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

Abstract

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.

Elemental uptake via immersion: a mass-marking technique for the early life-history stages of ­cephalopods

“…The successful management of cephalopod fisheries is hindered by an inability to evaluate population structure and connectivity (Doubleday et al 2008a, 2008b, Pecl et al 2010. Whilst significant advances in recent years have improved our understanding of movement and migration patterns of many cephalopod populations globally (Semmens et al 2007), methods to tag and track the poorly understood juvenile stage of cephalopods is recognised as a key priority for marine ecologists, as this is the stage most influenced by environmental fluctuations (Semmens et al 2007).…”

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

“…The population structure of O. pallidus, therefore, reflects an expected congruence between early life history strategy and level of dispersal from the parental population. In contrast, an elemental analysis study of an Octopus maorum population (a merobenthic species with planktonic hatchlings) indicated some structure, but also a degree of connectivity (Doubleday et al 2008). There are no published studies which have utilised elemental signatures to investigate populations of holobenthic cephalopods.…”

“…Elemental analyses were performed using LA-ICPMS at the Centre for Ore Deposit Research (CODES), University of Tasmania. For more details on the laser ablation system, analytical specifications, detection limits (DLs) and external and internal standards used, refer to Doubleday et al (2008). For the adults, the pre-hatch region visible within the stylet cross section was targeted (see Doubleday et al 2006) and ablation spot size was 35 µm (which is the approximate size of the pre-hatch region) with a laser pulse rate of 10 Hz.…”

“…Using a light microscope, individual photos were taken of each mounted stylet to aid in the detection of the stylet material once in the ablation chamber. Adult stylets were removed from mantle tissue (see Bizikov 2004 for stylet location) and processed according to the methods outlined in Doubleday et al (2008). All animals were fresh, except for 50% of the EFI individuals and all of the WFI individuals, which were frozen prior to dissection.…”

“…However, targeted elemental analysis has been applied successfully to adult stylets of a merobenthic octopus species (Doubleday et al 2008). Stylets are a pair of fine, cartilage-like rods embedded within the mantle musculature.…”