The current state of knowledge on taxonomy, modulating factors, ecological roles, and mode of action of phytoplankton allelochemicals

Highlights: • Allelopathic effects of cyanobacteria and microalgae occur in all aquatic habitats. • Allelopathy influence ecosystem dynamics, species variability, and bloom formation. • Studies confirm allelopathic properties in 61 genera of cyanobacteria and microalgae. • Cyanobacteria were the most frequently examined for their allelopathic activity. • Synechococcus sp. and Karenia brevis were the most studied organisms. Allelopathy is widespread in marine, brackish, and freshwater habitats. Literature data indicate that allelopathy could offer a competitive advantage for some phytoplankton species by reducing the growth of competitors. It is also believed that allelopathy may affect species succession. Thus, allelopathy may play a role in the development of blooms. Over the past few decades, the world's coastal waters have experienced increases in the numbers of cyanobacterial and microalgal blooming events. Understanding how allelopathy is implicated with other biological and environmental factors as a bloom-development mechanism is an important topic for future research. This review focuses on a taxonomic overview of allelopathic cyanobacteria and microalgae, the biological and environmental factors that affect allelochemical production, their role in ecological dynamics, and their physiological modes of action, as well as potential industrial applications of allelopathic compounds.