How many species of Cyanobacteria are there? Using a discovery curve to predict the species number

Although the number of biodiversity studies is increasing, the total number of species in different taxonomic groups remains uncertain. Estimates of the number of described species of Cyanobacteria range from 2,000 to 8,000. However, no studies have used discovery curves to estimate this number. The aim of this study was to understand the status of cyanobacterial biodiversity on a global scale and to estimate the number of still-unknown species, using a discovery curve. The species and year of descriptions of Cyanobacteria were obtained from the CyanoDB database. The cumulative number of species per year was adjusted using three asymptotic models (Logistic, Gompertz, and Extreme Value). These nonlinear models were compared through the Akaike information criterion. There are currently 2,698 described species of Cyanobacteria, and the best model (Gompertz) estimated that this group must contain 6,280 species. These three models proved to be quite idiosyncratic (Extreme value: 3,166 species and Logistic: 3,769 species), and therefore the choice of model is fundamental in studies using a discovery curve. Many Cyanobacteria species remain to be described, demonstrating the importance of increasing investment in research on the biodiversity of Cyanobacteria, in particular in understudied geographic regions.