Impact of natural metazooplankton assemblage on planktonic microbial communities in a newly flooded reservoir |
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Authors: | Thouvenot A; Debroas D; Richardot M; Devaux J |
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Institution: | Laboratoire de Biologie Comparee des Protistes, Unite associee CNRS, Universite Blaise Pascal Clermont Ferrand II, 63117 Aubiere Cedex, France |
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Abstract: | The grazing impact of a natural assemblage of metazoan zooplankton on
pigmented flagellates (PF), heterotrophic nanoflagellates (HNF), ciliates,
and non-flagellate algae and microcyanobacteria (NFAM) was measured
in situ during the period of thermal stratification in
a newly flooded reservoir (Reservoir de la Sep, France). Experiments were
conducted with diffusion chambers in the meta- and epilimnion over a period
of 7 h. The mean mortalities of PF in the epi- and metalimnion (0.08
0.02 and 0.06 ± 0.03
h-1, respectively), of HNF (0.04 ± 0.02
and 0.05 ± 0.02 h-1) and ciliates (0.09
± 0.04 and 0.11 ± 0.04 h-1)
demonstrate the impact of the metazoan zooplankton, and particularly of the
rotifer Asplanchna priodonta, on the components of the
microbial loop. The mortality of NFAM, accounting for 14 and 18% of total
mortality, remained low throughout the study. The taxa with the highest
mortality were pigmented flagellates of 4-19 m, HNF, and small-sized ciliates such as
Halteria sp. (0.10 ± 0.02
h-1 at 1 m and 0.30 ± 0.38
h-1 at 7 m) and Urotricha
furcata (0.11 ± 0.05 h-1 at 1
m and 0.12 ± 0.06 h-1 at 7 m).
Large-sized ciliates (Paradileptus elephantinus) and
sessile ciliates (Suctorida, Vorticella sp.) had a
very low mortality (>0.04 h-1). After
reservoir flooding, the organisms in the microbial trophic loop, favoured
by the high quantities of allochthonous organic matter, are subject to a
higher mortality than the phytoplankton.
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