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Impacts of nutrient loading and fish grazing on the phytoplankton community and cyanotoxin production in a shallow tropical lake: Results from mesocosm experiments

Abstract : Given the increasing eutrophication of water bodies in Africa due to increasinganthropogenic pressures, data are neededto better understand the responses ofphytoplankton communities to these changes in tropical lakes. These ecosystemsare used by local human populations for multiple purposes, including fish anddrinking water production, potentiallyexposing these populations to healththreats if, for example, an increase in toxic cyanobacterial blooms is associatedwith increasing eutrophication. To test the short‐term response of thephytoplankton community to the addition of nutrients (phosphorus and nitrogen,alone or in combination) and Nile tilapia, we developed an in situ mesocosmexperiment in a freshwater lagoon located near Abidjan (Ivory Coast). We foundthat phytoplankton growth (estimated by chlorophyll‐a quantification) was highlystimulated when both nitrogen and phosphorus were added, while there was noclear evidence for such colimitation by these two nutrients when consideringtheir concentrations in the lagoon. Phytoplankton growth was accompanied bysignificant changes in the diversity and composition of this community and didnot lead to an increase in the proportions of cyanobacteria. However, theaddition of fish to some mesocosms resulted in a drastic decrease inphytoplankton biomass and a dominance of chlorophytes in this community.Finally, these experiments showed that the addition of nitrogen, alone orcombined with phosphorus, stimulated microcystin production by cyanobacteria.
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Submitted on : Thursday, June 16, 2022 - 10:16:28 AM
Last modification on : Tuesday, September 6, 2022 - 3:40:31 AM

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Mathias Ahoutou, Eric Kouamé Yao, Rosine Djeha, Mamadou Kone, Kevin Tambosco, et al.. Impacts of nutrient loading and fish grazing on the phytoplankton community and cyanotoxin production in a shallow tropical lake: Results from mesocosm experiments. MicrobiologyOpen, Wiley, 2022, 11 (2), pp.e1272. ⟨10.1002/mbo3.1278⟩. ⟨hal-03662235⟩

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