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A cyanobacterial bloom prevents fish trophic cascades

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Niveau: Supérieur, Doctorat, Bac+8
A cyanobacterial bloom prevents fish trophic cascades CAROLINE RONDEL* , †, ROBERT ARFI ‡, DANIEL CORBIN*, FREDERIC LE BIHAN , EL HADJI NDOUR* AND XAVIER LAZZARO* *IRD, UR 167 CYROCO, Dakar, Senegal †Universite Montpellier II, Ecole Doctorale Biologie Integrative (EDBI), Montpellier cedex, France ‡IRD, UR 167 CYROCO, Centre d'Oceanologie, Marseille, France 108 Rue Saint-Maur, Paris, France SUMMARY 1. We experimentally compared the impacts of visually feeding zooplanktivorous fish and filter-feeding omnivorous fish in shallow tropical Dakar Bango reservoir, Senegal. We provoked a cyanobacterial Anabaena bloom under mesotrophic to eutrophic N-limited conditions in 18 enclosures assigned to six Nile tilapia life-stage treatments, at typical biomasses: fishless control (C), zooplanktivorous fry (Z), omnivorous juveniles (O), herbivorous fingerlings (H) and two combinations (OZ, OH). 2. All fish grew well, but as prevalent inedible phytoplankton dampened fish effects, community-level trophic cascades did not occur. Planktivore types acted independently and affected differentially the biomasses of total zooplankton, cyclopoids, nauplii, cladocerans, invertebrate carnivores, large herbivores, colonial cyanobacteria and Chlo- rophyta. They neither influenced the total biomass of phytoplankton, nor most water chemistry characteristics. Responses were apparently not fish-biomass related. The bloom collapsed synchronously in all enclosures, coinciding with enrichment ending, with a return to clear water within 12 days.

  • visually feeding

  • biomass levels

  • eutrophic conditions

  • plankton growth

  • effects

  • between visual

  • differences between

  • rate between

  • filter-feeding omnivores

  • dom- inate fish


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Reads 16
Language English
Freshwater Biology (2007)
doi:10.1111/j.1365-2427.2007.01894.x
A cyanobacterial bloom prevents fish trophic cascades C A R O L I N E R O N D E L * , † , R O B E R T A R F I , D A N I E L C O R B I N * , F R E´ D E´ R I C L E B I H A N § , E L H A D J I N D O U R * A N D X A V I E R L A Z Z A R O * * IRD, UR 167 CYROCO, Dakar, Senegal Universite´MontpellierII,´EcoleDoctoraleBiologieInte´grative(EDBI),Montpelliercedex,France IRD, UR 167 CYROCO, Centre d’Oce´anologie, Marseille, France § 108 Rue Saint-Maur, Paris, France S U M M A R Y 1. We experimentally compared the impacts of visually feeding zooplanktivorous fish and filter-feeding omnivorous fish in shallow tropical Dakar Bango reservoir, Senegal. We provoked a cyanobacterial Anabaena bloom under mesotrophic to eutrophic N-limited conditions in 18 enclosures assigned to six Nile tilapia life-stage treatments, at typical biomasses: fishless control (C), zooplanktivorous fry (Z), omnivorous juveniles (O), herbivorous fingerlings (H) and two combinations (OZ, OH). 2. All fish grew well, but as prevalent inedible phytoplankton dampened fish effects, community-level trophic cascades did not occur. Planktivore types acted independently and affected differentially the biomasses of total zooplankton, cyclopoids, nauplii, cladocerans, invertebrate carnivores, large herbivores, colonial cyanobacteria and Chlo-rophyta. They neither influenced the total biomass of phytoplankton, nor most water chemistry characteristics. Responses were apparently not fish-biomass related. The bloom collapsed synchronously in all enclosures, coinciding with enrichment ending, with a return to clear water within 12 days. 3. Our results support the hypothesis that excess nutrients and prevalent inedible cyanobacteria inhibit the cascading effects of natural biomass levels of both visually feeding zooplanktivores and filter-feeding omnivores. In N-limited meso-eutrophic shallow tropical lakes with predominantly small herbivorous zooplankton, neither the type nor the biomass of planktivorous fish present seems likely to prevent the transient outburst of cyanobacterial blooms. Such fragile ecosystems may thus not sustain a trophic state suitable for drinking water production, unless human impacts are restricted. The generality of restoration approaches based on ecological engineering should be further explored. Keywords : cyanobacterial bloom, food webs, Nile tilapia, omnivory, trophic cascade
blueback shad on large herbivorous cladocerans Introduction (mainly Daphnia ) and calanoid copepods (review in Two main types of planktivorous fish may coexist in Drenner & Hambright, 2002). Studies, performed in lakes: visual-feeding zooplanktivores and filter-feed- mesotrophic temperate lakes of North America, have ing omnivores (Lazzaro, 1987). Pioneer works have often focused on typical visual feeders (such as, focused on size-selective predation by benthic filter- bluegill, mosquitofish, alewife, whitefish, including feeding common carp and open-water visual-feeding 0+ stages of piscivores, such as yellow perch). In meso-eutrophic lakes of Europe, studies have con-Correspondence: Xavier Lazzaro, IRD, UR 167 CYROCO, cerned 0+ stages of predatory European perch, but Campus ISRA-IRD, BP 1386, Bel-Air, Dakar, CP 18524, Senegal. mostly generalist plankti-benthivorous cyprinids, E-mail: lazzaro@ird.sn especially roach and bream. Those species are partly 2007 The Authors, Journal compilation 2007 Blackwell Publishing Ltd 1