Environmental pH, O₂ and Capsular Effects on the Geochemical Composition of Statoliths of Embryonic Squid Doryteuthis opalescens

Spawning market squid lay embryo capsules on the seafloor of the continental shelf of the California Current System (CCS), where ocean acidification, deoxygenation and intensified upwelling lower the pH and [O₂]. Squid statolith geochemistry has been shown to reflect the squid’s environment (e.g., seawater temperature and elemental concentration). We used real-world environmental levels of pH and [O₂] observed on squid-embryo beds to test in the laboratory whether or not squid statolith geochemistry reflects environmental pH and [O₂]. We asked whether pH and [O₂] levels might affect the incorporation of element ratios (B:Ca, Mg:Ca, Sr:Ca, Ba:Ca, Pb:Ca, U:Ca) into squid embryonic statoliths as (1) individual elements and/or (2) multivariate elemental signatures, and consider future applications as proxies for pH and [O₂] exposure. Embryo exposure to high and low pH and [O₂] alone and together during development over four weeks only moderately affected elemental concentrations of the statoliths, and uranium was an important element driving these differences. Uranium:Ca was eight-times higher in statoliths exposed to low pH_T (7.57–7.58) and low [O₂] (79–82 µmol·kg⁻¹) than those exposed to higher ambient pH_T (7.92–7.94) and [O₂] (241–243 µmol·kg⁻¹). In a separate experiment, exposure to low pH_T (7.55–7.56) or low [O₂] (83–86 µmol·kg⁻¹) yielded elevated U:Ca and Sr:Ca in the low [O₂] treatment only. We found capsular effects on multiple elements in statoliths of all treatments. The multivariate elemental signatures of embryonic statoliths were distinct among capsules, but did not reflect environmental factors (pH and/or [O₂]). We show that statoliths of squid embryos developing inside capsules have the potential to reflect environmental pH and [O₂], but that these “signals” are generated in concert with the physiological effects of the capsules and embryos themselves. View Full-Text