Resting stages in the life cycle of Eudiaptomus graciloides (Lill.) (Copepoda: Calanoida) in Lake Glubokoe

Abstract

Seasonal changes in the abundance, age composition, vertical distribution, lipid and protein body content, development rates in the older copepodids (CIV and CV) and reproduction characteristics were studied in <it>Eudiaptomus graciloides</it> in the mesotrophic Lake Glubokoe (Moscow) region). Two periods of reproduction were observed: spring and late summer/autumn. The older copepodids, having accumulated lipid reserves during phytoplankton bloom, descended into the meta- and hypolimnion at the beginning of the summer. These copepods did not feed, but instead consumed their lipid reserves. A considerable delay in development (up to 40-60 days) of CIVs and CVs was found. The descended CIVs and CVs incubated under ambient temperature developed 4-5 times slower than their surface counterparts, while temperature dependence could only account for a 2-fold slow down. The descended copepods are believed to form a summer resting stock. In October, females began to produce resting eggs. The period of switching from subitaneous to resting egg production was very brief, not longer than 2-3 weeks. The percentage of subitaneous eggs produced in mid-October tended to increase when females were exposed to an increased photoperiod. At the beginning of February, latent eggs kept in a cooling container in the darkness started hatching. This process could be speeded up under natural photoperiod and increased temperature. The over-wintering population consisted largely of adults. Thus,<it>E.graciloides</it> includes three types of diapause in the life cycle: resting eggs, summer resting stage at CIV-CV, and overwintering adults.