Extirpation of Crayfish in a Lake Affected by Long‐Range Anthropogenic Acidification

Plastic Lake, Ontario, remote from any point sources of pollutants, is the most thoroughly investigated anthropogenically acidifying lake in North America. As the lake pH decreased from 5.8 to 5.6 over a period of six years, a resident population of the crayfish Orconectes virilis , which had previously exhibited abundances typical of those of nearby Canadian Shield lakes, became extinct. This is one of only half a dozen documented examples of biotic impoverishment due to the long‐range aerial transport of strong acids. The loss of crayfish could not be explained by changes in the predaceous fish community. However, the pH range over which extinction occurred matched that of experimentally acidified Lake 223 where O. virilis began to decline dramatically due to recruitment failures, calcium imbalances, and possibly parasite infection. O. virilis appears to be the third component of the benthic invertebrate fauna of Plastic Lake that has been extirpated by anthropogenic acidification.