in the processes that determine the production, persistence, and preservation of fossil assemblages. The PI will collect and assess sediment samples from various substrate conditions (gravel vs mud, shallow vs deep) from two notable shell gravel environments along the Eastern Pacific coast of North America: The warm-temperate Channel Islands of Southern California and the cold-temperate San Juan Islands of Washington, forming a latitudinal gradient across which benthic communities, sediment substrates, and their local feedback effects will be quantified. The PI will further increase scientific engagement in the San Francisco Bay area by collaborating with biomonitoring agencies, creating lesson plans for local schools, volunteering with the University of California Museum of Paleontology, and mentoring undergraduates in research. Three overarching investigations will be conducted during this project: (1) the development, persistence, and temporal scale of dead-shell assemblages with respect to sedimentation rates, water temperature, and bioturbation intensity, (2) the fidelity between dead-shell assemblages and living benthic communities, and its relationship with dead-shell persistence, and (3) feedback effects that link these ecological and taphonomic dynamics. The first investigation will use postmortem ages determined via radiocarbon dating to quantify the duration of time averaging and determine shell loss parameters (disintegration, sequestration, and burial) within and between each field area. The second investigation will assess correlations in both univariate ecological metrics and multivariate composition among sampled communities and dead-shell assemblages. The third investigation will combine these physical and biological results to model their interactions and identify taphonomic feedbacks that act on these habitats. This research will bridge important gaps between physical and biological oceanography by identifying mechanisms by which benthic habitats shape – and are themselves shaped by – the succession of invertebrate communities. These insights will improve both (1) paleoecological interpretations from the fossil record and (2) conservation strategies for managing coastal biodiversity in a world of changing ocean conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.