Metatranscriptomics of a cyanobacterial bloom in a freshwater estuary: Analysis of a community shift from a Planktothrix dominated community

Harmful algal blooms in Sandusky Bay of Lake Erie (U.S.) have been documented since the early 2000’s. The blooms, typically dominated by Planktothrix agardhii, are persistent from May through October. Biweekly sampling of the inner and outer portions of the bay was conducted from June through August of 2015. Heavy rainfalls occurred well into July throughout the region. This resulted in nitrogen loading from the surrounding agricultural areas until the rains subsided late July. Nitrate levels decreased as biomass increased during bloom formation, with N depletion also attributed to high rates of sedimentary denitrification.1 Nitrogen fixation was also attributed to Anabaena spp. present as a minor component of the bloom community.1 Metatranscriptomes prepared from these samples showed a shift from the dominance of Planktothrix sp. in early June in the inner bay to a transient abundance of N-fixing Anabaena spp. in July, then shifted back to Planktothrix dominance by August. The Planktothrix bloom persisted in the outer bay from June through August despite similar shifts in nitrogen availability. Understanding the dynamics of cyanobacterial blooms during shifts in N and P availability will be important in management decisions to prevent shifts in bloom taxa from Planktothrix to diazotrophic species. 1. Hampel, J.J., et al. Harmful algae, 81, pp.42-52. 2. Salk, K.R., et al.., 2018. Biogeosciences, 15(9), p.2891