Seasonally driven ecological adaptation in sea cucumbers Apostichopus japonicus: dynamic coupling of nutrient metabolism and gut microbial network reconfiguration

Seasonal variation in environmental conditions profoundly influences host-microbe interactions and nutrient dynamics in marine invertebrates. This study investigated the seasonal changes in body wall nutritional components and gut microbiota of the sea cucumber Apostichopus japonicus in a marine ranching system. Significant seasonal fluctuations were observed in crude protein, lipid content, and key fatty acid and amino acid profiles, with autumn identified as a peak phase for nutrient accumulation. High-throughput 16S rRNA sequencing revealed pronounced shifts in gut microbiota diversity and community composition across seasons, with Proteobacteria and Bacteroidetes as dominant phyla. Co-occurrence network and neutral model analyses indicated that microbial community assembly was primarily governed by stochastic processes, particularly ecological drift and dispersal limitation. Strong correlations between specific microbial taxa and host fatty acids or amino acids suggest that gut microbes actively participate in host metabolic regulation, especially under thermal and nutritional stress. These findings provide new insights into host-microbiota interactions and ecological adaptation mechanisms in sea cucumbers, with implications for sustainable aquaculture management.