Barnacle shells as biomonitoring material

During growth of the shell plates of barnacles it is possible that trace and minor metal ions replace calcium in the calcium carbonate lattice. By extension, there may then be a relationship between the concentration of trace metals in the shell and that in the environmental water. Should this relationship exist, then such calcified material may represent a permanent record of environmental trace metal concentrations. Semibalanus balanoides cyprid larvae were collected from the plankton and settled on slates in the laboratory. These slates with their barnacles of known age were placed at several sites around the coast of the Island of Anglesey, Wales. These sites were chosen for their differences in environmental trace metal loading and barnacle growth rates. Subsamples were taken from the populations from each of the sites at 5–6 week intervals over a period of 2 years. Barnacle shell weight and the shell concentrations of magnesium, strontium, manganese, zinc and copper were measured. Barnacles with similar growth rates had higher shell metal concentrations from environments with higher metal loading, while in general smaller shells had higher trace metal concentrations. However, it is concluded that barnacle shell cannot be considered to be an ideal biomonitoring material.