Stylet elemental signatures indicate population structure in a holobenthic octopus species, Octopus pallidus

Abstract

Targeted trace elemental analysis was used to investigate the population structure and dispersal patterns of the holobenthic octopus species Octopus pallidus (Hoyle, 1885). Multi-elemental signatures within the pre-hatch region of the stylet (an internal 'shell') were used to determine the common origins and levels of connectivity of individuals collected from 5 locations in Tasmania. To determine whether hatchling elemental signatures could be used as tags for natal origin, hatchling stylets from 3 of the 5 locations were also analysed. We analyzed 12 elements using laser ablation inductively-coupled plasma-mass spectrometry (LAICPMS). Of the 12 elements, 7 were excellent spatial discriminators. There was evidence of high-level structuring with distinct groupings between all sites (the 2 closest being 85 km apart) within the adult O. pallidus population, suggesting that all adults had hatched in or near their respective collection sites. The hatchling signatures showed significant spatial variation, and a high percentage of individuals could successfully be traced back to their collection locations. However, they could not be used to trace adults back to their natal site, due to significant differences in element concentrations in hatchling and adult stylets, which was likely the result of differences in Ca concentration. This study presents the first insights into the population structure of a holobenthic octopus species using stylet elemental signatures, which will have important implications for the sustainable management of O. pallidus.