The seasonal range of assimilation efficiencies for microcapsule standards (18–29%) and field-collected microheterotrophs (bacteria76–93% and heterotrophic nanoflagellates 87–94%) did not differ significantly during the year, whereas summer and autumn assimilation efficiencies for cellulosic detritus (22–24%), phytoplankton (71–79%) and benthic diatoms (89–93%) were up to twofold greater than those in winter and spring (13%, 40–59% and 45–81%, respectively).