Eco-Environmental, Health and Socio-Economic Perspectives on Cyanobacteria and Cyanotoxins

Cyanobacteria, or blue-green algae, the first oxygenic photosynthetic organisms on Earth, play indispensable ecological roles as primary producers and drivers of biogeochemical cycles, and are also sources of human food, nutraceuticals, and biotechnological products. However, cyanobacterial harmful algal blooms (CyanoHABs), intensified by eutrophication and global climate change, threaten water quality, biodiversity, and human health due to their production of diverse secondary metabolites, i.e., taste and odor (T&O) compounds and cyanotoxins. This Special Issue, “Ecology and Toxicology of Cyanobacteria and Cyanotoxins”, compiles 13 papers from 9 countries that collectively advance our understanding of these issues across multiple scales. Cyanotoxins, including microcystins, cylindrospermopsins, anatoxins, and saxitoxins, can cause various hazards to animals and humans, including systemic toxicity, hepatotoxicity, genotoxicity, carcinogenicity, reproductive/developmental toxicity, neurotoxicity, immunotoxicity, and endocrine disruption. CyanoHABs are governed by complex bottom-up and top-down regulation, and blooms and cyanotoxin production are closely linked, but not always consistent/synonymous. Environmental stressors, e.g., phosphorus limitation, cold shock, and grazing pressure, selectively favor toxigenic genotypes, or can increase the cellular cyanotoxin quota, although overall population growth is suppressed. This can be explained by the fact that cyanotoxins can help cyanobacteria to better adapt to environmental stressors. When blooms disperse, demise, or are disrupted by certain interventions, the reduced biomass may increase exposure to dissolved, extra-cellular cyanotoxins if intra-cellular toxins are released faster than they are degraded or removed. We term the uncoupling of biomass and toxicity as the “cyanobacterial biomass–toxicity paradox”. We propose a “3P framework”, i.e., prediction, prevention, and prioritization, for the evidence-based risk management of CyanoHABs and cyanotoxins. We also advocate for more studies using multi-omics and artificial intelligence, as well as multi-disciplinary, multi-sectoral, and multi-stakeholder collaboration under the “One Health” umbrella to translate science into actionable solutions for sustainable development.