Bleaching-driven reef community shifts drive pulses of increased reef sediment generation

The ecological impacts of coral bleaching on reef communities are well documented, but resultant impacts upon reef-derived sediment supply are poorly quantified. This is an important knowledge gap because these biogenic sediments underpin shoreline and reef island maintenance. Here we explore the impacts of the 2016 bleaching event on sediment generation by two dominant sediment producers (parrotfish and Halimeda spp.) on southern Maldivian reefs. Our data identifies two pulses of increased sediment generation in the three years since bleaching. The first occurred within ~6 months after bleaching as parrotfish biomass and resultant erosion rates increased, likely in response to enhanced food availability. The second pulse occurred 1-3 years post-bleaching, after further increases in parrotfish biomass and a major (~4-fold) increase in Halimeda spp. abundance. Total estimated sediment generation from these two producers increased from ~0.5 kg CaCO₃ m^-2 yr^-1 (pre-bleaching; 2016) to ~3.7 kg CaCO₃ m^-2 yr^-1 (post-bleaching; 2019), highlighting the strong links between reef ecology and sediment generation. However, the relevance of this sediment for shoreline maintenance likely diverges with each producer group, with parrotfish-derived sediment a more appropriate size-fraction to potentially contribute to local island shorelines.