Mesophotic mushroom coral (Fungiidae) beds form distinctive off-reef habitats in Indo-Pacific coral reef ecosystems. We mapped a large mushroom coral bed at Ningaloo Reef off north-western Australia. The 82-hectare (2700 m by 680 m) bed was comprised of Cycloseris distorta and C. fragilis , with densities at some sites more than 1100 m −2 (mean 774 m −2 ) and an estimated population of 653 million individuals making it the lar...