MORPHOLOGICAL RESPONSES BY BOSMINA-LONGIROSTRIS AND EUBOSMINA-TUBICENTO CHANGES IN COPEPOD PREDATOR POPULATIONS DURING A WHOLE-LAKE ACIDIFICATION EXPERIMENT

Changes in zooplankton populations during the experimental acidificati on of Little Rock Lake provided an opportunity to examine specific mec hanisms underlying the morphological responses of bosminids to changin g predation pressure. Two large copepods, Epischura lacustris and Meso cyclops edax, disappeared from the lake's acidified basin in 1986 and 1989, respectively, while a smaller copepod predator, Tropocyclops ext ensus, increased during later stages of acidification. The two bosmini d species showed distinctly different responses coinciding with the ch anges in copepod predation. Bosmina longirostris exhibited a significa nt decrease in mucro length with the decline of M.edax and E.lacustris . Its mean body and antennule length, however, did not change. We sugg est that the decoupling of B.longirostris mucro length and antennule l ength 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, an tennule or body length. Allometric analyses indicated, however, that m ucro length was related to size-dependent copepod predation for both B .longirostris and E.tubicen.