Strontium and manganese uptake in the barnacle shell: Electron probe microanalysis imaging to attain fine temporal resolution of biomineralization activity

Barnacles deposit a thin layer of calcium carbonate at the base of the shell in an incremental fashion. The shells are therefore well suited to provide a temporal record of metal exposure, if metals from the water are incorporated into the shell as growth increments form. Fine temporal resolution of metal exposure would prove useful for studying environmental exposure or biomineralization processes. For this study, barnacles were exposed to artificial sea water (ASW) enriched with either strontium, manganese or lead. Barnacles were exposed to different levels of Sr and Mn for different lengths of time from 2 h to 2 d. The elemental composition of the shells was determined by electron probe X-ray microanalysis (EPXMA) imaging. Strontium and Mn were incorporated into the shells in direct proportion to the metal levels in the ASW. A 2 h pulse of 1 mM Mn-enriched ASW did not result in a detectable band of Mn in the shell; however, a 6-h exposure yielded a clearly visible band of Mn-rich shell. Exposure to 0.24 μM Pb-enriched ASW caused marked reduction in the Ca content of the shell; however, a Pb-rich growth band was not detected in the shell. Barnacles analysed by EPXMA imaging provide a sequential record of metal exposure for Mn and Sr, with a time resolution of approximately 6 h. Enrichment of ASW with either Sr or Mn can be used as a probe to monitor biomineralization events.