Response of Bosmina size structure to the acidification and recovery of lakes near Sudbury, Canada

In response to biotic and abiotic cues, the cladoceran genus Bosmina can undergo changes in body size and appendage length and shape over successive generations. To improve our understanding of the environmental controls on Bosmina size structure, we used paleolimnological techniques to examine Bosmina size responses to the extreme acidification and metal contamination, and then subsequent chemical recovery, of lakes in the vicinity of mining and smelting operations near Sudbury, Canada. During the acidification period, Bosmina antennule and carapace length significantly increased in three of the five study lakes, while mucro length significantly decreased in four of the five lakes. However, despite the recent return to pre-impact pH levels, the size structure of the present-day Bosmina community still differs from the pre-impact size distributions. We suggest that the continued dominance of the food webs by small invertebrate predators (e.g., cyclopoid copepods) is responsible for the persistent changes to Bosmina size structure.