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Reciprocal Changes in Calcification of the Gastrolith and Cuticle During the Molt Cycle of the Red Claw Crayfish Cherax quadricarinatus

¹ Department of Life Sciences, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
² Department of Biotechnology Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
³ National Institute for Biotechnology in the Negev (NIBN), Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
⁴ Ilse Katz Center for Nanoscience and Nanotechnology and Reimund Stadler Minerva Center for Mesoscale Macromolecular Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel
⁵ The Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

^* To whom correspondence should be addressed. E-mail: sagia{at}bgu.ac.il

Mobilization of calcium during the molt cycle from the cuticle to transient calcium deposits is widely spread in crustaceans. The dynamics of calcium transport to transient calcium deposits called gastroliths and to the cuticle over the course of the molt cycle were studied in the crayfish Cherax quadricarinatus. In this species, calcium was deposited in the gastroliths during premolt and transported back to the cuticle during postmolt, shown by digital X-ray radiograph analysis. The predominant mineral in the crayfish is amorphous calcium carbonate embedded in an organic matrix composed mainly of chitin. Scanning electron micrographs of the cuticle during premolt showed that the endocuticle and parts of the exocuticle were the source of most of the labile calcium, while the epicuticle did not undergo degradation and remained mineralized throughout the molt cycle. The gastroliths are made of concentric layers of amorphous calcium carbonate intercalated between chitinous lamella. Measurements of pH and calcium levels during gastrolith deposition showed that calcium concentrations in the gastroliths, stomach, and muscle were about the same (10 to 11 mmol l^–1). On the other hand, pH varied greatly, from 8.7 ± 0.15 in the gastrolith cavity through 7.6 ± 0.2 in muscle to 6.9 ± 0.5 in the stomach.

Abbreviations: ACC, amorphous calcium carbonate • FTIR, Fourier transform infrared spectroscopy • MMI, molt mineralization index