title: Effect of microcystin on growth of single species and on mixed natural populations of heterotrophic nanoflagellates.
abstract: Natural populations of heterotrophic nanoflagellates were reduced in numbers and in situ growth rates during a toxic Microcystis bloom in a eutrophic lake. Microcystin was found in the particulate phase (algae) and in the dissolved phase (water) with maximum concentrations of 414 micrograms g freeze-dried algal material-1 and 141 micrograms l-1 lake water, respectively. An average reduction in growth rates of 49% was found when comparing the growth estimates before and after the toxic bloom had peaked. Similar reductions were found in laboratory experiments when growing mixed flagellate populations from two different systems with microcystin, but without predators. Concentrations of 10 micrograms toxin 1-1 reduced the growth rates by 36-41% (significantly different from the controls) and 1 microgram toxin 1-1 reduced the growth rates by 24-28% (not significant). Thus, natural populations of heterotrophic nanoflagellates seem very sensitive to microcystin. The growth characteristic of two cultured species was also tested in the presence of microcystin. Both the cultured species, Heteromita globosa and Spumella sp., grew well at 1-10 micrograms microcystin 1-1 and Spumella sp. was able to grow at 50 micrograms microcystin 1-1. However, the growth curves indicate that the decline in numbers during the stationary phase occurred faster in the presence of microcystin. The ecological consequences of a highly sensitive protozoan community may be that larger zooplankton species (copepods and cladocerans) are affected by reduced availability of food.
authors.affiliation: Freshwater Biological Laboratory, University of Copenhagen, Hillerød, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Christoffersen
mesh_terms: D000818:Animals; D002244:Carbon / Q000378:metabolism; D000458:Cyanobacteria / Q000254:growth & development / Q000378:metabolism; D056890:Eukaryota / Q000187:drug effects* / Q000254:growth & development*; D052998:Microcystins; D010456:Peptides, Cyclic / Q000378:metabolism / Q000633:toxicity*; D013045:Species Specificity
chemical_list: D052998:Microcystins; D010456:Peptides, Cyclic; D002244:Carbon; C078588:microcystin