Coral reefs are demolished from within by bio-eroding sponges. Seeking refuge from predators, these sponges bore tunnels into the carbonate coral structures, thus weakening the reefs. Scientists from the Royal NIOZ Netherlands Institute for Sea Research have uncovered how the sponges hollow out and take over reef skeletons. This finding, published in Scientific Reports on Thursday January 24th, helps to explain why sponges erode reefs faster as atmospheric CO2 levels rise.