MEPS 137:251-263 (1996)  -  doi:10.3354/meps137251

Abundance and bacterivory of mixotrophic flagellates were examined in a vertical profile during 1 wk in June 1992 in the Bay of Aarhus, Denmark. A stable pycnocline separated an upper water mass with low salinity, low inorganic nutrient concentration (< 0.1 umol l^-1) and low bacterial abundance (<10⁶ ml^-1) from a bottom water mass with higher salinity, inorganic nutrient concentration, and bacterial abundance (>10⁶ ml^-1). In the upper layer, bacterivorous, pigmented flagellates (mixotrophs) accounted for 49% of the pigmented biomass. In addition to their function as primary producers, mixotrophic flagellates were responsible for 86% of the entire flagellate bacterivory. The abundance of bacterial food particles (<10⁶ ml^-1) was probably not sufficient to sustain growth of most bacterivorous, colourless flagellates, and the nutrient-depleted water body prevented the strict phototrophs from dominating the environment. Below the pycnocline, nutrients were present, bacterial abundance exceeded 10⁶ ml^-1, and mixotrophic flagellates made up only 9% of the pigmented biomass and accounted for 19% of the flagellate bacterivory.

Marine plankton . Mixotrophic flagellates . Colourless flagellates . Bacterivory . Mixotrophic biomass . Microbial food web