Marine sponges and the microbial communities they host are critical to carbon and nutrient cycling in global reefs, and they often share unique, but poorly understood, symbiotic relationships. Lamellodysidea herbacea sponges, for example, obtain energy from photosynthetic Hormoscilla bacteria that live inside their bodies. These bacteria naturally produce compounds found in flame-retardant pollutants derived from consumer products. A new study describes how researchers are using metagenomics to understand how these creatures maintain a mutually beneficial relationship with sea sponges. Researchers obtained genetic material describing the relative abundance and metabolic capacities of 21 previously uncharacterized microbial populations associated with Lamellodysidea sponges. Analyses revealed genes coding for enzymes that break down halogenated aromatics, which could enable microbes to use pollutant-like compounds as carbon and energy sources. Future studies building off of this work could offer new insight into microbe–sponge relations and help scientists understand how these important cogs of the marine carbon cycle function together.