Status of Daphnia Resting Egg Banks in Bohemian Forest Lakes Affected by Acidification

Abstract

We studied the egg banks of Daphnia gr. longispina in four acidified lakes in the Bohemian Forest (Czech Republic, Europe). Daphnia had become extinct in three of the studied lakes due to anthropogenic acidification and we assessed the possibility of autochthonous recovery of the population after recent amelioration of the lake environment. We determined the ephippia distribution in eleven cores 10–30 cm long, and the state of Daphnia resting eggs in over 13 000 ephippia from eight cores. Apparently well-preserved eggs were used for hatching experiments and for DNA amplification. Vertical profiles of ephippia densities in several cores did not agree with historical data on the Daphnia presence in the lakes, as the sediment had been repeatedly disturbed by human activities in the past. Ephippia are present near the surface of the sediment in all lakes, and they might therefore receive hatching cues. We were not able, however, to prove that viable eggs are present in the ephippia banks of the lakes. The percentage of the well-preserved eggs in all but one core was below 1%. In addition, no egg hatched in the hatching experiments and we were not able to amplify DNA from the preserved eggs of lakes where Daphnia is extinct, although amplification from relatively young eggs from the fourth lake was successful in 60% of the cases. We conclude that the recovery of Daphnia populations in studied lakes from autochthonous sources is unlikely.