Assessing Chamelea gallina biomineralization dynamics in the Holocene of the Northern Adriatic (Italy)

This study investigates the variation of skeletal and growth parameters of the bivalve Chamelea gallina in the Holocene of the Po-Adriatic System (Italy). C. gallina is a valuable economic species in the Mediterranean Sea, expected to be impacted by numerous anthropogenic stressors that threaten the biological and economic sustainability of its fishery. Here, skeletal parameters (micro-density and apparent porosity) and growth parameters (bulk density, linear extension and net calcification rates) of C. gallina shells were investigated in four shoreface-related C. gallina shell-rich deposits. Two from present-day Adriatic shoreface seabeds and two from comparable settings of the middle Holocene, when regional sea temperatures were higher than today. In each horizon, 30 right valves of different sizes were measured and aged using three independent methods (shell surface growth rings, shell internal bands and 18O/16O ratio) to determine the Von Bertalanffy growth functions. Which, in turn, allowed us to estimate targeted parameters for each assemblage investigated. Differences in the skeletal and growth properties of C. gallina shells were also investigated in relation to animal sexual maturity. C. gallina appears to be sensitive to changes in environmental conditions, showing macro-scale variations in bulk and micro-density. Shells from the middle Holocene presented a denser exoskeleton than modern ones, probably because of different mineralization rates mainly driven by temperature. Nevertheless, linear extension and net calcification rates showed no differences between past and modern assemblages, also when immature and mature individuals were analyzed separately. C. gallina biomineralization dynamics evaluated on timescales well beyond ecological monitoring offer insights into its adaptive capacities to face near-future global warming.