Effects of field contamination by metals (Cd, Cu, Pb, Zn) on biometry and mechanics of echinoderm ossicles

Echinoderms are known to readily incorporate metals in their calcified endoskeleton. It is currently unclear if this has an impact on the skeleton function or if this can be considered as a detoxification mechanism. In the present work, populations of the sea urchin Echinus acutus and the starfish Asterias rubens were studied in stations distributed along a metal contamination gradient in a Norwegian fjord (Sørfjord). Ossicles involved in major mechanical functions - sea urchin spine and starfish ambulacral plate - were analyzed for their metal concentration (Cd, Cu, Pb and Zn) and their biometric and mechanical properties. Starfish plates were more contaminated by Cd, Pb and Zn than sea urchin spines. Cu concentrations were at background levels. In E. acutus, metals principally affected size. In A. rubens, material stiffness and toughness were decreased in the most contaminated station. This reduction is attributed either to the direct incorporation of metals in the calcite lattice and/or to deleterious effects of metals during skeleton ontogenesis. The contrasting incorporation of metals in the skeleton of the two investigated species accounts for the different impact of the metals, including in terms of fitness. The present results clearly indicate that, at least in A. rubens, incorporation of metals in the skeleton cannot be considered as a detoxification mechanism.