Hatching of Diapause Eggs of Eurytemora Affinis (Copepoda: Calanoida) Collected from Lake-Bottom Sediments

Hatching of diapause eggs of Eurytemora affinis collected from the bottom sediments of Lake Ohnuma, Hokkaido, Japan, during winter was examined under simulated natural environmental conditions in the laboratory. Diapause eggs synchronously hatched in the same manner as the subitaneous eggs in normal lake water under both light and dark conditions. However, anoxic condition and coverage by the bottom sediments completely suppressed the hatching. The eggs exposed to anoxic water survived for at least 1 month, whereas those buried in the sediments remained viable for more than 5 months. These results suggest that the diapause eggs buried in the lake-bottom sediments will continue to be dormant even if the refractory phase is completed unless they are resuspended into the water column.