Abstract

Post-molt exoskeleton mineralization of adult noble crayfish, Astacus astacus, in two calcium-poor lakes (L. Digeren (<2.2 mg Ca/L) and L. Dølisjøen (≈3.9 mg Ca/L)) were compared to a more calcium-rich lake (L. Einavann (=13.9 mg Ca/L)). One, two, and three weeks after molting 3-5 individuals were taken out from cages in each lake, and exoskeletons analysed for calcium and total mineral content. For comparison with the intermolt stage, exoskeletons from free-living L. Einavann crayfish were also analysed. There were no significant increases in calcium and mineral content of the crayfish exoskeletons during the 1-3 weeks post-molt period in any of the lakes, showing that a major part of the mineralization occurs during the first post-molt days with the process then slowing down. Crayfish caged in calcium- rich L. Einavann mineralized their exoskeleton at a significantly higher rate compared to those caged in calcium-poor L. Dølisjøen and L. Digeren. 1-3 weeks after molting the calcium and mineral content was 25% and 60% of exoskeleton dry weight in L. Einavann, compared to only 16% and 41% in L. Dølisjøen and L. Digeren. Corresponding figures for free-living intermolt crayfish in L. Einavann were 29% and 67%. That is, 1-3 weeks after molting, the crayfish held in L. Einavann had accumulated approx. 86% of the calcium and 90% of the mineral matter, compared to the intermolt situation, while crayfish held in the calcium-poor lakes had accumulated only 55% and 60%, respectively. Thus, in natural waters with calcium levels below 5 mg Ca/L post-molt exoskeleton mineralization rate seems to be significantly reduced. This probably makes crayfish populations in such waters more vulnerable to threats like predation and acidification.

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