Stony coral tissue loss disease (SCTLD) is a relatively new and complex disease affecting over 22 species of stony corals across the Caribbean. First detected near Miami, Florida, in 2014, it has since spread to reefs in 28 countries, causing significant coral mortality. SCTLD is characterized by rapid tissue loss, leading to total colony mortality within months if untreated.
Managers face significant challenges in combating SCTLD due to the limited understanding of its cause, transmission mechanisms, and effective treatments. This review synthesizes current knowledge to help guide efforts in mitigating the impacts of this disease.
Susceptibility and transmission
Coral susceptibility to SCTLD varies: highly susceptible species exhibit high disease prevalence, rapid lesion progression, and severe population declines. Moderately and less susceptible species experience slower progression and lower prevalence. While Caribbean Acropora species are believed to be unaffected, this lacks peer-reviewed confirmation. (See Table 1 for a list of species susceptibility.)
The exact transmission mechanism of SCTLD remains unknown, but it has been shown to spread through direct contact, waterborne, or exposure to contaminated sediments. Ship ballast water may also contribute to its spread across regions. On reefs, outbreaks can begin with just 0.05–0.1% of colonies infected. Incubation periods range from 4–10 days in laboratory settings to 6 days–6 months on reefs.
Contrary to expectations, SCTLD is more prevalent on reefs with higher biodiversity. Factors influencing prevalence include reef location (offshore more susceptible than nearshore), coral colony size structure (large colonies are more likely to contract the disease), and water temperature, with high temperatures leading to less disease. This may be explained by the loss of algal symbionts during bleaching, which may be linked to coral colony susceptibility to SCTLD. Coral-symbiont relationships also play a role: low-susceptibility corals associate exclusively with Symbiodinium, while highly susceptible species are linked to Breviolum.
Diagnosis and intervention methods
Identifying SCLTD underwater can be challenging due to how the disease presents in different species. Additional methods to confirm the disease include light microscopy of the tissues. Understanding early signs is critical for timely intervention. Approaches include amputation, culling, genetic rescue, trenching, chlorinated epoxy, antibiotics, chemotherapeutics, and probiotics. However, these various treatments for SCTLD have shown mixed success.
The most effective treatment to date is the amoxicillin/CoralCure Ointment Base2B, which has significantly reduced disease progression. However, this method requires ongoing monitoring and reapplication every few months and may have unintended impacts on nearby corals.
Promising alternatives include probiotics, such as the strain McH1-7, which has fully protected coral fragments from SCTLD transmission in one study. This marks the first known prophylactic treatment and offers hope for scalable preventative measures.
Genetic rescue, involving the removal and preservation of healthy corals before SCTLD outbreaks, is another strategy to safeguard coral diversity for future restoration efforts.
Implications for managers
- Implement diagnostic tools and techniques to identify SCTLD early, enabling timely and effective intervention.
- Focus monitoring efforts on highly susceptible species, which exhibit faster disease progression and significant population declines.
- Use standardized methods to record outbreak state, affected species, time since emergence, coral cover, and community composition to ensure comparability across regions.
- Contribute observations to centralized resources like www.agrra.org/coral-disease-outbreak to enhance collective understanding and management efforts.
- Discuss the use of amoxicillin-based treatments with stakeholders while understanding there are no published peer-reviewed studies or independent data demonstrating the impacts of antibiotics on the surrounding ecosystem. Use antibiotic-based treatments as the stakeholders deem fit.
- Continue supporting research into more scalable, safer, and cost-effective interventions or preventative methods.
Author: Papke, E, A. Carreiro, C. Dennison, J.M. Deutsch, L.M. Isma, S.S. Meiling, A.M. Rossin, A.C. Baker, M.E. Brandt, N. Garg, D.M. Holstein, N. Traylor-Knowles, J.D. Voss and B. Ushijima
Year: 2024
Frontiers in Marine Science 10:1321271. doi: 10.3389/fmars.2023.1321271
