9313673 Blades-Eckelbarger Populations of Calanus finmarchicus constitute a major portion of the zooplankton biomass in the Northwestern Atlantic, and comprise a fundamental food source for the cod and haddock that live on Georges Bank. The springtime arrival of this copepod on the Bank is reportedly due to recruitment of fifth stage copepodites from the deeper waters of the Gulf of Maine, where they overwinter in a state of dormancy or diapause. Recruitment success depends, to a large extent, on the duration of this diapause stage. Knowing the effects of environmental factors on the timing of diapause induction and termination, and the internal morphological changes that occur throughout this critical life stage, will contribute to a better understanding of the physical and biological factors that regulate the recruitment process of Calanus finmarchicus onto Georges Bank. The research to be conducted under this project is an in-depth investigation of ways in which variations of temperature and photoperiod may influence the physiological processes that control and regulate diapause in Calanus finmarchicus. A specially designed system for culturing multiple generations of C. finmarchicus will be used to subject the juvenile stages to various combinations of temperature and photoperiod. Light microscopy and TEM will be used to confirm the identity of the cue-receptive organs and neuroendocrine sites that control the cessation and induction of molting. Cytological features of gonad development in diapausing and nondiapausing individuals will be described and compared in both laboratory and field populations. ***
