MORPHOLOGICAL DEPENDENCE OF ELEMENT DISTRIBUTIONS IN THE ORGANIC AND MINERAL FRACTIONS OF THE H. AMERICANUS EXOSKELETON

The crustacean exoskeleton is a complex biocomposite of inorganic mineral and organic macromolecules with highly divergent morphologies across different taxa Structures and compositions of the organic framework show complex links to environmental and developmental pressures that complicate taphonomic interpretations.

Previous studies of the cuticle have assumed that magnesium, phosphorous, and other trace metals are largely contained in the inorganic mineral fraction. Due to analytical limitations of structural analyses and in situ spectroscopic methods, the distribution of elements between the organic and inorganic portions could not be resolved.

For example, previous Raman and XRD studies conclude the correlations between increased concentrations of trace elements, such as P and Mg measured in reinforced structures, e.g. the claw and abdomen, are primarily determined by the mineral fraction. Using the American Lobster (Homarus americanus) as a model organism to understand the interplay of body part and composition in determining cuticle composition, this study quantified the distributions of Mg and P in the mineral and organic fractions. The experiments were designed to dissolve the exoskeleton of 10 body parts using three types of solutions that were specific to extracting 1) the mineral phase, 2) protein, and 3) polysaccharide. Analysis of the solutions by ICP-OES shows the mineral phase contains magnesium and phosphorous at concentrations sufficient to support the formation of calcium-magnesium and phosphate minerals. The protein fraction of the body parts contain significantly more Mg and P than previously hypothesized, and the levels of P contained in the organic portion are fairly constant.

The findings demonstrate that the distribution of elements in the mineral components is highly variable and specific to individual body parts. A significant portion of P and Mg is contained in the organic fraction, specifically the protein component.