Effects of Microcystis aeruginosa and purified microcystin‐LR on the feeding behavior of Daphnia pulicaria

Abstract

We investigated the mechanisms behind the negative effects of cyanobacteria on zooplankton by comparing the effects of Microcystis aeruginosa single cells, colonies, and toxins on the feeding behavior of Daphnia pulicaria in three independent experiments. The animals were fed a mixture of Scenedesmus supplemented by increasing proportions (0, 20, 50, 80, 100%) of Microcystis or concentrations (0, 50, 500, 5,000 ng ml Ϫ1 ) of purified microcystin-LR. The changes in feeding behavior, as indicated by the appendage beat, mandible or labrum movement rates were evaluated by a direct observation method that coupled video recording and computerized image analysis. Daphnia responded in a different manner to the presence of single cells and colonies. In the case of the single cells, the mandibular movement rate (MMR) declined more than appendage beat rate (ABR), suggesting that Daphnia have the ability to discriminate between Microcystis and Scenedesmus. Colonies, on the other hand, produced a typical feeding interference response: the animals increased their labral rejection rate (LRR) and showed starvation signs. LRR increased in the presence of both unicellular and colonial Microcystis. In both cases, the changes in MMR and ABR were rapidly reversible and hence unlikely to be caused by intoxication from the presence of cellbound microcystins. In contrast, the addition of purified microcystin-LR at the concentration of 5,000 ng ml Ϫ1 produced a nonreversible impairment of Daphnia feeding behavior.

Consequences of acclimation to Microcystis on the selective feeding behavior of the calanoid copepod Eudiaptomus gracilis

“…The extent of zooplankton grazing on cyanobacteria has consequences for the bloom dynamics and the stability of plankton communities and, thus, has long been recognized as central for efforts to control algal blooms through top-down trophic cascades (Sarnelle and Wilson 2005;Rondel et al 2007;Wang et al 2010). However, toxicity from ingesting cellular metabolites produced by cyanobacteria limits the potential for a significant grazing induced decline in blooms because it is the main cause of negative effects on zooplankton populations (Ghadouani et al 2003;Wilson et al 2006;Tillmanns et al 2008).…”

“…Zooplankton minimizes toxicity by either reducing ingestion (via adaptations in feeding behavior) or increasing their physiological tolerance to ingested toxins (DeMott et al 1991;Gustafsson et al 2005). Further, toxicity is not necessarily due to such wellidentified toxins such as microcystin, and can be from several other, sometimes unidentified secondary metabolites (Lü rling 2003; Rohrlack et al 2004;Ger et al 2010b).…”

Effects of toxic and non-toxicMicrocystis aeruginosain different mixtures withScenedesmus obliquuson growth ofBrachionus calyciflorus

“…They can decrease the survival, growth, and reproduction rates of zooplankton (Ferrão-Filho et al 2000;Ghadouani et al 2004). In the current study, a significant correlation between the proportion of toxic Microcystis strain and the rotifers growth and survivorship was found in all treatments.…”

Responses in population growth and reproduction of the freshwater rotiferBrachionus calyciflorusto microcystin-LR at different temperatures

“…et al , 1999;Lu¨rling and Van der Grinten, 2003;Ghadouani et al, 2004;Wilson et al, 2006). Up to now, contrast with cladocerans, the researches about effects of purified MCs on rotifers are scarce .…”

“…Rotifers, especially Brachionus calyciflorus and Brachionus plicatilis, have been widely recognized as bioindicators of water quality (Sladece´k, 1983) and ideal bioassay animals in aquatic toxicology (Halbach et al, 1983;Janssen et al, 1993;Snell and Janssen, 1995). Although numerous studies have examined the effects of MCs on zooplankton, most investigations have focused on cladocerans, especially the genus Daphnia (Demott et al, 1991;Lu¨rling and van der Grinten, 2003;Ghadouani et al, 2004;Chen et al, 2005;Dao et al, 2010;Yang et al, 2011Yang et al, , 2012, few studies have focused on rotifers. Chen et al (2002) found that 1-20 mg.L x1 crude MC-LR has adverse effects on rotifer B. plicatilis.…”