The Role of Dormancy and Emergence Patterns in the Dynamics of a Freshwater Zooplankton Community

Emergence rates of two cladoceran species (Ceriodaphnia reticulata and Eubosmina longispina) and two calanoid copepod species (Epischura nordenskioldi and Diaptomus sanguineus) from sediments were monitored weekly in Bullhead Pond (Rhode Island) over a 3.5-yr period with permanently deployed plastic, inverted-funnel traps. Emergence rates of C. reticulata decreased over the study period, dropping to zero in the third year, and determined timing of first appearance as well as fluctuations in population size. Emergence of E. longispina was sporadic and correlated poorly with population abundance variations, but continued throughout the study. Significantly fewer ephippia of C. reticulata were recovered from under traps compared to adjacent sediments, suggesting that reserves of ephippia had been depleted during the study. Reserves of E. longispina ephippia were not significantly depleted under traps during the study. Patterns of emergence for E. nordenskioldi and D. sanguineus were very similar to each other in timing and importance in determining planktonic standing stocks. For each, nauplii emerged synchronously and initiated the population each year. Both species hatched during every year of the study, suggesting that eggs can remain viable in the sediments for at least 3 yr.