Cyanobacteria as a Food Source for Invertebrates: Results of a Model Experiment

Cyanobacterial blooms are regarded as a global environmental problem. The role of cyanobacteria in the food web of water bodies is still unclear. We have carried out an experimental study of invertebrate trophic relationships during the bloom of the cyanobacterium Aphanizomenon flos-aquae. The key links of the food web—plankton, microperiphyton, detritus, and benthic invertebrates—were collected for stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) after 20-day exposure in mesocosms simulating the conditions of the near-shore biotope of the Rybinsk Reservoir without cyanobacteria (variant I) and with high abundance of cyanobacteria (variant II). Statistically significant differences in the δ15N values for crustaceans (Cladocera, Copepoda, Asellus aquaticus and Gmelinoides fasciatus), and mayfly larvae have been revealed between the variants: these values were 1–4‰ lower in the variant with cyanobacteria than in the variant without them. The cyanobacteria-induced shifts in the δ15N value for consumers indicate an assimilation of diazotrophic nitrogen and incorporation of cyanobacterial nutrients into their food chains.