Histological changes of the digestive epithelium in Calanus finmarchicus: an index for diapause?
Samples collected in the Irminger Basin during the Marine Productivity Programme (2001–2004) were used to study Calanus finmarchicus vertical distribution and histological changes of its mid-gut epithelium in relation to overwintering strategy. Previous studies have shown that cell composition of the glandular part of the mid-gut, size and abundance of B cells responsible for digestive enzyme secretion and thickness of the epithelium could be good indicators of individual physiological state. We used C. finmarchicus abundance, vertical distribution, lipid sac volume and mid-gut epithelium histological composition of individuals collected in contrasting hydrographic areas of the Irminger Basin and sampled at different seasons to understand C. finmarchicus life cycle in the Irminger Basin. Lipid sac volumes were significantly different between the seasons but neither between the hydographic areas nor the various depths of the water column. B cells concentrations and thickness of the epithelium have allowed us to distinguish a non-diapausing surface population (350 m) in the East Greenland Current while individuals at depth (1,250 m) were overwintering. This result is correlated by a bimodal vertical distribution of the CV in this biozone. In the other hydrographic areas, all CV were dormant, although surface individuals were not analysed in the Southern Irminger Current.
KeywordsBiozones Digestive Enzyme Activity East Greenland Current Faecal Pellet Production Glandular Part
The authors are grateful to Dr. Keith Ryan and Tania Smith for helping with the preparation of the samples for microscope observations and to Dr. Jim Nott for commenting the TEM pictures. The work of D. Bonnet has been supported by a NERC Marine Productivity Grant NE/C508369/1. The authors want to thank the consortium project (NERC Marine Productivity Grant NER/T/S/2001/00164) for the use of the ARIES data
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