Just as buildings can be smashed to piles of rubble during earthquakes, coral reefs can be broken up into vast coral rubble beds following events like storms, bleaching, ship groundings and blast fishing. This can be bad! If rubble is rolling around too much, with the waves and currents, new baby corals are killed and reef recovery is limited. But, if rubble is stable for long enough, critters like sponges and coralline algae (the pink cement of the reef!) can grow over it, sticking it together again like a glue. Rubble beds that move around a lot, and don’t have much binding, are likely good candidates for rubble stabilisation interventions, e.g., rock miles, mesh, Reef Stars, which have been trialled in a few places around the world. We are working to identify where these unstable rubble beds are on the GBR, and which rubble beds won’t recover on their own naturally. To do this, we need to know how fast water flow needs to be to move rubble, as well as what critters bind rubble, and how quickly they do so!