Mutually beneficial relationships between bacteria and their hosts are common in the animal kingdom, and the tropical members of the sponge genus Ircinia are no exception. Ircinia are ecologically important residents in coral reef, seagrass, and mangrove environments. But how their symbiotic bacterial communities remain stable across species is poorly understood. So, researchers recently examined metagenomes — the collection of genes from a bacterial community — from 11 species of Ircinia. First, they found that important metabolic genes were repeated in the genomes of multiple bacterial groups. This redundancy could buffer Ircinia from changes in ambient conditions or fluctuations in the population of individual bacterial strains. The metagenomes tended to have few pathogenicity-associated genes and instead were rich with genes for ‘eukaryotic-like proteins’, which would resemble proteins made by their hosts' cells. Sterol synthesis genes were also widespread, suggesting that these molecules are important for the bacteria in these communities to survive. Overall, this study helped researchers better understand the complex microbial communities that reside in Ircinia sponges and could inform future conservation efforts.