Abstract

Field surveys and laboratory studies suggest that orconectid crayfish are more sensitive than cambarids to degraded water quality associated with lake acidification. Consequently, we predict that time trends in the relative abundances of orconectid crayfish will correlate with recent changes in acidification-related water quality to a greater degree than the abundances of cambarid crayfish. Ongoing efforts to monitor the recovery of small lakes in south-central Ontario that were once moderately impacted by acid rain provide 7 years of time-trend data to test this prediction. Crayfish relative abundances were estimated from mid-summer catches using baited traps. Water-quality data were collected from the same 13 lakes each year. Temporal coherence between time trends in crayfish relative abundances and water chemistry was assessed using the intraclass correlation. In contrast to our predictions, cambarid relative abundances exhibited more non-zero temporal coherence values than orconectid relative abundances. This finding suggests that short-term trends in orconectid relative abundances are not better indicators of water-quality trends than cambarid abundances. Consequently, the relative abundances of both cambarids and orconectids should be monitored to assess the biological effects of changes in acid-rain related water-chemistry parameters.

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