METABOLIC RATE AS A PREDICTOR OF MOLLUSCAN ABUNDANCE ACROSS THE MID-PLIOCENE WARM PERIOD IN THE VIRGINIA COASTAL PLAIN

Resting metabolic rate (RMR) is a potentially useful physiological predictor of species’ responses to climate warming because it represents the exchange of energy between an organism and its environment. Ectothermic species, like mollusks, will exchange heat energy at faster rates with the environment during warming, and enter a state of decreased respiration, heart rate, and metabolic rate. This allows mollusks with lower RMRs to better conserve energy and survive through periods of higher environmental pressure, including climate warming. By estimating RMR of fossil mollusks of the Yorktown Formation in Virginia, we can test whether the interaction between temperature and physiology influences fluctuations in molluscan abundance across the Mid-Pliocene Warm Period (MPWP). We hypothesized that bivalves and gastropods with higher RMRs would decrease in abundance across the MPWP.

We examined eight bulk samples from Yorktown Formation localities in southeastern Virginia collected from field sites and the Virginia Museum of Natural History collections. The Yorktown Formation is an ideal study system because: (1) the mollusks are well-preserved and sampled, highly abundant, and taxonomically well-resolved, and (2) paleotemperatures across the MPWP have been reconstructed recently for local outcrops. Each member of the Yorktown Formation represents a period of the MPWP: Sunken Meadow (before), Rushmere and Morgarts Beach (during), and Moore House (after). All bulk samples were sieved, then specimens were sorted, identified using taxonomic monographs, and counted to the species level when possible. For each species present in the Sunken Meadow Member, we estimated RMR using maximum length measurements of species type specimens and pre-warming temperature data derived from recently published paleoclimate reconstruction at the local scale.

Preliminary results suggest that genus-level changes in percent abundance from the Sunken Meadow to the Rushmere Member may vary according to estimates of pre-warming RMR. Understanding species-level responses to MPWP warming (1.8-3.6°C above pre-industrial) may be useful for predicting the response of extant mollusks, particularly those with economically important fisheries, to similar climate warming in the mid-Atlantic U.S. today.