Not-so-mutually beneficial coral symbiosis

The partnership between corals and their intracellular algal symbionts has long been a textbook example of a mutually beneficial association. Here I argue that this view has been made obsolete by a steady accumulation of evidence over the past three decades. The coral-algal relationship is perhaps better viewed as one of domestication - think of it like a cattle farm, in which the coral is the farmer and the algae are the cows. I synthesize old and new evidence in support of this updated view and highlight remaining knowledge gaps, the largest of which continues to be the natural history of algal symbionts.