IMPACTS OF WARM VS. COLD CLIMATE CONDITIONS ON THE LIFE HISTORY OF MODERN AND FOSSIL MERCENARIA SHELLS FROM THE US MID ATLANTIC COASTAL PLAIN OF NORTH CAROLINA

With the current trend of global warming, questions have been raised on the biological consequences of increasing water temperature and environmental change on economically and ecologically important bivalves. One way to assess such impacts is to evaluate changes in life history across space and time in the context of warm vs. cold climate conditions. This assessment can be accomplished using sclerochronlogy (i.e., the study of growth patterns in the accretionary hard parts of aquatic organisms). Today, marine bivalves exhibit a consistent latitudinal pattern regarding their life history. Bivalves from low latitudes tend to grow fast and have short lifespans, whereas those from mid to high latitudes show the opposite trend. This pattern may be related to environmental conditions, such as temperature and availability of nutrients. In part because of its economic importance, growth patterns in shells of the northern and southern hard clams (Mercenaria mercenaria and M. campechiensis, respectively) are well documented and have been established throughout its geographic range. Most of this work has been done using modern and archaeological specimens but fossil specimens remain to be investigated. How has the life history of fossil Mercenaria changed during climate conditions that were warmer or colder than today? Here, we provide preliminary life history data recorded in Mercenaria shells from three time intervals (modern and Plio-Pleistocene; Duplin and Waccamaw Formations, respectively) at similar latitudes in the US Mid Atlantic Coastal Plain of North Carolina. Differences in lifespan and growth rates among these populations will be approximated using the von Bertalanffy growth equation. We hypothesize that fossil bivalves from warm climate conditions (Pliocene Duplin Formation) will have shorter lifespans and faster growth rates compared with those found in cold climate conditions (early Pleistocene Waccamaw Formation). Future work will examine Mercenaria shells across a latitudinal gradient from Florida to Virginia. Results from this study will contribute to our understanding of how this bivalve species may respond to rising seawater temperature projected for the end of the 21^st century.