JPR Advance Access published online on December 8, 2005
Journal of Plankton Research, doi:10.1093/plankt/fbi112
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1 Centre IRD Bel Air, UR 167 CYROCO, BP 1386, Dakar, Senegal; Laboratoire Ecosystèmes Lagunaires, UMR-CNRS 5119, Université Montpellier II, Case 093, Place Eugène Bataillon, 34095 Montpellier, France
* To whom correspondence should be addressed. We studied the impact of various metazooplanktonic predators (two calanoid copepods and barnacle larvae) on microbial plankton isolated from the Senegal River Estuary. Experiments performed in microcosms were based on size-class fractionation (3, 12, 20 and 60 µm size-classes) of the microbial community in order to obtain different assemblages, including bacteria, heterotrophic nano-flagellates (HNF), ciliates, pico- and nanophytoplankton. Removal of bacterial predators larger than 3 µm increased the net growth rate of heterotrophic bacteria from 0.437 day-1 in the presence of all predators (fraction < 60 µm) to 0.682 day-1 (fraction < 3 µm). Removal of protozoa larger than 12 µm caused an increased net growth rate of flagellates from 0.102 day-1 (fraction < 60 µm) to 0.332 day-1 (fraction <12µm). The same results on protozoa dynamics were also observed in the presence of Temora stylifera (0.498 d -1) suggesting a trophic control of the protozoa larger than 12 µm by this copepod, allowing an increase in HNF growth rates through indirect effect. The highest ingestion rate over 60 h of experiment was recorded for the copepod Temora (61.1 µm3 ngC-1 h-1) and the lowest value for barnacle larvae (25.6 µm 3 ngC-1 h-1). An intermediate value (47.5 µm3 ngC-1 h-1) was recorded for the copepod Acartia clausi. All these ingestion rates were mainly channeled in the size-classes between < 3 and 15-18 µm ESD (6 and 2435 µm3, respectively), with the highest values noted between < 3 and 6-9 µm classes. In the presence of Temora , the cascading effects can explain both the decreases in mean volume and in growth rate for bacteria, due to the filtration of ciliates by the zooplanktonic predatorallowing the development of the HNF. The presence of a large size-class of bacteria (among the 5 classes identified by flow cytometry) and a high abundance of HNF suggest an efficient heterotrophic pathway within the microbial loop of this sub-saharan estuary. Communicating Editor: IR Jenkinson
Received October 24, 2005
Accepted December 7, 2005
Article
Functional structure of microbial food-web in the Senegal River Estuary (West Africa): impact of metazooplankton
Marc Bouvy 1 *,
Marc Pagano 2,
Maimouna M’Boup 2,
Patrice Got 3,
and
Marc Troussellier 3
2 Centre IRD Bel Air, UR 167 CYROCO, BP 1386, Dakar, Senegal
3 Laboratoire Ecosystèmes Lagunaires, UMR-CNRS 5119, Université Montpellier II, Case 093, Place Eugène Bataillon, 34095 Montpellier, France
Marc Bouvy, E-mail: bouvy{at}mpl.ird.fr
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