Quantified impacts of post-fire debris flows on the habitat, population, and recovery of the endangered black abalone.

Research on emergent ecological effects of climate change has largely focused on incremental shifts. Meanwhile, extreme climatic events (ECEs), predicted to increase in frequency and severity, produce extraordinary stressors that may be instrumental in determining whether and to what extent species can adapt to incremental environmental shifts. The inherent unpredictability of ECEs temporally, spatially, and in intensity often precludes quantification of impacts, leaving important knowledge gaps to effective resource management and conservation. Here, we identify one trans-ecosystem driver of marine change via multiple terrestrial ECEs (fire + flood = debris flow). After early recognition of the potential for fire-induced impacts to endangered black abalone habitat, we applied predictive modeling to gauge site-specific risks which enabled us to prioritize sites for ephemeral pre-disturbance data collection. Following impacts from multiple post-fire debris flows, we applied a novel model that coupled in situ sampling with long-term monitoring data and aerial imagery to quantify impacts. We attribute a loss of 21% of rocky intertidal habitat and a median population loss of 59.6% of black abalone within the study area to these events. Results highlight the potential for ECEs to disrupt ecological processes in intertidal systems and offer a pathway to meaningful quantification of impacts in the wake of unpredictable and uncontrollable events.