310
on the diatom Asterionella formosa. Katablepharis ovalis ,
bodonids, and small unifl agellated cells were not found to
ingest fl uorescent beads during the study. Katablepharis
ovalis may be specialized in the uptake of relatively larger
size particles (e.g., nanophytoplankton). Bodonids were
present only at 40 m depth and reached low densities. They
are specialized as surface grazers. Attached bacteria were
abundant at 40 m depth where decaying algae and detritus
were usually present (see Carrias et al. chapter 13 ). Other
heterotrophic fl agellates that were not found to ingest par-
ticles consisted of small (2–5 μm in size) undetermined
nonpigmented cells (Table 18.1 ). DAPI-stained bacteria
and ingested picocyanobacteria were never seen inside
these cells. Osmotrophy (see Sherr 1988 ) might be a poten-
tially important source of organic carbon for these small-
sized heterotrophic fl agellates. Another explanation is that
these cells belong to spores of fungi, especially spores of
chytrids (see Sime Ngando et al. chapter 20 ).
Pigmented fl agellates that were found to ingest particles
included Dinobryon cylindricum , Ochromonas sp., and
Uroglena. These phagotrophic algae appeared as common
taxa in freshwater plankton (Bird and Kalff 1986 ; Bennett
et al. 1990 ). Maximum grazing impact of pigmented fl agel-
lates was 4.5 × 10^6 bacteria L −1 h −1 during a bloom of
Dinobryon cylindricum. Pigmented fl agellates may have
accounted for 25 % of total protistan bacterivory at some
depth, but for all samples they contributed to only 3 % of the
total protistan bacterivory. Bacterivorous ciliates included
species of oligotrichs, scuticociliates, and peritrichs (Table
18.2 ). This community dominated total protistan bacterivory
at some dates but accounted for only 13 % of total bacteriv-
ory for all dates sampled. The maximum grazing impact ofOLIGOTRICHIDA HAPTORIDA
PERITRICHIDA
OTHERSPROSTOMATIDA
SCUTICOCILIATIDA
(A) (B)AASONDMJ J AMJ JA S ONDAASONDMJ J AMJ JA S ONDAASONDMJ J AMJ JA S OND
Sp Su Au Sp Su Au20%40%60%80%100%0%20%40%60%80%100%0%20%40%60%80%100%0%20%40%60%80%100%0%20%40%60%80%100%0%20%40%60%80%100%0%1 m15 m40 mFig. 18.3 Relative
importance of different
groups of ciliates, as a
percentage of abundance
( a ) and biomass ( b ). Sp:
Spring, Su: Summer, Au:
Autumn. From Carrias et al.
( 1998b ). This material is
reproduced with permission
of Schweizerbart’sche
Verlagsbuchhandlung
( http://www.schweizerbart.de )
J. Carrias et al.