| Summary: | Deep basins in the Gulf of Maine act as refuge for a large population of resting Calanus finmarchicus during the summer and fall. Dynamics of this population are not well understood, however, and loss terms from advection and starvation may be large. A three part study was therefore undertaken to determine potential diapause duration in C. finmarchicus , monitor changes in the summer-fall population, and to define the relative importance of energetic limitation as a control on C. finmarchicus population dynamics. Six standard stations were sampled in and around the Gulf of Maine on a series of four research cruises between June 2001 and January 2002. Samples were collected at each station to monitor the abundance and metabolic state of the local C. finmarchicus population. Three additional cruises were carried out in 2003 to collect animals for use in respiration experiments. From these experiments, I constructed an individual based respiration model for estimating potential diapause duration. Maximum potential diapause duration for a hypothetical animal of optimum size ranged between 3 and 9 months for temperatures between 10° and 0°C respectively. Maximum potential diapause duration at temperatures common in the Gulf of Maine ranged between 3.5 and 5.5 months. Observations from the 2001-2002 field season showed that the summer-fall diapause population decreased in abundance by 75% between August 2001 and January 2002. Application of the diapause duration model to the 2001-2002 field population demonstrated that 'mortality' due to energetic limitation could account for changes seen in the diapause population. This possibility was explored further using a box model of C. finmarchicus summer-fall population dynamics. In the model, energetic loss was combined with estimates of advection, production, and mortality as controlling factors. The model successfully predicted the changing trends in C. finmarchicus abundance during the summer-fall of 2001-2002 and, with realistic adjustments to surface mortality terms, differences between predicted and observed abundances were small. The similarities between box model predictions and field observations support the hypothesis that energetic limitation can play a major role in controlling C. finmarchicus population dynamics during diapause.
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