Exposure Type and Duration Determine Ecotoxicological Effects of Cyanobacteria Anatoxins on the Benthic Amphipod Hyalella azteca

Cyanobacteria can pose a threat to aquatic organisms by their ability to produce toxins such as neurotoxic anatoxins. Although cyanobacteria and their effects on aquatic fauna have been a research focus for a long time, the interactions between benthic cyanobacteria and benthic invertebrates are still largely unknown, especially with regard to how invertebrates cope with cyanotoxins which they are exposed to in their habitat. This study characterizes the effects of anatoxins on the benthic macroinvertebrate <i>Hyalella azteca</i>. In a first test, organisms were exposed to synthetically produced anatoxins dissolved in the ambient aqueous phase. In a second test, organisms were exposed to natural anatoxins within intact <i>Tychonema</i> cells as their sole food source. Over 10 days of aqueous exposure to anatoxins, survival of <i>H. azteca</i> was not affected, even at the highest nominal concentrations of 587.37 µg/L ATX and 590.31 µg/L dhATX. Over 42 days of dietary exposure to natural anatoxins, <i>H. azteca</i> readily accepted <i>Tychonema</i> as a food source. Survival, growth, reproductive success and storage compound concentrations (glucose, glycogen, lipid and protein) in the organisms' tissue, all assessed in the same individuals, were reduced. These findings suggest that the ecotoxicological effects of anatoxins on aquatic invertebrates not only depend on their concentration, but even more so on the type and duration of exposure. Furthermore, cyanobacteria like <i>Tychonema</i> seem to be insufficient as source of energy if they represent the only available food source.