Response of the crayfish Cambarus bartonii bartonii to acid exposure in southern Appalachian streams

Intermolt adult and juvenile Cambarus bartonii bartonii (Fabricius) from southern Appalachian Mountains streams tolerated considerable acidity when acutely exposed to greatly reduced pH levels in laboratory bioassays. Tolerance increased with increasing size or age of crayfish. Ninety-six-hour exposures yielded LC50 values of pH 2.43, 2.56, and 2.85 for adults, advanced juveniles, and early juveniles, respectively. Lowering the water temperature increased the acid tolerance and survival time of intermolt adults during severe acidification (temperatures ranged from 20.2 to 13.3 °C). Acid exposure of intermolt adults in soft water up to 96 h caused a linear decrease in hemolymph [Na]. Hemolymph [Ca] increased through 48 h and then returned to near pre-exposure levels. An initial increase in [K] was followed by a decrease to slightly below pre-exposure levels. Hemolymph [Mg] remained unchanged. No Ca was lost from carapaces. These observations indicate that occasional episodes of higher than normal acidity in southern Appalachian streams are not necessarily a threat to intermolt adult and juvenile C. b. bartonii. Nevertheless, gradually increasing acidity and loss of watershed buffering capacity could produce sublethal effects such as altered reproductive activity, or changes in early life history stages and more sensitive molt cycle stages, that could damage these populations.