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

Abstract

This study seeks to determine whether microcystins of unicellular Microcystis are the sole explanation for its adverse effects on rotifer growth. Brachionus calyciflorus were exposed to toxic and non-toxic strains of Microcystis aeruginosa separately and together with an edible alga (Scenedesmus obliquus) at different algal ratios and carbon compositions. Complete mortality was observed on B. calyciflorus cultured on toxic M. aeruginosa at all food concentrations (50, 100, and 400 mg CÁL À1) and nontoxic M. aeruginosa at 400 mg CÁL À1 . Rotifers fed the pure non-toxic strain exhibited reduced viability at lower food concentrations. Overall, growth rate decreased with increased proportions of M. aeruginosa. In mixed-diet experiments, rotifers showed greater tolerance to the non-toxic M. aeruginosa. Diets composed of both toxic and non-toxic Microcystis combined with Scenedesmus slightly supported rotifer growth at 100 mg CÁL À1. Due to the mixtures with sufficient S. obliquus at 400 mg CÁL À1 , nutritional deficiency could be excluded. Results are in agreement with the fact that unicellular M. aeruginosa cultured in the laboratory is a poor food for aquatic herbivores and might contain other toxic inhibiting substances to B. calyciflorus.

Maternal effects are no match for stressful conditions: a test of the maternal match hypothesis in a common zooplankter

“…The design of our experiment does not allow us to disentangle the factors leading to the cumulative decreased fitness under the Microcystis feeding regime, but many of the causes described above could be playing a role. As both nutrition and toxicity contribute to the negative effects of M. aeruginosa on B. calyciflorus (Zhao, Wang & Li 2014), we suggest that this offspring size-fitness relationship could be produced by constraints on the ability of rotifers to upregulate detoxifying enzymes, by inability to compensate for the nutritional inadequacy of M. aeruginosa, or by interaction of these two mechanisms. Both of these mechanisms would fall under the umbrella of transmissive maternal effects, whereby negative conditions experienced during the mother's life span may have negative effects on offspring, often through adverse effects on nutritional provisioning (Marshall & Uller 2007).…”

Persistent and delayed effects of toxic cyanobacteria exposure on life history traits of a common zooplankter

“…It could be that while the effects of toxins can be ameliorated through maternal effects (e.g., up‐regulation of enzyme production), nutritional deficiencies may not be so alleviated. Even non‐toxic strains of Microcystis have strong negative effects on the population growth of the rotifer B. calyciflorus , suggesting that nutrition plays a strong role in survival and reproduction (Zhao et al ). In the experiments carried out with D. magna , Gustafsson and Hansson () used mixed diets of Microcystis and Scenedesmus , which may have alleviated any nutritional deficiencies of a pure Microcystis diet.…”

“…With the methods that we used, untangling the relative contributions of these two factors was not possible. In a comparative study of the effects of a toxic and non‐toxic strain of M. aeruginosa , Zhao et al () found that non‐toxic strains of M. aeruginosa could not sustain population growth of B. calyciflorus . This suggests that although toxicity has a negative impact on B. calyciflorus , it is not the sole reason for decreased population growth rates in rotifers exposed to M. aeruginosa (Zhao et al ).…”

“…In a comparative study of the effects of a toxic and non‐toxic strain of M. aeruginosa , Zhao et al () found that non‐toxic strains of M. aeruginosa could not sustain population growth of B. calyciflorus . This suggests that although toxicity has a negative impact on B. calyciflorus , it is not the sole reason for decreased population growth rates in rotifers exposed to M. aeruginosa (Zhao et al ). In another non‐toxic cyanobacterium, Synechococcus elongatus , deficiencies in sterols and amino acids limited the population growth of B. calyciflorus (Wacker and Martin‐Creuzburg ).…”

Life strategy and grazing intensity responses of Brachionus calyciflorus fed on different concentrations of microcystin-producing and microcystin-free Microcystis aeruginosa

“…The effects of toxic cyanobacteria that produce secondary metabolites that suppress the population growth and reproduction of rotifers have been well demonstrated 14 . An overall collapse of Brachionus populations was observed within 3 days of being fed toxic M. aeruginosa 15 . Studies of factors affecting rotifer population growth have mainly focused not only on the algae type and species, but also on particle density 16 17 .…”