Sedimentary Vibrio Blooms in the Xisha Islands May Associate with the 2020 Coral Bleaching Event

Coral reefs exert important roles in maintaining the sustainability of marine ecosystems but decline worldwide due to various drivers, especially pathogenic microorganisms. Here, we investigated the distribution pattern and interactions of total bacteria and Vibrio spp. in the sediments from Xisha Islands during the coral bleaching event of 2020. ABSTRACT Coral reefs are among the most biodiverse ecosystems, providing habitats for various organisms. Studies on coral bleaching have been increasing recently, but little is known about the distribution and community assembly of coral pathogenic bacteria (e.g., several Vibrio species). We elucidated the distribution pattern and interaction relationships of total bacteria and Vibrio spp. in sediments from the Xisha Islands, which are characterized by their high coverage and diversity of coral resources. Vibrio spp. showed significantly higher relative abundance values in the Xisha Islands (1.00 × 108 copies/g) than in other areas (approximately 1 × 104 to 9.04 × 105 copies/g), indicating that the coral bleaching event of 2020 may have promoted the bloom of vibrios. A spatial shift in community composition was observed between the northern (Photobacterium rosenbergii and Vibrio ponticus) and southern (Vibrio ishigakensis and Vibrio natriegens) sites, accompanied by a clear distance-decay pattern. The spatial distance and coral species (e.g., Acroporidae and Fungiidae) had much greater correlations with the Vibrio community than did environmental factors. However, complex mechanisms may exist in the community assembly of Vibrio spp. due to the large proportion of unexplained variation. Stochastic processes may play an important role, as shown by the neutral model. Vibrio harveyi had the highest relative abundance (77.56%) and niche breadth, compared to other species, and it was negatively correlated with Acroporidae, likely reflecting its strong competitive ability and adverse effects on specific corals. Our study provides insights into the bloom and underlying assembly mechanisms of sedimentary vibrios in the Xisha Islands, thereby contributing to identify the potential indicator of coral bleaching and provide inspiration for the environmental management of coral reef areas. IMPORTANCE Coral reefs exert important roles in maintaining the sustainability of marine ecosystems but decline worldwide due to various drivers, especially pathogenic microorganisms. Here, we investigated the distribution pattern and interactions of total bacteria and Vibrio spp. in the sediments from Xisha Islands during the coral bleaching event of 2020. Our results showed that the abundances of Vibrio (1.00 × 108 copies/g) were high across the whole sites, indicating the bloom of sedimentary Vibrio spp. Coral pathogenic Vibrio species were abundant in the sediments, likely reflecting adverse effects on several kinds of corals. The compositions of the Vibrio spp. were separated by geographical location, which was mainly attributable to the spatial distance and coral species. Overall, this work contributes by providing evidence for the outbreak of coral pathogenic vibrios. The pathogenic mechanism of the dominant species (especially V. harveyi) should be comprehensively considered by laboratory infection experiments in the future.