Potential use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) techniques for determining larval dispersal of Austrovenus stutchburyi in Whangarei Harbour

Abstract

Population connectivity is a fundamental component of population dynamics in marine systems, understanding of which can improve ecological understanding and management. Direct observation of larval dispersal at appropriate spatial and temporal scales is difficult. The use of LA-ICP-MS based elemental fingerprinting overcomes many problems with directly observing dispersal and is therefore a powerful tool for tracking population connectivity. This thesis examined the potential for LA-ICP-MS to estimate population connectivity of Austrovenus stutchburyi in Whangarei Harbour and its surrounds. I determined optimal methods for the preparation of shell material for analysis by LA-ICPMS to achieve high sample throughput and accurate analyses. Comparison of different cleaning and mounting options suggested that optimal preparation should include cleaning the shell with deionised water and mounting shells on a microscope slide whole for ablation. I used laboratory culturing experiments to investigate the effect of increased [Sr], [Mg], and [Ba] on trace element uptake from surrounding water by A. stutchburyi. Of the elements measured, only increased [Sr] resulted in increased strontium content of shell material. Results suggested that the elemental composition of A. stutchburyi shell likely reflects a number of environmental and biological conditions. Separate experiments examined the effect of different sediment chemical signatures, and showed no significant influence of sediment on elemental composition. No relationship was found between elemental composition of sediment and shell in the field. I utilised LA-ICP-MS elemental fingerprinting of A. stutchburyi in Whangarei Harbour to investigate spatial differences in the settled shell of individuals collected from 14 sites within the harbour. Strong spatial differences were found to exist (44-100% discriminant function analysis classification success). Higher classification success occurred when sites were grouped regionally (88% classification success). Variation in elemental fingerprints over time was investigated at one site for 3 sampling events over 6 months. Temporal changes negatively affected results (45-99% classification success). Elemental signatures on the prodissoconch within settled shells showed high variation, indicating multiple larval sources. This thesis concluded that LA-ICP-MS based elemental fingerprinting is a potentially valuable technique for determining larval origins of A. stutchburyi in Whangarei Harbour and neighbouring estuaries, and informing population connectivity of this species.