Microcystins in transitional and marine ecosystems: Source categories, distribution patterns, and ecological impacts

Microcystins (MCs) are the algal toxins produced by freshwater blooms, and the environmental problems associated with them in both the aquatic and terrestrial environments are well known. However, in recent years, MCs have been continuously recorded in the marine settings such as brackish, estuarine, and coastal waters. To date, the review regarding the sources, distribution, and impacts of MCs in the marine ecosystems remains limited. This review elucidates the MCs' sources, distribution, and ecological impacts beyond freshwater systems. The study provides a global overview of the delivery of MC-producing algae from freshwater to the marine ecosystems and the secondary outbreaks of MC-producing algae in the marine environment. The distribution of MCs in contexts outside of freshwater is addressed by thoroughly examining all the current literature related to their existence in exclusive marine habitats. By examining MCs' effects at various trophic levels, the paper comprehends the environmental implications of MCs' existence in the marine environment. Overall, this review will provide new insights for addressing future issues, opportunities, and critical gaps, such as a comprehensive understanding of the fate and environmental behavior, long-term potential consequences, and the impact of MCs on microbial communities in marine settings, urging targeted management strategies for safeguarding the marine ecosystem health.