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Journal of Experimental Biology 114,181-196 (1985)
Published by Company of Biologists 1985

Apparent H⁺ Excretion and CO₂ Dynamics Accompanying Carapace Mineralization in the Blue Crab (Callinectes Sapidus) Following Moulting

James N. Cameron ¹ and Chris M. Wood ²

¹ The University of Texas at Austin, Port Aransas Marine Laboratory, Port Aransas, Texas 78373, U.S.A.
² McMaster University, Department of Biology, Hamilton, Ontario, Canada L8S4K1

To whom correspondence should be addressed.

Just after moulting the blue crab, Callinectes sapidus, is soft and defenceless, but in the following days, a hard calcareous shell is formed for support and protection. The carapace of intermoult (hard) crabs constitutes 27% of the wet weight and 53% of the dry weight, with 14% of the body water contained in a carapace fluid compartment. The pH of the shell fluid compartment is maintained at 0.3 to 0.5 pH units above that of the blood. The mineral portion of the carapace is primarily CaCO₃, with minor components of Mg²⁺ and PO₄^-3 plus traces of other ions. The formation of a new shell after moulting is accomplished by apparent H⁺ excretion and Ca²⁺ uptake at remarkable rates, averaging 12.5 and reaching as high as 21 mequiv kg^-1 h^-1. Direct bicarbonate uptake from the sea water appears to be an important component of the apparent H⁺ efflux, since CO₂ is deposited in CaCO₃ at a rate greater than metabolic production, and the animals show a net CO₂ uptake for several days.

Key words: Crab, calcification, moulting.

Accepted on June 8, 1984