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Where have all the crayfish gone?

Researchers from Queen’s University, working with colleagues from the Ontario Ministry of the Environment and Climate Change, have linked the localized near-extinction of a native crayfish species in four lakes in Algonquin Park to declining calcium levels, a long-term legacy of acid rain on forest soils and aquatic ecosystems.

“Crayfish are an integral component of aquatic food webs, because they function at multiple trophic levels and are a key element in the diets of popular recreational and economically important fish species,” says Kris Hadley, the lead author of the study and a PhD student at Queen’s University at the time the study was conducted.

Acid rain “mobilizes” calcium found in the soil and bedrock. Once mobilized, calcium levels in the water increase, before declining as calcium stores are used up.

Cambarus bartonii found in Clayton Lake. (Photo by Ron Ingram, OMOECC)

In areas such as Kingston, where much of the bedrock is comprised of limestone, the effect is mitigated by the high volume of calcium found in the bedrock. The lakes analyzed by the research team are farther north on Canadian Shield bedrock, which has a much lower concentration of calcium. The lakes selected allowed for a much clearer analysis of the effects of calcium decline on larger organisms.

Because long-term data records of lake water pH and calcium levels are typically not available, researchers analysed fossilized microscopic organisms (i.e., algal remains) to reconstruct past lake water pH levels and fossils of water fleas to track past changes in lake water calcium concentrations. Using this technique, the team was able to examine environmental trends in the four lakes over the past 150 years.

Read the full story in the Queen’s Gazette.