Venerid bivalve Venus verrucosa as a high-resolution archive of seawater temperature in the Mediterranean Sea

High-resolution stable isotope data (delta O-18, delta C-13) were used to study growth strategies of the bivalve Venus verrucosa collected from three sites of the eastern coast of the Adriatic Sea. The principal objectives of this study were to identify the main growing season and to evaluate the potential applicability of delta O-18(shell) values to reconstruct the seasonal temperature variability. Calcium carbonate for oxygen and carbon isotope analyses was obtained by drilling the outer shell layer. Temporal and spatial variations in temperature and salinity values at the study sites were simulated using the 3D numerical ocean model ROMS. Annual periodicity of growth patterns was confirmed by delta O-18(shell) cycles which corresponded to the number of observed seasonal growth marks. Temporal alignment of stable oxygen data with modelled seawater temperature data indicates that V. verrucosa deposits shell material from March/April to December. Shell growth slowdown and/or cessation occurred between late winter and early spring when the seawater temperature dropped below 12 degrees C at the two northern sites, Istria and Pag Bay, and below 13 degrees C at the southern site, Kastela Bay. Summer temperatures reconstructed from V. verrucosa agreed well with modelled summer temperatures, but lowest reconstructed temperatures were consistently higher than the modelled winter values. The range of delta O-18(shell) values obtained from V. verrucosa shells is higher than the range obtained previously from other species in the eastern Adriatic Sea, indicating the high potential of V. verrucosa for temperature reconstructions.