Systematic evaluation of oxygen isotopes in cephalopod statoliths as thermal proxies

Abstract

Temperature histories are critical for understanding and predicting ecological functioning in marine systems. Stable oxygen isotopes (delta O-18) locked within calcified tissues can uncover experienced temperatures of marine animals, but have been little evaluated in the statoliths of cephalopods. As such, we investigated field applications of oxygen isotope ratios in statoliths (delta O-18(statoliths)) for reconstructing the thermal histories of cuttlefish, octopus, and squid. In doing so, we collated measured (instrumental and modelled) temperature and salinity data, alongside delta O-18(statoliths) data, of ocean-caught species from Taiwan and Australia. To navigate potential species-bias or vital effects, two aragonite-specific thermometry equations were compared, whilst simulation modelling evaluated variation and addressed uncertainties. Linear regressions identified environmental and biological influences on the differences between measured and reconstructed temperatures. Variable trends in temperature reconstructions were observed between taxa, which may be due to ecological traits. For squid, the relationship was highly aligned with no significant model predictors. For cuttlefish and octopus, differences between measured and reconstructed temperatures increased in warmer conditions, and may indicate thermoregulation behaviour. Here, we demonstrate that delta O-18(statoliths) values can function as natural proxies of ocean temperature and are an invaluable tool for broadening the field of thermal ecology for the important, yet understudied, cephalopods.