Low Mg/Ca ratio alters material properties in sea urchin larvae skeleton

Biomineralization in organisms is strictly regulated, and therefore, chemical compositions as well as crystal structures of the minerals are species specific. During the embryonic development, sea urchin larvae produce a calcite endoskeleton (spicules) that contains about 5% of Mg. For sea urchins and other organisms, it is assumed that Mg is important for the process of biomineralization and for the mechanical properties of the resulting biomineral. To study the influence of Mg on skeletal growth and on biomineral structure and composition, sea urchin larvae spicules were chosen as an in vivo test system. For this purpose, the Mg/Ca ratio was modified in the artificial seawater medium wherein sea urchin larvae were growing. It was shown that Mg deficiency during larval development caused morphology defects of the larvae and of their calcite spicules. The Mg distribution within the larvae skeleton was analyzed and found to be homogenous. An in vivo reduction of the Mg content influenced the mechanical performance of larval spicules (Young’s modulus and hardness). The investigations of larvae exposed to reduced Mg conditions highlight the important role Mg plays for sea urchin larvae development, biomineralization process and the resulting biomineral. The sea urchin larvae are presented as an ideal model to study different effects on larval development and morphology, especially on the biomineral properties.