Growth cessation and metabolism complicate the use of Rangia cuneata shells as environmental proxies

A comparison of high-resolution δ 18 O values in the aragonite shells of Rangia cuneata with sub-monthly δ 18 O water , temperature, and salinity data reveals extended and unpredictable periods of growth cessation from late fall to early spring. We hypothesize that fluctuations in temperature and salinity cause this growth cessation. We utilized δ 13 C shell , δ 13 C DIC , and tissue δ 13 C values to estimate the amount of metabolic carbon incorporated into the shell carbonate in R. cuneata as a proxy for metabolic rate. Increases in the average amount of metabolic carbon incorporated into the shell carbonate increased with the average salinity along the Neuse River Estuary in North Carolina, USA, suggesting that variations in salinity lead to stress, despite the species' wide salinity tolerance. Alternative species are preferable for paleoclimate reconstructions until the triggers of growth cessation in this species are identified. • Rangia shells show long winter growth cessation, disrupting seasonal isotope records. • δ 13 C analyses show higher metabolic carbon incorporation into shell at higher-salinity sites. • Higher % metabolic carbon incorporation into s osmoregulatory stress along the salinity gradient. • Rangia shells are unreliable for paleoclimate reconstructions until growth triggers and metabolic-environmental interactions are better constrained.