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.