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Skistodiaptomus pallidus made diapausing eggs from late June through October in two artificial ponds in Ithaca, New York. There was no observable difference in the timing of production of diapausing eggs between the two ponds even though one contained fish and the other did not. However, between August and October 1994, the females in the pond with fish produced a significantly greater proportion of immediately hatching eggs than those in the pond without fish. Diapausing egg densities in a 10-cm sediment core taken from the pond with fish were approximately 105 eggs/M2. Each 1-cm slice in the top 5 cm of the core had high egg densities, the 5-6 cm to 7-8 cm slices had lower egg densities and the bottom two slices had high egg densities. About 50% of the total diapausing eggs in the sediment core hatched within 7 wk after exposure to hatching conditions, and the median time to hatch increased significantly with depth. No conclusions can be made regarding the effect of fish presence or absence on the timing of diapause among S. pallidus since treatment effects were not replicated. However, high density of diapausing eggs and high hatching success of eggs in the sediment can act as a buffer against local extinction following years of low reproduction and recruitment. |
