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Aims: The study aims to investigate the bacterial community profiles on the surface of red algae (Kappaphycus alvarezii) and persistent bacteria that can adapt to long-term cultivation in a closed circulation system. Methodology and results: Kappaphycus alvarezii explants were cultured in a controlled laboratory setting for 30 days to investigate related bacterial adaptability to controlled culture conditions. Bacterial isolates associated with seedlings were subjected to 16S rDNA amplification and sequencing, followed by the construction of a phylogenetic tree using MEGA X software. The results show distinct microbial composition between the first and 30th days. The derived phylogenetic tree features three dominant phyla: Proteobacteria (Vibrio and Thalassospira), Pseudomonadota (Pseudoalteromonas, Alteromonas, Grimontia, Ruegeria, Phaebacter and Bacterioplanes) and Firmicutes (Bacillus). A comparative examination of these two bacterial groups (day 1 and day 30) reveals evidence of persistent marine bacteria, such as the genera Vibrio, Pseudoalteromonas, Alteromonas, Phaaebacter and Bacterioplanes, that successfully adapt to long-term cultivation within closed circulation systems. Conclusion, significance and impact of study: The findings of this study contribute to the understanding of bacterial ecology in the controlled red algae cultivation environment and also provide valuable insights into the optimization of an ideal closed cultivation system for sustainable K. alvarezii production, benefiting the seaweed industry. [ABSTRACT FROM AUTHOR]