I wrote another guest blog post! This time, for my friends at Evolution Diving in Malapascua, Philippines, who are also hosting the Evolution Photoganza this September. The post is about the interesting interactions between corals, algae and algae-eating fish. It turns out that algae-eaters are necessary to keep corals free of algal overgrowth, and that corals give these fish shelter and spawning grounds. In this way, either a coral or an algae-dominated state can be stable. Marine biologists have only recently started to understand these dynamics.