Development of Acartia bifilosa (Copepoda: Calanoida) eggs in the northern Baltic Sea with specialreference to dormancy

Development of eggs produced by Acartia bifilosa in summer and autumn was studied in the northern Baltic Sea. Resting eggs of the species have previously been found in sediments, and the aim of this study was to reveal the type of dormancy in the eggs. Eggs were incubated at temperatures ranging from 1.5 to 18degreesC. The effect of continuous darkness on hatching was also tested. Hatching success in the experiments varied between 56 and 97%. Egg development was similar in summer and autumn, indicating that A. bifilosa does not produce diapause eggs in the area. Furthermore, dormancy was not induced at any of the temperatures tested, nor by darkness. Results are compared with those of Castro-Longoria and Williams (Castro-Longoria and Williams, 1999b, J. Plankton Res., 21, 65-84) who studied A. bifilosa in the English Channel, where both production of diapause eggs and arrest of development in the subitaneous eggs at low temperatures occurred. The possible causes of the difference in dormancy strategies in the two areas are discussed.