Orbicella faveolata, a major reef-building Caribbean coral species, has significantly declined due to a combination of stressors including infectious disease. Caribbean Yellow Band Disease (CYBD), although slow in progression, often results in complete colony mortality. Antibiotics have proven effective in treating several coral diseases in the laboratory and the field. We applied an amoxicillin-laced Base2B ointment to CYBD lesions on O. faveolata within Buck Island Reef National Monument, St. Croix, USVI to attempt to halt disease progression. Another CYBD lesion on the same colony served as a paired untreated control. Microbiomes of the apparently healthy tissue adjacent to the treatment were characterized pre-treatment and two days post-treatment along with the paired controls and nearby healthy colonies. Diseased colonies had significantly higher alpha diversity and different microbial communities from healthy colonies. Amoxicillin treatment significantly changed the microbial community composition. The bacterial family Vibrionaceae, a putative pathogen for CYBD and often associated with other coral diseases, was enriched post-treatment. The progression rates of amoxicillin-treated lesions were similar to the untreated lesions. Our results suggest that amoxicillin may disrupt the microbiome of apparently healthy tissue allowing for opportunistic bacteria to colonize within days and may not be an effective treatment for CYBD.
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