Frequent coral disease interventions reduces tissue loss.

Stony coral tissue loss disease is a highly contagious coral disease, causing rapid colony mortality and local extinctions. Conducting disease interventions on all corals in a region during an outbreak is virtually impossible, therefore, intervention strategies must be considered. Prioritizing specific colonies for frequent monitoring and treatment can improve disease management outcomes by enabling early disease treatment to reduce colony tissue loss and pathogen load in the environment. Since little is known about the longer-term effectiveness of proactive large scale disease interventions, this study examined the effectiveness of monthly interventions on the largest known Orbicella faveolata colonies in southeast Florida over seven years and forecasted colony fates under present environmental conditions. In 2015, 78 large (> 2 m) O. faveolata colonies were identified and monitored. In 2018, 42 colonies with the greatest living tissue area were designated as priority corals, receiving monthly monitoring with disease interventions, and the remaining 36 colonies were designated non-priority corals and revisited in 2021. All corals lost significant amounts of tissue before disease interventions began (2015–2018). Once monthly monitoring and disease interventions started (2018–2022), tissue loss slowed significantly on the treated priority colonies but continued to decline significantly on the non-priority colonies. Over 66% (24/36) of the non-priority corals died versus none of the priority colonies. While disease interventions were highly successful at reducing the amount of tissue lost to disease, priority corals continually developed new lesions and treatments were still required nearly every month. These frequent treatments are projected to prolong the lifespan of the priority colonies for at least the next 30 years, potentially enabling them to spawn and contribute to the O. faveolata population. Our findings support that disease interventions are a proactive response to SCTLD that saves existing coral genetic diversity and reduces the need for post hoc reef restoration.