Seasonal changes in planktonic bacterivory rates under the ice-covered coastal Arctic Ocean

Bacterivory was determined in surface waters of Franklin Bay, western Arctic, over a seasonal ice-covered period (winter-spring, 2003-2004). The objectives were to obtain information on the functioning of the microbial food web under the ice, during winter (from 21 December 2003 to 21 March 2004) and during spring (from 22 March 2004 to 29 May 2004), and to test whether bacterial losses would increase after the increase in bacterial production following the spring phytoplankton bloom. Chl a concentrations ranged from 0.04 to 0.36 mu g L-1, increasing in March and reaching a peak in April. Bacterial biomass showed no consistent trend for the whole period, and protist biomass followed a pattern similar to that of Chl a. Bacterial production increased 1 week after Chl a concentrations started to increase, while bacterivory rates increased very slightly. Average bacterivory rates in winter (0.16 +/- 0.07 mu g C L-1 d(-1)) were not significantly different from those in spring (0.29 +/- 0.24 mu g C L-1 d(-1)). Average bacterial production, on the other hand, was similar to bacterivory rates in winter (0.19 +/- 0.38 mu g C L-1 d(-1)), but higher than bacterivory in spring (0.93 +/- 0.28 mu g C L-1 d(-1)). Therefore, bacterial production was controlled by grazers during winter and by substrate concentration in spring.