LAUSR

Corals are small marine invertebrates that band together to create the world’s largest animal engineered structures: the coral reef. Some of these reef structures such as The Great Barrier Reef in Australia are so large they can be seen from the International Space Station. Often referred to as the Amazon Rainforests of the ocean, coral reefs support a diverse array of marine ecosystems and harbor much of the oceans biodiversity. Recently, corals have gained global attention due to a massive global die off event in 2016, in which almost 30% of all corals on the Great Barrier Reef died. Before this massive reef die off many of the corals underwent a process called coral bleaching in which the coral animal expels its photosynthetic symbiont, a dinoflagellate of the genus Symbiodinium, into the surrounding water revealing a ghost-like white skeleton. Corals receive most of their required nutrients from their Symbiodinium partner in the form of photosynthetically fixed carbon therefore after Symbiodinium expulsion the coral animal is physiologically weak and vulnerable to disease. Despite this sensitive coralSymbiodinium partnership, corals have been around for 10–100 s of millions of years begging the question why has not a more robust relationship evolved? In the current issue, Blackstone and Golladay address this fundamental question, “Why do corals bleach?” They propose that bleaching is caused by a breakdown of the mechanisms that mediate conflict between corals and their symbionts. A mechanism of conflict mediation in this case is a means to check if the Symbiodinium partner is conforming to a particular behavior, which is to export photosynthate to the coral. Blackstone and Golladay focus on how the breakdown of two mechanisms co-opted from features of