Turbid coral reefs in northwestern Australia exhibit high tolerance to successive extreme heat stress events

Abstract Suspended particulates on turbid coral reefs can mitigate thermal stress and bolster coral energy acquisition, improving resilience to climate change. Yet, questions remain regarding how corals on turbid reefs respond to successive heat stress events and whether certain coral taxa are more likely to survive under increasingly variable environmental conditions. We investigated the response of coral communities across a natural turbidity gradient in the Dampier Archipelago (Western Australia) to successive heat stress events in 2022 and 2023 (12.7 and 14.4 degree heating weeks, respectively). We then examined the influence of environmental variables, such as wave exposure, total suspended solids (TSS) and light attenuation (KD490), on coral bleaching and changes in coral cover across this turbidity gradient. Prior to heat stress, coral cover across 11 consistently surveyed reefs ranged from 17 to 68%. Approximately 30% of hard corals bleached each summer, and there was an overall 8% decline in mean cover (from 34 to 26%). Moderately turbid reefs, dominated by stress-resistant Pavona spp. exhibited comparatively low bleaching and maintained high coral cover throughout the study period, suggesting higher resilience to successive stress events. Conversely, Porites spp. showed increasing susceptibility over repeated heat stress events. Reefs dominated by plating or branching Acropora spp. experienced the highest bleaching prevalence and the greatest shifts in community composition. Variations in significant wave height and TSS concentration were strong, but nuanced, predictors of total hard coral bleaching and community-level bleaching susceptibility (respectively), whilst maintenance of coral cover was associated with higher KD490. Our findings highlight the capacity of corals on turbid reefs to withstand severe, repeated heat stress and bleaching, and the potential for such reefs to act as climate change refugia.