Mitigating high-temperature bleaching impacts on high-value corals using low-cost shading approaches, and assessments of a potentially novel coral disease affecting key reef building corals (phase 2)

Florida’s Coral Reef continues to experience declines in live coral cover through a myriad of stressors, but two of the most impactful are hyperthermal events and coral disease. Neely lab projects from this funding cycle addressed these threats through testing in-water shading structures over bleaching-susceptible corals, and through a collaborative synthesis of field observations, histology, TEM, and microbiome work on a potentially novel disease affecting some of the largest corals in Florida. 

The deployment of in-water shade structures over two species of brain coral (Colpophyllia natans and Pseudodiploria clivosa) at a nearshore Lower Keys site showed that shading did significantly minimize paling of these two species during the 2024 summer. Samples taken during regular monitoring are being analyzed for symbiont community structure by the Baker lab (University of Miami) and are expected to provide further insight. The impacts of bleaching to corals are not only immediate, but also have long-term effects like increased susceptibility to some diseases and reduced reproductive effort in subsequent years. Thus deployment of shades is also expected to have positive longer-term effects on protected corals. Shades were low-cost and held up well during their temporary three-month deployment. As such, they may be a useful tool for protecting targeted corals during future bleaching events. 

Many of the largest Orbicella faveolata colonies in the Florida Keys have suffered extensive or total mortality from rapidly progessing linear lesions. During FY 2024-25, we collaboratively assessed field observations, histological studies, TEM observations, and microbiome analyses in order to better understand and describe these lesions, and as a result propose the name “Orbicella acute tissue loss disease” (OATLD). OATLD lesions had a different appearance than those of SCTLD, sometimes halted on their own, and were largely unaffected by amoxicillin application. Through historic assessment of intervention photos and data, these lesions were found to have been present since at least 2019 (before interventions were initiated), to peak in prevalence during late summer/early fall, and, concerningly, to disproportionately affect large corals. Histological examination shows that most of the characteristic traits of SCTLD (lytic necrosis and endosymbiont deformities) are not present in OATLD samples. Rather, OATLD samples are characterized by absent or necrotic mesenterial filaments, ghost symbionts, and degraded granular amoebocytes. TEM analyses are reported on in the Ushijima (UNCW) final report, but also found distinct differences from SCTLD, including high numbers of starch and lipids, as well as high numbers of accumulation bodies within the endosymbionts. Microbiome analyses are reported on in the Meyer (UF) final report, but in brief, found many ASVs that were similar between OATLD and SCTLD, but five bacterial taxa that are unique to OATLD. Overall, we conclude that OATLD is unlikely to be a variant of SCTLD, but instead a distinct disease that requires alternate management considerations. The consortium recommends prioritizing experimental testing of inter- and intraspecific transmissibility, and also trialing potential treatment options to prevent further loss of these large colonies.