Annual bacterioplankton biomasses and productivities in a temperate west coast canadian fjord

Bacterioplankton numbers, biomasses, and productivities, as well as chlorophyll a concentrations and phytoplankton productivities, were assayed from 1 March 1984 to 12 August 1985 through a 250-m-deep seawater column in Howe Sound, a temperate fjord-sound on the southern coast of British Columbia, Canada. Primary production during this 18-month period was 845 g of C m. Bacterial production was assayed over this same period as 193 g of C m (thymidine incorporation) and 77 g of C m (frequency of dividing cells). Bacterial productivities per cubic meter were usually greater in the euphotic zone than in deeper aphotic water, but when integrated through the water column, approximately half of the bacterial production occurred in the deeper aphotic portion. Bacterial production occurred throughout the year, although at reduced rates in late fall and early winter; primary production almost ceased during late fall and early winter. Because of this heterotrophic bacterioplankton production was a very large portion of the microbial (bacterial plus phyto-plankton) production at this time. In mid-summer bacterial production was a small proportion of the microbial production. Because of this asynchrony in peaks and troughs of bacterial and phytoplankton production through the year, data comparison is best done over an annual cycle. On this basis the bacterial production in the Howe Sound water column was between 23 and 9% of the phytoplankton production when a bacterial C to biovolume ratio of 0.107 pg of C mum was assumed; the corresponding values were 64 and 29% when a ratio of 0.300 pg of bacterial C mum was assumed.