Relationship between body zinc concentration and allometric growth measurements in the mussel Mytilus edulis

The frequency distribution of shell lengths in the mussels Mytilus edulis (L.) taken from a site in the Tyne Estuary (UK) in summer, 1980, typically displayed a bimodal shape, with a small peak in the 8 to 20 mm size range and a much broader peak in the 22 to 50 mm region. A collection of mussels was made consisting of two groups, one from each of the above size peaks. The group of larger mussels had a significantly higher mean zinc concentration than the group of smaller mussels, mainly because a few large individuals had very high zinc concentrations. The ratios of shell width:height, width:length and length:height were also significantly higher in larger mussels. However, the ratio of flesh dry wt:shell dry wt (flesh condition) was lower in larger individuals. The whole soft tissue zinc concentration was positively correlated with width:height and width:length, but negatively correlated with flesh wt:shell wt. It was concluded that allometric ratios may provide an attractive alternative to simple size characteristics as a basis for trace metal determinations, particularly in a comparison of metal levels in mussel populations from widely differing habitats where absolute size is a poor indicator of age or growth rate.Contribution No. 1221 of the Center for Estuarine and Environmental Studies of the University of Maryland