ABSTRACT: Nanoflagellate grazing was investigated in the subtropical convergence region off the east coast of the South Island, New Zealand, in the summer of 1995. Clearance rates were estimated using 0.5 µm fluorescently labelled beads and fluorescently labelled bacteria to represent bacterial populations and 1.0 µm fluorescently labelled beads representing picophytoplankton populations. Nanoflagellate grazing by mixotrophs was on average lower than heterotrophic nanoflagellate clearance rates per individual for all prey types, and both heterotrophic and mixotrophic nanoflagellates showed a preference for picophytoplankton-sized particles over bacteria-sized particles when grazing on artificial prey. Despite lower clearance rates per individual, higher numbers of mixotrophic nanoflagellates meant that they contributed 57% of measured grazing impact on picophytoplankton-sized particles, 40% of grazing on bacteria-sized particles and 55% of grazing on stained bacteria per day. In addition to assessing grazing rates, by identifying the major genera involved we were able to distinguish the predominate grazers in 3 water masses and investigate how changes in species composition may be linked to grazing in this region.

KEY WORDS: Nanoflagellates · Mixotrophy · Grazing · Autotrophy · Heterotrophy · Microbial food web

Published in AME Vol. 20, No. 1 (1999) on November 30
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1999