Temperature and salinity effects on elemental uptake in the shells of larval and juvenile softshell clams Mya arenaria

Abstract

The chemical composition of biogenic carbonate has great potential to serve as a natural tag in studies of marine population connectivity. Yet the degree to which carbonate chemistry reflects ambient water composition may be influenced by environmental parameters, physiology, and uptake kinetics. We explored the effects of temperature and salinity on the uptake of elements into shells of larval and juvenile softshell clams Mya arenaria. Clams were reared under controlled conditions using combinations of temperatures (15, 20, and 24°C) and salinities (22 and 30‰) commonly encountered in their natural habitat. We analyzed the ratios of a suite of elements (Mg, Mn, Sr, Ba and Pb) to Ca in seawater and shells using solution-based inductively coupled plasma-mass spectrometry (ICP-MS). Elemental ratios were translated into discrimination coefficients (Delement) to account for water chemistry variability among treatments. For larval shell, we found that DMn was lower in the low-temperature treatment than at higher temperatures, had mixed results for correlations with salinity, and exhibited an interactive effect between salinity and temperature. We also found that DBa of larval shell was higher in the 15°C treatment than at the other 2 temperatures. In juvenile shell, we found a temperature effect for DMn, however the exact relationship was unclear because DMn was higher in the mid-temperature treatment than either the low- or high-temperature treatments. DSr was negatively correlated with salinity in juveniles, with evidence of an interactive effect for temperature and salinity. DBa and DPb were both higher in juveniles in the low-temperature treatment than in the 2 higher temperatures. When discrimination coefficients significantly differed based on ANOVA, we used post hoc comparisons to further explore the effects of temperature and salinity. Correlation analyses showed that uptake differed significantly between larval and juvenile M. arenaria shell for all elements, with no predictable relationship in shell uptake between the 2 stages except for DBa. All of the elements examined in this study have the potential to be useful in tagging studies where geographic variability in temperature, salinity or elemental concentrations exists, although caution should be used to ensure any biological interactions with these variables are accounted for in data interpretation.