Sediment exposure decreases diversity in the surface mucus layer microbiome of Porites lobata at Honoliʻi, Hawaiʻi

Joseph W. P. Nakoa III^1,2*John H.R. Burns^2,3Makoa Pascoe^2,4Manuela Cortes^2,5Sofia B. Ferreira^2,4Kailey H. Pascoe^1,2Haunani Kane^2,6Cliford A. Kapono^2,7

• ¹School of Life Sciences, Arizona State University, Tempe, United States
• ²MEGA Lab, Hilo, United States
• ³Marine Science, Data Science, and Tropical Conservation Biology and Environmental Science, University of Hawaii at Hilo, Hilo, United States
• ⁴Tropical Conservation Biology and Environmental Science, University of Hawaii at Hilo, Hilo, United States
• ⁵Marine Science, University of Hawaii at Hilo, Hilo, United States
• ⁶School of Ocean and Earth Science Technology, University of Hawaii at Manoa, Honolulu, United States
• ⁷School of Ocean Futures, Arizona State University, Tempe, United States

Coral reefs are diverse marine ecosystems that provide essential ecological services, yet they are becoming increasingly degraded by anthropogenic stressors. Sediment deposition from land-based runoff can smother corals, reduce light availability, and alter the chemical and microbial composition of the water column. Prolonged sediment exposure disrupts coralassociated microbial communities, particularly within the surface mucus layer (SML), a physical barrier that mediates host-microbe interactions. We investigated shifts in the SML microbiome of Porites lobata corals in response to an acute sedimentation event at Honoliʻi, Hawaiʻi. Microbial community structure was characterized using 16S rRNA gene sequencing, at three time points, before, during, and after the sedimentation event, to identify changes in microbial composition and diversity. Sedimentation caused a significant decline in microbial diversity and shifted community composition, with the most pronounced changes observed post-sedimentation. Indicator species analyses identified 206 bacterial taxa associated with specific sedimentation periods, including enrichment of Flavobacteriales during sedimentation and dominance of Endozoicimonaceae after sedimentation. These findings demonstrate that sedimentation induces both immediate and delayed shifts in the SML microbiome, with potential implications for coral resilience. This study advances our understanding of how sedimentation affects coral-associated microbiomes and emphasizes the need to investigate the functional roles of microbial taxa involved in community transitions and recovery to inform conservation strategies.