A Holistic Time-series Analysis of Stony Coral Tissue Loss Disease

Stony coral tissue loss disease (SCTLD) continues to be a threat to Caribbean coral reefs causing a massive decline in reef-building corals and reducing ecosystem function. A potentially novel disease, Orbicella acute tissue loss disease (OATLD), has emerged as an additional threat to Orbicella corals in Florida. These projects focused on identifying cellular-level changes associated with SCTLD exposure over time and comparing them with other stressors including OATLD, nitrogen enrichment, and temperature stress. Using transmission electron microscopy (TEM), physiological and morphological changes within the algal endosymbionts were examined to improve the understanding of disease pathology and identify potential diagnostic markers. The results indicate clear differences between SCTLD and OATLD. While potential bioindicators for SCTLD include the decrease in the number of starch granules in the endosymbionts in diseased tissue and the presence of nitrogen-related crystal structures, there was an increase in starch granules for OATLD diseased tissue and crystals seem to be unrelated to pathology. These findings may indicate that SCTLD and OATLD affect coral and algal physiology through different mechanism and support the hypothesis that these are two different diseases. Experiments examining environmental stressors showed limited effects of nitrogen enrichment on algal growth, photosynthetic activity, and cellular morphology. Temperature stress showed an increased in lipid droplets and greater starch granules, indicating physiological changes. SCTLD and OATLD create distinct morphological changes from each other as well as from nitrogen enrichment and temperature stress. Overall, this research continues to establish baseline cellular characteristics for corals of various health states, diseases, and stressors and highlight the importance of cellular-level diagnostics in coral disease research.