Role of Heterotrophic Microflagellates in Plankton Communities

摘要

The distribution, feeding behavior and ingestion of bacterivorous microflagellates (2-20 micrometers protozoa) were examined in an attempt to assess the importance of these protozoa as a trophic link between planktonic bacteria and zooplankton. The abundance of microflagellates relative to other picoplankton (0.2-2.0 micrometers) and nanoplankton (2-20 micrometers) populations in water samples and on macro-aggregates in the North Atlantic was determined using direct microscopical and cultural estimation techniques. Microflagellates constituted 1/3 to 1/2 of the nanoplankton in the euphotic zone and dominated the nanoplankton in the aphotic zone. Microflagellates were highly concentrated on macro-aggregates relative to their densities in the surrounding water (enrichment factors exceeded 10 (to the 4th power)) where they numerically dominated the culturable bacterivorous protozoa by one to two orders of magnitude. Microflagellates grown in continuous culture displayed an ability to grow on low concentrations of bacteria and therefore appear to be well-adapted for grazing bacterioplankton. It is concluded that due to their potential as consumers of planktonic bacteria and their acceptability as food for zooplankton, microflagellates may constitute an important trophic link between bacteria and zooplankton.