Using stylet elemental signatures to determine the population structure of Octopus maorum

A novel method was used to investigate the population structure and dispersal patterns of Octopus maorum, an octopus species with a planktonic larval stage, which forms a distinct and large aggregation in southeast Tasmania. Single and multi-elemental signatures within the 'early life history' region of the stylet (an internal 'shell') were used to determine levels of connectivity and the common origins of individuals collected from 5 locations across Tasmania, South Australia and New Zealand. Using laser ablation inductively coupled plasma-mass spectrometry (LA ICPMS) the stylets were analysed for 12 elements, 8 of which were found to be excellent spatial discriminators. There was evidence of population structuring within the O. maorum population, with a distinct separation of the aggregation site in southeast Tasmania from other groups. Octopuses from the aggregation shared a common origin and appeared to be coming from a local neighbouring source. The 2 northern sample locations shared a similar elemental signature, which could be due to either similar water chemistries or long-distance dispersal. This study presents the first insights into the population structure of O. maorum, and provides vital information for the sustainable management of this species. Furthermore, this technique will have direct application to other more heavily fished octopus species around the world.