Harmful Cyanobacterial Blooms in Tropical and Neotropical Freshwaters: Environmental Drivers, Toxin Dynamics, and Management Gaps

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Cyanobacterial blooms are intensifying globally under climate warming, eutrophication, and hydrological alteration, yet most mechanistic understanding derives from temperate lakes. Tropical and neotropical freshwaters operate under persistently warm conditions, weak seasonality, and hydrological variability that can sustain extended bloom windows and alter toxin production patterns spatiotemporally, requiring targeted synthesis. This review synthesizes recent experimental and field evidence, complemented by foundational frameworks, to evaluate cyanobacterial diversity, functional ecology, and cyanotoxin dynamics in tropical freshwater habitats. We highlight recurring trait syndromes, coordinated sets of physiological and functional traits, that recur across warm systems, including buoyancy regulation, diazotrophy, and thermal tolerance, which confer competitive advantages under warm, nutrient-rich conditions. These traits are prominent in dominant genera such as Microcystis, Raphidiopsis, and Planktothrix. We assess how temperature, nutrient stoichiometry, water residence time, and light interact to modulate bloom persistence and toxin production. We summarize appropriate monitoring and management approaches suited to warm, hydrologically dynamic basins. These including strategies addressing internal loading and integrated early-warning frameworks combining molecular tools and remote sensing. Substantial gaps persist in toxin quantification, biogeochemical fluxes, molecular surveillance, and coordinated risk assessment across the tropics. We argue that region-specific, integrative frameworks are urgently needed to improve early-warning capacity and mitigate cyanoHAB risks in tropical freshwater ecosystems.

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