Harnessing Microalgae for Aquatic Ecosystem Restoration: Implementation Strategies, Challenges and Future Perspectives

Aquatic ecosystems are increasingly impacted by anthropogenic pressures, including nutrient over-enrichment, industrial discharge and physical habitat alteration, resulting from industrialization, urbanization, agricultural intensification and population growth. In recent years, microalgae have been extensively studied in engineered and controlled systems for their potential role in aquatic ecosystem restoration, owing to their capacity to assimilate nutrients, sequester contaminants and interact with microbial consortia, alongside valuable biomass generation. While most of the existing studies are based on ex situ systems, such as high-rate algal ponds, wastewater treatment reactors, algal–bacterial granular sludge, constructed wetlands and aquaculture effluent treatment units, these processes provide mechanistic insights relevant to aquatic ecosystem restoration. Hence, this review critically evaluates the emerging role of microalgae in aquatic ecosystem restoration, mainly through two implementation pathways, namely ex situ engineered systems and in situ applications, based on the current state of the art in microalgae-driven processes, with particular emphasis on nutrient uptake pathways and mechanisms. Furthermore, key challenges and future directions associated with the translational potential of microalgae-based approaches, including field-scale validation, ecological performance assessment, operational stability and regulatory integration, essential for real-world aquatic ecosystem restoration, are discussed. Despite the limitations in direct field-scale restoration, microalgae-based strategies are promising and sustainable platforms for aquatic ecosystem rehabilitation, which align with Sustainable Development Goals 6 and 14.