Metabolic proxy for cephalopods: Stable carbon isotope values recorded in different biogenic carbonates

1. Measuring the metabolic rate of marine animals in their natural environment is challenging, impeding our understanding of their physiological ecology. Recently, a novel metabolic proxy, namely the δ13C values of biogenic carbonates (otoliths), was experimentally validated in teleost fishes. Cephalopods possess several types of biogenic carbonates, such as statolith, cuttlebone, and other internal and external shells, which are all potential metabolic recorders, but few have been evaluated. 2. To test the feasibility of the δ13C metabolic proxy in cephalopods, we conducted a temperature-controlled experiment with the pharaoh cuttlefish Sepia pharaonis to assess whether the proportion of metabolically derived carbon (Cresp) incorporated into statoliths and cuttlebones increases with metabolism in a warm environment. Moreover, we conducted multiple-species analysis by using the published δ13C values of various biogenic carbonates to evaluate the consistency of the proxy among cephalopod...