DIAPAUSE DYNAMICS OF 2 DIAPTOMID COPEPOD SPECIES IN A LARGE LAKE

Skistodiaptomus oregonensis and Leptodiaptomus minutus produce diapaus ing eggs in a large lake, Oneida Lake, in New York State. The timing o f the switch from production of subitaneous (immediately hatching) egg s to diapausing eggs for both species is in October. This timing is co nsistent with a pattern, reviewed here, for other populations of diapt omid copepods: populations living in large lakes tend to begin product ion of diapausing eggs later in the season than those living in small lakes. Populations living in temporary ponds tend to switch still earl ier in the season. All populations reviewed here live in the north tem perate zone. The sediments of Oneida Lake contain densities of diaptom id diapausing eggs on the order of 10(5) m-2 per cm below the sediment surface down to 5 cm. Below this sediment depth, egg densities declin e. The highest egg densities were found in sediments under the deepest water. Diapausing eggs of L. minutus survive in the sediments at leas t two years, as shown by the recovery of the population after a year i n which no new diapausing eggs were produced, and probably for two or more decades. Long-term dormancy can have the effect of ensuring the c ontinuation of a population through periods of poor recruitment, and c an help create conditions for the coexistence of competing species. Ot her investigators have suggested that S. oregonensis and L. minutus ar e competitors in other lakes when they co-occur.