Gut Microbiome and This Potential Roles in Abalone (Haliotis discus hannai) Collected from the Korean Coast according to Urchin Barren Severity
Kelp forests are vital marine ecosystems that support biodiversity and provide economic benefits. Recently, decline of kelp forest, known as urchin barrens, has been observed globally, including Korea. Overgrazing by kelp herbivores such as sea urchin and abalone is most widely reported cause of kelp forest decline. However, the relationship between their gut microbiome and urchin barrens remains poorly understood. Here, we analyzed the gut microbiome of abalone (Haliotis discus hannai) from four urchin barren regions in South Korea (three mild and one severe regions) using 16S rRNA sequencing. We found significant differences between wild and aquaculture abalone, largely driven by elevated suspended particulate matter (SPM) in aquaculture environments. Seasonal shifts in gut microbial composition were observed in wild abalone, with mediation analysis indicating that seawater temperature and Season indirectly influenced microbial communities via geochemical mediators such as dissolved oxygen (DO), chemical oxygen demand (COD), nitrite nitrogen (NO2-N), and total phosphorus (TP). Notably, barren severity influenced gut microbiota only in August, when metabolic demand was higher. Severe barren regions exhibited simplified microbial networks and reduced energy metabolism, with keystone taxa (Flavobacteriales, Cytophagales) potentially supporting minimal host metabolism under low-food conditions. Our findings highlight the dynamic and season-dependent nature of gut microbiota in abalone, with pronounced alterations linked to urchin barren severity, and provide new insights into host–microbiome–environment interactions in marine ecosystems.