The Role of Coral Rubble on Modern Coral Reefs

Abstract Sedimentary deposits in coral reefs represent more than 50% of their composition. The term coral rubble refers to unconsolidated sediment particles originating from the breakdown of the skeletons of coral and other calcifying organisms. Rubble results from destruction and deposition during high-energy events and stabilization can occur naturally facilitating coral regrowth. Under climate change, modern coral reefs are undergoing catastrophic bleaching events leading to production of large amounts of rubble. Here we discuss the nature of the new rubble generated and whether is good or bad for coral reef ecosystems. We argue that coral rubble can be good when it drives constructive processes on coral reefs and islands. Otherwise, bad rubble occurs when deposition impedes corals growth, and/or when where it cannot be transported to constructive rubble environments. For One Tree Island, southern Great Barrier Reef Tropical Cyclone Gabrielle (February 2023) drove rubble transport from the SE reef flat towards the island while causing an overall island erosion of 3%. Additionally, ongoing bleaching in 2024 is currently generating large amounts of rubble, further highlighting the need to understand its implications for reef stability and recovery.