Beyond Nutrients: Disturbance–Competition Feedback Regulates Harmful Algal Blooms

Abstract Harmful algal blooms (HABs) are intensifying globally yet their absence in some high-nutrient lakes, challenging nutrient-centric paradigms. Using a nutrient-rich lake ecosystem, we quantified how environmental disturbance regulates algal dynamics under chronic nutrient loading. By integrating metagenomics, microbial source tracking, and interpretable machine learning across contrasting disturbance conditions, we identified a disturbance–competition–feedback mechanism. Moderate environmental disturbance increased community diversity, with dominant algal richness rising 3.5-fold, intensified interspecific competition, and redirected functional investment from biomass accumulation toward stress tolerance. Together, these responses suppressed HAB-forming taxa despite persistently high-nutrient levels. The relative importance of cyanobacteria decreased by 68%, accompanied by increased representation of multiple competing algal groups. These findings demonstrate that bloom development is not determined by nutrient availability alone but emerges from the interactions among environmental disturbance and community-level ecological feedbacks. The proposed framework extends nutrient-centric perspectives by highlighting disturbance-mediated algal community regulation and provides a mechanistic basis for improving HAB prediction and adaptive management in eutrophic water ecosystems.