Estimating potential diapause duration in Calanus finmarchicus

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Deep basins in the Gulf of Maine act as refuge for a large population of diapausing Calanus finmarchicus during the summer and fall. This population acts as the primary seed population for Georges Bank in the spring and is thought to be composed primarily of individuals that developed during the previous spring bloom. The factors affecting growth and mortality in the summer-fall population are not well understood, however, and loss terms from advection and starvation may be large. To assess the potential energetic limitation and loss of C. finmarchicus from the Gulf of Maine basins, a new nitrogen-specific respiration model has been developed for the resting stage of the species. Stage C5 C. finmarchicus were collected during July, September, and December 2003 from Wilkinson and Georges Basins. Animals were collected using both MOCNESS tows and zooplankton samplers on the Johnson Sea Link II submersible. Metabolic rates were measured using a Micro-Oxymax gas analyzer and Winkler incubation techniques both at sea and on animals kept in culture on shore. Respiration rates measured in the field were not significantly different from those measured on shore, with a mean of 130 μmol O2 gN-1 h-1 (14.4 μmol O2 gC-1 h-1) at 0 °C and a Q10 of 2.77 (2.58 for carbon-specific respiration). Using the nitrogen-specific rates in conjunction with visual estimates of nitrogen weight and lipid stores, we derived a discrete function for predicting potential diapause duration based on an animal's length, oil sac volume, and the in situ temperature. The maximum potential diapause duration for a C5 C. finmarchicus is predicted to range from 280 days at 0 °C to approximately 90 days at 11 °C. The maximum potential diapause duration in the Gulf of Maine is predicted to be between 3.5 and 5.5 months. These results suggest that energetic limitation may play a role in controlling the population dynamics of diapausing C. finmarchicus in the Gulf of Maine. A reassessment of the importance of summer production to the Gulf of Maine C. finmarchicus population may be required to account for its year-round presence on the Northeast American Shelf. © 2006 Elsevier Ltd. All rights reserved.

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Deep-Sea Research Part II: Topical Studies in Oceanography