Marine benthic proliferations are increasing in occurrence, range and duration by way of anthropogenic nutrient loading and climate change. The spread of these cyanobacteria within a variety of regions has made it fundamental to recognize the diversity and the species involved in these blooms. To expand knowledge on marine cyanobacterial diversity and reveal their phylogenetic relationships, sampling and isolation of benthic proliferative events from underexplored regions were conducted in the USA (Florida) and France (Loire-Atlantique). Cyanobacteria were described with the polyphasic approach using morphology, 16S rRNA gene phylogeny, 16S–23S rRNA ITS secondary structures and pairwise distances. Sampling of marine cyanobacteria from seagrasses, lagoons and marine coastal waters from nine Florida localities, in addition to Florida freshwater canals and French salt flats, revealed floating, epipsammic and epiphytic mats. A total of 30 cyanobacteria were isolated of which 21 represented two novel genera, Sirenicapillaria and Tigrinifilum. Sirenicapillaria is a genus that is found in massive benthic blooms throughout the western and southern Florida Coast.

A 72 h small-scale trial was conducted in enclosed mesocosms in the Lake Okeechobee waterway to evaluate the effectiveness of a USEPA-registered peroxide-based algaecide (formulated as sodium carbonate peroxyhydrate) for controlling a natural cyanobacteria population. Mesocosms were initially subjected to either no algaecide or the maximum label rate of 10 mg H₂O₂·L⁻¹. A subset of mesocosms were then subjected to a sequential application of 5 mg H₂O₂·L⁻¹ at 48 h after initial treatment. Following application, peroxide concentrations rapidly decreased and were undetectable by 48 h. At 24 h after treatment, significant decreases in all biomass indicators were observed (compared to untreated mesocosms), including extracted chlorophyll a, microscopic counts (total phytoplankton and total cyanobacteria), and cyanobacteria-specific 16S rRNA gene copies by over 71%. Although peroxide treatment reduced cyanobacteria biomass, there was no change in overall community structure and the remaining population was still dominated by cyanobacteria (>90%). After 48 h exposure, some biomass recovered in single application mesocosms resulting in only a 32–45% reduction in biomass. Repeated peroxide dosing resulted in the greatest efficacy, which had a sustained (60–91%) decrease in all biomass indicators for the entire study. While a single application of the peroxide was effective in the first 24 h, a sequential treatment is likely necessary to sustain efficacy when using this approach to manage cyanobacteria in the field. Results of this study support that this peroxide-based algaecide is a strong candidate to continue with scalable field trials to assess its potential future utility for operational management programs in the Lake Okeechobee waterway.