A new article in PLoS ONE uses social network theory to study global interactions in coral reefs using social networks. Reefs are built up over thousands of years by hard corals with the help of their symbiotic partner, Symbiodinium, a single-celled algae that lives within the coral tissue – a symbiont. The study found that most corals have very few Symbiodinium partners, but that a handful of corals have many symbionts. This was important because it’s generally believed that most corals have few symbiont options to choose from. The study also found that transmission mode was important in these communities: young corals get their Symbiodinium from their parents or from the environment, but not both. Symbiodinium types were usually passed on through only one of these strategies, nearly dividing the networks in half. This research is important to understanding basic interaction patterns between corals and Symbiodinium. With a greater understanding of this important mutualistic interaction, we’ll be better equipped to protect coral reef communities – and the species they support.