Morphological responses by Bosmina longirostris and Eubosmina tubicen to changes in copepod predator populations during a whole-lake acidification experiment
Changes in zooplankton populations during the experimental acidilication of Little Rock Lake provided an opportunity to examine specific mechanisms underlying the morphological responses of bosminids to changing predation pressure. Two large copepods, Epischura lacustris and Mesocyclops edax, disappeared from the lake’s acidified basin in 1986 and 1989, respectively, while a smaller copepod predator, Tropocyclops extensus, increased during later stages of acidification. The two bosminid species showed distinctly different responses coinciding with the changes in copepod predation. Bosmina longirostris exhibited a significant decrease in mucro length with the decline of M.edax and E.lacustris. Its mean body and antennule length, however, did not change. We suggest that the decoupling of B.longirostris mucro length and antennule length may have been related to the persistence of the smaller copepod predator, T.extensus. Eubosmina tubicen showed no apparent response to declines in M.edax and E.lacustris abundance in either mean mucro, antennule or body length. Allometric analyses indicated, however, that mucro length was related to size-dependent copepod predation for both B.longirostris and E.tubicen.