Statolith chemistry: a new tool to understand the ecology and provenance of octopus

Abstract

Growing commercial interest in octopus fisheries has increased the need to develop rapid and inexpensive methods to determine the geographical origins (provenance) of individuals. Identifying the provenance of marine species not only supports high-quality and sustainable fisheries, as seafood distributors are held accountable for accurately sourced products, but can address important ecological questions on movement and connectivity. Multi-elemental signatures in statoliths, the cephalopod equivalent of otoliths, could act as geographical proxies but have never been analysed in octopus. As such, we investigated the statolith chemistry of commercially harvested Octopus berrima collected across two seasons (summer and winter) and from four sites along the South Australian coast with different temperature and salinity profiles. Statoliths were analysed using laser ablation inductively coupled plasma mass spectrometry, targeting the central portion of the structure, to measure concentrations of chosen elements (⁷Li, ²⁴Mg, ⁵⁵Mn, ⁸⁸Sr, ¹³⁷Ba, ¹¹B, ²³Na, ³¹P, ³⁹K, ⁵⁹Co, ⁶⁰Ni, ⁶⁵Cu, ⁶⁶Zn, ²⁰⁸Pb). Significant differences between region and season were found for most elements, except ⁸⁸Sr and ⁶⁰Ni. Cross-validation classification found that 85% of octopus from environmentally distinctive regions were able to be correctly classified back to region of origin, regardless of harvest season. Regions with similar environmental profiles had lower classification success (70%). We also found that ¹¹B, ¹³⁷Ba, and ⁵⁵Mn contributed most to the discrimination among regions. This study reveals that distinctive geographic signatures are present in statoliths of octopus, establishing the potential of statolith elemental chemistry as a powerful tool for tracking the movement and provenance of octopus.