Biomass and production of small and large free‐living and attached bacteria in Lake Constance1

Abstract

Cell numbers, biomass, and secondary production of small (0.2–1 µm) and large (1.0–3.0 µm) free‐living and attached bacteria were studied in Lake Constance. Biomass as well as production rates exhibited large fluctuations vertically and seasonally. When averaged over a year, small free‐living bacteria were most important for recycling of organic matter since they comprised 77% of total cell numbers and 66% of bacterial secondary production. Large free‐living bacteria contained roughly half of the total bacterial biomass because of their relatively larger cell size. Although attached bacteria usually were of minor importance, they occasionally comprised about half of total bacterial production. During the phytoplankton spring bloom when bacterial production reached its maximum, 60–80% of all free‐living bacteria were active as shown by autoradiography. During that period a high portion of detrital particles was colonized by metabolically active cells.The data suggest that biomass, cell size, and production of free‐living bacteria are controlled by substrate input and grazing of either heterotrophic microflagellates or crustacean zooplankton. In contrast, biomass and production of attached bacteria appear to be predominantly controlled by substrate input of readily decomposable particulate organic matter.