Thermal stress interacts with surgeonfish feces to increase coral susceptibility to dysbiosis and reduce tissue regeneration

Coral microbiome is sensitive to local and global stressors such as global climate change, pollution, overfishing but also biotic interactions. An array of marine organisms are suspected to vector microbes to corals through corallivory or fecal pellet deposition. For instance, the widely distributed surgeonfish Ctenochaetus striatus was shown to vector bacterial opportunists to Porites lobata via fecal pellet deposition. Yet, it remains unknown how environmental parameters, such as temperature, influence these interactions. In this study, we investigated the combined effects of fish feces deposition by C. striatus and increased sea surface temperature on P. lobata bacterial communities using a factorial manipulative experiment. Corals were therefore exposed to the following treatments : a control treatment with P. lobata corals exposed to ambient temperature, a treatment where corals were exposed to elevated temperature, a treatment where a fecal pellet of C. striatus was disposed on each coral fragment and exposed to ambient temperature and a treatment in which corals were exposed to the combined stressors. Samples were collected at 3 time points (T0, T24h and T48h) to track the temporal changes in coral microbiomes. Water samples were also collected at each time points within each treatments. Additionally, we tracked the recovery of coral microbiomes (under low and high temperature) and tissue regeneration following the removal of fecal material at 48h.