The Life-Cycle of the Freshwater Copepod Cyclops leuckarti Claus in Esthwaite Water

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Abstract
An active planktonic phase, in which all stages in the life cycle may be found and which extends from March to October, alternates with a dormant profundal phase in which only stage V copepodids (i.e. the last pre-adult larval stage) and a small proportion of stage IV are found and which extends from October to March. During the active phase there are 2 maxima coinciding with breeding activity, the first exclusively adult in May, the second of all stages in July. This second maximum is followed by an arrest of development in the last larval stage which remains planktonic until the autumn overturn at the end of September when they descend to the profundal to enter the dormant phase. Since the end of the dormant phase is not associated with any obvious environmental change, it is deduced that the length of the dormant phase is governed primarily by internal physiological processes. Possible ways in which the dormant phase may be initiated are considered and the life cycle is compared with that in other waters.

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