MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14791

ABSTRACT: To predict octocoral resilience to climate change, it is critical to understand how these corals respond to their naturally dynamic thermal environments. Traditional assessments often overlook the effects of variable temperatures, focusing on single-time-point measurements and assessments of thermal performance at stable temperatures. Here, we examined the thermal performance of the symbiotic octocoral Muricea laxa across a range of ecologically relevant stable and fluctuating temperatures and exposure times. Our findings reveal that average temperature, fluctuations, and duration of exposure collectively determine M. laxa’s thermal performance. While M. laxa exhibited low mortality at stable high temperatures up to 31°C, fluctuating conditions around elevated averages significantly increased mortality and metabolic depression. These physiological declines, particularly under prolonged exposures, suggest cumulative energetic stress under repeated thermal fluctuations, reflecting similar resilience breakdowns documented in other corals. Additionally, our results underscore the condition-dependent success of symbiotic relationships, as prolonged thermal stress impaired symbiont performance, potentially constraining the energy balance of the holobiont. These findings highlight the role of thermal variability and exposure time as critical components of thermal tolerance, expanding our understanding of octocoral resilience in dynamic ocean environments. M. laxa’s response to these conditions suggests that, while it may tolerate short-term warming, prolonged or frequent heat events could exceed its resilience threshold. By emphasizing these environmental complexities, our study contributes to a growing body of research indicating that octocorals may persist in warming oceans, potentially filling ecological niches vacated by more vulnerable stony corals.