Cyanobacteria Blooms shift food-web pathways in freshwater lakes?

Research suggests that cyanobacteria blooms do not lead to trophic dead-ends. Consequently, as the frequency of cyanobacteria blooms increases globally, the need to discern how cyanobacteria influence food-web pathways also increases. We hypothesized that 1) cyanobacteria blooms short-circuit essential fatty acid (EFA) transfer all the way to tertiary consumers because of the low EFA content of cyanobacteria, and 2) the relative importance of the “brown” food web (i.e., detrital and bacterial energy pathways) increased compared to the “green” food web (i.e., phytoplankton-based pathway) during and after blooms. To test these hypotheses, we sampled across trophic levels in Missisquoi Bay, Lake Champlain, Vermont, which experiences annual cyanobacteria blooms. We compared fatty acid (FA) composition of seston, zooplankton, benthic invertebrates, and fishes during pre-, peak-, and post-bloom conditions. We also compared these data to fish and seston FA from less impacted regions of Lake Champlain. EFAs significantly decreased across trophic levels during and after the bloom in Missisquoi Bay and FA indicators of bacterial pathways increased, suggesting cyanobacteria blooms shifted the food web towards a brown pathway.