Role of Core Microbiome Shifts in Octocoral Litophyton Under Diurnal Temperature Fluctuations: Implications for Thermal Stress Mitigation and Nutrient Acquisition- a study of Chien-Yi, Wu et al.

Climate change is expected to impact marine environments by increasing sea temperatures and diurnal temperature fluctuations, threatening the survival of both stony corals and octocorals. Litophyton is a common octocoral in Taiwan’s shallow reefs that is exposed to large daily temperature fluctuations and heat stress, and exhibits bleaching during summer. In coral holobionts, the bacterial composition will change under heat stress and temperature fluctuations, and it is known that bacterial constituents play a vital role in coral health. In this study, we addressed two key questions: (1) Will Litophyton exhibit stress responses leading to bleaching under larger diurnal temperature fluctuations? (2) If so, how will its bacterial composition change? To answer these questions, we conducted a four-week experiment with Litophyton under three conditions: daily temperature fluctuations of ± 5°C and ± 7°C (with a gradual temperature increase from 25°C to 27.8°C) and a control without fluctuations. Physiological stress responses were assessed, SOD and CAT activities were measured, and bacterial community dynamics were monitored. We found that subjecting Litophyton to large daily temperature fluctuations induced physiological stress responses and significant shifts in bacterial composition. Greater temperature fluctuations caused the shifts to increasingly resemble those observed during bleaching. Furthermore, Endozoicomonadaceae in Litophyton exposed to temperature fluctuations showed closer phylogenetic relationships to those observed in wild bleached Litophyton. We therefore conclude that changes within Endozoicomonadaceae might support the holobiont in coping with stress response and adaptation of nutrient acquisition strategy to transition between autotrophic and heterotrophic modes.