Pyropia haitanensis cultivation enhances water quality and reshapes microbial communities in coastal water and connected aquaculture ponds

Abstract

Seaweed cultivation offers nature-based bioremediation for aquaculture effluents, yet its cascading effects on microbial ecosystems remain poorly understood. This study evaluated Pyropia haitanensis cultivation impacts across four phenological stages in nearshore marine (Cultivation Area, PS; Control Sea, CS) and connected aquaculture ponds (Influenced Pond, PA; Control Pond, CA). Results showed that P. haitanensis cultivation significantly improved water quality in PS and PA by increasing dissolved oxygen and pH while reducing NH₄⁺-N, TN, TC, and TOC. Microbial diversity and community structures were markedly influenced by cultivation: α-diversity increased in PS and PA, counteracting seasonal declines in controls. Meanwhile, community composition shifted significantly, with reduced Proteobacteria and increased Bacteroidota and Actinobacteriota . The abundance of potentially parasitic eukaryotes (e.g., Apicomplexa ) also decreased in PA. Co-occurrence networks in cultivation-influenced areas exhibited greater complexity, positive correlations, and modularity. Assembly processes diverged: bacterial communities followed deterministic assembly, whereas eukaryotes were governed by stochastic processes and dispersal limitation. These findings demonstrate P. haitanensis cultivation serves dual roles—as an effective bioremediator improving water quality and an ecological engineer fostering more diverse, stable microbial consortia—supporting its integration for sustainable aquaculture and coastal ecosystem restoration.