PALEOBIOGEOGRAPHICAL AND PALEOECOLOGICAL TRENDS THROUGH THE LATE PALEOCENE AND EARLY EOCENE: A COMPARISON BETWEEN REEFAL AND MOLLUSCAN COMMUNITIES (Invited Presentation)

Today there are serious concerns about the declining health of marine ecosystems associated with significant environmental changes. Similar events in the geological past, such as the early Cenozoic hyperthermals (e.g., the Paleocene-Eocene Thermal Maximum or PETM) provide important information about how current ecosystems might survive major climate change. Here we test the hypothesis that these climate warming events, in particular the PETM, led to significant ecological changes in the structure of benthic ecosystems. To address this hypothesis, we have investigated paleoecological changes in two different regions of the world: molluscan communities from the US Gulf Coastal Plain and the warm-water carbonate communities (coral reefs and foraminiferal shoals) from the Tethyan Adriatic Carbonate Platform in Slovenia. We collected field data from both regions (combined with existing datasets) and used quantitative ecological metrics (e.g., diversity, richness, hierarchical clustering, and network analyses) to assess how these shallow-water communities changed through the Paleocene and Eocene. Quantitative ecological data from the Adriatic Carbonate Platform reveal significant changes in community structure of coral reefs and foraminiferal shoals across the Paleocene/Eocene boundary. In contrast, none of the Early Cenozoic Hyperthermals (including the PETM) caused significant changes in the richness or composition of molluscan marine communities from the Gulf Coastal Plain. These data highlight the importance of assessing different community types across major environmental events. In comparison to sensitive ecosystems, such as coral reefs, mollusk communities are relatively tolerant of thermal stress. We propose that the Gulf Coast communities were resilient to change because they were dominated by mollusks, the mollusks in the Gulf are interpreted to have been better adapted to high temperatures, which is demonstrated by their evolutionary history. Our work shows that the current biodiversity crisis will likely impact marine communities differently depending on their particular sensitivities to stresses, such as warming. Furthermore, the current rate of climate change is exceeding the rates observed during the early Cenozoic hyperthermals, meaning that these events may not be the best analogues for expected community shifts in the coming decades.