174-10 Understanding the Impacts of Climate Change on Biodiversity: Changes in Molluscan Diversity and Community Structure in Southeastern Virginia in Response to the mid-Piacenzian Warm Period

Session: Environmental Instability During Greenhouse Periods: Impact on Terrestrial and Marine Ecosystems

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With warming sea surface temperatures and shifting climate conditions, understanding how marine organisms will respond to these changes is crucial to determining effective conservation strategies for Earth’s biodiversity. Furthermore, marine organisms often play a significant role economically and ecologically by providing ecosystem services to many communities, such as those around the Chesapeake Bay. This research studies the effects of global climate change during the mid-Piacenzian Warm Period (MPWP) on fossil molluscan assemblages in southeastern Virginia. The MPWP lasted ~240,000 years from 3.264 to 3.025 Ma during the Pliocene. Environmental conditions rapidly changed as sea surface temperatures rose ~3 ^oC and atmospheric CO₂ concentrations reached a possible maximum of ~425 ppmv. This context makes the MPWP comparable to future temperature and CO₂ estimates and may provide insight into how modern molluscan assemblages will react to ongoing climate change.

The Yorktown Formation is a key geologic unit that contains an abundance of fossil mollusks and records a useful stratigraphic sequence from before to after the MPWP. Samples were compiled from field and museum collections using a bulk sampling protocol. Taxonomic identification was completed using monographs and online databases. We employed the minimum number of individuals counting method to estimate relative abundances of taxa. Changes in richness, diversity, and community structure were analyzed to assess population-level responses to climate change. We applied rarefaction, Hill numbers, Detrended Correspondence Analysis (DCA), and Permutational Analysis of Variance (PERMANOVA) techniques to our data. Taxon-specific responses to climate change were evaluated using percent abundance.

Our results demonstrate that the diversity of molluscan assemblages peaks during the warming interval. With subsequent cooling, diversity did not immediately revert back to pre-warming levels. Furthermore, molluscan community structure differed significantly between each geologic member across the MPWP. We noted no major differences between our analyses of genera-level data and species-level data. Taxa often exhibited species-specific changes in abundance in response to changes in climate and showcased no phylogenetic- or ecological-based pattern. Based on our data, it is evident that modern molluscan fauna will experience long-term shifts in diversity and community structure with rising temperatures, which may have implications for global economies, ecosystem services, and marine biodiversity.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7709

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