Notes on soft coral responses during a coral bleaching event in a shallow reef flat in southern Okinawa Island, Japan

Soft corals (Octocorallia) are major benthic components of Indo-Pacific reefs, yet their responses to thermal stress remain poorly documented compared to those of scleractinian corals. The 2024 Global Coral Bleaching Event provided an opportunity to closely examine soft coral dynamics on a shallow reef flat in the subtropical Okinawa Island, Japan. Permanent quadrats containing colonies of Lobophytum , Sarcophyton , Sclerophytum , and Klyxum were surveyed from August to December 2024, covering the period from just before to immediately after a severe bleaching event. Overall soft coral cover based on the haphazardly selected quadrats declined from 48.5% in August to 12.8% in December. Lobophytum , Sclerophytum , and Klyxum experienced substantial mortality, including the complete loss of some colonies by October. In contrast, Sarcophyton showed no significant decline and exhibited signs of recovery, with some colonies regaining Symbiodiniaceae by December as indicated by colony colors. Colony-level differences in bleaching outcomes suggest possible interspecific and intraspecific variations in heat tolerance. Additional observations including cyanobacterial overgrowth, partial tissue dissolution, and the presence of detached soft coral fragments illustrate the multiple processes by which soft corals degrade during heat stress events. These results show that soft corals can undergo rapid and often cryptic mortality during bleaching, with important implications for reef structure, biodiversity, and ecosystem functioning. Given their ecological importance and distinct degradation processes, long-term and fine-scale monitoring of soft coral communities is essential for understanding their resilience and for predicting potential phase shifts on warming oceans.