RECONSTRUCTING THE HABITAT, LOCAL EXTINCTION AND POTENTIAL TSUNAMI TRANSPORT OF THE PROLIFIC ISRAELI GLYCYMERIS NUMMARIA

The Mediterranean beaches of Israel are distinguished by nearly monospecific shell pavements of Glycymeris nummaria of previously unknown provenance. These small clams are rarely observed live off the coast of the region yet are the most common beach fossil observed from Haifa to Ashkelon, implying past populations were extensive and that environmental change may have contributed to their local extirpation in the modern fauna. Radiocarbon dating has determined that the beach assemblage shells range from 6500 to 800 yr bp in age, but little is known about the environmental niche of this species in the Eastern Mediterranean. We utilized oxygen isotope paleothermometry to constrain the complete temperature life history of three specimens sampled from shells collected near Caesarea, Israel, and determined that the three individuals survived for 1.5-2 years each, growing around 2 cm/year as determined by the seasonal temperature oscillations recorded, and recorded temperatures ranging from 19 to 24°C. One shell, radiocarbon dated at 4300 yr bp and found articulated within a tsunami deposit, was likely transported quickly and buried alive. Conservatively assuming a 5°C annual range of temperatures experienced in aggregate, this implies that the shells could not have originated at shallow than 50-70 m depth based on modern temperature observations. These depths are not recorded until >2.5 km off the coast of Northern Israel, meaning that a strong onshore transport mechanism is needed to explain their prevalence. In the case of the tsunami-transported shell, we hope to constrain the precise energy to suddenly transport the articulated animal over 2.5 km. G. nummaria is a detritus feeder which may have proliferated during a long-term decline in productivity which allowed it to opportunistically colonize a shelf where other bivalves could not obtain adequate nutrition from surface phytoplankton. Preliminary results from comparison of LA-ICP-MS measurements of Barium and Strontium/Calcium ratios in fossil and modern shells corroborate a change in available food supply and potentially substrate availability in the time coinciding with their disappearance.