Monitoring of cyanobacteria for water quality: doing the necessary right or wrong?

Cyanobacteria are an essential biological component of phytoplankton water quality assessment. However, there are some problems associated with the widely used everyday practices of sampling, estimation and use of cyanobacteria when calculating phytoplankton indices assessing water quality. Many indices were developed during the implementation of the Water Framework Directive, considered the most innovative European environmental legislation. Most indices include cyanobacteria as a composition or bloom metric. Problems with the indices concern the exclusion of most chroococcalean taxa from cyanobacterial biovolume estimations in lakes and reservoirs of the Mediterranean region, treatment of the mucilage of colonial chroococcalean taxa in biovolume estimations and overlooking of deep-water cyanobacterial blooms due to sampling depth. These problems may lead to a biased view of water quality. In this paper we argue in favour of including all cyanobacteria taxa and their mucilage in biovolume estimations and considering a sampling depth that covers deep-water maxima, such as those formed by Planktothrix rubescens or colonial chroococcalean taxa. Cyanobacteria are an influential and widely acknowledged biological component of lake water quality assessment. Nevertheless, there are gaps in the monitoring of cyanobacteria. In this article we review widespread problems in the use of cyanobacteria in Water Framework Directive-related water quality assessment (i.e. exclusion of taxa, mucilage carbon of the colonial species, sampling depth) and suggest solutions to optimise water quality assessment. [ABSTRACT FROM AUTHOR]