Positive relationship between <i>Clostridium</i> abundance and bacterial community diversity in the aquaculture water of hybrid grouper ( <i>Epinephelus fuscoguttatus</i> ♀ × <i>E. lanceolatus</i> ♂) in coastal areas of Hainan Island

The hybrid grouper, characterized by its accelerated growth rate, robust disease resistance, and superior nutritional-economic value, has emerged as a pivotal mariculture species in China and Southeast Asia. This study systematically revealed the microbial communities within aquaculture waters across five coastal regions of Wenchang, Wanning, Lingshui, Ledong, and Dongfang in Hainan Island, and elucidated potential interspecific interactions in microbiota. The α-diversity indices, principal coordinate analysis and β-diversity metrics demonstrated substantial variations in bacterial abundance, species diversity, and community structure. Conversely, fungal assemblages showed no statistically significant spatial differentiation. Taxonomic profiling identified Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, and Cyanobacteria as dominant bacterial phyla. Fungal communities were predominantly composed of Ascomycota and Basidiomycota. Notably, Clostridium abundance in the outdoor mariculture ponds exhibited positive correlations with key bacterial parameters, suggesting its potential as a bioindicator for microbial community dynamics. These findings advocate for precision management strategies when utilizing Clostridium -based probiotics in outdoor mariculture systems. We propose implementing a dose-response protocol to optimize probiotic supplementation thresholds and prevent dysbiosis-induced fluctuations in aquatic microbial diversity. This approach provides critical insights for microbiome engineering in industrialized grouper aquaculture systems.