Laser ablation ICP-MS analysis of larval shell in softshell clams (Mya arenaria) poses challenges for natural tag studies
Limnol. Oceanogr. Methods 5:241-249 (2007) | DOI: 10.4319/lom.2007.5.241
ABSTRACT: We investigated whether laser ablation inductively coupled plasma mass spectrometry (ICP-MS) could be used to quantify larval shell compositions of softshell clams, Mya arenaria. The composition of aragonitic otoliths has been used as a natural tag to identify natal habitat in connectivity studies of fish; if it is possible to measure larval shell reliably, this technique could also be applied to marine bivalves. To determine whether the first larval shell (prodissoconch I) could be measured independent of underlying material, we conducted laboratory experiments in which larval M. arenaria were exposed to enrichments of the stable isotope 138Ba during different stages in shell development. We were unable to isolate the chemical signature of the prodissoconch I from subsequent life stages in all combinations of shell preparation and instrument settings. Typical instrument settings burned through the prodissoconch I on a post-settlement juvenile and at least nine days of second larval shell (prodissoconch II) growth. Our results suggest instrumental and technical improvements are needed before laser ablation ICP-MS can be useful for connectivity studies that require analysis of larval shell on a post-settlement M. arenaria juvenile. Laser burn-through is potentially a problem in any connectivity study where it is necessary to assay the small amounts of shell material that are deposited before a larva disperses away from its natal location.