Abstract
Coral reefs are critically important marine ecosystems that are facing many threats, including a significant rise in disease prevalence, specifically in the Caribbean. Stony coral tissue loss disease (SCTLD) is a serious and often fatal disease impacting scleractinian corals in the Western-Atlantic. While a single causal pathogen has not been identified, studies have shown that SCTLD causes shifts in the coral microbiome, suggesting the disease signs may be the result of a complex dysbiosis of multiple holobiont members. In more recent years, novel coral disease treatments have been developed, including the antibiotic treatment, Base2B with amoxicillin, and the antimicrobial treatment Coral Cure D (CCD). The objective of this study was to investigate changes in the microbial community of the major reef building species Orbicella annularis, in response to SCTLD and several disease treatments. The microbial communities of Disease lesion, Disease Unaffected, and Healthy tissue were found to be distinct from one another where the disease unaffected tissue acts as a transition zone, sharing similarities to both the healthy and disease lesion tissue. As the disease progressed, Terasakiellaceae decreased in abundance and Vibrionaceae increased. Treatment with both Base2B and CCD caused shifts in the microbiome and in both cases, these differences were most observed in the disease lesion tissue. Both treatments tended to decrease the prevalence of Rhodobacteraceae, a known SCTLD associate. Arcobacteracea and Nitrincolaceae were present after treatment in the Disease Lesion tissue of the CCD Active and Placebo treatments, but neither were present in the Base2B series. Alteromonaceae and Cyanobactereaceae were observed in the Base2B series after treatment but not in the CCD. In the Basse2B series, an increase in francisellaceae was noted post treatment across both disease lesion and disease unaffected samples. Microbiome changes were observed in both the CCD Placebo and Base2B Placebo, suggesting that one (or more) of the non-active ingredients or the physical act of smothering the coral tissue is partially responsible for changing the microbiome. Both Base2B with amoxicillin and CCD were shown to be effective treatments in stopping the progression of SCTLD.