Abstract

Life history characteristics of the crayfish Orconectes virilis were examined during 1979-81 in four small Canadian Shield basins in the Experimental Lakes Area, northwestern Ontario. One of these lakes, Lake 223, has been undergoing experimental acidification since 1976 to simulate the effects of acid precipitation. Carapace rigidity and Ca⁺⁺ content were significantly lower in L223 crayfish, possibly as a result of postmolt inhibition of Ca⁺⁺ uptake. Growth in L223 has not been affected by acidification to pH 5.35. Incomplete hardening of the cuticular glair-cement compound forming the egg capsule membrane and stalk has resulted in a failure of secure pleopod egg attachment causing the L223 population to suffer severe recruitment failure. Lake 223 crayfish have responded to acidification-related remobilization of heavy metals with an increased bioaccumulation of Mn and Hg. Thelohania sp. infection in the L223 population was 1.7% during 1979 compared to 0.3% for the control lakes. In 1980 this prevalence had risen to 6.5% in L223 with no increases in the control populations. It is suggested that loss of crayfish populations to gradual lake acidification will be brought about by reproductive impairment and possibly increased susceptibility to parasitic infection before those acid levels are reached that result in direct toxic damange to crayfish stocks. Present findings are summarized and incorporated with a literature discussion forming a thesis on the critical importance of the often insidious interaction between H⁺ and environmental Ca⁺⁺ in determining the future of crayfish populations exposed to cultural acidification.

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