PEARL

Where have all the crayfish gone?

Crayfish are keystone species in many aquatic environments, yet numbers have been declining steadily in many soft-water lakes. 

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

“Aquatic osteoporosis” has recently been identified as an environmental stressor impacting many soft-water lakes in North America and elsewhere, that may have serious ecological consequences, including the “jellification” of lakes.
 
“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 Dr. Kris Hadley, the lead author of the study and currently a post-doctoral research fellow at Queen’s University and Hutchinson Environmental Sciences Ltd.

“One of the biggest problems we have in environmental research is the lack of direct long-term monitoring data”, explains Dr. John Smol , a professor in the Department of Biology at Queen’s University and the Canada Research Chair in Environmental Change. 

Because long-term data records of lakewater pH and calcium levels are rarely available, researchers used a paleoecological approach using fossil microscopic organisms (i.e., algal remains to reconstruct past lakewater pH levels and fossils of water fleas to track past changes in lakewater calcium concentrations) from sediment cores.  “Sediments act as a history book of past changes in a lake, recording what happened before the problem was identified,” adds Prof. Smol. Using this technique, the team was able to examine environmental trends covering the last ~150 years.

The research team found evidence that acid rain had impacted some of the lakes over time, but they also inferred marked declines in lakewater calcium levels – a known legacy of acid rain. 

“The acidification of lakes in this region was not a surprise, however we found that acidification alone could not explain the striking decline of crayfish populations in these lakes” say Dr. Hadley. “Instead our evidence suggests that calcium concentrations began declining in these lakes as early as the 1960s, and may now have fallen below the threshold required for their survival” says Dr. Hadley.

Crayfish shed their protective calcareous carapace several times during their life cycle, and as such have high calcium requirements.

“Although lakewater pH has been recovering in many waterways with controls on acid emissions, there has been no such recovery in calcium levels, and thus aquatic organisms are beginning to show the negative effects of what we are colloquially calling ‘aquatic osteoporosis’”  concludes Prof. Smol.

 “Of greater concern is that calcium declines are expected to continue in many lakes, making the recovery of crayfish populations uncertain in these and other soft-water Ontario lakes.” says Dr. Hadley.

This research was funded by the Natural Sciences and Engineering Research Council of Canada.

Also on the research team are Dr. Jim Rusak, Dr. Keith Somers, Ron Reid and Ron Ingram of the Ontario Ministry of the Environment and Climate Change.

The study was published in the international journal Freshwater Science and a number of high-resolution images of the organisms and techniques used in this study can be found on the Paleoecological Environmental Assessment and Research Laboratory website. A copy of the study can be obtained from John Smol at smolj@queensu.ca or from the journal web site.

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Contact:

Anne Craig
News and Media Services
Queen's University
Kingston, Ontario, Canada
Anne 613-533-2877 anne.craig@queensu.ca

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NOTE:  For high-resolution JPEGS related to this paper, Click Here.

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Links to media coverage of this article:

EurekAlert! Science Daily PHYS.ORG Demanjo As It Happens Queen's Gazette The Fish Site

Ottawa Citizen