title: Do high concentrations of microcystin prevent Daphnia control of phytoplankton?
abstract: Toxin-producing cyanobacteria have frequently been hypothesized to limit the ability of herbivorous zooplankton (such as Daphnia) to control phytoplankton biomass by inhibiting feeding, and in extreme cases, causing zooplankton mortality. Using limnocorral experiments in hyper-eutrophic ponds located in Alabama and Michigan (U.S.A.), we tested the hypothesis that high levels of cyanobacteria and microcystin, a class of hepatotoxins produced by several cyanobacterial genera, prevent Daphnia from strongly reducing phytoplankton abundance. At the start of the first experiment (Michigan), phytoplankton communities were dominated by toxic Microcystis and Anabaena (∼96% of total phytoplankton biomass), and concentrations of microcystin were ∼3 μg L⁻¹. Two weeks after adding Daphnia pulicaria from a nearby eutrophic lake, microcystin levels increased to ∼6.5 μg L⁻¹, yet Daphnia populations increased exponentially (r = 0.24 day⁻¹). By the third week, Daphnia had suppressed phytoplankton biomass by ∼74% relative to the no Daphnia controls and maintained reduced phytoplankton biomass until the conclusion of the five-week experiment. In the second experiment (Alabama), microcystin concentrations were greater than 100 μg L⁻¹, yet a mixture of three D. pulicaria clones from eutrophic lakes in southern MI increased and again reduced phytoplankton biomass, in this case by over 80%. The ability of Daphnia to increase in abundance and suppress phytoplankton biomass, despite high initial levels of cyanobacteria and microcystin, indicates that the latter does not prevent strong control of phytoplankton biomass by Daphnia genotypes that are adapted to environments with abundant cyanobacteria and associated cyanotoxins.
authors: Department of Fisheries and Allied Aquacultures, 203 Swingle Hall, Auburn University, Auburn, AL 36849, USA.
authors: Michael F
authors: MF
authors: Chislock
authors: Orlando
authors: O
authors: Sarnelle
authors: Lauren M
authors: LM
authors: Jernigan
authors: Alan E
authors: AE
authors: Wilson
mesh_terms: D000220:Adaptation, Biological; D000407:Alabama; D017033:Anabaena / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D000818:Animals; D001427:Bacterial Toxins / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D019976:Cloning, Organism; D000458:Cyanobacteria / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D003621:Daphnia / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D005068:Eutrophication; D020387:Food Chain; D057097:Harmful Algal Bloom / Q000187:drug effects*; D008824:Michigan; D056265:Microbial Interactions / Q000187:drug effects; D052998:Microcystins / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D046931:Microcystis / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D010572:Pest Control, Biological; D010839:Phytoplankton / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism; D061005:Ponds / Q000737:chemistry / Q000382:microbiology*; D060753:Water Quality; D015048:Zooplankton / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D052998:Microcystins; C078588:microcystin