Ecology and biodiversity of picoplanktonic cyanobacteria in coastal and brackish environments

Planktonic picocyanobacteria (PPC) are known to be a minor component of the pelagic phytocoenoses of coastal and brackish waters but recent studies have shown an increase in the biomass of these microorganisms, particularly in environments subject to anthropogenic pollution. PPC can play an important role in the functioning of the food webs and can modulate their metabolism in response to environmental changes. Most of the information available on PPC concerns open waters but this overview seeks to examine the existing literature on the diversity and ecology of these prokaryotes in coastal and brackish environments. Some recent studies have demonstrated the existence of a large number of picocyanobacterial strains, but their structural diversity (taxonomy) is still largely unknown. Genomics is greatly enhancing our knowledge of picocyanobacterial genetic diversity, but without complementary cytomorphological, ecophysiological and biochemical analyses, correct taxonomic classification cannot be achieved. As coastal environments provide a wide range of goods and services, managers need information on environmental quality and how they can preserve it. Together with other planktonic microbes, PPC are potentially useful as sensitive environmental indicators. More research is needed, not only to forecast and manage their harmful effects on coastal environments, but also to provide new insights into the biotechnological use of selected strains, in the framework of the blue economy.