IRON AND MANGANESE DEPOSITION IN THE PERIOSTRACA OF SEVERAL BIVALVE MOLLUSCS

Abstract

The Fe and Mn contents of the periostraca of specimens of the freshwater mollusks Anodonta californiensis and Unio novahollandae, and marine mollusk Mytilus californianus were determined. The freshwater mollusks concentrate Fe and Mn. The Mn being concentrated in regions high in Ca and P, which regions appear to be amorphous Ca3(PO4)2 in a proteinaceous matrix. Fe appears in these Ca-P regions but also occurs elsewhere in the periostracum. ESR measurements indicate the oxidation states of the Mn to be +2 and +4, while chemical experiments suggest Fe is present in the +3 oxidation state. The levels of Mn and Fe in the periostracum can be several percent. Local concentrations, determined by electron microprobe measurement, are as high as 15 and 5%, respectively, for A. californiensis, and 40 and 13%, respectively, for U. novahollandae. Mn and Fe may be removed directly from muds rich in these metals. Fe and Mn levels in the marine mollusk M. californianus do not locally exceed 0.05%. Mn and Fe in the periostracum of a mollusk can act as a defensive buffer against degradation from acidic conditions. The concentration of these metals, in the presence of phosphate and protein, produces a condition which can maximize nutritive value to microorganisms.