Strontium incorporation into calcified structures: separating the effects of ambient water concentration and exposure time

Chemical elements within calcified structures of organisms such as fish, corals, bivalves, gastropods and foraminiferal shells can provide a record of the environmental characteristics at the time of calcification. To predict accurately the environmental characteristics at the time of calcification, it is important to understand the influence of exposure time on elemental incorporation. We examined the effect of enhanced ambient strontium: calcium (Sr:Ca) (2x and 4x ambient concentrations) and different periods of exposure (2, 4, 8, 16 and 32 d) on Sr:Ca uptake and incorporation into fish otoliths of the black bream Acanthopagrus butcheri (family: Sparidae). Sr:Ca ratios (hereafter referred to as concentrations) in bream otoliths increased with increasing ambient concentrations, with the amount of Sr:Ca incorporated into otoliths being positively affected by the period of exposure. Saturation of Sr:Ca in otoliths occurred after 20 d of exposure. Importantly, by measuring multiple variables of elemental uptake and incorporation, the relative effect of enhanced concentration and exposure time can be separated, which to date has not been possible. This research will allow for greater accuracy when interpreting environmental histories of fish.