Barium : calcium and molybdenum : calcium ratios were investigated in shells of the tropical scallop Comptopallium radula . Three juvenile specimens were harvested alive in the southwest lagoon of New Caledonia after a 1‐yr hydrological survey. Calcite samples representing a few hours of biomineralization were laser‐ablated along the maximal growth axis and analyzed for Ba and Mo content with an inductively coupled plasma mass...