Symbiotic algae living inside corals provide those animals with their vibrant color, as well as many of the nutrients they need to survive. That algae, and other microbes within the bodies of corals, have been extensively studied—yet until now, researchers have largely ignored the microbial communities just outside of the coral colonies.

A new study recently sampled the seawater surrounding Caribbean corals across multiple reefs. Cuban reefs provided a perfect opportunity for this study: Because they’re so remote, they have limited impact from human activities.

In addition to understanding which microbes are living next to corals, the researchers also looked at the microorganisms’ potential ecological functions. They found that the seawater microbes contained genes that let them interact with the coral surface, suggesting that there may be important interactions between seawater microorganisms and the coral surface. Microbes immediately next to the corals could play a role in breaking down waste products from the colonies, introducing new nutrients and potentially letting symbiotic algae or pathogens into the corals themselves.

This project was funded by the Dalio Explore Fund, which supports scientific research at the Woods Hole Oceanographic Institution. The fund is part of Dalio Philanthropies’ larger commitment to ocean exploration and discovery, including the new OceanX initiative.