Feeding of Ctenocalanus citer in the eastern Weddell Sea:: low in summer and spring, high in autumn and winter

The feeding activity and diet of the small dominant Antarctic copepod, Ctenocalanus citer, were studied throughout the seasonal cycle from samples taken during several Polarstern cruises to the eastern Weddell Sea. Two indices of feeding activity were used, percentage of copepods with food inside and length of the faecal pellets. C. citer guts contained food throughout the year thus confirming the year-round activity of this species without diapause. Both indices demonstrated a seasonal pattern of foraging, unusual for a predominantly herbivorous copepod: high-feeding activity in autumn-winter and low in spring-summer. Our results suggest that feeding is at least partially decoupled from the phytoplankton bloom. Diet of C. citer was assessed by analyzing the gut contents. The bulk of the recognizable food in the guts of all copepodite stages consisted of small-sized phytoplankton, and no evidence of switching to a more carnivorous diet at low-phytoplankton concentrations was obtained. Usage of ice-associated algae was proposed to explain high winter-feeding activity. This knowledge of seasonal feeding patterns fills in a gap in our understanding of the life-cycle strategy of C. citer.